Role of silicon in alleviating boron toxicity and enhancing growth and physiological traits in hydroponically cultivated Zea mays var. Merit.

BACKGROUND: Boron (B) is a micronutrient, but excessive levels can cause phytotoxicity, impaired growth, and reduced photosynthesis. B toxicity arises from over-fertilization, high soil B levels, or irrigation with B-rich water. Conversely, silicon (Si) is recognized as an element that mitigates stress and alleviates the toxic effects of certain nutrients. In this study, to evaluate the effect of different concentrations of Si on maize under boron stress conditions, a factorial experiment based on a randomized complete block design was conducted with three replications in a hydroponic system. The experiment utilized a nutrient solution for maize var. Merit that contained three different boron (B) concentrations (0.5, 2, and 4 mg L-1) and three Si concentrations (0, 28, and 56 mg L-1). RESULTS: Our findings unveiled that exogenous application of B resulted in a substantial escalation of B concentration in maize leaves. Furthermore, B exposure elicited a significant diminution in fresh and dry plant biomass, chlorophyll index, chlorophyll a (Chl a), chlorophyll b (Chl b), carotenoids, and membrane stability index (MSI). As the B concentration augmented, malondialdehyde (MDA) content and catalase (CAT) enzyme activity exhibited a concomitant increment. Conversely, the supplementation of Si facilitated an amelioration in plant fresh and dry weight, total carbohydrate, and total soluble protein. Moreover, the elevated activity of antioxidant enzymes culminated in a decrement in hydrogen peroxide (H2O2) and MDA content. In addition, the combined influence of Si and B had a statistically significant impact on the leaf chlorophyll index, total chlorophyll (a + b) content, Si and B accumulation levels, as well as the enzymatic activities of guaiacol peroxidase (GPX), ascorbate peroxidase (APX), and H2O2 levels. These unique findings indicated the detrimental impact of B toxicity on various physiological and biochemical attributes of maize, while highlighting the potential of Si supplementation in mitigating the deleterious effects through modulation of antioxidant machinery and biomolecule synthesis. CONCLUSIONS: This study highlights the potential of Si supplementation in alleviating the deleterious effects of B toxicity in maize. Increased Si consumption mitigated chlorophyll degradation under B toxicity, but it also caused a significant reduction in the concentrations of essential micronutrients iron (Fe), copper (Cu), and zinc (Zn). While Si supplementation shows promise in counteracting B toxicity, the observed decrease in Fe, Cu, and Zn concentrations warrants further investigation to optimize this approach and maintain overall plant nutritional status.

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.

Detection of exogenous siRNA inside sweet corn bundle sheath cells and the RNAi dynamics in the early stage of Maize dwarf mosaic virus infection.

Maize dwarf mosaic virus (MDMV) is one of the most serious viruses of sweet corn. Utilising the process of RNA interference, the exogenous introduction of small RNA molecules mimicking virus-derived small interfering RNA (siRNA) into the plant prior to infection triggers the antiviral RNA silencing effect, thereby promoting more effective antiviral protection. Hence, a treatment with MDMV-derived small RNA was applied to sweet corn plants one day before MDMV virus inoculation. ALEXA FLUOR®488 fluorophore-bound exogenous siRNA was successfully detected inside intact sweet corn cells using confocal fluorescence microscopy. Furthermore, it was demonstrated that the exogenous siRNA treatment led to a notable upregulation of the AGO1, AGO2b, AGO10b, AGO18a, DCL1, DCL3a, DCL4, RDR1, and MOP1 genes within 24 h of the treatment. Overall, exogenous siRNA treatment resulted in better virus control of infected sweet corn plants, as indicated by the lower viral RNA and coat protein levels compared to the infected group without pre-treatment. Supplementary Information: The online version contains supplementary material available at 10.1007/s12298-024-01500-2.

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 ß-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.

First report of sweet corn root rot caused by Pythium graminicola in southeast China.

