Integrating machine learning and empirical evapotranspiration modeling with DSSAT: Implications for agricultural water management

The availability of accurate reference evapotranspiration (ETo) data is crucial for developing decision support systems for optimal water resource management. This study aimed to evaluate the accuracy of three empirical models (Hargreaves-Samani (HS), Priestly-Taylor (PT), and Turc (TU)) and three machine learning models (Multiple linear regression (LR), Random Forest (RF), and Artificial Neural Network (NN)) in estimating daily ETo compared to the Penman-Monteith FAO-56 (PM) model. Long-term data from 42 weather stations in Florida were used. Moreover, the effect of ETo model selection on sweet corn irrigation water use was investigated by integrating simulated ETo data from empirical and ML models using the Decision Support System for Agrotechnology Transfer (DSSAT) model at two locations (Citra and Homestead) in Florida. Furthermore, a linear bias correction calibration technique was employed to improve the performance of empirical models. Results were consistent in that the NN and RF models outperformed the empirical models. The empirical models tended to underestimate and overestimate small and high daily ETo values, respectively, with the HS model exhibiting the least accuracy. However, calibrated PT and TU models performed comparably to the ML models. Results also revealed that using an inappropriate ETo model could lead to over-irrigation by up to 54 mm during a single crop season. Overall, ML models have proven reliable alternatives to the PM model, especially in regions with access to long-term data due to their site-independent performance. In areas without long-term data for ML model training and testing, calibrating empirical models is viable, but site-specific calibration is needed. It is important to highlight that distinct plant species exhibit varying transpiration characteristics and, consequently, have different water requirements. These differences play a pivotal role in shaping the overall impact of ETo models on crop water use.

sachharata) inbred lines through morphological, biochemical and marker-based approaches

BACKGROUND

Sweet corn is gaining tremendous demand worldwide due to urbanization and changing consumer preferences. However, genetic improvement in this crop is being limited by narrow genetic base and other undesirable agronomic traits that hinder the development of superior cultivars. The main requirement in this direction is the development of potentially promising parental lines. One of the most important strategies in this direction is to develop such lines from hybrid-oriented source germplasm which may provide diverse base material with desirable biochemical and agro-morphological attributes.

METHODS AND RESULTS

The study was undertaken to carry out morphological and biochemical evaluation of 80 early generation inbred lines (S2) of sweet corn that were developed from a cross between two single cross sweet corn hybrids (Mithas and Sugar-75). Moreover, validation of favourable recessive alleles for sugar content was carried out using SSR markers. The 80 sweet corn inbreds evaluated for phenotypic characterization showed wide range of variability with respect to different traits studied. The highest content of total carotenoids was found in the inbred S27 (34 μg g-1) followed by the inbred S65 (31.1 μg g-1). The highest content for total sugars was found in S60 (8.54%) followed by S14 (8.34%). Molecular characterization of 80 inbred lines led to the identification of seven inbreds viz., S21, S28, S47, S48, S49, S53, and S54, carrying the alleles specific to the sugary gene (su1) with respect to the markers umc2061 and bnlg1937. Comparing the results of scatter plot for biochemical and morphological traits, it was revealed that inbreds S9, S23, S27 and S36 contain high levels of total sugars and total carotenoids along with moderate values for amylose and yield attributing traits.

CONCLUSION

The inbred lines identified with desirable biochemical and agro-morphological attributes in the study could be utilized as source of favourable alleles in sweet corn breeding programmes after further validation for disease resistance and other agronomic traits. Consequently, the study will not only enhance the genetic base of sweet corn germplasm but also has the potential to develop high-yielding hybrids with improved quality. The inbreds possessing su1 gene on the basis of umc2061 and bnlg1937 markers were also found to possess high sugar content. This indicates the potential of these lines as desirable candidates for breeding programs aimed at improving sweet corn yield and quality. These findings also demonstrate the effectiveness of the molecular markers in facilitating marker-assisted selection for important traits in sweet corn breeding.

Impact of low temperature on the chemical profile of sweet corn kernels during post-harvest storage

Fresh sweet corn has a limited shelf-life due to its high moisture and high sugar content. Low temperature storage is an effective technique employed to extend the shelf-life. However, changes in the chemical composition of sweet corn kernels at low temperatures are not fully understood. In this study, kernels stored at low temperature exhibited higher levels of soluble sugars and lower starch content. In total, 1365 metabolites were characterized in sweet corn kernels. 593 and 308 differentially accumulated metabolites (DAMs) were identified in sweet corn kernels stored at normal and low temperature, respectively. 607 DAMs were identified at low temperature compare to normal temperature. DAMs were consistently enriched in flavonoid biosynthesis, linoleic acid metabolism and sphingolipid metabolism. Moreover, dozens of metabolites were identified as potential biomarkers for post-harvest storage effects in sweet corn. These results extend our knowledge of the dynamic changes in sweet corn kernels stored at low temperatures.

Preharvest 24-epibrassinolide treatment prolongs harvest duration and shelf life in sweet corn

Sweet corn is perishable and have limited harvest duration and shelf life due to their quality deterioration. Reactive oxygen species (ROS) are one of the most predominant factors for maintaining quality of sweet corn during and after harvest. Brassinosteroids (BRs) can enhance the activity of antioxidant enzymes and decrease the ROS level in plants. In this study, we found that a bioactive BR (24-epibrassinolide, EBR) treatment before harvest markedly inhibited change of quality indicators (MDA content, weight loss rate, and soluble sugar content) during and after harvest. Further analysis revealed that EBR promoted the activity and transcriptions of antioxidant enzymes, maintaining lower ROS level in kernels. Meanwhile, exogenous EBR increased the expression level of genes controlling sucrose transport in sweet corn kernels. Bioinformatics and binding analysis identified that BR transcription factor ZmBES1/ZmBZR1-10 might potentially bind to and upregulate transcriptions of antioxidant enzyme genes including SOD and POD genes, and sucrose transport-related genes including SUT and SWEET genes. These results indicated that exogenous application of EBR ameliorates quality during and after harvest by improving the antioxidant capacity and photosynthetic assimilates accumulation rate of sweet corn, thus prolonging harvest duration and shelf life in sweet corn.

