Preliminary study of disease prediction in mango using environmental cues.
Oosthuyse S. A., Schutte T.
Author Affiliation: HortResearch SA, P.O. Box 3849, Tzaneen 0850, South Africa.
Yearbook - South African Mango Growers' Association 18 : 43-46
Abstract : An anthracnose fruit-infection-prediction-model for mangoes was derived from daily ascospore counts and data obtained from an electronic weather station set-up in an orchard at Mahuka Landgoed in the Letsitele valley in South Africa during 1997-98. Hours of leaf wetness, relative humidity, air temperature, mm of rainfall, and wind speed were recorded. The effectiveness of the derived model is to be tested during the 1998-99 growing season. Additionally, variation in the extent of fruit infection with time was determined by weekly bagging of individual Kent and Keitt fruits from the time the fruits were golf-ball size. On ripening after harvest, disease severity of each fruit was assessed. Anthracnose, caused by Colletotrichum gloeosporioides [Glomerella cingulata], was the overwhelming disease in Kent, and soft-brown rot, caused by Nattrassia mangiferae, was that in Keitt. The manifestation of both diseases increased markedly after the first major rain event, after which disease manifestation declined with bagging date. The reductions in disease were probably related to the duration of bag enclosure as opposed to the number of infections, since wetness (resulting from fruit transpiration) in the bag would be expected to favour disease manifestation. The conclusion is reached that the spores causing anthracnose and soft-brown rot are similarly dispersed by water flow, and that infections are dependent on the wetting of fruits by water originating from infected parts of the canopy.