Sweet Corn Research around the World 2015–2020

Optimizing feature selection with gradient boosting machines in PLS regression for predicting moisture and protein in multi-country corn kernels via NIR spectroscopy

Differences in moisture and protein content impact both nutritional value and processing efficiency of corn kernels. Near-infrared (NIR) spectroscopy can be used to estimate kernel composition, but models trained on a few environments may underestimate error rates and bias. We assembled corn samples from diverse international environments and used NIR with chemometrics and partial least squares regression (PLSR) to determine moisture and protein. The potential of five feature selection methods to improve prediction accuracy was assessed by extracting sensitive wavelengths. Gradient boosting machines (GBMs), particularly CatBoost and LightGBM, were found to effectively select crucial wavelengths for moisture (1409, 1900, 1908, 1932, 1953, 2174 nm) and protein (887, 1212, 1705, 1891, 2097, 2456 nm). SHAP plots highlighted significant wavelength contributions to model prediction. These results illustrate GBMs' effectiveness in feature engineering for agricultural and food sector applications, including developing multi-country global calibration models for moisture and protein in corn kernels.

Analysis of nutritional composition in opaque2- and crtRB1-based single- and double-biofortified super sweet corn

Sweet corn has emerged as a favorite food item worldwide owing to its kernel sweetness. However, traditional sweet corn cultivars are poor in provitamin-A (proA) and essential amino acids, viz., lysine and tryptophan. So far, no sweet corn hybrid with high nutritional qualities has been commercialized elsewhere. Here, we analyzed accumulation of provitamin-A (proA), lysine, and tryptophan in a set of mutant versions of (i) crtRB1-, (ii) o2-, and (iii) crtRB1 + o2-based sweet corn inbreds and hybrids with (iv) traditional sweet corn (wild-type: O2 + CrtRB1). The crtRB1- and crtRB1 + o2-based genotypes possessed significantly higher proA (17.31 ppm) over traditional sweet corn (2.83 ppm), while o2- and crtRB1 + o2-based genotypes possessed significantly higher lysine (0.345%) and tryptophan (0.080%) over traditional sweet corn (lysine 0.169%, tryptophan 0.036%). Late sowing favored high kernel lysine, proA, and green cob yield among hybrids. Sweetness (17.87%) among the improved inbreds and hybrids was comparable to the original sweetcorn genotypes (17.84%). Among the four genotypic classes, crtRB1 + o2-based improved genotypes showed stronger association among traits over genotypes with o2 and crtRB1 genes alone. Significant association was observed among (i) proA and BC (r = 0.99), (ii) proA and BCX (r = 0.93), (iii) lysine and tryptophan (r = 0.99), and (iv) green cob yield with fodder yield (r = 0.73) in sweet corn hybrids. The study demonstrated that combining crtRB1 and o2 genes did not pose any negative impact on nutritional, yield, and agronomic performance. Sweet corn with crtRB1 + o2 assumes significance for alleviating malnutrition through sustainable and cost-effective approach.

Feasibility of replacing waxy rice with waxy or sweet-waxy corn viewed from the structure and physicochemical properties of starches

To explore the feasibility of substituting waxy rice with waxy or sweet-waxy corn, eight varieties of waxy and sweet-waxy corns were selected, including three self-cultivated varieties (Feng nuo 168, Feng nuo 211, and Feng nuo 10). Their starches were isolated and used as research objects, and commercially available waxy rice starch (CAWR) and waxy corn starch (CAWC) were used as controls. X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, rapid viscosity analyzer, and rotational rheometer were used to analyze their physicochemical and structural characteristics. The morphologies of all corn starch granules were generally oval or round, with significant differences in particle size distributions. All ten starches exhibited a typical A-type crystal structure; however, their relative crystallinity varied from 20.08% to 31.43%. Chain length distribution analysis showed that the A/B ratio of Jing cai tian nuo 18 and Feng nuo 168 was similar to that of CAWR. Peak viscosities of corn starches were higher than that of CAWR, except for Feng nuo 10, while their setback values were lower than that of CAWR. Except for Feng nuo 10, the paste transparency of corn starches was higher than that of CAWR (10.77%), especially for Jing cai tian nuo 18 (up to 24%). In summary, Jing cai tian nuo 18 and Feng nuo 168 are promising candidates to replace CAWR in developing various rice-based products.