Frequency of heterotic hybrids in relation to general combining ability of parents in sweet corn

The success of developing prominent hybrids directly depends on the selection of parents with good combining ability which can transfer desirable genes with additive effects to their progeny. The data of 42 hybrids generated using 7 × 7 full diallel design; their seven parents along with three check hybrids were subjected to combining ability analysis from the experiment that was carried out during rainy season 2019. The analysis of variance showed significant general combining ability, and specific combining ability mean sum of squares for all the thirteen characters studied. It is obvious from the results that three lines (SC Sel 2, SC Sel 1 and SC Sel 3) showed high overall general combining ability status, suggesting these lines as good general combiners across traits. Eighteen hybrids had high overall specific combining ability status, while nearly 52% (22 hybrids), 57% (24 hybrids) and 47% (20 hybrids) of crosses showed high overall mid-parent, better-parent and standard heterosis. The unique superiority of crosses involving high overall general combiner parent in the crosses highlighted the importance of using such parents to realize high heterotic crosses. A non-linear relationship between high overall specific combining ability status and heterotic status of hybrids was noticed. The probability of obtaining a cross with high standard heterosis was more with employing parents with high general combining ability status.

Effect of foliar application of phosphorus nanoparticles on the performance and sustainable agriculture of sweet corn

Traditional phosphorus fertilizers are necessary for plant growth but about 80-90% are lost into the surrounding environment via irrigation, therefore nano-fertilizers have been developed as slow-release fertilizers to achieve sustainable agriculture. This trial investigated the impact of the foliar application of hydroxyapatite nanoparticles (HA-NPs) as a source of nano-phosphorus (P-NPs) on two cultivars of sweet corn (yellow and white) throughout two seasons. The morphology and structure of the prepared HA-NPs were characterized via transmission electron microscopy (TEM) and X-ray diffractometry (XRD). In addition, agro-morphological criteria, chemical contents (i.e., photosynthetic pigments, phenols, indoles, minerals, etc.), and genomic template stability percentage (GTS%) were evaluated in the produced sweet corn. The application of 50 mg/l HA-NPs improved the growth characteristics, yield per hectare, leaf pigments, and chemical content of yellow sweet corn, whereas the application of 100 mg/l of HA-NPs to white sweet corn enhanced the vegetative characteristics, production, photosynthetic pigments, phenols, and indoles. The difference in results may be due to the presence of a +ve unique band with SCoT-4 and SCot-2 primers at 1250 and 470 bp in yellow and white corn treated with 50 and 100 mg/l, respectively. The minimum GTS% was recorded at a concentration of 75 mg/l for both white and yellow corn. The HA-NPs can be applied as a foliar source of P-NPs to achieve agricultural sustainability.

Effect of thermal treatments on volatile profiles and fatty acid composition in sweet corn (Zea mays L.)

This study analyzed the effects of thermal processing on volatiles and fatty acids in sweet corn. There were 27 volatiles measured in fresh samples, and 33, 21, and 19 volatiles identified in the steaming, blanching, and roasting groups, respectively. Relative odor activity values (ROAVs) showed that characteristic aroma-active volatiles of sweet corn after thermal treatments included: (E)-2-nonenal, 1-octen-3-ol, beta-myrcene, dimethyl trisulfide, 1-(4,5-dihydro-2-thiazolyl)-ethanone, and d-limonene. Thermal treatments significantly increased the unsaturated fatty acids (oleic acid and linolenic acid) of sweet corn by 110 to 183% compared to fresh samples. Meanwhile, many characteristic volatiles were found that derived from the oxidative cleavage of fatty acids. The sweet corn aroma obtained by steaming for 5 min was considered the closest to fresh corn. Our research provided insight into aroma composition of different thermally processed sweet corn and laid the foundation for further exploring the sources of aroma compounds in thermally processed sweet corn.

Provitamin A, lysine and tryptophan enrichment in shrunken2-based sweet corn genotypes through genomics-assisted breeding for crtRB1 and opaque2 genes

BACKGROUND

Malnutrition affects large section of population worldwide. Vitamin A and protein deficiencies have emerged as the major global health-issue. Traditional shrunken2 (sh2)-based sweet corn is deficient in provitamin A (proA), lysine and tryptophan. Natural variant of β-carotene hydroxylase1 (crtRB1) and opaque2 (o2) enhances proA, lysine and tryptophan in maize. So far, no sweet corn hybrid rich in these nutrients has been released elsewhere. Development of biofortified sweet corn hybrids would help in providing the balanced nutrition.

METHODS AND RESULTS

We targeted three sh2-based sweet corn inbreds (SWT-19, SWT-20 and SWT-21) for introgression of mutant crtRB1 and o2 genes using molecular breeding. The gene-based 3'TE-InDel and simple sequence repeat (SSR) (umc1066) markers specific to crtRB1 and o2, respectively were utilized in foreground selection in BC₁F₁, BC₂F₁ and BC₂F₂. Segregation distortion was observed for crtRB1 and o2 genes in majority of populations. Background selection using 91-100 SSRs revealed recovery of recurrent parent genome (RPG) up to 96%. The introgressed progenies possessed significantly higher proA (13.56 µg/g) as compared to the original versions (proA: 2.70 µg/g). Further, the introgressed progenies had accumulated moderately higher level of lysine (0.336%) and tryptophan (0.082%) over original versions (lysine: 0.154% and tryptophan: 0.038%). Kernel sweetness among introgressed progenies (17.3%) was comparable to original sweet corn (17.4%). The introgressed inbreds exhibited higher resemblance with their recurrent parents for yield and morphological characters.

CONCLUSION

These newly developed biofortified sweet corn genotypes hold immense promise to alleviate malnutrition.

