Genetic analysis of popping quality traits and development of superior quality popcorn hybrids for a sustainable popcorn breeding program in India.

BACKGROUND: Popcorn is the most popular specialty maize and it makes a significant contribution to the Indian and global economies. Despite perfect exploration of heterosis in field corn, progress in popcorn breeding remains constrained due to its narrow genetic base, leading to a significant dependence on imports. In this study, 15 landrace- and population-derived inbreds from temperate and tropical germplasm were crossed with five testers, which are the parents of superior popcorn hybrids, in a line × tester mating design. RESULTS: Significant variation was observed in popping quality and agronomic traits among crosses evaluated across three locations representing diverse maize-based agro-climatic zones in India. Additive genetic variance governed the traits related to popping quality, whereas dominance variance was responsible for the agronomic traits. In addition to significant heterosis specific to certain traits, we identified promising crosses that exhibited superior performance in both popping quality and grain yield (GY). The genotype + genotype × environment (GGE) biplot methodology identified PMI-PC-104 and PMI-PC-101 as the best discriminating testers for popping quality traits and Dpcl-15-90 for GY. Lines PMI-PC-205, PMI-PC-207, and PMI-PC-209 were the best general combiners for popping quality traits and GY. The heterotic groups identified based on GGE-biplots and the magnitude, direction and stability of combining ability effects would serve in the development of competitive popcorn hybrids for a sustainable popcorn market. CONCLUSION: Using the additive nature of popping quality traits and the dominant nature of GY, recurrent intrapopulation selection can be employed to derive desirable popping quality inbreds with high GY for genetic enhancement. Desirable popping quality alleles from novel germplasm can thus be combined with high-yielding domestic elite inbreds to establish a sustainable popcorn breeding program. © 2024 Society of Chemical Industry.

Molecular characterization, haplotype analysis and development of markers specific to dzs18 gene regulating methionine accumulation in kernels of subtropical maize.

Maize kernel protein is deficient in sulfur-containing essential amino acid such as methionine. The dzs18 gene encodes methionine-rich 18-kDa δ-zein in maize kernels. In this study, we sequenced full-length of dzs18 gene (820 bp) among 10 maize inbreds, revealing 43 SNPs and 22 InDels (average length-7.58 bp). Three InDels (4 bp at 113th, 15 bp at 463rd and 3 bp at 615th position) distinguished the wild-type (functional) from the mutant (non-functional) allele of dzs18. The 4 bp (TTAT) insertion caused a frameshift mutation, resulting in truncated DZS18 protein. The 15 bp insertion (ATG-TCT-TCG-ATG-ATA) added methionine-serine-serine-methionine-isoleucine, while the 3 bp deletion (CAA) led to loss of a glutamine residue in the mutant allele. Three gene-based PCR markers were developed for diversity analysis of dzs18 gene among 48 inbreds, which had an average methionine content of 0.136 %. (range: 0.031-0.340 %). Eight haplotypes were identified with methionine content varying from 0.066 % (Hap7) to 0.262 % (Hap3). Haplotypes with 4 bp deletion accumulated more methionine (0.174 %) than haplotypes with 4 bp insertion (0.082 %). The average methionine in 15 bp deletion and insertion haplotypes was 0.106 % and 0.150 %, respectively. The 3 bp insertion had 0.140 % methionine, while the deletion possessed 0.117 % methionine. Protein-protein association analysis predicted that DZS18 protein interacts with 19-kDa α-zein, 27- and 16-kDa γ-zeins, WAXY and O2 protein. A paralogue of dzs18 gene with 74 % sequence identity was identified. The functional markers reported here could facilitate the development of high methionine maize cultivars, which holds great significance to combat malnutrition, especially in developing countries. Supplementary Information: The online version contains supplementary material available at 10.1007/s13205-024-04088-2.

Unraveling popping quality through insights on kernel physical, agro-morphological, and quality traits of diverse popcorn (Zea mays var. everta) inbreds from indigenous and exotic germplasm.

Popcorn is a specialty corn with worldwide popularity as a snack. Despite having great market demand, genetic improvement in popping quality is limited, which is caused by the limited germplasm utilization and narrow genetic base. An assortment of diverse germplasm, their effective characterization, and integration into popcorn breeding pipeline is the foundation for an efficient breeding program. Here, kernel characteristics, popping quality traits, and agro-morphological traits were evaluated across three locations on a diverse panel of 48 popcorn inbreds derived from diverse landraces and populations of exotic and indigenous origin. The variations due to genotypes, locations, and genotype × location interaction were highly significant. The popping quality traits recorded wide variation with a high coefficient of genotypic determination. The kernel dimensions, kernel density, test weight, and grain yield were negatively correlated with popping quality traits. Genotypes with rice-type kernels exhibited better popping quality than pearl-type kernels. Analysis of genotype × location (G×L) interaction identified two target locations for the key popping quality trait, popping expansion volume. PMI-PC-175, PMI-PC-187, PMI-PC-188, and PMI-PC-189 were identified as superior genotypes over checks for desirable popping quality, agronomic performance, and high grain yield. The contrasting inbreds for popping quality and flake shape (mushroom vs. butterfly) can be utilized for developing mapping populations to enhance our understanding of molecular aspects of popping quality traits. Further, the promising inbreds can be utilized in the genetic improvement of popcorn and crossed to develop superior popcorn hybrids. The results suggest a potential opportunity to establish an efficient popcorn breeding program.

Maize genotypes with favourable dgat1-2 and fatb alleles possess stable high kernel oil and better fatty acid health and nutritive indices.

