Pistachio (Pistacia vera L.) phenology and thermal requirements: BBCH-based characterization of 'Kerman', 'Peters', and 'Amarillo-M' cultivars in an arid environment of San Juan, Argentina.

The expansion of pistachio cultivation into new environments requires precise phenological characterization to ensure reproductive success and adaptive management. This study aimed to (i) develop a comprehensive BBCH scale for pistachio, (ii) evaluate the reproductive and vegetative development of cultivars 'Kerman', 'Peters', and 'Amarillo-M' under arid conditions of San Juan, Argentina, and (iii) determine the chilling and heat requirements for flowering and fruit maturation. The adapted BBCH scale encompasses 40 detailed developmental stages, covering vegetative growth, flowering, fruit development, ripening, and leaf senescence. This standardized framework integrates and refines previous descriptors, enabling consistent monitoring of both male and female cultivars and facilitating comparisons across studies and environments. Phenological observations were conducted over three seasons (2022-2025) in a commercial orchard located in an arid region south of San Juan Province, combining field surveys with bioclimatic indices. Results revealed marked interannual variability in flowering synchrony associated with chill accumulation. In 2023, insufficient chilling led to delayed and extended male flowering, disrupting overlap with 'Kerman'. Fruit development showed consistent thermal requirements but advanced markedly in 2024. Overall, the proposed BBCH scale provides a robust framework for monitoring pistachio phenology and supports climate-resilient orchard management and regional suitability assessments.