2019 ASHS Annual Conference

In this work, we compared the abscission dynamics of citrus rootstocks US-802, US-897 and US-942, and how they may affect abscission in the grafted variety. This may have profound implications for the fruit lifespan on the tree, affecting final yield. Rootstocks selected are among the most demanded by growers in Florida. We used an in vitro explant system that allow a high number of comparisons in a short period of time to study abscission in leaf explants in response to increasing concentrations of 1-aminocyclopropane-1-carboxylic acid (ACC). Treatments were water, 0.1mM ACC and 1mM ACC on US-802, US-897 and US-942 rootstock leaf explants, and on ‘Valencia’ and ‘Hamlin’ leaf explants from mature trees grafted on these rootstocks. Then, we compared these results with smaller in vitro trials on detached fruit and stems. Leaves of all three rootstocks responded differently to ACC advancing abscission, being US-897 more resistant to abscise. By 6 days of 1mM treatment, 95% of US-802 and US-942 explants were abscised as compared to only 40% of US-897 explants. Similar but muted results were observed in ‘Hamlin’ and ‘Valencia’ leaves, since differences here were visible only at lower (0.1mM) ACC concentrations, but not at 1mM. At this higher concentration both varieties had the same abscission dynamics irrespective of the rootstock, and by day 4, 100% of explants had abscised. Abscission and sensitivity to ACC in detached rootstock fruit was advanced with maturation irrespective of ACC concentration. In mature fruit, abscission dynamics was accelerated in US-942 and US-802 as compared to US-897. This is coincident with the results obtained in leaf explants. Abscission in ‘Hamlin’ and ‘Valencia’ fruit was also affected by the rootstock, but to a lesser extent. In general, fruit from ‘Hamlin’ on US-942 was more prone to abscise than on US-897, whereas in ‘Valencia’ there was less fruit abscission irrespective of the rootstock. Taken together, these results show how rootstock selection may affect fruit lifespan and ultimately, yield of sweet oranges in Florida.