Nicosulfuron stress on the glyoxalase system and endogenous hormone content in sweet maize seedlings

To reduce the harmful effects of nicosulfuron on sweet corn, the physiological regulation mechanism of sweet corn detoxification was studied. This study analyzed the effects of nicosulfuron stress on the glyoxalase system, hormone content, and key gene expression of nicosulfuron-tolerant "HK301" and nicosulfuron-sensitive "HK320" sweet corn seedling sister lines. After spraying nicosulfuron, the methylglyoxal (MG) content in HK301 increased first and then decreased. Glyoxalase I (GlyI) and glyoxalase II (GlyII) activities, non-enzymatic glutathione (GSH), and the glutathione redox state glutathione/(glutathione + glutathione disulfide) (GSH/(GSH + GSSG)) showed a similar trend as the MG content. Abscisic acid (ABA), gibberellin (GA), and zeatin nucleoside (ZR) also increased first and then decreased, whereas the auxin (IAA) increased continuously. In HK301, all indices after spraying nicosulfuron were significantly greater than those of the control. In HK320, MG accumulation continued to increase after nicosulfuron spraying and GlyI and GlyII activities, and GSH first increased and then decreased after 1 day of stress. The indicators above were significantly greater than the control. The GSH/(GSH + GSSG) ratio showed a decreasing trend and was significantly smaller than the control. Furthermore, ABA and IAA continued to increase, and the GA and ZR first increased and then decreased. Compared with HK320, HK301 significantly upregulated the transcription levels of GlyI and GlyII genes in roots, stems, and leaves. Comprehensive analysis showed that sweet maize seedlings improved their herbicide resistance by changing the glyoxalase system and regulating endogenous hormones. The results provide a theoretical basis for further understanding the response mechanism of the glyoxalase system and the regulation characteristics of endogenous hormones in maize under nicosulfuron stress.

Comparative transcriptome analyses shed light on the regulation of harvest duration and shelf life in sweet corn

Harvest duration and postharvest shelf life are two of the most important characters for sweet corn. However, the regulatory mechanism remains unclear. We performed a comparative transcriptome analysis of long harvest-duration and shelf-life sweet corn (LHS) and short harvest-duration and shelf-life field corn (SHS) at three stages, i.e. 10 days after pollination (10DAP), 22 days after pollination (22DAP), and 7 days after harvest (7DAH). We have observed the major transcriptome changes accompanying the harvest process in LHS corn. Gene expression pattern analysis and differentially expressed genes (DEGs) functional enrichments suggested an association between ROS metabolism in kernels with harvest duration and postharvest shelf life. The genes encoding cytochrome P450, peroxidase, peroxiredoxin, glutathione peroxidase, and glutathione S-transferase were upregulated specifically in LHS kernels during and after harvest compared to SHS kernels. These novel findings reveal a new regulatory mechanism of corn post-harvest shelf life and should be useful for extending harvest duration and shelf life for sweet corn.

Biocontrol endophytes Bacillus subtilis R31 influence the quality, transcriptome and metabolome of sweet corn

During colonization of soil and plants, biocontrol bacteria can effectively regulate the physiological metabolism of plants and induce disease resistance. To illustrate the influence of Bacillus subtilis R31 on the quality, transcriptome and metabolome of sweet corn, field studies were conducted at a corn experimental base in Zhuhai City. The results show that, after application of B. subtilis R31, sweet corn was more fruitful, with a 18.3 cm ear length, 5.0 cm ear diameter, 0.4 bald head, 403.9 g fresh weight of single bud, 272.0 g net weight of single ear, and 16.5 kernels sweetness. Combined transcriptomic and metabolomic analyses indicate that differentially expressed genes related to plant-pathogen interactions, MAPK signaling pathway-plant, phenylpropanoid biosynthesis, and flavonoid biosynthesis were significantly enriched. Moreover, the 110 upregulated DAMs were mainly involved in the flavonoid biosynthesis and flavone and flavonol biosynthesis pathways. Our study provides a foundation for investigating the molecular mechanisms by which biocontrol bacteria enhance crop nutrition and taste through biological means or genetic engineering at the molecular level.

Mathematical modelling and characterization of drying of pre-treated sweet corn (Zea mays L.) kernels

The pre-treated sweet corn samples were dried at temperatures of 55, 60, 65 and 70 °C and thin layer drying characteristics of sweet corn were assessed. Mathematical models were fitted and evaluated using R2, χ2, RMSE values. The effective diffusivities for the drying process were 4.32 × 10-10 to 1.08 × 10-9 m2/s and activation energies were 34.51 to 38.99 kJ/mol. Total sugar and ascorbic acid of dehydrated sweet corn kernels varied from 5.50 to 13.00 g/100 g and 3.30 to 10.50 mg/100 g respectively. The sample pre-treated with microwave blanching and dried at 70 °C obtained higher sensory score after rehydration, indicating suitability of the dehydrated sweet corn.

Introgression of the RppQ gene from field corn improves southern rust resistance in sweet corn

Southern rust, one of the most destructive foliar diseases of sweet corn (Zea mays convar. saccharata var. rugosa), is caused by Puccinia polysora Underw. and leads to enormous yield losses and reduced quality of sweet corn in China. Utilization of resistance genes is an effective and environmentally friendly strategy for improving southern rust resistance of sweet corn. However, improvement is hampered by a lack of resistance genes in Chinese sweet corn germplasm. In this study, we introgress the southern rust resistance gene RppQ from Qi319, an inbred line of southern rust-resistant field corn, into four elite sweet corn inbred lines (1401, 1413, 1434, and 1445) using marker-assisted backcross breeding. These are parental inbred lines of four popular sweet corn varieties: Yuetian 28, Yuetian 13, Yuetian 26, and Yuetian 27. We developed five RppQ-based markers (M0607, M0801, M0903, M3301, and M3402) and employed these markers for foreground selection; 92.3 to 97.9% of the recurrent parent genomes were recovered following three or four rounds of backcrossing. The four newly developed sweet corn lines all showed significant improvement of southern rust resistance compared with their respective parent lines. Meanwhile, there was no significant difference in phenotypic data for agronomic traits. In addition, reconstituted hybrids derived from the converted lines retained resistance to southern rust, while other agronomic traits and sugar content remained unchanged. Our study provides an example of successful development of southern rust-resistant sweet corn using a resistance gene from field corn.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-022-01315-7.

