S12 - Session O2 - Using micro-tensiometers to manage water stress to maximize fruit size of apple orchards

Authors: Luis Gonzalez Nieto *, Annika Huber, Rui Gao, Lailiang Cheng, Abraham D. Stroock, Alan N. Lakso, Terence L. Robinson

Apple fruit size is affected by plant water status in addition to crop load. The objective of the current study was to understand apple fruit growth dynamics and relate it to water stress to manage irrigation for maximizing fruit size and crop value in 'Gala' apple. During the 2021 growing season we continuously measured stem water potential using micro-tensiometers (MT; FloraPulse sensors) embedded in the trunks of trees. We also measured fruit diameter each week and related fruit growth rate to stem water potential. Two different water regimes were compared (fully irrigated and rain exclusion to induce water stress). All treatments had similar fruit number per tree. Our results suggest stem water potential was effectively measured in apple trees with the MT. Trees subjected to rain exclusion showed lower stem water potentials (greater stress) compared to fully irrigated trees. The fully irrigated trees had the highest fruit growth rate (mm diameter increase/day) which declined over the course of the season. The rain exclusion trees had lower fruit growth rate throughout the season and lower final fruit weight and less fruit color when compared to fully irrigated trees. This study was our first attempt to relate apple fruit growth dynamics to continuous water stress for maximizing fruit size, color and crop value in apple orchards. Our future work will utilize fruit growth dendrometers to relate daily fruit growth patterns to stem water potential to fully automate irrigation management.