Improvement of a popcorn population using selection indexes from a fourth cycle of recurrent selection program carried out in two different environments

Production and Selection of Quality Protein Popcorn Hybrids Using a Novel Ranking System and Combining Ability Estimates

Popcorn varieties are agronomically sub-optimal and genetically limited compared to other maize subspecies. To increase genetic diversity and improve popcorn agronomics, dent germplasm has been introduced to popcorn with limited success and generally, major loss of popping. Between 2013 and 2018, 12 Quality Protein Popcorn (QPP) inbreds containing Quality Protein Maize (QPM) and popcorn germplasm were produced that maintained popping while carrying the opaque-2 allele conferring elevated kernel lysine. This is an opportune trait in the growing market for healthier snacks and a model for mining QPM traits into popcorn. We crossed QPP inbreds to explore the effects of heterosis on popcorn protein, popping quality, and plant agronomics and selected hybrids for further production. To rank and intermediately prescreen hybrids, we utilized a novel hybrid-ranking model adapted from a rank summation index while examining the inbred general combining ability and hybrid specific combining ability estimates for all traits. We observed a biological manifestation of heterosis by categorizing hybrids by pedigree that resulted in a stepwise progression of trait improvement. These results corroborated our hybrid selection and offered insight in basic heterosis research. Estimates for popcorn quality and agronomic trait covariances also suggest the synergistic introgression of highly vitreous dent maize (QPM) into popcorn, providing a likely explanation for the successfully maintained vitreous endosperm, protein quality and popping traits in line with a remodeled proteome. QPP hybrids maintained improved amino acid profiles although different popping methods variably affected popcorn's protein bound and free amino acid levels. This preliminary screening of QPP hybrids is enabling further quantitative selection for large-scale, complex trait comparison to currently marketed elite popcorn varieties.

Differentially abundant proteins associated with heterosis in the primary roots of popcorn

Although heterosis has significantly contributed to increases in worldwide crop production, the molecular mechanisms regulating this phenomenon are still unknown. In the present study, we used a comparative proteomic approach to explore hybrid vigor via the proteome of both the popcorn L54 ♀ and P8 ♂ genotypes and the resultant UENF/UEM01 hybrid cross. To analyze the differentially abundant proteins involved in heterosis, we used the primary roots of these genotypes to analyze growth parameters and extract proteins. The results of the growth parameter analysis showed that the mid- and best-parent heterosis were positive for root length and root dry matter but negative for root fresh matter, seedling fresh matter, and protein content. The comparative proteomic analysis identified 1343 proteins in the primary roots of hybrid UENF/UEM01 and its parental lines; 220 proteins were differentially regulated in terms of protein abundance. The mass spectrometry proteomic data are available via ProteomeXchange with identifier “PXD009436”. A total of 62 regulated proteins were classified as nonadditive, of which 53.2% were classified as high parent abundance (+), 17.8% as above-high parent abundance (+ +), 16.1% as below-low parent abundance (− −), and 12.9% as low parent abundance (-). A total of 22 biological processes were associated with nonadditive proteins; processes involving translation, ribosome biogenesis, and energy-related metabolism represented 45.2% of the nonadditive proteins. Our results suggest that heterosis in the popcorn hybrid UENF/UEM01 at an early stage of plant development is associated with an up-regulation of proteins related to synthesis and energy metabolism.

A collection of popcorn as a reservoir of genes for the generation of lineages

In the present study, we analyze the genetic structure and diversity among accessions of popcorn obtained from the CIMMYT International Maize and Wheat Improvement Center that represent the diversity available for current use by breeding programs. The main objectives were to identify SSR loci that were the best indicators of genetic diversity, to measure the genetic diversity within popcorn genotypes, and to analyze the genetic structure of the promising populations destined for use in breeding programs. The mean gene diversity of all SSR loci was 0.6352. An extremely high population differentiation level was detected (F(st) = 0.3152) with F(st) for each locus ranging from 0.1125 (Umc1229) to 0.4870 (Umc1755). Analyzing the genetic structure of eight popcorn accessions was especially important for identifying both SSR loci with high levels of heterozygosity and genotypes showing high heterozygosity (BOYA462 and ARZM13 050). This analysis should be the medium and long-term selection goal for the generation of inbred lines and the future production of new cultivars. Plant accessions ARZM05 083, ARZM13 050, and URUG298 may also be useful varieties that exhibit important agronomic characteristics that can be used through crosses to broaden the genetic basis of popcorn.

Combining ability of tropical and temperate inbred lines of popcorn

In Brazil, using combining ability of popcorn genotypes to achieve superior hybrids has been unsuccessful because the local genotypes are all members of the same heterotic group. To overcome this constraint, 10 lines (P(1) to P(10)) with different adaptations to tropical or temperate edaphoclimatic environments were used to obtain 45 F(1) hybrids in a complete diallel. These hybrids and three controls were evaluated in two environments in Rio de Janeiro State. Grain yield (GY), popping expansion (PE), plant height (PH), ear height (EH), and days to silking (FL) were evaluated in randomized complete blocks with three replications. Significant differences between genotypes (P <or= 0.05) were detected for GY, PE and EH. General combining ability was significant for EH, PH, PE, and GY, and specific combining ability was significant only for PE and GY. The most promising inbred lines that improved GY were P(3) and P(4), unlike P(8), P(9) and P(10), which improved PE, and P(2), which improved both PE and GY. The additive effects were much more important for PE than for GY. The hybrid combinations gave positive estimates of heterosis for GY but not for PE.