Genetic diversity, correlations and path coefficient analysis in popcorn (Zea mays L. everta)
Popcorn is the most popular snack food in the world. Genetic diversity is of major concern in popcorn breeding. High genetic diversity allows manipulation of different genotypes to breed new varieties. There is very little published work on popcorn production in Sub-Saharan Africa primarily in South Africa. Popcorn production in South Africa could be hampered by the lack of superior and adapted varieties with large genetic base, good popping ability and high yield. Studies relating popping expansion volume and grain yield are of fundamental importance for popcorn improvement, but they are limited. Furthermore, there is limited number of studies regarding popcorn genetic diversity among locally developed popcorn varieties. The objectives of the study were; (i) to investigate genetic variability among the popcorn inbred lines, (ii) to study the magnitude of genetic diversity among the popcorn inbred lines, (iii) to establish the relationship between popping ability and seed yield, and with secondary traits, and (iv) to evaluate the effect of popping methods on popping ability of different popcorn inbred lines. Two populations designated as Population 1 and Population 2 with 83 and 81 inbred lines, respectively, were used in the study.On the study of the appraisal of popping methods, the highest popping expansion volume (cm³) and less number of unpopped kernels were obtained from hot air popping than in the microwave popping method. The study revealed that hot air popping method is more effective and efficient in discriminating popping ability of the inbred lines. The study further revealed that the two methods rank genotypes differently. The presence of genotype × popping method interaction resulted in three different groups. (i) Genotype adaptation across methods, (ii) specific adaptation to microwave popping, and (iii) specific adaptation to hot air popping method. Hence, when breeders evaluate popping ability of different genotypes, they should consider the method, depending on the way consumers will do the popping. The study of relationship between traits showed that popping expansion volume and seed yield was positively and significantly correlated. Nevertheless, the relationship between seed yield and popping expansion volume was weak. Popping expansion volume was negatively and weakly correlated with most secondary traits except kernel aspect and number of unpopped kernels. The direct effects of kernel aspect score on popping expansion volume were large and negative. Other traits showed small direct and indirect effects on popping expansion volume. Traits including days to anthesis, ear prolificacy and ear aspect exhibited large direct effects on seed yield. Indirect and direct effects of other traits on seed yield were small. Relationship among several secondary traits was small. The results obtained showed that selection for high seed yield will not negatively impact popping expansion volume and vice versa, therefore, popping expansion volume and seed yield can be improved concurrently. Overall, indirect effects of secondary traits on seed yield and popping expansion volume were small; this supported the focus on direct selection of these traits to improve seed yield and popping ability. Based on the study of genetic diversity and variability, inbred lines showed large genetic variation and high heritability for 18 traits. Phenotypic and genetic coefficient of variation was high in seven and six traits, respectively. A large percentage of genetic advance was recorded in 11 traits. Dendogram derived from phenotypic data grouped the inbred lines into four to seven clusters depending on heritability. Dendogram produced from 22 SSR markers grouped inbred lines into five clusters. Overall, the study showed that, maximum popping ability of inbred lines is dependent on the method used. Simultaneous improvement of seed yield and popping expansion volume is possible through selection of inbred lines combining both high popping expansion volume and seed yield. Improvement of the two traits should be based on selection for traits with large direct effects. The magnitude of genetic diversity among the inbred lines was large; therefore, distant inbred lines can be selected as parents and crossed to develop new varieties that are locally adapted. Above all, the results have implications for the methods which would be used to process popcorn by consumers especially in developing rural communities.