Variation in pigments in pecan testa during kernel development and storage

The pecan (Carya illinoinensis) is an important tree nut worldwide. Browning of the testa during storage considerably reduces its quality. However, the pigments that cause browning and their accumulation patterns are poorly understood. We analyzed the color changes in the testa during the five developmental stages of the kernel after storage at room temperature to compare differences in their color and identify the pigments. Samples exhibiting different colors along with their corresponding -80 °C storage samples were selected for metabolomic analysis. A total of 591 phenolic compounds were detected, 52 phenolics showed regulatory effects on testa discoloration, and 59 metabolites were identified as possible precursors of the pigments. This study revealed the most thorough phenolic composition of pecan to date. Further, the findings provide new insights into the mechanisms of testa browning, deepens our understanding of the bioactive value of pecans, and contributes to the breeding of less browning-susceptible varieties.

Transcriptome profile of pecan scab resistant and susceptible trees from a pecan provenance collection

Pecan scab is a devastating disease that causes damage to pecan (Carya illinoinensis (Wangenh.) K. Koch) fruit and leaves. The disease is caused by the fungus Venturia effusa (G. Winter) and the main management practice for controlling the disease is by application of fungicides at 2-to-3-week intervals throughout the growing season. Besides disease-related yield loss, application of fungicides can result in considerable cost and increases the likelihood of fungicide resistance developing in the pathogen. Resistant cultivars are available for pecan growers; although, in several cases resistance has been overcome as the pathogen adapts to infect resistant hosts. Despite the importance of host resistance in scab management, there is little information regarding the molecular basis of genetic resistance to pecan scab.The purpose of this study was to elucidate mechanisms of natural pecan scab resistance by analyzing transcripts that are differentially expressed in pecan leaf samples from scab resistant and susceptible trees. The leaf samples were collected from trees in a provenance collection orchard that represents the natural range of pecan in the US and Mexico. Trees in the orchard have been exposed to natural scab infections since planting in 1989, and scab ratings were collected over three seasons. Based on this data, ten susceptible trees and ten resistant trees were selected for analysis. RNA-seq data was collected and analyzed for diseased and non-diseased parts of susceptible trees as well as for resistant trees. A total of 313 genes were found to be differentially expressed when comparing resistant and susceptible trees without disease. For susceptible samples showing scab symptoms, 1,454 genes were identified as differentially expressed compared to non-diseased susceptible samples. Many genes involved in pathogen recognition, defense responses, and signal transduction were up-regulated in diseased samples of susceptible trees, whereas differentially expressed genes in pecan scab resistant samples were generally down-regulated compared to non-diseased susceptible samples.Our results provide the first account of candidate genes involved in resistance/susceptibility to pecan scab under natural conditions in a pecan orchard. This information can be used to aid pecan breeding programs and development of biotechnology-based approaches for generating pecan cultivars with more durable scab resistance.

CiAP2/ERF65 and CiAP2/ERF106, a pair of homologous genes in pecan (Carya illinoensis), regulate plant responses during submergence in transgenic Arabidopsis thaliana

When plants are entirely submerged, photosynthesis and respiration are severely restricted, affecting plant growth and potentially even causing plant death. The AP2/ERF superfamily has been widely reported to play a vital role in plant growth, development and resistance to biotic and abiotic stresses. However, no relevant studies exist on flooding stress in pecan. In this investigation, we observed that CiAP2/ERF65 positively modulated the hypoxia response during submergence, whereas CiAP2/ERF106 was sensitive to submergence. The levels of physiological and biochemical indicators, such as POD, CAT and among others, in CiAP2/ERF65-OE lines were significantly higher than those in wild-type Arabidopsis thaliana, indicating that the antioxidant capacity of CiAP2/ERF65-OE lines was enhanced under submergence. The RNA-seq results revealed that the maintenance of the expression levels of the antenna protein gene, different signaling pathways for regulation, as well as the storage and consumption of ATP, might account for the opposite phenotypes of CiAP2/ERF65 and CiAP2/ERF106. Furthermore, the expression of some stress-related genes was altered during submergence and reoxygenation. Overall, these findings enhance our understanding of submergence stress in pecan, providing important candidate genes for the molecular design and breeding of hypoxia resistant in plants.

