Comparative study of leaf antioxidant activity as a possible mechanism for frost tolerance in ‘Hass’ and ‘Ettinger’ avocado cultivars

Abstract

Abstract A major drawback of avocado ( Persea americana Mill.) is susceptibility to frosts, which reduces yields and limits its geographic distribution and market growth. Whereas the frost-susceptible cultivar ‘Hass’ leads the global avocado market, cv. ‘Ettinger’, although commercially less important, is considered frost-tolerant. The mechanism behind the greater frost tolerance of ‘Ettinger’ has not yet been elucidated; therefore, the aim of the current study was to evaluate the differences between the frost responses of the two cultivars. The results showed that detached ‘Ettinger’ branches had greater tolerance than ‘Hass’ to controlled frost stress. Tissue browning caused by methyl viologen oxidative cell damage, superoxide accumulation in leaf discs following wounding and browning of cut surfaces in branches were much lower in ‘Ettinger’ than in ‘Hass’, suggesting greater antioxidant activity (AA) in the former. In leaf extracts, AA was significantly higher in ‘Ettinger’ than in ‘Hass’, but osmolarity was similar in the two cultivars. Total phenolics content was significantly higher in ‘Ettinger’ but addition of a protein mask did not significantly reduce AA in either cultivar. Interestingly, following the freezing treatment, AA increased in ‘Ettinger’ and remained almost unchanged in ‘Hass’, while osmolarity was unaffected in either cultivar. These results suggest that the greater frost-tolerance of ‘Ettinger’ than ‘Hass’ is due largely to its greater AA, which springs mainly from a non-enzymatic source, i.e. accumulation of phenolic compounds. Based on the current study, future applications may be developed to minimize frost damage in avocado orchards.