Diverse uses of maize oil attracted various stakeholders, including food, feed, and bioenergy, highlighting the increased demand for sustainable production. Here, 48 diverse sub-tropical maize genotypes varying for dgat1-2 and fatb genes governing oil attributes, were evaluated in three diverse locations to assess trends of oil content, fatty acid (FA) profile, the effect of environment on oil attributes, the impact of different gene combinations and determine FA health and nutritional properties. The genotypes revealed wide variation in oil content (OC: 3.4-6.8 %) and FA compositional traits, namely palmitic (PA, 11.3-24.1 %), oleic (OA, 21.5-42.7 %), linoleic (LA, 36.6-61.7 %), and linolenic (ALA, 0.7-2.3 %) acids. Double-mutants with both favourable alleles (dd/ff) exhibited 51.6 % higher oil, 33.2 % higher OA, and 30.2 % reduced PA compared to wild-types (d+d+/f+f+) across locations. These double-mutants had lower saturated FA (12.2 %), and higher unsaturated FA (87.0 %), indicating reduced susceptibility to autooxidation, with lower atherogenicity (0.14), thrombogenicity (0.27) and peroxidisability (48.15), higher cholesterolemic index (7.16), optimum oxidability (5.27) and higher nutritive-value-index (3.35) compared to d+d+/f+f+, making them promising for significant health and nutritional benefits. Locally adapted stable novel double-mutants with high-oil and better FA properties identified here can expedite the maize breeding programs, meeting production demands and addressing long-standing challenges for breeders.

Genetic dissection of embryo size and weight related traits for enhancement of kernel oil in maize.

Embryo is a key determinant of kernel-oil in maize. Higher calorific value of maize kernel is attributed to increment in kernel-oil and it stores in specialised structure called embryo. Understanding the genetic behaviour of embryo size and weight related-traits is inevitable task for genetic improvement of kernel-oil. Here, the six-basic generations (P1, P2, F1, F2, BC1P1 and BC1P2) of three crosses (CRPBIO-962 × EC932601, CRPBIO-973 × CRPBIO-966 and CRPBIO-966 × CRPBIO-979) between contrasting embryo-sized maize inbreds were field evaluated at three locations to decipher the genetics of twenty embryo, kernel and embryo-to-kernel related-traits through generation-mean-analysis (GMA). Combined ANOVA revealed the significance of all the traits among generations; however, location and generation × location were found to be non-significant (P > 0.05) for most of the traits. Significance (P < 0.05) of scaling and joint-scaling tests revealed the presence of non-allelic interactions. Elucidation of six-parameters disclosed the predominance of dominance main-effect (h) and dominance × dominance interaction-effect (l) for most of traits. The signs of (h) and (l) indicated the prevalence of duplicate-epistasis type across crosses and locations. Thus, the population improvement approaches along with heterosis breeding method could be effective for improvement of these traits. Quantitative inheritance pattern was observed for all the traits with high broad-sense heritability and better-stability across locations. The study also predicted one to three major-gene blocks/QTLs for embryo-traits and up to 11 major-gene blocks/QTLs for embryo-to-kernel traits. These findings could provide deep insights to strategize extensive breeding methods to improve embryo traits for enhancing kernel-oil in sustainable manner.

Expression Dynamics of lpa1 Gene and Accumulation Pattern of Phytate in Maize Genotypes Possessing opaque2 and crtRB1 Genes at Different Stages of Kernel Development.

Phytic acid (PA) acts as a storehouse for the majority of the mineral phosphorous (P) in maize; ~80% of the total P stored as phytate P is not available to monogastric animals and thereby causes eutrophication. In addition, phytic acid chelates positively charged minerals making them unavailable in the diet. The mutant lpa1-1 allele reduces PA more than the wild-type LPA1 allele. Further, mutant gene opaque2 (o2) enhances lysine and tryptophan and crtRB1 enhances provitamin-A (proA) more than wild-type O2 and CRTRB1 alleles, respectively. So far, the expression pattern of the mutant lpa1-1 allele has not been analysed in maize genotypes rich in lysine, tryptophan and proA. Here, we analysed the expression pattern of wild and mutant alleles of LPA1, O2 and CRTRB1 genes in inbreds with (i) mutant lpa1-1, o2 and crtRB1 alleles, (ii) wild-type LPA1 allele and mutant o2 and crtRB1 alleles and (iii) wild-type LPA1, O2 and CRTRB1 alleles at 15, 30 and 45 days after pollination (DAP). The average reduction of PA/total phosphorous (TP) in lpa1-1 mutant inbreds was 29.30% over wild-type LPA1 allele. The o2 and crtRB1-based inbreds possessed ~two-fold higher amounts of lysine and tryptophan, and four-fold higher amounts of proA compared to wild-type alleles. The transcript levels of lpa1-1, o2 and crtRB1 genes in lpa1-1-based inbreds were significantly lower than their wild-type versions across kernel development. The lpa1-1, o2 and crtRB1 genes reached their highest peak at 15 DAP. The correlation of transcript levels of lpa1-1 was positive for PA/TP (r = 0.980), whereas it was negative with inorganic phosphorous (iP) (r = -0.950). The o2 and crtRB1 transcripts showed negative correlations with lysine (r = -0.887) and tryptophan (r = -0.893), and proA (r = -0.940), respectively. This is the first comprehensive study on lpa1-1 expression in the maize inbreds during different kernel development stages. The information generated here offers great potential for comprehending the dynamics of phytic acid regulation in maize.