Unveiling the molecular regulatory mechanisms underlying sucrose accumulation and oil reduction in peanut kernels through genetic mapping and transcriptome analysis

Sucrose content is a key factor for the flavor of edible peanut, which determines the sweet taste of fresh peanut and also attribute to pleasant flavor of roasted peanut. To explore the genetic mechanism of the sucrose content in peanut, an F2 population was created by crossing the sweet cultivar Zhonghuatian 1 (ZHT1) with Nanyangbaipi (NYBP). A genomic region spanning 28.26 kb on chromosome A06 was identified for the sucrose content through genetic mapping, elucidating 47.5% phenotypic variance explained. As the sucrose content had a significantly negative correlation with the oil content, this region was also found to be related to the oil content explaining 37.2% of phenotype variation. In this region, Arahy.42CAD1 was characterized as the most likely candidate gene through a comprehensive analysis. The nuclear localization of Arahy.42CAD1 suggests its potential involvement in the regulation of gene expression for sucrose and oil contents in peanut. Transcriptome analysis of the developing seeds in both parents revealed that genes involved in glycolysis and triacylglycerol biosynthesis pathways were not significantly down-regulated in ZHT1, indicating that the sucrose accumulation was not attributed to the suppression of triacylglycerol biosynthesis. Based on the WGCNA analysis, Arahy.42CAD1 was co-expressed with the genes involved in vesicle transport and oil body assembly, suggesting that the sucrose accumulation may be caused by disruptions in TAG transportation or storage mechanisms. These findings offer new insights into the molecular mechanisms governing sucrose accumulation in peanut, and also provide a potential gene target for enhancing peanut flavor.

Unveiling the sweetness: evaluating yield and quality attributes of early generation sweet corn (Zea mays subsp. 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.

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.

Ultrasound-assisted hydrogen peroxide-ascorbic acid method to degrade sweet corncob polysaccharides can help treat type 2 diabetes via multiple pathways in vivo

In this study, we aimed to investigate the impact of various ultrasound durations on the structure and bioactivity of sweet corncob polysaccharides treated with ultrasound-assisted degradation using hydrogen peroxide and ascorbic acid (H2O2-Vc). We subjected sweet corncob polysaccharides to ultrasound treatment for 0, 30, 60, and 90 min alongside the H2O2-Vc method. We then analyzed their chemical composition and structure. Additionally, we administered these polysaccharides to mice with type 2 diabetes (T2DM) through gavage at a dosage of 200 mg/kg/day. The results indicated a significant reduction in the molecular weight of the degraded sweet corncob polysaccharides, while their composition remained relatively stable. However, the basic structure of the polysaccharides was retained. In vivo experiments demonstrated that ultrasound-assisted degradation of these polysaccharides had a positive impact on T2DM, particularly the 60-minute ultrasound treatment (UH-DSCBP-60 min), which effectively controlled blood glucose levels by regulating glycolipid metabolism in the livers of mice with T2DM. This approach also reduced inflammation and oxidative stress levels and inhibited disaccharide activity in the small intestine. We demonstrated that ultrasound can positively affect the sweet corncob polysaccharides hypoglycemic activity. The findings of our study provide a theoretical foundation for the valuable utilization of sweet corncob polysaccharides.