Sweet corn (Zea mays L.) is widely consumed as fresh or frozen vegetable worldwide, and Zhengtian68 is a popular commercial variety cultivated extensively in southeast China. In May 2021, 40% of the inbred line YK063 (the female parent of Zhengtian68) showed early yellowing of the leaves at flowering time in a commercial seed production field with a total area of 0.5 ha in Guangzhou, Guangdong Province after a heavy rain. Black and rotten roots were observed in the diseased plants after digging the whole plant out of the soil. Grain filling was also severely affected, adversely impacting seed production. Diseased plants were more easily found in the lower section of the field, where water accumulated after rainfall. Three plants with rotten roots were collected randomly from the field to identify the causal pathogen. The diseased roots were cut into 2-3 mm sections, washed in 75% ethanol for 2 minutes and rinsed three times in sterile distilled water. Four to five sections per plant were placed on potato dextrose agar (PDA) and incubated at 28℃ in the dark for three days. Three isolates GF1, GF2, and GF3 from different plants were purified by hyphal tip isolation and transferred to new PDA and 10% V8 juice agar (16 g agar, 3 g CaCO3, 100 ml V8 juice, and 900 ml distilled water) and incubated at 28℃ for 10 days in darkness for further investigation. Translucent, glassy mycelial growth was observed on the PDA media. Morphological characteristics of the 3 isolates were observed under a microscope from the 10%V8 media. The hyphae were aseptate and 2.7 to 4.5 µm wide (mean±SD,3.3±0.44µm, n=44). Sporangia were inflated, or lobulate, terminal, or intercalary. Oogonia were globose, smooth-walled, terminal, or occasionally intercalary, with a diameter of 17.2-24.1 µm (mean±SD, 21.3±2.14µm, n=29). Oospores were globose, plerotic, smooth, and 14.5-21.2 µm (mean±SD, 18.7±2.07µm, n=35) in diameter. The antheridia were diclinous or monoclinous, not intercalary, and one to six antheridia were attached to each oogonium. Based on these morphological characteristics, 3 isolates were identified as Pythium spp. including Pythium graminicola (Van der Plaats-Niterink 1981). Genomic DNA was extracted from the mycelia grown on PDA using a Fungal Genomic DNA kit (Scintol, Beijing, China) according to the manufacturer's instructions. The cytochrome oxidase II (Cox II) gene and internal transcribed spacer (ITS) region of the rDNA were amplified using the primers FM58/FM66 (Martin 2000) and ITS4/ITS5 (White et al. 1990) respectively. Amplification was performed in a 50µl reaction volume using 25 µl PCR Mix (Trans Gene, Beijing, China), 3 µl genomic DNA (50 ng/µl), 1 µl each forward and reverse primer (10 µM), and 20 µl ddH2O. The PCR program was as follows: initial denaturation at 95°C for 30 s, 35 cycles of denaturation at 95°C for 30 s, annealing at 60°C for 60 s, extension at 72°C for 60 s, and a final extension at 72°C for 10 min. PCR products were sequenced and submitted to GenBank (accession no. OQ504322, OQ933130, and OQ933212 for ITS; OQ512002, OQ942203, and OQ942204 for Cox II). BLASTn analysis revealed that the ITS and Cox II sequences showed more than 98.62% similarity (721/724bp, 722/724bp,723/724bp for ITS; 514/514bp, 506/507bp, 500/507bp for Cox II) to P. graminicola ATCC96234 (accession no. AB095045 for ITS, and AB160849 for Cox II), respectively, supporting the morphological analysis. A neighbor-joining phylogenetic analysis of the ITS and Cox II concatenated sequence further confirmed that the isolates were P. graminicola. To test the pathogenicity of GF1, GF2, and GF3 a wheat seed inoculum was prepared as previously described (Qu et al. 2016). Sweet corn YK063 plants were planted in sterilized nutrient soil in plastic pots (one plant per pot) and grown in a greenhouse at 28℃ with 60% humidity and a 12-h/12-h light-dark cycle. For each isolate,10 plants were inoculated with 20 infected wheat seeds around the roots at the V5 stage, while 10 other YK063 plants were inoculated with the non-infected wheat seeds as a control. The experiment was repeated once. Three weeks later, the non-inoculated plants were asymptomatic. In contrast, inoculated plants showed stunning, yellowing of the leaves, root rot, and decreased production of lateral roots, exhibiting symptoms similar to those originally described for the disease. P. graminicola was successfully reisolated from the diseased roots and identified by morphological characteristics and sequencing of the ITS and Cox II as the causal agent for this root rot disease, fulfilling Koch's postulate for defining a causal agent. P. graminicola was reported as a causal agent of damping-off on dent corn in Georgia (Li et al. 2018). To our knowledge, this is the first report of P. graminicola causing root rot in sweet corn in southeast China. Identification of this pathogen will facilitate further research on this disease and the development of effective strategies to control the disease.

The Regulatory Network of Sweet Corn (Zea mays L.) Seedlings under Heat Stress Revealed by Transcriptome and Metabolome Analysis.

