Blossom-end rot in relation to growth rate and calcium content in fruits of sweet pepper (Capsicum annuum L.)

The relative importance of growth rate and calcium concentration in sweet pepper fruits (Capsicum annuum L.) for the induction of blossom-end rot (BER) was investigated in (1) four pollination treatments in one cultivar, (2) four cultivars with the same fruit load and (3) three fruit load treatments in four cultivars. For fruits with the same pollination treatment those eventually developing BER had a higher initial fruit growth rate than those not developing BER. Within the same experiment both the growth rate of the young fruit and BER increased with the number of seeds. The Ca concentration of the pericarp in mature fruits was negatively related to both fruit size and BER incidence. Differences in levels of BER between different pollination experiments could not be explained solely by differences in growth rate of the young fruit, but related to different Ca concentrations in the mature fruits. In the spring, but not in the summer, cultivars more susceptible to BER had a larger final size but lower Ca concentration in the young fruit than the resistant ones. By lowering the fruit load in the summer both the final fruit size and the BER incidence increased, but the Ca concentrations of both proximal and distal pericarp in the young fruit of all cultivars were not consistently affected. Despite a correlation between growth rate and low Ca concentration in the fruit, the incidence of BER may only be predicted from separate effects of fruit growth and of Ca concentration of fruit. The data indicated that at a higher growth rate a higher Ca concentration is required to prevent the induction of BER. The usefulness of the total Ca concentration of the fruit for determining the critical Ca concentration in the induction of BER is discussed.Key words: Capiscum annuum L., sweet pepper, blossom-end rot, calcium, growth rate, pollination, fruit load.