No abstract

Black spot corresponds to a physiological disorder of the type of oxidative stress that occurs after the prolonged postharvest storage of Persea americana Mill. cv. Hass fruit. Industry tends to confuse this disorder with pathogen attack (Colletotrichum gloeosporioides), chilling injury, mechanical damage during harvest and transport or lenticel damage. The main objectives of this research were: (i) to develop a method to assess and differentiate lenticel damage and black spot and (ii) to study the correlation between mechanical damage and lenticel damage on the development of black spot. Avocado fruits from different orchards were evaluated at two sampling times using different harvesting systems (conventional and appropriate) and at two times of the day (a.m. or p.m.). Here, we report a method based on image analysis to differentiate and quantify lenticel damage and black spot disorder. In addition, the results show that conventional harvest increased lenticel damage and lenticel damage did not correlate with black spot development but correlated with increased weight loss during prolonged postharvest storage. These results have important commercial implications since the appropriate harvesting of avocado cv. Hass would not only control the incidence of lenticel damage, which would be an advantage in terms of external quality, but also reduce weight loss during transport to distant markets.

As it was previously reported, black spot development in the skin of Hass avocado has been related to a decreased antioxidant defense system. The aim of this study was to investigate the effect of different postharvest storage conditions on controlling black spot development targeting their effect on the antioxidant system (non-enzymatic and enzymatic) of the skin. Four postharvest treatments (T1: regular air storage (RA) at 5 °C for 40 d; T2: controlled atmosphere storage (CA) of 4 kPa O2 and 6 kPa CO2 at 5 °C for 40 d; T3: 10 d RA + 30 d CA and T4: 5 µM methyl jasmonate (MeJA) for 30 s + 10 RA + 30 d CA) were tested on controlling black spot incidence in fruit from six orchards from different agroclimatic zones and harvests. Then, on two selected orchards and harvests, the evolution of total phenolics (TPC), antioxidant capacity (AC) and antioxidant enzymes (catalase (CAT), polyphenol oxidase (PPO), superoxide dismutase (SOD), peroxidase (POD), phenylalanine ammonia lyase (PAL)) was monitored. Results revealed that incidence of black spot disorder was not associated to an agroclimatic zone and harvest stage. Immediate application of CA (T2) controlled black spot development during prolonged storage (40 d) and under these conditions TPC content remained higher compared to the other treatments. No clear role of CAT, PPO, SOD, POD and PAL on controlling black spot was observed. The results obtained are of value for the Hass avocado supply chain since a clear performance of CA was evidenced that will result in reduction of postharvest losses associated to this problem.