Physiological Characterization of Young ‘Hass’ Avocado Plant Leaves Following Exposure to High Temperatures and Low Light Intensity

The worldwide demand for avocados has resulted in the planting of millions of young plants each year. However, global warming, resulting in high temperatures, sensed as heat stress, may severely damage these new plantings. The objective of this study was to assess the risks of heat stress on young avocado plants. We aimed to characterize different physiological parameters of young ‘Hass’ plant leaves following exposure to high temperatures under low light (LL) intensity and to pinpoint the temperature threshold for significant heat stress damage in these plants. To this end, young potted plants were subjected to different temperature gradients in a controlled-climate chamber. Minor and severe leaf damage was apparent in plants subjected to the 51 °C and 53 °C treatments, respectively. Minor and vast reductions in optimal quantum yield efficiency of photosystem II (Fv/Fm) values were observed in plants subjected to 51 °C and 53 °C, respectively. Heat stress treatments significantly reduced CO2 assimilation in plants subjected to 49 °C and higher temperatures. Stomatal conductance to water vapour and substomatal internal CO2 concentration were less sensitive to the heat treatments. These results imply that the heat damage threshold for young avocado plants under LL conditions is between 49 °C and 51 °C, whereas at 53 °C, severe and irreversible leaf damage occurs

Monitoring multiyear individual tree flowering and yield reveals high variation among ‘Pinkerton’ avocado trees

Most avocado cv. Pinkerton scions in Israel are grafted on seedling rootstocks, resulting in unstable yields. The objective of this study was to evaluate tree multiyear yield variation among ‘Pinkerton’ trees. We evaluated the flowering and yield variations among trees in two commercial avocado orchards, in Kibbutz Dan and Kibbutz Kfar-HaNassi, for 4 years. The multiyear average yield of the individual trees ranged from 9.5 to 73.7 kg tree−1 in Dan, and 1.7 to 53.8 kg tree−1 in Kfar-HaNassi, with coefficient of variation (CV) of 42% and 54%, respectively. Multiyear flowering intensity ranged from 2.7 to 4.9 and 2.41 to 5 (out of 5), with generally lower CV values of 14% and 26%, respectively. Multiyear alternate bearing index (ABI) ranged from 0.24 to 0.85 and 0.2 to 1, with CV of 25% and 32%, respectively. In Dan, the yield was negatively correlated with ABI. In Kfar-HaNassi, the yield was positively correlated with flowering intensity and negatively correlated with ABI. These results show that it may be important to monitor long-term individual tree yield, because removing low-yielding trees and selecting genetic material characterised by high yield and low ABI may be advantageous for establishing orchards with stable high yields.</p