First report of Fusarium concentricum as a causal agent of Fusarium leaf blotch on pecan (Carya illinoinensis) in Southeast China

The economically important nut crop pecan (Carya illinoinensis (Wangenh.) K. Koch) is seriously affected by increasing incidence of fungal disease worldwide (Xiao et al 2021). The top leaves of the pecan variety 'Pawnee' in the orchard of Zhejiang A&F University, Zhejiang, China were damaged by massive dark brown plaques in summer to autumn 2021. The causal agent was isolated from leaves with target plaques following the steps: sterilized with 70% alcohol (30 s × 2), rinsed with sterilized water (3 ×) before and after 5% sodium hypochlorite (30 s), excised the plaques, and placed on PDA medium at 28℃ in a dark incubator for 3-d. The mycelium on the edge of each colony was transferred to fresh SNA medium in dark for 2 weeks to induce conidia formation. A few conidia-germinated mycelia were transferredand inoculated on new plates containing fresh PDA medium to obtain the purified cultures. Koch's postulates were applied to validate the pathogenicity of the purified isolates. Non-woundedly healthy leaves (disinfected with 5% sodium hypochlorite) of 'Pawnee' seedlings were inoculated with 5 mm 7-d old purified cultures. Dark-brown spots appeared on the leaves 2 days post inoculation at 25℃. The spots became larger accompanied by partially cracking and slight deformation of inoculated leaves from day 2 to day 4, while the control leaves remained asymptomatic. A re-isolated strain ZJ-6 from these infected leaves was identified as the pathogenic isolate with the same symptom as the previous one. Morphologically, aerial mycelia of the pathogenic isolate ZJ-6 cashmere and white. The reverse of colony orange. The edge of the colony appeared gradually thinner, the aerial mycelia loose and flocky, and the matrix mycelium whitened. Hyphae were septate, translucent with smooth wall and 1.47-7.14 µm in width. Microconidia (n = 20) obovoid to fusoid, mainly with 0-septate, 4.45-7.78×4.79-16.25 µm. Macroconidia (n = 20) sickle, mainly with 3-5 septa, 5.56-10.28×56.67-114.54 µm. Simultaneous of monophialidic and polyphialidic conidiophores. Conidiophore width 1.47-3.68 µm, slightly smaller than vegetative hyphae. The morphological characteristics matched with previous descriptions of Fusarium species (Nirenberg and O'Donnell 1998; Wang et al 2013). The identity of ZJ-6 was confirmed by phylogenetic reconstruction using the concatenated sequences of the ATP citrate lyase (ACL1), Calmodulin (CaM), the internal transcribed spacer (ITS) rDNA region, ribosomal RNA gene (LSU), the largest subunit of DNA-dependent RNA polymerase II (RPB1), partial translation elongation factor-1 alpha (TEF) and β-Tubulin (TUB). To this end, the genomic DNA of ZJ-6 was extracted by the M5 hipermix-MF859 (Mei5 Biotechnology) and submitted to GenBank under the accession numbers OP933646, OP933647, OP925890, OP925889, OP933396, OP933648, and OP933397, respectively. The obtained sequences of ZJ-6 were used for nucleotide BLAST against thetandard databases, respectively, and the strains with sequence identification values above 98% were selected to construct multiple alignment for building a phylogenetic tree. This analyses allowed the identification of ZJ-6 as Fusarium concentricum Nirenberg & O'Donnell, a species with few reports that can cause serious damage to the fruits and branches of other hosts (Hasan et al 2020; Huda-Shakirah et al 2020; Wang et al 2013). This is the first report of pathogenic F. concentricum on pecan in Southeast China that caused no harvest of infected plants.

Mineral nutrient dynamics in pecans (Carya illinoensis) 'Mahan' grown in southern China

