Genetic divergence between onion populations derived from three different crossing methods
The production of onion hybrids depends on the development of genetically pure lineages. Successive self-fertilization guarantees obtaining endogenous lines quickly. However, onion undergoes a strong process of inbreeding depression when self-fertilized for several generations, which reduces plant vigor, bulb size and seed production, increasing the cost to produce hybrid seed. An estimate of the genetic distance between genotypes is a way of predicting if genetic variability is being maintained. We evaluated possible negative effects in populations due to self-fertilization, compared to interbreeding between two or three plants. Eleven onion populations in different genetic segregation stages, obtained from generations that already had low or moderate inbreeding levels were included. The populations were from the breeding program of Bayer Vegetable Seeds. In order to assess the agronomic descriptors contribution for the genetic divergence, three types of crossing methods of populations were performed: self-fertilization of plants, crossing between two plants and crossings between three plants, during two consecutive years (2014 and 2015). Morphological differences were detected through dissimilarity measures. The traits bulbs/plot (28.32%), fruit fixation (13.12%) and seed weight/umbel (13.41%) together contributed 54.85% to the divergence of onion genotypes. The crosses between two and three plants provided greater divergence among the genotypes, compared to self-fertilization. Economically important traits such as bulb production per plot, fruit fixation, resistance to disease caused by Alternaria porri (Pleosporaceae) and seed weight per umbel can be measured to assess divergence for appropriate selection of onion lineages among segregant populations.