Vegetative Growth, Flowering, and Physiological Parameters of Young Avocado ‘Hass’ and ‘Hass’-Like Cultivars under Extreme Weather Conditions

Abstract

Avocado is a commercially important subtropical evergreen fruit tree. Extreme climate events may damage foliage, floral buds, flowers, and fruit, reducing avocado crop yield and restricting its geographical distribution and expansion. This study evaluates the performance of young ‘Hass’ and ‘Hass’-like (‘Gem’, ‘BL122’ [‘BL’] and ‘Maluma’) avocado cultivars under extreme weather conditions in northern Israel, an area prone to such occurrences. Over 2 years (2021–2023), trees experienced significant frost and heat events, with temperatures dropping to -2.49 °C and rising to 45.3 °C. ‘Gem’ avocados exhibited superior frost tolerance, sustaining significantly less floral bud damage than other cultivars. Both ‘Gem’ and ‘BL’ consistently showed higher CO2 assimilation, stomatal conductance, and Fv/Fm values during the winter than ‘Maluma’, suggesting better resilience to cold stress. In contrast, ‘Maluma’ exhibited the highest flowering intensity despite greater frost damage to floral buds. Under extreme heat conditions, ‘Gem’ and ‘BL’ also performed better than ‘Hass’ and ‘Maluma’, with higher CO₂ assimilation and stomatal conductance observed following heat events. In addition, ‘BL’ maintained the highest chlorophyll content throughout the study, suggesting better adaptation to adverse conditions. This study highlights the potential of ‘Gem’ and ‘BL’ as resilient alternatives to ‘Hass’ in extreme climates, emphasizing the importance of cultivar selection and adaptive management strategies for sustainable avocado production under changing environmental conditions.