It is of great significance to study the nutritional characteristics of plants. Further understanding of plant mineral nutrient dynamics can provide theoretical basis for scientific fertilization to improve fruit quality and yield. In this study, eight mineral elements (N, P, K, Ca, Mg, Mn, Zn, B) were measured at regular intervals in leaves and kernels of the pecan "Mahan" planted in southern China. The study discussed the characteristics of mineral nutrient dynamics of pecan through the indicators of concentration, accumulation and cumulative relative rate, a new first proposed indicator, and focused on critical time, intensity, amount of mineral nutrients required in pecan during the fruit developing period, as well as the transfer information of the elements in leaves and kernels. The results show that the mineral nutrient requirements of the leaves and kernels are not identical, with an upward trend in nutrient accumulation within the kernel. The most abundant mineral nutrients in the leaves and kernels were N, K and Ca with Ca being greater than N in leaves. In particular, the concentration of Mn in pecan 'Mahan' is higher than that of other plants, and its Mg content is also higher than that of P in kernels. The dynamic changes of mineral nutrients in walnut showed obvious stages, with a trend of "slow (before mid-July) - fast (mid-July to late August) - slow (late August to late September) - fast (late September to harvest)". The "critical period" of kernels was before mid-July, during which the cumulative relative rates increased rapidly, indicating that the kernels had a great potential to absorb mineral nutrients. Significant accumulation of mineral nutrients occurred from mid-July to late August and late September to the end.

First Report of Scab Disease Caused by Venturia effusa on Pecan in Anhui Province of China

Pecan (Carya illinoinensis) is a world-famous nut tree which widely cultivated in China. Quanjiao County, located in Anhui province, is reputed to be the capital of pecan production in China. Since 2019, typical scab symptoms were observed on most pecan cultivars in orchards located in the regions of Quanjiao (32°5'7.08″ N, 118°16'2.91″ E). In April, dark brown to black lesions of scab could be observed on both the abaxial and adaxial surface of the lamina, and were often associated with the veins or midrib. In July, small, brownish, and circular lesions ranging from 1 to 2 mm in diameter were observed at the end of stems and shoulder of the fruit. In the surveyed orchards, disease incidence on the leaves reached more than 35%. While, according to the number of infected nut clusters, disease incidence ranged from 40 to 60% on the infected fruits. Using a sterilized scalpel, conidia were scraped from the surface of a single lesion from the infected leaves or fruits, and a dilute spore suspension was prepared in sterile distilled water, of which 100 microliters was spread on 1% water-agar plate (Bock et al. 2014). The conidia were incubated at 25°C for 48 h under fluorescent lights with a 12-hphotoperiod. Single germinated conidia were selected and transferred into potato dextrose agar (PDA) plate to obtain monospore isolates. From 2019 to 2020, more than 20 isolates were obtained from the infected leaves and fruits. Incubated at 24°C for 6 weeks in darkness on PDA, the colonies were gray-black with circular morphology and floccose texture, which were consistent with the characteristics of Venturia effusa described previously (Gottwald 1982). The conidia were pyriform to ellipsoid, zero to one septate, smooth, attenuated towards apex and base, base truncate, pale brown and 10.08 to 18.14 × 4.86 to 9.56 μm (n = 50) in size. To further identify the isolates, the regions of internal transcribed spacer (ITS), beta-tubulin 2 (TUB2) and translation elongation factor 1 alpha (EF1-a) were amplified and sequenced from genomic DNA for the three representative isolates (AH-81 and AH-82 from the infected leaves, and AH-41 from the infected fruits), respectively (White et al. 1990; Young et al. 2018; Bensch et al. 2006). Sequences of them were deposited in GenBank under nos. OP199056 to OP199058 (ITS), OP566581 to OP566583 (TUB2) and OP566578 to OP566580 (EF1-a). Multilocus phylogenetic analysis revealed that three isolates and V. effusa were clustered in the same clade, indicating high genetic similarity between these organisms. Their morphological and molecular characteristics were consistent with those for V. effusa. The pathogenicity of three isolates were tested on two-year-old container-grown pecan seedlings, which were grown in the nursery. The conidial suspension with a concentration of 5 × 105 conidia/ml was sprayed evenly on the surface of leaves of a healthy pecan seedling, and each isolate inoculated four pecan seedlings. The pathogenicity experiment was repeated three times. The plants inoculated with sterile water were used a negative control. The inoculated plants were enclosed in plastic bags for 2 days, and kept in the nursery greenhouse. Four weeks after inoculation, a similar symptom of scab was observed on leaves of cultivar Mahan, and V. effusa was isolated again from inoculated leaves with the frequency of 100% by the single-spore isolation, whereas no symptoms were observed on the control plants. To our knowledge, this is the first report of V. effusa as a scab pathogen on pecan in Anhui Province of China and underscores the need for monitoring this disease and developing disease control strategies to prevent severe reduction in the value of fruit. References: Bensch, K., et al. 2006. Studies in Mycology, 55(1): 299-305. Bock, C. H., et al. 2014. Forest Pathology, 44(4): 266-275. Gottwald, T. R. 1982. Taxonomy of the pecan scab fungus Cladosporium caryigenum. Mycologia. 74 (3), 382-390. White, T. T., et al. 1990. Page 315 in: PCR Protocols: A Guide to Methods and Application. Academic Press, San Diego, CA. Young, C. A., et al. 2018. Phytopathology, 108(7): 837-846. The author(s) declare no conflict of interest. Keywords: Venturia effusa, Scab, Pecan, Identification †Indicates the corresponding author.Y. Q. Zhao; zhaoyuqiang123@126.com.

