Seasonal Dynamics of Black Leaf Mould (Pseudocercospora fuligena) on Greenhouse‐Grown Fresh Market Tomatoes

Abstract

Black leaf mould (BLM), caused by Pseudocercospora fuligena, is a major fungal foliar disease of greenhouse-grown tomatoes in the humid tropics. Quantifying the disease and yield loss from seasonal plantings will help mitigate the heavy reliance on frequent sprays of curative fungicides. In this study, severity of BLM was investigated in sequential plantings of tomatoes in two 50-mesh BioNet greenhouses in central Thailand from June 2005 to January 2007. Each planting consisted of a block of six plants that received two applications of mancozeb and another block of six plants with no fungicide application at all. Two BLM peak epidemic periods were identified, that is, from plantings that were started in August-September and in January. On average, a yield loss of 30.6% was recorded from the two peak epidemic periods based on comparison of fungicide-sprayed and non-sprayed plants. Two sprays of mancozeb resulted in 71.6% reduction in disease severity during these peak epidemic periods. Mean disease severity (DS*) was highly correlated with a favourability index of relative humidity (RH), which was quantified on a scale of 0 (<85%, nonfavourable) to 1 (≥85%, extremely favourable). A three-parameter logistic function explained the data well (R 2 = 0.81, P < 0.0001). Marketable yield (MY) was positively correlated with maximum plant height (PH max ) but negatively correlated with DS*. In addition, MY was higher from plantings during October to December. It was predicted well (R 2 = 0.60; P < 0.0001) using the model MY = (a + b 9 PH max ) 9 (1-c 9 DS*), which combined both PH max and DS*. Using this model, a reduction of 1.05% in marketable yield was predicted for each 1% increase in mean disease severity. The outcomes of this study implicated the need for management of RH and critical relevance of protecting tomato plants against BLM when they are grown during the peak epidemic periods.

Light and Electron Microscopy Studies Elucidating Mechanisms of Tomato Leaf Infection by Pseudocercospora fuligena

“…Hartman et al (1991) reported up to 32% of yield loss due to BLM on susceptible varieties without fungicide application in Taiwan. Mersha et al (2014b) reported an average of 30.6% yield loss from two peak epidemic periods in Thailand.…”