Genotypic and environmental variation in autumn-sown onions

Seven onion cultivars of Japanese and European origin were evaluated in autumn-sown trials, at six sites over two seasons. Within each season genotypic differences were detected for winter-kill, bolting, maturity time and yield. In general the Japanese cultivars showed consistently lower levels of bolting and winter-kill and earlier maturity relative to the European cultivars. Environmental effects were important with differences between seasons, sites and sowings recorded for most characters. It was concluded that the use of early and late August sowings would provide suitable screening environments for bolting and winter-kill respectively. There were also differences between genotypes in their linear response to environments as shown by joint regression analyses. 'Express Yellow O-X' (hybrid) showed least response to environments for bolting and winter-kill and 'Senshyu semi-globe Yellow' gave the most consistent time to maturity over environments.