Enzyme inhibitory activities of phenolic compounds in pecan and the effect on starch digestion

Pecan has been widely recognized for its high phenolic content and related health benefits. Previous studies indicated that pecan consumption might be beneficial in treating type 2 diabetes mellitus (T2DM). The objective of this study was to investigate the enzyme inhibitory activities of pecan phenolic compounds (PPC) and the effect in starch hydrolysis by in vitro simulation digestion. PPC was extracted with a solvent mixture from pecan powder and freeze-dried. PPC was tested for the inhibitory effects on α-amylase and α-glucosidase via enzyme kinetics study. Static in vitro digestion trials were conducted to evaluate the effect of intake of PPC and pecan powder on starch digestion. PPC displayed a potent inhibition effect against α-amylase and α-glucosidase with IC₅₀ of 77.9 μg/mL and 9.02 μg/mL, respectively. Both PPC and pecan powder inhibited starch hydrolysis during in vitro digestion. However, the level of inhibition was lower than that from the catalytic kinetics study, and PPC exhibited a higher inhibition effect than pecan powder. The results confirmed the potential of PPC as a novel enzyme inhibitor for T2DM management. The information is helpful to promote the intake of pecan nuts for health-enhancing effects.

Pecan agroforestry systems improve soil quality by stimulating enzyme activity

BACKGROUND

Forest and plantation intercropping are efficient agroforestry systems that optimize land use and promote agroforestry around the world. However, diverse agroforestry systems on the same upper-plantation differently affect the physical and chemical properties of the soil.

METHODS

The treatments for this study included a single cultivation (CK) pecan control and three agroforestry systems (pecan + Paeonia suffruticosa + Hemerocallis citrina, pecan + Paeonia suffruticosa, and pecan + Paeonia lactiflora). Soil samples were categorized according to the sampling depth (0-20 cm, 20-40 cm, 40-60 cm).

RESULTS

The results demonstrated that the bulk density (BD) of soil under the pecan agroforestry system (PPH and PPL) was reduced by 16.13% and 7.10%, respectively, and the soil moisture content (MC) and total soil porosity (TPO) increased. Improvements in the physical properties of the soil under the PPS agroforestry system were not obvious when compared with the pecan monoculture. The soil total phosphorus (TP), total nitrogen (TN), available potassium (AK), and total carbon (TC) increased significantly, while the soil urease (S-UE), alkaline phosphatase (S-AKP), and 1,4-β-N-acetylglucosamines (S-NAG) enzyme activity also increased significantly, following agroforestry. Overall, the pecan agroforestry system significantly improved the physical properties of the pecan plantation soil, enriched the soil nutrients, and increased the activity of soil enzymes related to TC, TN, and TP cycles.

Comparison analysis of widely-targeted metabolomics revealed the variation of potential astringent ingredients and their dynamic accumulation in the seed coats of both Carya cathayensis and Carya illinoinensis

Pecan and hickory nuts are two of consumers' favorite ones. Pecan seeds can be eaten fresh, while hickory ones must remove astringency before eating. Here, we reported that total phenols, flavonoids and condensed tannins of hickory seeds were reduced after de-astringent treatments. They gradually increased with development, showing higher levels in hickory seed coat at mid-late periods than that in pecan's. Widely-targeted metabonomics analysis of developing testa identified 424 kinds of components, including 101, 38, 58, 27 classes of flavonoids, tannins, phenolic acids, organic acids and others, showing 16 different changing trends. Notably, most kinds of flavonoids, hydrolysable tannins and phenolic acids at maturity were more than that of pecan's, while oligomeric condensed tannins were opposite. Gene expression analysis provided further explanations for their dynamic accumulation. These results unraveled potential astringent components in hickory testa and preliminary molecular mechanisms of their dynamic changes, offering theoretical basis for the targeted de-astringency.

