Fruit load in almond spurs define starch and total soluble carbohydrate concentration and therefore their survival and bloom probabilities in the next season

Abstract Nonpareil almonds trees have compact shoots, known as spurs. Spurs are the main bearing structure of many fruit trees. However, in almonds, spurs show alternate bearing and low winter survival if fruit load is high or if leaf area is low at the spur level. To better understand the source sink relationships that govern the effects of fruit load on spur survival and return bloom, a total of 1920 spurs with varying fruit load (non-fruiting spurs, one fruiting spurs, two fruiting spurs, and one fruiting spurs de-fruited at 40 and 70 days after full bloom) were labeled and tracked for two seasons in fully mature trees. Spur variables such as leaf area, total soluble carbohydrates (TSC), starch concentration, winter survival and return bloom were collected and analyzed with generalized linear mixed models and structural equation models. Starch concentration in non-fruiting spurs (excluding de-fruited spurs) was twice as high as starch concentration of fruiting spurs. Similarly, in the following season, the probabilities of survival and bloom in non-fruiting spurs were 55% and 61% higher than fruiting spurs, respectively. Structural equation modeling suggests that starch concentration in a spur is correlated with spur leaf area, number of fruits, fruit weight, and TSC. Thus, this work improves our understanding of return bloom and winter spur survival.