Chilling Requirement: A Main Step to Get Productive Response in Walnut and Pecan Cultivars in Catamarca (Argentina)

Abstract

The thermal requirements of deciduous fruit trees are crucial for expanding walnut and pecan cultivation in Catamarca, a warm region in northwestern Argentina. This study evaluated the chilling requirements of two Persian walnut cultivars (‘Chandler’ and ‘Trompito INTA’) and three pecan cultivars (‘Stuart’, ‘Pawnee’, and ‘Western’). Well-lignified budsticks, one-year-old branches of 40 cm, were removed from trees twice, in the autumns of 2018 and 2019, without damaging any apical (TB) or lateral buds (LT). They were stored at 5 ± 0.5°C to accumulate chilling hours (CH) across ten treatments (0-1000 CH in 100 CH intervals) before sprouting in greenhouse conditions. Results were quantified as the mean time (days) to reach budbreak (MTB) and as the percentage of budbreak. The ‘Western’ pecan required the least chilling (300-400 CH), followed by ‘Pawnee’ (400-500 CH) and ‘Stuart’ (600-800 CH). It should be noted that the pecan tree in cvs 'Pawnee' and 'Western' sprouted without cold in the first-year trials. Considering walnut, ‘Trompito INTA’ and ‘Chandler’, showed a chilling requirement of 500 and 800 CH, respectively. Persian walnuts needed at least 200 CH to budbreak. The study shows that pecan requires less cold to reach 50% sprouting than to stabilize MTB. ‘Trompito INTA’ stands out as a Persian walnut cultivar with low chilling requirements. This cultivar may be better adapted to milder winters and could contribute to climate change adaptation in walnut-growing regions. These results are valuable for cultivar selection and planning expansion of nut orchards in warm regions of Argentina