Floral biology and pollen viability of parental lines of onion hybrids

Parental lines (inbred and hybrid male-sterile lines and inbred pollinators) of prospective F, hybrids from the NVRS spring-sown bulb onion breeding programme were examined to study their floral biology and aspects of pollination under glasshouse conditions. Inbreeding depression occurred in both pollinator and male-sterile inbreds in terms of reduced flower numbers per umbel and a greater proportion of defective pistils. Male-sterile and male-fertile lines differed in their stigma and style characteristics and pattern of development. At flower opening, the styles of male-sterile lines were longer and the stigmatic knob became receptive relatively sooner. The inbred male-sterile line II/3 ms appeared to have a reduced receptive area on its stigmatic knob and remained receptive for a relatively shorter period. Individual lines differed for time of flowering, nectar content and its sugar concentration, and in their effectiveness as male and female parents as judged from pollen tube growth down the style in specific pairings. Assessment of pollen viability using the fluorescein diacetate test did not correlate with assessments based on pollen grain germination and subsequent growth down the style, perhaps as a result of differential receptivity in the inbred lines tested. These results are discussed in relation to future hybrid seed production.