Enhancing Maize Productivity and Soil Health under Salt Stress through Physiological Adaptation and Metabolic Regulation Using Indigenous Biostimulants

Salinity poses a persistent threat to agricultural land, continuously jeopardizing global food security. This study aimed to enhance sweet corn (SC) fitness under varying levels of salinity using indigenous biostimulants (BioS) and to assess their impacts on plant performance and soil quality. The experiment included control (0 mM NaCl), moderate stress (MS; 50 mM NaCl), and severe stress (SS; 100 mM NaCl) conditions. Indigenous biostimulants, including compost (C), Bacillus sp., Bacillus subtilis (R), and a consortium of arbuscular mycorrhizal fungi (A) were applied either individually or in combination. Growth traits, physiological and biochemical parameters in maize plants, and the physico-chemical properties of their associated soils were assessed. SS negatively affected plant growth and soil quality. The RC combination significantly improved plant growth under SS, increasing aerial (238%) and root (220%) dry weights compared to controls. This treatment reduced hydrogen peroxide by 54% and increased peroxidase activity by 46% compared to controls. The indigenous biostimulants, particularly C and R, enhanced soil structure and mineral composition (K and Mg). Soil organic carbon and available phosphorus increased notably in C-treated soils. Furthermore, RC (437%) and CAR (354%) treatments exhibited a significant increase in glomalin content under SS. Indigenous biostimulants offer a promising strategy to mitigate salinity-related threats to agricultural land. They improve plant fitness, fine-tune metabolism, and reduce oxidative stress. In addition, the biostimulants improved the soil structure and mineral composition, highlighting their potential for reconstitution and sustainability in salt-affected areas. This approach holds promise for addressing salinity-related threats to global food security.

Effects of Blanching, Freezing and Canning on the Carbohydrates in Sweet Corn

Sweet corn is frequently consumed in the US and contains carbohydrates as major macronutrients. This study examined the effects of blanching, freezing, and canning on carbohydrates in sweet corn. Fresh bi-color sweet corn was picked in the field and processed immediately into frozen and canned samples. Simple sugars, starch, and dietary fiber (DF) (including total DF (TDF), insoluble DF (IDF) and two fractions of soluble DF (SDF)) were measured according to the AOAC methods. Additional glycomic analysis including oligosaccharides, monosaccharide composition of total polysaccharides (MCTP) and glycosidic linkage of total polysaccharides (GLTP) were analyzed using UHPLC-MS. Sucrose is the major simple sugar, and IDF is the main contributor to TDF. Sucrose and total simple sugar concentrations were not altered after blanching or freezing but were significantly reduced in canned samples. Kestose was the only oligosaccharide identified in sweet corn and decreased in all heat-treated or frozen samples. Starch content decreased in frozen samples but increased in canned samples. While two SDF fractions did not differ across all samples, blanching, freezing and canning resulted in increases in TDF and IDF. Six monosaccharides were identified as major building blocks of the total polysaccharides from MCTP analysis. Glucose and total monosaccharide concentrations increased in two canned samples. GLTP was also profoundly altered by different food processing methods. This study provided insights into the changes in the content and quality of carbohydrates in sweet corn after food processing. The data are important for accurate assessment of the carbohydrate intake from different sweet corn products.

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.

Integration of miRNA and mRNA analysis reveals the role of ribosome in to anti-artificial aging in sweetcorn

Sweetcorn is a kind of maize with high sugar content and has poor seed aging tolerance, which seriously limits its production. However, few studies have explored the artificial aging (AA) tolerance by miRNA-mRNA integration analysis in sweetcorn. Here, we characterized the physiological, biochemical and transcriptomic changes of two contrasting lines K62 and K107 treated with AA during time series. Both the germination indexes and antioxidant enzymes showed significant difference between two lines. The MDA content of AA-tolerant genotype K62 was significantly lower than that of K107 on the fourth and sixth day. Subsequently, 157 differentially expressed miRNAs (DEMIs) and 8878 differentially expressed mRNAs (DEMs) were identified by RNA-seq analysis under aging stress. The "ribosome" and "peroxisome" pathways were enriched to respond to aging stress, genes for both large units and small ribosomal subunits were significantly upregulated expressed and higher translation efficiency might exist in K62. Thirteen pairs of miRNA-target genes were obtained, and 8 miRNA-mRNA pairs might involve in ribosome protein and translation process. Our results elucidate the mechanism of sweetcorn response to AA at miRNA-mRNA level, and provide a new insight into sweetcorn AA response to stress.