Immunoproteomic identification of allergenic proteins in pecan (Carya illinoinensis) pollen

Pecan (C. illinoinensis) pollen is an important cause of allergic respiratory disease. Pecan is distributed worldwide as shade, ornamental or cultivation tree. To date three well known pecan food allergens have been reported, however, pollen allergens have not been identified. Here, we describe the first identification of IgE recognized pecan pollen proteins, for which proteins were analyzed by 2-DE and immunoblotting using a pool of 8 sera from pecan sensitive patients as primary antibody. IgE recognized protein spots were analyzed by LC-MS/MS and identified using a database of translated protein sequences obtained by the assembly of C. illinoinensis public transcriptomic information. This study has identified 17 IgE binding proteins from pecan pollen including proteins widely recognized as allergens and panallergens. These findings will contribute to develop specific diagnosis and treatment of pecan pollen allergy. SIGNIFICANCE: Pecan is a tree highly valued for its fruits that have a great commercial value. To date three pecan seed storage proteins have been officially recognized by the WHO/IUIS allergen nomenclature subcommittee as food allergens (Car i 1, Car i 2 and Car i 4). Pecan tree pollen is highly allergenic and a clinically relevant cause of allergies in North America (USA and Mexico) and regions where the tree is extensively cultivated (Israel, South Africa, Australia, Egypt, Peru, Argentina, and Brazil). Here, we describe the first identification of IgE recognized pollen proteins using an immunoproteomics approach and a protein database created by the assembly of pecan public transcriptomic information. The findings described here will allow the development of new diagnostic and therapeutic modalities for pecan pollen allergy.

Stem canker caused by Phomopsis spp. Induces changes in polyamine levels and chlorophyll fluorescence parameters in pecan leaves

Pecan plants are attacked by the fungus Phomopsis spp. that causes stem canker, a serious and emerging disease in commercial orchards. Stem canker, which has been reported in several countries, negatively affects tree canopy health, eventually leading to production losses. The purpose of this study was to inquire into the physiology of pecan plants under stem canker attack by Phomopsis spp. To this end, pecan plants were inoculated with an isolate of Phomopsis spp. and several parameters, such as polyamines, proline, sugars, starch, chlorophyll fluorescence and canopy temperature were analysed. Under artificial inoculation, a high disease incidence was observed with symptoms similar to those in plants showing stem canker under field conditions. Furthermore, the infected stem showed dead tissue with brown necrotic discolouration in the xylem tissue. The free polyamines putrescine, spermidine, and spermine were detected and their levels decreased as leaves aged in the infected plants with respect to the controls. Chlorophyll fluorescence parameters, such as Sm, ψEO, and QbRC decreased under plant infection and therefore the K-band increased. Canopy temperature and proline content increased in the infected plants with respect to the controls while sugar content decreased. These data suggest that stem canker caused by Phomopsis spp. induces physiological changes that are similar to those observed in plants under drought stress. To our knowledge, this is the first study that documents the physiological and biochemical effects derived from pecan-Phomopsis interaction.

Transcriptomic analysis reveals potential pathways associated with salt resistance in pecan (Carya illinoensis K. Koch)

