CONICET | Buscador de Institutos y Recursos Humanos

Temperate crops have winter-chilling and spring-heat requirements that have to be fulfilled in order to break the dormancy of the vegetative and floral buds and to achieve normal spring phenology and yield performance. Knowledge of these requirements is valuable for the selection of appropriate cultivars for a particular region. Over recent years, the walnut production area in Argentina has expanded southwards, turning northern Patagonia (39-41°S) into a relevant production region. The aim of this research is to determine the winter-chilling and spring-heat requirements of Persian walnut cultivars in the lower valley region of the river Negro in Argentina (north Patagonia 40°8´S, 63°1´W). The experiment was carried out from March to November in 2012, 2013 and 2015 on the ´Chandler´ cultivar and in 2013 and 2015 on the ´Franquette´ cultivar, both wide spread in the region. After 50% leaf-fall, 1- year-old twigs were collected, placed in plastic bags, and kept in chilling chambers at 3±1°C for 300 to 1500 h. After chilling, the excised twigs were transferred to a plant growth chamber at 20±1°C, exposed to 12 h of light day-1, from 0 to 8 weeks. To achieve dormancy break and budburst, the ´Franquette´ cultivar required over 150- 300 chill hours and 4500-5000 growing degree hours (°C) more than ´Chandler´. Moreover, in both cultivars, bud break on twigs with terminal buds took 5 to 7 days more than for those without. Even though catkins seemed to have a more advanced bud break it was statistically insignificant. This analysis will allow an evaluation of the suitability of each cultivar according to the bioclimatic factors of the region, laying the basis for future forecasts of phenological models for regional walnut production.

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