Characterization of crtRB1- and vte4-based biofortified sweet corn inbreds for seed vigour and physico-biochemical traits

Sweet corn possessing recessive shrunken2 (sh2) gene is popular worldwide. Traditional sweet corn is poor in vitamin A and vitamin E. Plant breeders during the selection of sweet corn genotypes mainly emphasize on plant architecture and yield. Seed germination and seedling vigour play important role for early establishment in field, thereby increasing yield and income. Here, we analysed a set of 15 sh2-based biofortified sweet corn inbreds with crtRB1 (β-carotene hydroxylase1) and vte4 (γ-tocopherol methyltransferase) genes and three traditional sh2-based sweet corn inbreds for nutritional quality, seed vigour and various physico-biochemical traits. The newly developed inbreds possessed significantly higher provitamin A (proA: 15.60 µg/g) and vitamin E [α-tocopherol (α-T): 20.42 µg/g] than the traditional sweet corn inbreds (proA: 2.51 µg/g, α-T: 11.16 µg/g). The biofortified sweet corn inbreds showed wide variation for germination (80.67-87.33%), vigour index-I (2097.17-2925.28 cm), vigour index-II (134.27-216.19 mg) and electrical conductivity (10.19-13.21 μS cm^-1 g^-1). Wide variation was also observed for dehydrogenase (1.29-1.59 OD g^-1 ml^-1), super oxide dismutase (4.01-9.82 g^-1), peroxidase (11.66-16.47 μM min^-1 g^-1), esterase (22.98-34.76 nM min^-1 g^-1) and α-amylase (5.91-8.15 OD g^-1 ml^-1). Enrichment of proA and vitamin E in sweet corn did not affect seed vigour and physico-biochemical traits. Correlation analysis revealed that electrical conductivity and α-amylase activity was the reliable indicator for assessing seed germination and vigour. The study identified superior biofortified sweet corn genotypes that would contribute to better vigour and establishment in field. This is the first report of analysis of biofortified sweet corn genotypes for seed vigour and physico-biochemical traits.

Marker-assisted pyramiding of γ-tocopherol methyltransferase and glutamate formiminotransferase genes for development of biofortified sweet corn hybrids

Micronutrients, including vitamins, minerals, and other bioactive compounds, have tremendous impacts on human health. Much progress has been made in improving the micronutrient content of inbred lines in various crops through biofortified breeding. However, biofortified breeding still falls short for the rapid generation of high-yielding hybrids rich in multiple micronutrients. Here, we bred multi-biofortified sweet corn hybrids efficiently through marker-assisted selection. Screening by molecular markers for vitamin E and folic acid, we obtained 15 inbred lines carrying favorable alleles (six for vitamin E, nine for folic acid, and three for both). Multiple biofortified corn hybrids were developed through crossing and genetic diversity analysis.

Evaluation of seedling age and nutrient sources on phenology, yield and agrometeorological indices for sweet corn (Zea mays saccharata L.)

The field experiment was conducted during Kharif season of 2020 at Agronomy farm of Faculty of Agriculture, Wadura, SKUAST-K to study the influence of age of seedling and sources of nutrients on phenology, yield and agrometeorological indices for sweet corn. The experiment included two factors viz. age of seedlings (12, 22 and 32 days old seedling) and sources of nutrients (control, RDF, 50 percent RDF + FYM @ 12 t ha⁻¹, 50 percent RDF + vermi-compost @ 4 t ha⁻¹ and 50 percent RDF + poultry manure @ 2 t ha⁻¹) tested in RCBD with three replications. Transplanting 12 days old seedlings required maximum number of days to attain different phenological stages, thereby accumulated maximum heat units followed by 22 days old seedlings. While as transplanting 22 days old seedling recorded significantly highest HUE, HTUE, PTUE and HyTUE and consequently resulted in the highest green cob and biological yield compared to other ages of seedlings. Among various sources of nutrients, application of 50 per cent RDF + poultry manure @ 2 t ha⁻¹ took maximum number of days to attain various phenophases thereby accumulated maximum heat units and registered highest HUE, HTUE, PTUE and HyTUE followed by application of 100 per cent RDF.

Development of ready to reconstitute dehydrated traditional sweet corn halwa

The halwa is a traditional thick sweet generally consumed by millions in the Middle East with more concentrated population in the South and Central Asia. Sweet corn halwa is one such traditional type prepared in the tribal region of middle Gujarat, India. It is one of the dairy delicacies of traditional Indian desserts, which needs to be optimized and dehydrated to assure the availability of the product during off-season and to provide good value in terms of money and enhancement of shelf life. The milk and sugar were added in 50 to 250 g/100 g and 12 to 14 g/100 g respectively for cooking of ingredients for 10 to 20 min to provide value to this traditional product for getting higher return to the entrepreneurs. The optimized sweet corn halwa was dehydrated in thin layers at 60 °C and drying data was fitted thin layer drying models. The physico-chemical properties and sensory evaluation of sweet corn halwa were evaluated during this experiment. The rehydrated product maintained similar overall acceptability, indicating comparable sensory characteristics with fresh sweet corn halwa.