Heat stress is an increasingly significant abiotic stress factor affecting crop yield and quality. This study aims to uncover the regulatory mechanism of sweet corn response to heat stress by integrating transcriptome and metabolome analyses of seedlings exposed to normal (25 °C) or high temperature (42 °C). The transcriptome results revealed numerous pathways affected by heat stress, especially those related to phenylpropanoid processes and photosynthesis, with 102 and 107 differentially expressed genes (DEGs) identified, respectively, and mostly down-regulated in expression. The metabolome results showed that 12 or 24 h of heat stress significantly affected the abundance of metabolites, with 61 metabolites detected after 12 h and 111 after 24 h, of which 42 metabolites were detected at both time points, including various alkaloids and flavonoids. Scopoletin-7-o-glucoside (scopolin), 3-indolepropionic acid, acetryptine, 5,7-dihydroxy-3',4',5'-trimethoxyflavone, and 5,6,7,4'-tetramethoxyflavanone expression levels were mostly up-regulated. A regulatory network was built by analyzing the correlations between gene modules and metabolites, and four hub genes in sweet corn seedlings under heat stress were identified: RNA-dependent RNA polymerase 2 (RDR2), UDP-glucosyltransferase 73C5 (UGT73C5), LOC103633555, and CTC-interacting domain 7 (CID7). These results provide a foundation for improving sweet corn development through biological intervention or genome-level modulation.

Anti-Inflammatory Activity and Mechanism of Sweet Corn Extract on Il-1ß-Induced Inflammation in a Human Retinal Pigment Epithelial Cell Line (ARPE-19).

Age-related macular degeneration (AMD) is an eye disease associated with aging. Development of AMD is related to degeneration and dysfunction of the retinal pigment epithelium (RPE) caused by low-grade chronic inflammation in aged RPE cells leading to visual loss and blindness. Sweet corn is a good source of lutein and zeaxanthin, which were reported to exert various biological activities, including anti-inflammatory activity. The present study aims to investigate the anti-inflammatory activity and mechanisms of SCE to inhibit the production of inflammatory biomarkers related to AMD development. Cells were pretreated with SCE for 1 h followed by stimulation with IL-1ß for another 24 h. The results demonstrated that SCE attenuated IL-1ß-induced production of IL-6, IL-8, and MCP-1 and the expression of ICAM-1 and iNOS in a dose-dependent manner. In addition, SCE suppressed the phosphorylation of ERK1/2, SAPK/JNK, p38, and NF-κB (p65) in IL-1ß-stimulated ARPE-19 cells. These results proved that SCE protected ARPE-19 cells from IL-1ß-induced inflammation by inhibiting inflammatory markers partly via suppressing the activation of MAPK and NF-κB signaling pathways. Overall, SCE is a potential agent for the prevention of AMD development, which should be further evaluated in animals.

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 ß-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.

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.

First report of bacterial leaf streak in sweet corn caused by Pantoea ananatis in southeast China.

Sweet corn (Zea mays convar. saccharata var. rugosa) is a popular vegetable crop in southeast China. During the spring seasons of 2018-2021, a serious outbreak of bacterial leaf streak was observed in sweet corn variety Yuetian28 in the field in Guangzhou, Guangdong Province. The disease incidence was 50%-70%. Infected leaves initially displayed long, chlorotic streaks parallel to veins at the V5-V6 stage, and then turned white or brown and dried out over the course of disease development. In severe infections, leaf lesion coalesced to form large irregular blight areas (Fig. S1A). To investigate this disease, we collected 0.5 cm2 samples of infected leaves from four plants after surface sterilization and rinsed them three times with sterile distilled water. We placed all leaf samples on nutrient agar (NA) medium and incubated them at 28℃ for 48 hours. Bright-yellowish colonies were observed near the edges of the samples. We picked the colonies and re-streaked them onto NA medium three times to obtain pure cultures. Four isolates, GZ2201, GZ2202, GZ2203, and GZ2204, were selected for further study. All isolates were gram-negative rods and were negative for oxidase, urease, nitrate reductase reactions, and gelatin liquefaction. They were positive for catalase, citrate utilization, indole production, and the Voges-Proskauer test. We sequenced the 16S rDNA, rpoB, leuS, and gyrB sequences using previously reported primers (Brady et al. 2008) and deposited the sequences in GenBank (accession nos. ON740665 to ON740668 for 16S rDNA; ON755167 to ON755170 for rpoB; ON755171 to ON755174 for leuS; and OP227136 to OP227139 for gyrB). The sequences share >98% identity with sequences from Pantoea ananatis type strain LMG2665 (GenBank JFZU01) indicating that the causal pathogen of bacteria leaf streak of sweet corn is P. ananatis (Fig. S1B). Phylogenetic analysis of gyrB, leuS, and rpoB concatenated sequence showed that the four isolates clustered with P. ananatis (Fig S2). To test the pathogenicity of the isolates of P. ananatis on the sweet corn variety Yuetian28, we inoculated plants at the V3 stage by syringe infiltration of bacterial suspension (108 CFU/ml) (Kini et al. 2020) or sterile distilled water as a negative control. Inoculated plants were placed in a growth chamber at 28 ℃, 60% relative humidity, 16-h/8-h light-dark cycle. After 7 days of incubation, chlorotic streaks resembling the original symptoms developed on inoculated plants (Fig. S1D), while control plants remained symptomless (Fig. S1C). We successfully re-isolated bacteria from the inoculated plants and confirmed their identity by sequencing of 16S rDNA, rpoB, leuS, and gyrB. P. ananatis was previously reported to cause leaf spot disease in maize grown in Argentina, Ecuador, and China (Alippi et al. 2010; Toaza et al. 2021; Cui et al. 2022). To our knowledge, this is the first report of P. ananatis causing leaf streak in sweet corn in southeast China. Further research on P. ananatis management is needed to help control disease spread.

