Gibberellin treatments enhance foliar coverage, fruitlet retention, and next-season yield in young ‘Hass’ avocado trees: field measurements and UAV-based remote sensing

Abstract In evergreen avocado ( Persea americana Mill.), flowering occurs in parallel with shedding of the previous season’s mature leaves, leaving partially leafless trees highly exposed to heat-induced damage in the spring. Foliar application of gibberellins (GAs) is known to increase vegetative growth while reducing flowering in various fruit trees. Here, we examined the effects of autumn GA 3 treatment on different growth parameters of young ‘Hass’ avocado trees over two years. Our results showed that 200 ppm GA₃ treatment applied in the fall slightly reduced flowering levels. In addition, both 100 and 200 ppm GA₃ treatments significantly increased foliar coverage and the indeterminate-to-determinate floral shoot ratio, changes that were associated with elevated expression of the floral repressor PaTFL1. Furthermore, GA 3 treatment also increased leaf area and chlorophyll content, enhanced fruitlet retention, and increased yield in subsequent seasons. In conjunction with field measurements, we acquired high-resolution unmanned aerial vehicle (UAV) imagery, including multispectral imagery and 3D point cloud data, at distinct time intervals after applying the GA₃ treatment. UAV imagery and random forest machine learning models were used to estimate flowering intensity, leaf area density, canopy volume, and chlorophyll content across orchards. The 3D point cloud data revealed significantly more developed canopies in GA₃-treated trees. Furthermore, UAV-derived estimates of flowering, canopy leaf area, and chlorophyll content closely matched field data measurements. Together, our results suggest that GA 3 treatment applied during the fall to young ‘Hass’ trees contributes to protection against heat damage in the spring, thereby increasing yield in the next season.