Changes in physiology, gene expression and ethylene biosynthesis in MDMV-infected sweet corn primed by small RNA pre-treatment

The physiological condition of plants is significantly affected by viral infections. Viral proliferation occurs at the expense of the energy and protein stores in infected plant cells. At the same time, plants invest much of their remaining resources in the fight against infection, making them even less capable of normal growth processes. Thus, the slowdown in the development and growth processes of plants leads to a large-scale decrease in plant biomass and yields, which may be a perceptible problem even at the level of the national economy. One form of protection against viral infections is treatment with small interfering RNA (siRNA) molecules, which can directly reduce the amount of virus that multiplies in plant cells by enhancing the process of highly conserved RNA interference in plants. The present work demonstrated how pre-treatment with siRNA may provide protection against MDMV (Maize dwarf mosaic virus) infection in sweet corn (Zea mays cv. saccharata var. Honey Koern). In addition to monitoring the physiological condition of the maize plants, the accumulation of the virus in young leaves was examined, parallel, with changes in the plant RNA interference system and the ethylene (ET) biosynthetic pathway. The siRNA pre-treatment activated the plant antiviral defence system, thus significantly reducing viral RNA and coat protein levels in the youngest leaves of the plants. The lower initial amount of virus meant a weaker stress load, which allowed the plants to devote more energy to their growth and development. In contrast, small RNA pre-treatment did not initially have a significant effect on the ET biosynthetic pathway, but later a significant decrease was observed both in the level of transcription of genes responsible for ET production and, in the amount of ACC (1-aminocyclopropane-1-carboxylic acid) metabolite. The significantly better physiological condition, enhanced RNAi response and lower quantity of virus particles in siRNA pretreated plants, suggested that siRNA pre-treatment stimulated the antiviral defence mechanisms in MDMV infected plants. In addition, the consistently lower ACC content of the plants pre-treated with siRNA suggest that ET does not significantly contribute to the successful defence in this maize hybrid type against MDMV.

Expression analysis of β-carotene hydroxylase1 and opaque2 genes governing accumulation of provitamin-A, lysine and tryptophan during kernel development in biofortified sweet corn

Traditional sweet corn possesses low levels of provitamin-A (proA), lysine and tryptophan. Mutant version of β-carotene hydroxylase1 (crtRB1) gene affecting the accumulation of β-carotene (BC), β-cryptoxanthin (BCX) and proA, and opaque2 (o2) gene governing the enhancement of lysine and tryptophan were introgressed together into elite sweet corn inbreds through marker-assisted selection. Here, we analyzed the expression pattern of crtRB1 and o2 genes among introgressed and traditional sweet corn inbreds at 20-, 24- and 28-days after pollination (DAP). The introgressed inbreds possessed two- to sevenfolds higher BC, BCX, proA, lysine and tryptophan compared to their original inbreds. However, all the nutrients attained the peak at 20-DAP (BC: 9.95 µg/g, BCX: 8.21 µg/g, proA: 14.05 µg/g, lysine: 0.301%, tryptophan: 0.074%), which gradually reduced through 24-DAP (BC: 8.24 µg/g, BCX: 7.53 µg/g, proA: 12.01 µg/g, lysine: 0.273%, tryptophan: 0.057%) and 28-DAP (BC: 5.84 µg/g, BCX: 5.82 µg/g, proA: 8.75 µg/g, lysine: 0.202%, tryptophan: 0.037%). Biofortified sweet corn inbreds possessed significantly lower expression levels of crtRB1 (4.1-fold) and o2 (2.2-fold) compared to their wild type alleles in traditional sweet corn inbreds across DAPs. The expression of crtRB1 and o2 increased from 20-DAP to attain the highest peak at 24-DAP, and further decreased by 28-DAP. The transcript levels of crtRB1 were negatively correlated with BC (r = - 0.83), BCX (r = - 0.79) and proA (r = - 0.83) across dates of harvest. Lysine (r = - 0.83) and tryptophan (r = - 0.73) were also inversely associated with o2 transcript levels. This is the first report on expression of crtRB1 and o2 genes during kernel development in biofortified sweet corn. This information holds immense promise in understanding the dynamics of gene-regulation during kernel development in sweet corn.

Allelic variation in sugary1 gene affecting kernel sweetness among diverse-mutant and -wild-type maize inbreds

Sweet corn is popular worldwide as vegetable. Though large numbers of sugary1 (su1)-based sweet corn germplasm are available, allelic diversity in su1 gene encoding SU1 isoamylase among diverse maize inbreds has not been analyzed. Here, we characterized the su1 gene in maize and compared with allied species. The entire su1 gene (11,720 bp) was sequenced among six mutant (su1) and five wild (Su1) maize inbreds. Fifteen InDels of 2-45 bp were selected to develop markers for studying allelic diversity in su1 gene among 19 mutant- (su1) and 29 wild-type (Su1) inbreds. PIC ranged from 0.15 (SU-InDel7) to 0.37 (SU-InDel13). Major allele frequency varied from 0.52 to 0.90, while gene diversity ranged from 0.16 to 0.49. Phylogenetic tree categorized 48 maize inbreds in two clusters each for wild- type (Su1) and mutant (su1) types. 44 haplotypes of su1 were observed, with three haplotypes (Hap6, Hap22 and Hap29) sharing more than one genotype. Further, comparisons were made with 23 orthologues of su1 from 16 grasses and Arabidopsis. Maize possessed 15-19 exons in su1, while it was 11-24 exons among orthologues. Introns among the orthologues were longer (77-2206 bp) than maize (859-1718 bp). SU1 protein of maize and orthologues had conserved α-amylase and CBM_48 domains. The study also provided physicochemical properties and secondary structure of SU1 protein in maize and its orthologues. Phylogenetic analysis showed closer relationship of maize SU1 protein with P. hallii, S. bicolor and E. tef than Triticum sp. and Oryza sp. The study showed that presence of high allelic diversity in su1 gene which can be utilized in the sweet corn breeding program. This is the first report of comprehensive characterization of su1 gene and its allelic forms in diverse maize and related orthologues.

