Abstract
We investigated the budbreak rate in Taiwanese pear Yokoyama and Japanese pear strain TH3 (S1 of ‘Osa-Nijisseiki’ and homozygous for the S4sm gene) and their F1 for 3 years. All F1 plants were identified as the offspring from a cross of TH3 × Yokoyama by S-allele genotypes and SSR marker analysis. The rate of budbreak in Yokoyama was higher than 60% on all observational days. Thus, Yokoyama did not show endodormancy from late November to early January for the 3 years. The rate of budbreak in TH3 was lower than in Yokoyama on all observational days, and it gradually increased from early December to early January. The rate of budbreak in F1 plants was widely distributed between that of Yokoyama and TH3 on all observational days. On 8 of all a observational days, the average rate of budbreak in F1 plants was nearer to that of TH3 rather than Yokoyama. We formulated the hypothesis that TH3 is homozygous for a dominant gene involved in the depth of endodormancy, but the hypothesis was rejected based on a chi-square test. From these results, it was suggested that pear plants had quantitative trait loci determining chilling requirements as a genetic factor. The defoliation period in many F1 plants was closer to that in Yokoyama rather than TH3. Most F1 plants foliated in April 9th when the day of foliation between that of Yokoyama and TH3.