Physiological and Molecular Characteristics of Southern Leaf Blight Resistance in Sweet Corn Inbred Lines.

Southern corn leaf blight is one of the most widespread foliar diseases in maize-producing areas worldwide and can seriously reduce the yield and quality of sweet corn. However, the molecular mechanisms underlying the disease in sweet corn have not been widely reported. In this study, two sweet corn inbred lines, resistant K13 (RK13) and susceptible K39 (SK39), were used to explore the disease resistance mechanism of southern leaf blight. We observed morphological characteristics and assessed the changes in protective enzymatic activity in sweet corn leaves after inoculation of C. heterostrophus. RNA-seq was performed to elucidate the transcriptional dynamics and reveal the key pathways involved in southern leaf blight resistance without pathogens (Mock) and at 1 and 3 days post inoculation (1 and 3 dpi). Differentially expressed genes (DEGs) were identified in the SK39 group (including three pairwise combinations: SK39-0d_vs_SK39-1d, SK39-1d_vs_SK39-3d and SK39-1d_vs_SK39-3d), the RK13 group (including three pairwise combinations: RK13-0d_vs_RK13-1d, RK13-1d_vs_RK13-3d and RK13-1d_vs_RK13-3d), and the SK39_vs_RK13 group (including three pairwise combinations: SK39-0d_vs_RK13-0d, SK39-1d_vs_RK13-1d, and SK39-3d_vs_RK13-3d). In our study, 9455 DEGs from the RK13 group, 9626 from the SK39 group, and 9051 DEGs from the SK39_vs_RK13 group were obtained. Furthermore, 2775, 163, and 185 DEGs were co-expressed at SK39_vs_RK13, RK13, and SK39, respectively. A functional analysis of the DEGs revealed that five pathways-i.e., photosynthesis, plant hormone signal transduction, MAPK signaling pathway, phenylpropanoid biosynthesis, and biosynthesis of secondary metabolites-and transcription factor families play crucial roles in disease resistance. The results from the present study enabled the identification of the JA and SA signaling pathways, which are potentially involved in the response to southern leaf blight in maize. Our findings also highlight the significance of ZIM transcription factors and pathogenesis-related (PR) genes during pathogen infection. This study preliminarily explored the molecular mechanisms of the interaction between sweet corn and C. heterostrophus and provides a reference for identifying southern leaf blight resistance genes in the future.

Effects of Different Freezing Methods on Physicochemical Properties of Sweet Corn during Storage.

Fresh sweet corn has a series of physiological and biochemical reactions after picking due to the high moisture content, leading to damaged nutritional value. Rapid freezing of sweet corn after harvest can minimize tissue damage and quality deterioration. In this study, freshly harvested sweet corn was frozen by ultrasound-assisted freezing, brine freezing, strong wind freezing, and refrigerator freezing. The effects of different freezing methods on hardness, water loss, color, epidermal structure, soluble solids content, soluble sugars content, peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) activities of frozen sweet corn during storage were investigated. The results showed that brine freezing and strong wind freezing could effectively reduce the quality loss of sweet corn, keep the color, soluble sugars, and soluble solids content of the sweet corn, delay the decrease in antioxidant enzyme activity, and maintain the quality of sweet corn during long term storage.

