Effects of simulated acid rain on the foliage and fruit yield of Malm domestica Borkh.

The effects of rain acidity on field-grown apple trees (Malus domestica Borkh. cv. Sum- merred) under natural conditions were investigated. One group of four trees was exposed to ambient rainfall. Four other groups were covered with rain-shields and for two growing seasons received simulated rain consisting of deionized water or an acid solution at pH 5.6,4.0 or 3.0 respectively. Simulated acid rain, particularly at pH 3.0, injured leaves and petals, reduced fruit production and impaired marketability. SEM examination showed that damage to the leaves (necrosis and lesions) was most extensive at the moment of full leaf expansion, whereas damage to the fruit (russeting and lesions into the mesocarp) was most severe when the fruit was almost fully ripe. The reduction in production was 19% with the pH 4.0 spray and 37% with the pH 3.0 spray (compared with rainfall-fruit). The acidity of the ambient rainfall encountered in this study caused spotting and necrosis of the leaves but did not significantly affect fruit production.