Structural Characterization, In Vitro Digestion Property, and Biological Activity of Sweet Corn Cob Polysaccharide Iron (III) Complexes

This study aimed to enhance the utilization value of sweet corn cob, an agricultural cereal byproduct. Sweet corn cob polysaccharide-ron (III) complexes were prepared at four different temperatures (40 °C, 50 °C, 60 °C, and 70 °C). It was demonstrated that the complexes prepared at different temperatures were successfully bound to iron (III), and there was no significant difference in chemical composition; and SCCP-Fe-C demonstrated the highest iron content. The structural characterization suggested that sweet corn cob polysaccharide (SCCP) formed stable β-FeOOH iron nuclei with −OH and −OOH. All the four complexes’ thermal stability was enhanced, especially in SCCP-Fe-C. In vitro iron (III) release experiments revealed that all four complexes were rapidly released and acted as iron (III) supplements. Moreover, in vitro antioxidant, α-glucosidase, and α-amylase inhibition studies revealed that the biological activities of all four complexes were enhanced compared with those of SCCP. SCCP-Fe-B and SCCP-Fe-C exhibited the highest in vitro antioxidant, α-glucosidase, and α-amylase inhibition abilities. This study will suggest using sweet corn cobs, a natural agricultural cereal byproduct, in functional foods. Furthermore, we proposed that the complexes prepared from agricultural byproducts can be used as a potential iron supplement.

Sensory Evaluation and Model Prediction of Vacuum-Packed Fresh Corn during Long-Term Storage

The postharvest shelf life of fresh corn largely depends on the packaging method and storage temperature. This study investigated the effect of vacuum packaging (VP) with high-barrier (HB) or ordinary (OR) nylon/nylon/polypropylene (PP) composite films and the impact of storage temperature (4, 25, and 38 °C) on the shelf life of fresh corn. The sensory quality and color changes of the corn were evaluated, indicating a significant improvement in the glossiness (GL), sourness (SO), and color changes compared to corn packaged using OR films. The results showed that the HB films preserved corn freshness under refrigerated and normal temperature storage conditions, delaying color changes and SO development. A shelf-life model was established based on the Arrhenius equation. The predicted values of the corn at different temperatures were compared with the experimental data, indicating that the model could accurately predict the shelf life. The shelf life observed via sensory evaluation was more than 50% shorter than the results obtained by instrumental measurements. Therefore, sensory evaluation could be applied to determine shelf life and avoid food waste.

Breaking the tight genetic linkage between the a1 and sh2 genes led to the development of anthocyanin-rich purple-pericarp super-sweetcorn

The existence of purple-pericarp super-sweetcorn based on the supersweet mutation, shrunken2 (sh2), has not been previously reported, due to its extremely tight genetic linkage to a non-functional anthocyanin biosynthesis gene, anthocyaninless1 (a1). Generally, pericarp-pigmented starchy purple corn contains significantly higher anthocyanin. The development of purple-pericarp super-sweetcorn is dependent on breaking the a1-sh2 tight genetic linkage, which occurs at a very low frequency of < 1 in 1000 meiotic crossovers. Here, to develop purple-pericarp super-sweetcorn, an initial cross between a male purple-pericarp maize, 'Costa Rica' (A1Sh2.A1Sh2) and a female white shrunken2 super-sweetcorn, 'Tims-white' (a1sh2.a1sh2), was conducted. Subsequent self-pollination based on purple-pericarp-shrunken kernels identified a small frequency (0.08%) of initial heterozygous F3 segregants (A1a1.sh2sh2) producing a fully sh2 cob with a purple-pericarp phenotype, enabled by breaking the close genetic linkage between the a1 and sh2 genes. Resulting rounds of self-pollination generated a F6 homozygous purple-pericarp super-sweetcorn (A1A1.sh2sh2) line, 'Tim1'. Genome sequencing revealed a recombination break between the a1 and yz1 genes of the a1-yz1-x1-sh2  multigenic interval. The novel purple-pericarp super-sweetcorn produced a similar concentration of anthocyanin and sugar as in its purple-pericarp maize and white super-sweetcorn parents, respectively, potentially adding a broader range of health benefits than currently exists with standard yellow/white sweetcorn.