An outbreak of human listeriosis associated with frozen sweet corn consumption: Investigations in the UK

The use of Whole genome sequencing (WGS) identified a multi-country outbreak of human listeriosis associated with consumption of frozen sweet corn produced in Hungary. The purpose of this report was to summarise information on the cases occurring in the UK which were part of this outbreak and outline investigations on the presence of Listeria monocytogenes in the affected food chain. Prior to the international recall of this product in 2018, 12 UK cases of listeriosis were identified as infected by the outbreak strain between 2015 and 18. Epidemiological and microbiological investigations confirmed these cases as belonging to the outbreak. A further case occurred in 2019 and a contaminated frozen pack from one of the implicated batches of sweet corn was recovered from the patient's domestic freezer. The outbreak strain was also detected in products from a sandwich manufacturer in 2018 which added frozen sweet corn directly to sandwich fillings. The sandwich manufacturer's sweet corn was supplied by a distributor in England which obtained frozen products from the Hungarian manufacturer implicated in the outbreak. Within the distributor's premises, 208 food and environmental samples were taken: L. monocytogenes was detected in 44% of 70 samples of frozen sweet corn and 5% of 79 other foods. The outbreak strain was detected in the frozen sweet corn, in one other frozen food (mixed vegetables) and in the factory environment. The outbreak strain was also recovered from frozen beans on retail sale in the first four months of 2019. Five other L. monocytogenes strains together with two other Listeria species were detected in samples from the importer's premises. One of the L. monocytogenes strains in the importer's factory, which was distinct from the outbreak strain, was also recovered from sweet corn collected from the sandwich manufacturer, sweet corn tested in England in 2013 and 2016 and the blood of two cases of human listeriosis which occurred in England in 2014. This report shows how analysis by WGS provides evidence to understand complex food chains. This report also highlights risks for transmission of human listeriosis from frozen sweet corn and the potential for misuse of this food as a ready-to-eat product.

QTL mapping and transcriptome analysis identify candidate genes regulating pericarp thickness in sweet corn

BACKGROUND

In recent years, the planting area of sweet corn in China has expanded rapidly. Some new varieties with high yields and good adaptabilities have emerged. However, the improvement of edible quality traits, especially through the development of varieties with thin pericarp thickness, has not been achieved to date. Pericarp thickness is a complex trait that is the key factor determining the edible quality of sweet corn. Genetic mapping combined with transcriptome analysis was used to identify candidate genes controlling pericarp thickness.

RESULTS

To identify novel quantitative trait loci (QTLs) for pericarp thickness, a sweet corn BC₄F₃ population of 148 lines was developed using the two sweet corn lines M03 (recurrent parent) and M08 (donor parent). Additionally, a high-density genetic linkage map containing 3876 specific length amplified fragment (SLAF) tags was constructed and used for mapping QTLs for pericarp thickness. Interestingly, 14 QTLs for pericarp thickness were detected, and one stable QTL (qPT10-5) was detected across multiple years, which explained 7.78-35.38% of the phenotypic variation located on chromosome 10 (144,631,242-145,532,401). Forty-two candidate genes were found within the target region of qPT10-5. Moreover, of these 42 genes, five genes (GRMZM2G143402, GRMZM2G143389, GRMZM2G143352, GRMZM6G287947, and AC234202.1_FG004) were differentially expressed between the two parents, as revealed by transcriptome analysis. According to the gene annotation information, three genes might be considered candidates for pericarp thickness. GRMZM2G143352 and GRMZM2G143402 have been annotated as AUX/IAA transcription factor and ZIM transcription factor, respectively, while GRMZM2G143389 has been annotated as FATTY ACID EXPORT 2, chloroplastic.

CONCLUSIONS

This study identified a major QTL and candidate genes that could accelerate breeding for the thin pericarp thickness variety of sweet corn, and these results established the basis for map-based cloning and further functional research.

The association between health literacy and pesticide use behaviors among sweet corn farmers in the Pak Chong district of Thailand: a cross-sectional study

Background: Pesticide toxicity is an important health problem in Thailand due to the intensive use of hazardous pesticides.  This study aimed to determine and discuss patterns of pesticide use, health literacy, pesticide use behaviors and whether there is an association between health literacy and pesticide use behaviors among sweet corn farmers in the Pak Chong district of Thailand. Methods: This work was carried out between May 2017 and July 2017 and 161 participants were enrolled. Participant questionnaires were completed during face-to-face interviews. Results: 161 sweet corn farmers (89.98%) were interviewed about patterns of chemical pesticide use. Two of the pesticides used in the pre-planting phase were moderately toxic: paraquat (used by 55.2% of farmers) and imidacloprid (used by 15.5% of farmers). In the pre-emergence phase, participants reported using two moderately toxic pesticides: alachlor (used by 48.8% of farmers) and chlorpyrifos (used by 2.4% of farmers). At the post-emergence phase, participants reported using six moderately toxic pesticides: chlorpyrifos (used by 60.7% of farmers), paraquat (used by 38.1% of farmers), imidacloprid (used by 7.2% of farmers), 2-4D (used by 3.6% of farmers), abamectin (used by 3.6% of farmers) and cypermethrin (used by 1.2% of farmers). Health literacy levels were moderate level (Mean score = 91.62, SD = ± 7.06) and pesticide use behaviors were low level (Mean score = 67.80, SD = ± 4.04). When examining the association between health literacy and pesticide use behaviors, we found that functional literacy was significantly associated with pesticide use behaviors. These findings suggest that health literacy, which includes self-management and decision-making skills, should be given greater attention as pesticide use behaviors were unsafe. Conclusion: It may be necessary to develop approaches to reduce pesticide use and promote health literacy, thereby protecting farmers, consumers, the environment (soil, water, and air) and ecosystems from pesticide-related hazards.

