Fruit development in almond is influenced by early Spring temperatures in California.

The period from full bloom (FB) to fruit maturity for individual cultivars of peach, nectarine, plum, and prune is influenced by daily temperatures between the start of FB and 30 d after FB (DAFB). Typically, warm Springs accelerate fruit development. Almond is closely-related to peach, but the date of fruit maturity is not always closely- related to the date of harvest. Normally the date of "hull-split" (HS) signals the beginning of fruit maturity. The aim of this study was to determine if the length of the period between FB and HS in several important Californian almond cultivars was related to temperatures shortly after the start of FB. Data on the dates of FB and HS from three locations in the Central Valleys of California (North, Central, and South) were analysed over 8 years to determine the effect of Spring temperatures on the duration of fruit development. Data on 28 cultivars were evaluated, but only the results for 12 of the most important cultivars are reported here. The length of the period of fruit development from FB to HS was negatively correlated with the accumulation of degree-days between FB and 90 DAFB (mean R2 = 0.51 ± 0.3), with generally poorer correlations with degree-days to 30 or 50 DAFB (mean R² = 0.31 ± 0.02 and 0.36 ± 0.3, respectively). These results suggest that temperatures in the first 90 DAFB are the primary factor influencing the time of nut maturity in almond cultivars in California. This information will be used to develop a harvest prediction model to assist growers in planning harvest dates. To facilitate this, we are in the process of developing a webpage on the UC Davis Fruit and Research Information Website similar to the one for peach and plum growers. [ABSTRACT FROM AUTHOR]