Comparison of the physicochemical properties of starches from maize reciprocal F1 hybrids and their parental lines

Heterosis on maize yield and quality is highly variable and depends on parental selection. This study investigated and compared the starch structure and physicochemical properties among four sweet-waxy maize lines, four waxy maize lines, and their eight reciprocal F1 hybrids. Compared with the sweet-waxy maize, waxy maize and F1 hybrids had lower extent of branching of amylopectin and relative crystallinity, and larger starch granule size. Waxy maize starch had higher breakdown viscosity and retrogradation percentage, and lower setback viscosity and gelatinization enthalpy than the sweet-waxy maize starch. Meanwhile, the peak and setback viscosities, and retrogradation enthalpy of most F1 hybrid starches were higher than those of their female parent, while gelatinization enthalpy was the opposite. The F1 hybrid starches had higher onset temperature and retrogradation percentage and lower gelatinization enthalpy than their male parent in general. In conclusion, this study provides a framework for the production of new hybrids.

Stability yield indices on different sweet corn hybrids based on AMMI analysis

Currently, sweet corn is considered an important crop due to its high sugar content and low starch content. Important sugars in sweet corn include sucrose, fructose, glucose, and maltose. The purpose of the present study was to use the yield indices of the eight examined sweet corn hybrids and the correlation of the yield indices together. Concentration is important for consumers in terms of yield indices. The research site was located at the Látókép Experimental Station of the University of Debrecen. The small plot experiment had a strip plot design with four replications. The previous crop was sweet corn; the plant density was 64 thousand/ha. The obtained result indicates that Biplot AMMI based on IPCA1 showed that the DB, NO, GS, and GB hybrids had stability and high performance in terms of yield indices. At the same time, fructose and glucose had stable parameters for the hybrids involved in the study. IPCA1 AMMI biplot showed that the ME hybrid had stability and high performance in terms of iron and zinc as well. IPCA2 AMMI biplot showed that DE, GB, and GS hybrids had stability and the highest performance on yield parameters in the scope of the research. Fructose, glucose, and sucrose had stable parameters on hybrids based on IPCA2. The DB and SE hybrids had desirable performance in Lutein and Zeaxanthin based on the biplot. The DE hybrid had a maximum performance on iron and zinc parameters.

Transcriptome Analysis Identifies Novel Genes Associated with Low-Temperature Seed Germination in Sweet Corn

Typically, sweet corn, particularly sh2 sweet corn, has low seed vigor owing to its high sugar and low starch content, which is a major problem in sweet corn production, particularly at low temperatures. There is considerable variation in the germination rates among sweet corn varieties under low-temperature conditions, and the underlying mechanisms behind this phenomenon remain unclear. In this study, we screened two inbred sweet corn lines (tolerant line L282 and sensitive line L693) differing in their low-temperature germination rates; while no difference was observed in their germination rates at normal temperatures. To identify the specifically induced genes influencing the germination capacity of sweet corn at low temperatures, a transcriptome analysis of the two lines was conducted at both normal and low temperatures. Compared to the lines at a normal temperature, 3926 and 1404 differently expressed genes (DEGs) were identified from L282 and L693, respectively, under low-temperature conditions. Of them, 830 DEGs were common DEGs (cDEGs) that were identified from both L282 and L693, which were majorly enriched in terms of microtubule-based processes, histone H3-K9 modification, single-organism cellular processes, and carbohydrate metabolic processes. In addition, 3096 special DEGs (sDEGs), with 2199 upregulated and 897 downregulated, were detected in the tolerant line L282, but not in the sensitive line L693. These sDEGs were primarily related to plasma membranes and oxygen-containing compounds. Furthermore, electric conductivity measurements demonstrated that the membrane of L282 experienced less damage, which is consistent with its strong tolerance at low temperatures. These results expand our understanding of the complex mechanisms involved in the cold germination of sweet corn and provide a set of candidate genes for further genetic analysis.