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.

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.

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.

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.

Prediction of Sweet Corn Seed Germination Based on Hyperspectral Image Technology and Multivariate Data Regression.

Vigor identification in sweet corn seeds is important for seed germination, crop yield, and quality. In this study, hyperspectral image (HSI) technology integrated with germination tests was applied for feature association analysis and germination performance prediction of sweet corn seeds. In this study, 89 sweet corn seeds (73 for training and the other 16 for testing) were studied and hyperspectral imaging at the spectral range of 400-1000 nm was applied as a nondestructive and accurate technique to identify seed vigor. The root length and seedling length which represent the seed vigor were measured, and principal component regression (PCR), partial least squares (PLS), and kernel principal component regression (KPCR) were used to establish the regression relationship between the hyperspectral feature of seeds and the germination results. Specifically, the relevant characteristic band associated with seed vigor based on the highest correlation coefficient (HCC) was constructed for optimal wavelength selection. The hyperspectral data features were selected by genetic algorithm (GA), successive projections algorithm (SPA), and HCC. The results indicated that the hyperspectral data features obtained based on the HCC method have better prediction results on the seedling length and root length than SPA and GA. By comparing the regression results of KPCR, PCR, and PLS, it can be concluded that the hyperspectral method can predict the root length with a correlation coefficient of 0.7805. The prediction results of different feature selection and regression algorithms for the seedling length were up to 0.6074. The results indicated that, based on hyperspectral technology, the prediction of seedling root length was better than that of seed length.

Effects of temperature stress on the accumulation of ascorbic acid and folates in sweet corn (Zea mays L.) seedlings.

BACKGROUND: Extreme temperatures are among the primary abiotic stresses that affect plant growth and development. Ascorbic acid (AsA) is an efficient antioxidant for scavenging relative oxygen species accumulated under stress. Folates play a significant role in DNA synthesis and protect plants against oxidative stress. Sweet corn (Zea mays L.), a crop grown worldwide, is sensitive to extreme temperatures at seedling stage, which may cause yield loss. This study was conducted to explore the biosynthetic regulative mechanism of AsA and folates in sweet corn seedlings under temperature stress. RESULTS: The AsA and folate composition and relative gene expression in sweet corn seedlings grown under different temperature stresses (10, 25, and 40 °C) were evaluated. The imposition of temperature stress altered the AsA content mainly by modulating the expression of Zm DHAR, whose encoded enzyme dehydroascorbic reductase (DHAR) is essential in the AsA recycle pathway. Low temperature stress raised the expressions of relative genes, leading to folate accumulation. High temperature stress modulated the folate content by influencing the expression of the correspondence gene for aminodeoxychorismate synthase, Zm ADCS, as well as downstream genes that connected with DNA methylation. CONCLUSION: These results provided a theoretical basis, at a genetic level, for understanding the stress responses mechanism in sweet corn seedlings, offering guidance for sweet corn cultivation. © 2019 Society of Chemical Industry.

Optimization of enzyme-assisted extraction of ferulic acid from sweet corn cob by response surface methodology.

BACKGROUND: Sweet corn cob (SCC), an agricultural by-product of the corn-processing industry, contains more than 80% insoluble bound ferulic acid (FA). Extraction of these bound phenolics can be achieved through chemical or enzymatic hydrolysis; however, the shift towards greener chemistry has raised awareness about the use of enzymatic hydrolysis. In the present study, the ability of ferulic acid esterase (FAE) and xylanase (XY) to catalyze the hydrolysis of FA from SCC was investigated. Response surface methodology (RSM), based on a five-level, four-factor central composite rotatable design (CCRD), was used to establish the optimum conditions for enzymatic hydrolysis of FA from SCC. Sweet corn cob was treated with a combination of FAE and XY at various concentrations (FAE: 0.00 to 0.04 U/g; XY: 0.00 to 18 093.5 U/g), temperatures (45 to 65 °C), and pH levels (pH 4.5 to 6.5). RESULTS: The optimum extraction conditions predicted by the model were: FAE concentration of 0.02 U/g, XY concentration of 3475.3 U/g, extraction pH of 4.5, and an extraction temperature of 45 °C. CONCLUSION: Under these conditions, the experimental yield of FA was 1.69 ± 0.02 g kg-1 of SCC, which is in agreement with the value predicted by the model. © 2019 Society of Chemical Industry.

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.