2018 ASHS Annual Conference

Pistachio (Pistacia vera L.) nut growth has 3 successive/simultaneous stages: 1) first, pericarp expansion growth that produces the final in-shell nut size; 2) second, thickening and hardening of the pistachio endocarp which is a process of lignification; 3) and simultaneously with the late lignification, embryo growth. In pistachio, it is crucial for growers to know when these specific growth stages will happen to maximize efficiency of irrigation, pest management, and harvest time to optimize quality, yield and profit. Based on three years’ data, a pistachio nut growth model was developed to describe the three growth stages as a function of heat units for the cultivars Kerman, Lost Hills, Golden Hills, Kaleghouchi and Pete 1. The three nut growth stages were measured weekly starting with bloom and ending with harvest. Hourly temperatures were monitored in each location and the thermal unit accumulation was calculated with the base temperature of 7 ^oC. Four non-linear models–the Asymptotic Regression, Michaelis – Menten, 3-parameter Logistic and Gompertz models–were coded and analyzed using R Statistics software with functions of SSasympoff, MMoff, SSlogis and SSgompertz, separately. The Gompertz model produced a better coefficient of determination and Akaike’s Information Criterion values. It best predicted pistachio nut growth at both low and high heat unit accumulation. Based on the selected Gompertz model, a service website, powered by the Spring Framework, was developed heat units by applying the prediction curve. Pistachio growers only need to input the orchard information of the bloom date, cultivar and location.