|ROBINSON, TERENCE - Cornell University|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 5/11/2022
Publication Date: N/A
Technical Abstract: Apple rootstocks modify scions at the molecular level modulating gene expression and hormone flux. Reports about some of the Geneva® apple rootstocks showing increased productivity in low chill environments by causing more floral and vegetative buds to break in the top 1/3 of apple trees featuring high chilling requirement scions like Gala (~890) and Fuji (~1150) stimulated us to validate these observations. We used an existing, mature (8th leaf) orchard featuring a full sib population of rootstocks derived from the cross between ‘Ottawa 3’ and ‘Robusta 5’ that had been grafted with Gala scion. We harvested 30 cm one-year growth shoots for a replicated experiment to measure the effect of rootstocks on bud break. In 2017 we tested one level of chilling hour accumulation (800 hours) measured according to the North Carolina model to see if we could observe the phenomenon in Geneva, NY. In 2018 we tested three chilling hour accumulation levels (Treatment 1: 585 hours, Treatment 2: 702 hours, Treatment 3: 906 hours). In 2017 shoots were harvested when the trees had accumulated 800 hours of chilling were then placed directly into a greenhouse environment (20° C day/17° C night). In 2018 shoots were harvested on November 22 when the trees had accumulated 585 chill hours and shoots in treatment 1 were place in the greenhouse at 20° C day/17° C night while shoots from treatment 2 and treatment 3 were stored at 5° C until they had reached the desired chilling hour accumulation and then were placed in the same greenhouse environment for pushing. Bud break was recorded at 15 and 30 days after introduction on the greenhouse. The rootstock genotype and chilling treatment had a significant effect on apical and lateral bud opening in both years. In general, apical buds opened first and were followed by laterals. In 2017 approximately 50% of the rootstock genotypes had one or more buds open after 30 days indicating a significant rootstock effect on the scion chilling requirement. In 2018 the proportion of rootstock genotypes displaying open buds after 30 days increased with increasing chilling hours (585h=10%; 706h=20%; 906h=38%) perhaps indicating a quantitative trait effect. Chilling requirement is related to endodormancy while the ability of buds to open when placed in a warm environment is related to ecodormancy (accumulation of heat units). The number of buds open after 30 days is interpreted as a genotype effect on endodormancy while rootstock effects on ecodormancy could be interpreted as the differences in the proportion of open bud genotypes between the first and second observation times in the greenhouse. Although these are preliminary results, they show that in the germplasm tested, there is a definite effect by apple rootstock on scion chilling requirement.