Allelic variation in shrunken2 gene affecting kernel sweetness in exotic-and indigenous-maize inbreds

Sweet corn has become a popular food worldwide. It possesses six-times more sugar than field corn due to the presence of recessive shrunken2 (sh2) gene. Despite availability of diverse sweet corn germplasm, comprehensive characterization of sh2 has not been undertaken so far. Here, entire Sh2 gene (7320 bp) among five field corn-(Sh2Sh2) and six sweet corn-(sh2sh2) inbreds was sequenced. A total of 686 SNPs and 372 InDels were identified, of which three SNPs differentiated the wild-(Sh2) and mutant-(sh2) allele. Ten InDel markers were developed to assess sh2 gene-based diversity among 23 sweet corn and 25 field corn lines. Twenty-five alleles and 47 haplotypes of sh2 were identified among 48 inbreds. Among markers, MGU-InDel-2, MGU-InDel-3, MGU-InDel-5 and MGU-InDel-8 had PIC>0.5. Major allele frequency varied from 0.458–0.958. The gene sequence of these maize inbreds was compared with 25 orthologues of monocots. Sh2 gene possessed 15–18 exons with 6-225bp among maize, while it was 6–21 exons with 30-441bp among orthologues. While intron length across maize genotypes varied between 67-2069bp, the same among orthologues was 57–2713 bp. Sh2-encoded AGPase domain was more conserved than NTP transferase domain. Nucleotide and protein sequences of sh2 in maize and orthologues revealed that rice orthologue was closer to maize than other monocots. The study also provided details of motifs and domains present in sh2 gene, physicochemical properties and secondary structure of SH2 protein in maize inbreds and orthologues. This study reports detailed characterization and diversity analysis in sh2 gene of maize and related orthologues in various monocots.

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.

Responses of Soil Carbon Pools and Carbon Management Index to Nitrogen Substitution Treatments in a Sweet Maize Farmland in South China

In China, excessive nitrogen fertilizer application in sweet maize fields contributes to greenhouse gas emissions. This study used maize straw (MS), cow dung (CD), biogas residue (BR), and straw-based biochar (CB) to substitute the mineral nitrogen fertilizer at 20% and 50% ratios in the Pearl River Delta in China. In comparison with a conventional amount of mineral nitrogen fertilizer (CK), the soil organic carbon (SOC) storages of the different treatments increased by 6.5–183.0%. The CB treatment significantly improved the inert organic carbon pool in the soil, while other types of organic materials promoted the formation of activated carbon pools. The treatments increased the soil carbon pool management index by 21.1–111.0% compared to the CK. Moreover, the CB treatments increased the soil carbon sequestration index by 78.3% and 155.8% compared to the CK. In general, substituting the mineral N fertilizer with BR, CB, and CD could improve the SOC accumulation in sweet maize farmland in South China. The CB at the high substitution level was the best measure for stabilizing carbon sequestration in the sweet maize cropping system. This experiment provides valuable information for ensuring the clean production of sweet maize in a typical subtropical area in East Asia.

Multi-Gene Phylogenetic Approach for Identification and Diversity Analysis of Bipolaris maydis and Curvularia lunata Isolates Causing Foliar Blight of Zea mays

Bipolaris species are known to be important plant pathogens that commonly cause leaf spot, root rot, and seedling blight in a wide range of hosts worldwide. In 2017, complex symptomatic cases of maydis leaf blight (caused by Bipolaris maydis) and maize leaf spot (caused by Curvularia lunata) have become increasingly significant in the main maize-growing regions of India. A total of 186 samples of maydis leaf blight and 129 maize leaf spot samples were collected, in 2017, from 20 sampling sites in the main maize-growing regions of India to explore the diversity and identity of this pathogenic causal agent. A total of 77 Bipolaris maydis isolates and 74 Curvularia lunata isolates were screened based on morphological and molecular characterization and phylogenetic analysis based on ribosomal markers—nuclear ribosomal DNA (rDNA) internal transcribed spacer (ITS) region, 28S nuclear ribosomal large subunit rRNA gene (LSU), D1/D2 domain of large-subunit (LSU) ribosomal DNA (rDNA), and protein-coding gene-glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Due to a dearth of molecular data from ex-type cultures, the use of few gene regions for species resolution, and overlapping morphological features, species recognition in Bipolaris has proven difficult. The present study used the multi-gene phylogenetic approach for proper identification and diversity of geographically distributed B. maydis and C. lunata isolates in Indian settings and provides useful insight into and explanation of its quantitative findings.

