Combining Abilities for Yield and Bulb Quality among Long- and Intermediate-day Open-pollinated Onion Populations

Abstract

A factorial mating design, using three male-sterile F1 lines in testcrosses with a sample of open-pollinated (OP) onion populations, was used to estimate combining abilities and heterosis for bulb yield, size, storage ability, pungency, soluble solids content (SSC), and water loss after 3 months in storage. Samples of testcross bulbs were flowered and scored for fertility to estimate frequencies of the nuclear allele maintaining cytoplasmic male sterility. General combining ability (GCA) estimates for OP populations (males) were significant (P < 0.05) for yield, SSC, and proportion of bulbs with diameters >7.5 cm. GCA estimates for female testers were significant for storage ability and proportion of bulbs with diameters <5.0 cm. Male × female interactions (specific combining ability estimates) were significant for SSC and storage ability. Our analyses did not reveal any storage population from which inbreds would likely yield significantly better with the male-sterile tester lines. Spanish OP populations tended to produce testcrosses with larger bulbs, lower pungency and SSC, and poorer storage ability. Heterosis estimates were most often significant for yield and SSC; less often for pungency, storage ability, and bulb size; and not significant for water loss in storage. Overall, significant GCA estimates indicate that superior onion inbreds and populations may be developed using recurrent-selection strategies that increase the frequency of desirable alleles with additive effects.