The association between health literacy and pesticide use behaviors among sweet corn farmers in the Pak Chong district of Thailand: a cross-sectional study

Background: Pesticide toxicity is an important health problem in Thailand due to the intensive use of hazardous pesticides.  This study aimed to determine and discuss patterns of pesticide use, health literacy, pesticide use behaviors and whether there is an association between health literacy and pesticide use behaviors among sweet corn farmers in the Pak Chong district, Thailand. Methods: This work was carried out between May 2017-July 2017 and 161 participants were enrolled. Participant questionnaires were completed during face-to-face interviews. Results:  This study found the response rate was 98.98%. 161 farmers were interviewed about patterns of chemical pesticide use. Two of the pesticides used in the pre-planting phase were moderately toxic: paraquat (used by 55.2% of farmers) and imidacloprid (used by 15.5% of farmers). In the pre-emergence phase, participants reported using two moderately toxic pesticides: alachlor (used by 48.8% of farmers) and chlorpyrifos (used by 2.4% of farmers). At the post-emergence phase, participants reported using six moderately toxic pesticides: chlorpyrifos (used by 60.7% of farmers), paraquat (used by 38.1% of farmers), imidacloprid (used by 7.2% of farmers), 2-4D (used by 3.6% of farmers), abamectin (used by 3.6% of farmers) and cypermethrin (used by 1.2% of farmers). Health literacy levels were moderate level (Mean score = 91.62, SD = ± 7.06) and pesticide use behaviors were low level (Mean score = 67.80, SD = ± 4.04). When examining the association between health literacy and pesticide use behaviors, we found that functional literacy was significantly associated with pesticide use behaviors. This suggests that health literacy, which includes self-management and decision-making skills, should be given greater attention as pesticide use behaviors were unsafe. Conclusion: It may be necessary to develop approaches to reduce pesticide use and promote health literacy, thereby protecting farmers, consumers, the environment (soil, water, and air) and ecosystems from pesticide-related hazards.

Process kinetics on physico-chemical and peroxidase activity for different blanching methods of sweet corn

Blanching was performed to inactivate the enzyme using microwave, steam and hot water blanching methods and effect on the enzymatic activity, chemical properties and physical properties of the sweet corn were studied. The effectiveness of each blanching process was evaluated by measuring the loss of peroxidase activity, which was lost after 60, 90 and 120 s with k-values 0.016, 0.024 and 0.028 s^-1 following first order kinetics for microwave, steam and hot water blanching respectively. The total sugar, ascorbic acid, moisture content, kernel mass and geometric diameter changed from 8.40 to 6.30, 7.20 and 7.50 g/100 g; 7.15 to 5.70, 6.10 and 6.60 mg/100 g; 76 to 79.20, 78.20 and 75.30%; 0.47 to 0.53, 0.50 and 0.42 g; 8.00 to 8.50, 8.30 and 7.20 mm at optimum level of blanching during microwave, steam and hot water blanching respectively, indicating higher retention of total sugar and ascorbic acid in microwave blanching. The change in colour, especially increase in brownness was observed during blanching processes. The average R² for zero-order model was 0.945, suggesting use of model for prediction of physico-chemical parameters during blanching process of sweet corn.

Effects of ultraviolet C, controlled atmosphere, and ultrasound pretreatment on free ferulic acid in canned sweet corn kernels

Because canned sweet corn kernel (CSCK) products are subject to high market competitiveness, producing them with a higher content of free ferulic acid (FFA), a functional ingredient, using non-thermal and green technologies may be an alternative solution for Thai exporters. This study aimed to investigate the effects of pre-canning ultraviolet C (UVC), controlled atmosphere (CA), and ultrasound treatments on the FFA content, texture, and colour of CSCKs. UVC irradiation (0, 1.94 and 4.01 kJ/m²) was tested in combination with storing corn under CA at %O₂:%CO₂:%N₂ ratios of 21:0.03:78, 3:10:87, and 3:15:82 before canning. Based on the FFA content, two UVC-CA pretreatments were selected for the ensuing experiment. The effects of the selected UVC-CAs in combination with 0, 10, or 20 min of 35 kHz ultrasound before canning were measured. The FFA content, moisture, texture, and colour of the CSCKs treated with the nine UVC-CA combinations were not significantly different. Corn irradiated with 1.94 kJ/m² UVC and stored under 3:15:82 %O₂:%CO₂:%N₂ before canning exhibited the highest FFA content, followed by corn treated with no UVC and stored at 3:15:82 %O₂:%CO₂:%N₂. Corn treated with ultrasound combined with the two selected UVC-CA treatments showed no differences in FFA content, moisture, texture, or colour. Corn kernels treated with UVC-CA-ultrasound had a higher FFA content than untreated kernels. UVC-CA-ultrasound pretreatment showed a trend of increasing CSCK FFA content with no change in physical properties. Thus, UVC-CA-ultrasound pretreatment appears to be an alternative process that might add value to CSCKs by increasing FFA content.

Genetic diversity of sweet corn inbreds using agro-morphological traits and microsatellite markers

Assessment of genetic diversity is a pre-requisite to broaden the genetic background of cultivated base of sweet corn, an endosperm mutant of field corn that alters starch biosynthesis pathway in endosperm. In the current investigation, genetic divergence among 39 inbred lines was assessed on the basis of 14 agro-morphological traits, two quality parameters and 63 microsatellite markers, selected on the basis of their association with QTLs affecting kernel quality. The cluster analysis based on unweighted pair-group method using arithmetic averages for agro-morphological and quality traits grouped the 39 inbreds into three clusters with 5, 14 and 20 genotypes, respectively. The unweighted neighbor-joining method for microsatellite markers also categorized the inbred lines into three major clusters grouping 10, 9 and 20 genotypes in cluster I, II and III, respectively. The two cluster distribution patterns showed approximately 36 percent similarity. The assay of 30 microsatellite repeats identified 82 alleles with allele size ranging from 80 to 400 bp. The major allele frequency and PIC value of the markers ranged from 0.42 to 0.79 and 0.27 to 0.63, respectively, which suggested the presence of high amount of polymorphism among the inbreds. The average heterozygosity was recorded to be 0.19 which signifies proper maintenance of inbred population. Principle co-ordinate analysis also depicted diverse nature of inbred lines and agreed well with the previously determined clustering pattern. This study has identified several inbreds, having good yield and high sugar content which will not only enhance the genetic background of sweet corn germplasm but will also lead to development of high-yielding hybrids with improved quality.