Diverse Planting Density-Driven Nutrient and Yield Enhancement of Sweet Corn by Zinc and Selenium Foliar Application

Corn (Zea mays L.) is one of the major cereal crops cultivated worldwide. Zinc and selenium are important nutrients for humans and plants, and their deficiency is a cause for concern in most developing countries. Sweet corn fertilized with zinc and selenium can mitigate this problem. Therefore, the objective of this study was to investigate the effects of fertilization with Zn and Se on the yield and quality of sweet corn varieties under different planting densities. The experimental design used was a split-plot based on a randomized complete block design with three replications. Compared to the control, significant differences were recorded in grain yield, leaf area index, and plant height (i.e., Zn/Se + density + variety) treatments. Non-significant differences in the number of kernels per cob, sugar content and crude protein were recorded under different treatments. Significant differences in grain yield, water-soluble sugar, and zinc and selenium content in grain were recorded. Grain yield was higher in Selenium than in Zinc treatments, with a mean difference of 0.05 t ha−1. We conclude that grain yield and selenium content in grain were influenced by selenium foliar application, while water-soluble sugar and zinc content in grain were influenced by foliar zinc application.

High Plains wheat mosaic virus: An enigmatic disease of wheat and corn causing the High Plains disease

BRIEF HISTORY

In 1993, severe mosaic and necrosis symptoms were observed on corn (maize) and wheat from several Great Plains states of the USA. Based on the geographical location of infections, the disease was named High Plains disease and the causal agent was tentatively named High Plains virus. Subsequently, researchers renamed this virus as maize red stripe virus and wheat mosaic virus to represent the host and symptom phenotype of the virus. After sequencing the genome of the pathogen, the causal agent of High Plains disease was officially named as High Plains wheat mosaic virus. Hence, High Plains virus, maize red stripe virus, wheat mosaic virus, and High Plains wheat mosaic virus (HPWMoV) are synonyms for the causal agent of High Plains disease.

TAXONOMY

High Plains wheat mosaic virus is one of the 21 definitive species in the genus Emaravirus in the family Fimoviridae.

VIRION

The genomic RNAs are encapsidated in thread-like nucleocapsids in double-membrane 80-200 nm spherical or ovoid virions.

GENOME CHARACTERIZATION

The HPWMoV genome consists of eight single-stranded negative-sense RNA segments encoding a single open reading frame (ORF) in each genomic RNA segment. RNA 1 is 6,981-nucleotide (nt) long, coding for a 2,272 amino acid protein of RNA-dependent RNA polymerase. RNA 2 is 2,211-nt long and codes for a 667 amino acid glycoprotein precursor. RNA 3 has two variants of 1,439- and 1,441-nt length that code for 286 and 289 amino acid nucleocapsid proteins, respectively. RNA 4 is 1,682-nt long, coding for a 364 amino acid protein. RNA 5 and RNA 6 are 1,715- and 1,752-nt long, respectively, and code for 478 and 492 amino acid proteins, respectively. RNA 7 and RNA 8 are 1,434- and 1,339-nt long, code for 305 and 176 amino acid proteins, respectively.

BIOLOGICAL PROPERTIES

HPWMoV can infect wheat, corn (maize), barley, rye brome, oat, rye, green foxtail, yellow foxtail, and foxtail barley. HPWMoV is transmitted by the wheat curl mite and through corn seed.

DISEASE MANAGEMENT

Genetic resistance against HPWMoV in wheat is not available, but most commercial corn hybrids are resistant while sweet corn varieties remain susceptible. Even though corn hybrids are resistant to virus, it still serves as a green bridge host that enables mites to carry the virus from corn to new crop wheat in the autumn. The main management strategy for High Plains disease in wheat relies on the management of green bridge hosts. Cultural practices such as avoiding early planting can be used to avoid mite buildup and virus infections.