Abstract:

Advanced backcross QTL (AB-QTL) method can combine QTL detection with elite variety improvement and apply unadapted germplasm efficiently, which has been used in tomato, rice, wheat, and normal maize. Previous studies showed that normal maize inbreds could enrich the germplasm of popcorn through interspecies cross and improve the popping characters and plant traits of hybrids through 1 to 2 cycles of backcrosses with popcorn inbred. When BC₁ and F_2:3 generations were used, QTL for popping fold have been detected, but no research has been done with advanced backcrosses. In this study, a total of 220 BC₂S₁ families, derived from the cross between a dent corn inbred Dan 232 and a popcorn inbred N04, were evaluated for their popping fold and other 13 traits of kernel yield component, plant and popping in a replicated experiment under two environments. 188 pairs of SSR markers with polymorphism were selected to analyze their genotypes. QTL were identified, and their genetic effects were estimated with single marker method (SMM). Our first objective was to compare the detection of QTL in the BC₂S₁ generation with a previous study by F_2:3 families of the same population grown at the same location and in the same year. The second objective was to combine QTL analysis with popcorn breeding and develop popcorn inbreds simultaneously. The results are as follows: There were significant differences among BC₂S₁ families and between two environments for popping fold, but the family × environment interaction was not significant. Its hB2 was 0.60, with confidence interval of 0.43 to 0.72. The values of skewness and kurtosis indicated its normal distributions under both environments with transgressive segregations exceeding the high parent N04. 12.27% and 19.09% of BC₂S₁ families were higher than N04 in popping fold. Totally, 16 QTL were detected, and only two of them (qBPF-1-2 and qBPF-10-1) shared under two environments. Nine QTL detected in spring were located on chromosomes 1 (three), 2 (two), 4 (one), 8 (one), and 10 (two), whereas seven QTL detected in summer were on chromosomes 1 (three), 7 (one), and 10 (three). Contribution to phenotypic variation of a single QTL varied from 3% to 9%, with qBPF-1-1 the largest, and qBPF-7-1, qBPF-10-1 the next (all 6%). Total contributions of all QTL under two environments were 42% and 33%, respectively. In our previous study using F_2:3 generation, we detected 22 QTL (associating with 37 marker loci), among which 7 QTL were detected in the same marker loci and 4 in the near marker loci in this study, totally accounting for 29.73%, and three QTL were only detected in this study. The performance of BC₂S₁ families for other traits showed that most families were significantly improved in ear-kernel and plant traits, with 10%–100% of the families higher than the popcorn parent N04. The kernel weight per ear of 186 and 204 BC₂S₁ families in two environments was 10% higher than the popcorn parent N04, among which 23 and 46 families were the same or higher than N04 in popping fold. Therefore, modified N04 could be developed from them and used in popcorn breeding.

Key words: Popcorn, Popping fold, AB-QTL, SSR marker, Testcross