Microsatellite-based genetic diversity analyses of sugary1-, shrunken2- and double mutant- sweet corn inbreds for their utilization in breeding programme

Sweet corn has recently experienced sharp rise in demand worldwide. Recessive sugary1 (su1) and shrunken2 (sh2) that enhances kernel sweetness have been abundantly used in sweet corn breeding. Analyses of genetic diversity among sweet corn inbreds assume great significance for their effective utilization in hybrid breeding. A set of 48 diverse sweet corn genotypes encompassing su1su1, sh2sh2 and su1su1/sh2sh2 types were analyzed using 56 microsatellite markers. A total of 213 alleles with mean of 3.8 alleles per locus were generated. Two unique- and 12 rare- alleles were identified. The average PIC and genetic dissimilarity was 0.50 and 0.73, respectively. Cluster analysis grouped the inbreds into three major clusters, with each of the su1su1-, sh2sh2- and su1su1/sh2sh2-types were broadly clustered together. Principal coordinate analyses also depicted the diverse origin of the genotypes. The study identified inbreds for synthesis of pools and pedigree populations to develop novel inbreds. The study led to the identification of prospective heterotic combinations in various genetic backgrounds (sh2sh2 × sh2sh2, su1su1 × su1su1, su1su1/sh2sh2 × su1su1/sh2sh2, sh2sh2 × su1su1/sh2sh2 and su1su1 × su1su1/sh2sh2).

Exogenous spermidine improves seed germination of sweet corn via involvement in phytohormone interactions, H2O2 and relevant gene expression

BACKGROUND

The low seed vigor and poor field emergence are main factors that restricting the extension of sweet corn in China. Spermidine (Spd) plays an important role in plant growth and development, but little is known about the effect of Spd on sweet corn seed germination. Therefore the effect of exogenous Spd on seed germination and physiological and biochemical changes during seed imbibition of Xiantian No.5 were investigated in this study.

RESULTS

Spd soaking treatment not only improved seed germination percentage but also significantly enhanced seed vigor which was indicated by higher germination index, vigor index, shoot heights and dry weights of shoot and root compared with the control; while exogenous CHA, the biosynthesis inhibitor of Spd, significantly inhibited seed germination and declined seed vigor. Spd application significantly increased endogenous Spd, gibberellins and ethylene contents and simultaneously reduced ABA concentration in embryos during seed imbibition. In addition, the effects of exogenous Spd on H₂O₂ and MDA productions were also analyzed. Enhanced H₂O₂ concentration was observed in Spd-treated seed embryo, while no significant difference of MDA level in seed embryo was observed between Spd treatment and control. However, the lower H₂O₂ and significantly higher MDA contents than control were detected in CHA-treated seed embryos.

CONCLUSIONS

The results suggested that Spd contributing to fast seed germination and high seed vigor of sweet corn might be closely related with the metabolism of hormones including gibberellins, ABA and ethylene, and with the increase of H₂O₂ in the radical produced partly from Spd oxidation. In addition, Spd might play an important role in cell membrane integrity maintaining.

Sensory determinants of stated liking for vegetable names and actual liking for canned vegetables: A cross-country study among European adolescents

Sensory properties are reported as one of the main factors hindering an appropriate vegetable intake by the young. In the present work the sensory determinants of likings for vegetables were explored in adolescents of four European countries (Denmark, n = 88; France, n = 206; Italy, n = 110 and United Kingdom, n = 93). A questionnaire was designed to study cross country differences in stated liking for and familiarity with a list of vegetables popular among European markets (between-vegetable approach). A within-vegetable comparison approach with actual tasting was used to analyze differences and similarities in liking for canned pea and sweet corn samples across the countries. A close positive relationship between stated liking and familiarity was found. Irrespective of the country, one group of highly liked vegetables (carrots, tomatoes, green salad) was identified, characterized by innately liked tastes (sweet, umami), delicate flavour and bright appealing colour. A second group of highly disliked vegetables consists of cauliflowers and broccoli, characterized by disliked sensations such as bitter taste and objectionable flavour. Internal Preference Maps from actual liking scores indicate that the generally disliked tastes (bitter, sour), are clearly correlated with a negative hedonic response for both peas and sweet corn. The hedonic valence of a generally well accepted taste such as salty and texture descriptors depends on the type of vegetable. Internal preference maps from actual liking data indicate that flavour and appearance descriptors of the distinct sensory properties of each type of vegetable positively affect liking, while the intensity of unusual flavours is related to sample disliking.

A morel improved growth and suppressed Fusarium infection in sweet corn

A post-fire morel collected from Populus simonii stands in Mt. Qingling was identified as Morchella crassipes Mes-20 by using nuclear ribosomal DNA internal transcribed spacer phylogeny. It was inoculated into sweet corn to observe colonized roots in purified culture and in greenhouse experiments. The elongation and maturation zones of sweet corn were remarkably colonized at the cortex intercellular and intracellular cells, vessel cells, and around the Casparian strip, forming ectendomycorrhiza-like structures. Colonization was also observed in the zone of cell division proximal to the root cap. Greenhouse assays with sweet corn showed that this morel stimulated the development of the root system and significantly increased the dry root biomass. M. crassipes also significantly reduced the incidence of Fusarium verticillioides in the kernels of mature ears when inoculated into young ears before Fusarium inoculation and prevented Fusarium infection in corn ears compared with that of the control in the greenhouse. When grown under axenic conditions, M. crassipes produced the phytohormones abscisic acid, indole-3-acetic acid, and salicylic acid. The benefits to plants elicited by M. crassipes may result from these phytohormones which may improve the drought resistance, biomass growth and resistance to Fusarium.