Soil salinity is a serious abiotic stress worldwide. Pecan plants (Carya illinoensis K. Koch) have been suggested for cultivation in soils with high levels of salinity owing to their huge demand. To understand the potential molecular mechanisms in pecan in response to salt stress, RNA-sequencing technology was used to compare the transcriptomes of pecan plants treated with 0, 0.3 %, or 0.6 % NaCl solutions. The results indicated that 170,086 unigenes were obtained from pecan leaf cDNA samples. Based on the assembled de novo transcriptome, 53, 535, and 7358 differentially expressed genes (DEGs) were detected between untreated and salt-treated leaves at 8, 24, and 48 h, respectively. Because of the large number of DEGs across different contrasts, a Gene Set Enrichment Analysis was selected to identify gene pathways associated with salt treatment. A total of 1858 DEGs were enriched in 66 gene sets, including 22 up-regulated and 47 down-regulated gene sets in the salt treatment groups, compared with those in the control groups. The up-regulated gene sets were mainly involved in the response to salicylic acid; the regulation of the jasmonic acid-mediated signalling pathway during the short-term treatment (8 h); and the cellular response to hypoxia, cellular respiration, and RNA modification during the long-term treatment (24-48 h). The down-regulated gene sets were predominately associated with photosynthesis, water transport, and the metabolic biosynthetic process under salt stress. Genes related to the Really Interesting New Gene superfamily protein and F-box domain protein in the ubiquitin-dependent degradation pathway were significantly up-regulated or down-regulated in different periods of the regulating process. Overall, these results not only enrich genomic resources but also provide insights into the molecular mechanism in pecan under salt stress.

Characterization and the evaluation of antimicrobial activities of silver nanoparticles biosynthesized from Carya illinoinensis leaf extract

A green, direct and cost-effective fabrication method is proposed for Eco-environmentally silver nanoparticles (AgNPs) through leaf extraction of Carya illinoinensis from Iran. Formation of Ag NPs was confirmed through different characterization techniques such as UV–Vis Spectroscopy, X-ray Diffraction (XRD), Scanning Electron Microscope (SEM) and Transmission Electron Microscopy (TEM). UV-Visible spectrophotometer showed absorbance peak at 440 nm due to the Surface Plasmon Resonance (SPR). Based on XRD results and SEM and TEM analysis, AgNPs were crystalline with face-centered cubic geometry and in different sizes ranged 12–30 nm. Furthermore, FTIR Spectroscopy was utilized to recognize the specific functional groups responsible for reducing ion silver to silver nanoparticles and the capping agents available in the leaf extract. In addition, the antibacterial effect of Eco-friendly synthesized nanoparticles and also leaf extract, were evaluated on four pathogens by implementing minimum inhibitory concentration test (MIC) and agar diffusion assay. The MIC results exhibits more inhibiting activity against gram-negative microorganisms (Escherichia coli and Pseudomonas aeruginosa) rather than gram-positive microorganisms (Staphylococcus aureus and Listeria monocytogenes). Compared to leaf extract, nanoparticles have better antimicrobial activity against both Gram-positive and Gram-negative bacteria.

Application of Multiantigen Profiling To Detect Pecan

A problem often encountered in the detection and identification of undeclared tree nut food allergens is the lack of analytical methods. This problem is accentuated by the current trend, whereby the primary methods used to detect food allergens are antibody-based enzyme-linked immunosorbent assays (ELISAs) and the development of analyte-specific antibodies takes months. The recently developed xMAP food allergen detection assay (xMAP FADA) has the ability to generate multiantigen profiles with tree nuts, thereby providing a potential solution to this problem. The xMAP FADA includes 22 antibodies targeting peanut, soy, and nine tree nuts. The high number of antibodies to a diverse group of tree nuts and legumes and the propensity of tree nuts to cross-react have enabled the development of multiantigen profiling, whereby an analyte reacts with the various antibodies to generate a profile. Recently, a question arose regarding the possible presence of pecan dust at a manufacturer of pecan products that also stored fresh produce. The lack of suitable pecan ELISAs created an analytical challenge that was resolved using multiantigen profiling with the xMAP FADA. Pecan was detected on swab samples by using multiantigen profiling and confirmed by DNA analysis. The use of multiantigen profiling provided an analytical capability beyond what was possible with an analyte-specific analytical method.

Draft genome sequence of Fusicladium effusum, cause of pecan scab

Pecan scab, caused by the plant pathogenic fungus Fusicladium effusum, is the most destructive disease of pecan, an important specialty crop cultivated in several regions of the world. Only a few members of the family Venturiaceae (in which the pathogen resides) have been reported sequenced. We report the first draft genome sequence (40.6 Mb) of an isolate F. effusum collected from a pecan tree (cv. Desirable) in central Georgia, in the US. The genome sequence described will be a useful resource for research of the biology and ecology of the pathogen, coevolution with the pecan host, characterization of genes of interest, and development of markers for studies of genetic diversity, genotyping and phylogenetic analysis. The annotation of the genome is described and a phylogenetic analysis is presented.