Relationship of Airborne Botrytis cinerea Conidium Concentration to Tomato Flower and Stem Infections: A Threshold for De-leafing Operations

Abstract

Carisse, O., and Van der Heyden, H. 2015. Relationship of airborne Botrytis cinerea conidium concentration to tomato flower and stem infections: A threshold for de-leafing operations. Plant Dis. 99:137-142.Gray mold, caused by Botrytis cinerea, is an important threat for toma to greenhouse producers. The influence of airborne conidia concentra tion (ACC) on both flower and stem-wound infections was studied in a greenhouse maintained at a temperature of 15, 20, or 25°C using dis eased tomato leaves as the unique source of dry inoculum. Spore sam plers were used to monitor ACC, and a previously developed real-time qPCR assay was used to quantify airborne B. cinerea conidia. The proportion of infected flowers remained low at ACC < 10 conidia/m3; above this concentration, flower infection increased with increasing ACC. The influence of ACC on proportion of infected flowers was well described by a sigmoid model (R2 = 0.90 to 0.92). The mean propor tion of infected stem wounds over the three trials was 0.021; no infect ed wounds were observed at ACC < 100 conidia/m3. Based on logistic regression, the probability that a stem becomes infected increased rapidly with mean probabilities of 0.24 and 0.87 at ACCs of 315 and 3,161 conidia/m3, respectively. The results suggest that the amount of airborne B. cinerea inoculum in the greenhouse is often above the action threshold for flower infection and that monitoring airborne B. cinerea inoculum could help in timing de-leafing operations.Botrytis cinerea is a pathogenic and necrotrophic fungus of sev eral fruit and vegetable crops that causes pre-and postharvest rot. Gray mold, caused by B. cinerea, is one of the most commonly occurring diseases in greenhouse vegetable crops in Canada (1), which are among the country's highest-value horticultural com modities. Total yield losses attributed to gray mold are significant and average 10 to 20% (1). However, when conditions are favora ble for disease development, crop losses can reach up to 40% at the end of a cropping period (1). On tomato (Lycopersicon esculentum Mill.), B. cinerea can infect all aerial plant parts, although most crop losses are due to flower infections, which result in direct loss es of fruit, and to stem-wound infections, which may induce the death of an entire plant, causing losses of fruit production over several months (14,21,27).Tomato plants are susceptible to B. cinerea infection at any growth stage, but tender, recently injured, and senescing or dead tissues are most susceptible. Under favorable conditions, large numbers of conidia are produced on lesions, blighted tissues, and plant debris. These conidia are disseminated by air currents and, to a lesser extent, by splashing water, and are responsible for initiat ing new disease cycles. In addition to the amount of conidia, dis ease progress is influenced by temperature and relative humidity. Briefly, optimal conditions for infection are tissue wetness or high relative humidity (>90%) for at least 8 h at a temperature of 15 to 20°C. B. cinerea colonizes i...

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“…The pieces were dried between sterile Whatman No.1 filter paper and cultured on water agar plates and incubated at 28±2°C for 24 h. Single hyphal tips were transferred to Petri dishes containing V8 medium and incubated at 28±2°C for 5 days under a 12 h photoperiod (Carisse and Van Der Heyden, 2015). Purified cultures were visually identified utilizing laboratory manuals (Dugan, 2006).…”