Phytoparasitica (1997) 25, p. 252 (Shlevin et al.)

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E. Shlevin, J. Katan, Y. Mahrer, I. Saguy, W. van der Werf and T. Ruissen (1997)
Dry heat mortality of pathogen propagules: experimental and numerical studies
Phytoparasitica 25 (3), 252-252
18th Congress of the Israeli Phytopathological Society, February 3-4, 1997, Bet Dagan, Israel, lecture
Abstract: Greenhouse space solarization, by closing the structure, is complementary to soil disinfestation for the elimination of residual inoculum surviving on the greenhouse structure. The goal is sanitation to avoid reinfestation of soil and plants by the surviving inoculum. Closing the greenhouse during the summer, raises air temperatures under Mediterranean conditions to 55-65°C; this is accompanied by a decrease in relative humidity, resulting in dry heating. Dry heating reduces control effectiveness as compared with wet heating. However, previous studies have shown that if heating time is extended, we can achieve control of a variety of pathogens. Our aim in this study was to develop a dynamic model to predict rate of pathogen mortality using climatological data from a closed greenhouse. Two pathogens were tested: sclerotia of Sclerotium rolfsii, and soil naturally infested with Fusarium oxysporum f.sp. radicis-lycopersici (F.o.r.l.), incitant of crown and root rot of tomatoes. Under practical agricultural conditions some of these propagules remain on the greenhouse structure, with the potential of functioning as a source of contamination. With both pathogens, a series of survival tests were performed at several different constant temperatures. These tests were conducted at a temperature range of 44-67.5°C, in order to specify reaction order and constants of thermal inactivation for each tested temperature and pathogen. Thermal survival curves were verified by two methods: by adjusting to the Arrhenius model and by the 'boxcars' method. In addition, dynamic models developed for fluctuating temperature regimes in both methods were validated with observed survival data. We found that the thermal survival curve of the fungus F.o.r.l. (which has unicellular resting structures, chlamydospores) obeys first-order kinetics and has an activation energy value of 60,000 cal/g-mol. S. rolfsii sclerotia, which are multicellular structures, do not obey first-order kinetics. Dynamic models for fluctuating temperatures were developed and are in the course of validation, in an attempt to predict mortality rates of various pathogens in the process of greenhouse space solarization.
Database assignments for author(s): Wopke van der Werf, Jaacov Katan

Research topic(s) for pests/diseases/weeds:
control - general
general biology - morphology - evolution

Pest and/or beneficial records:

Beneficial Pest/Disease/Weed Crop/Product Country Quarant.

Athelia rolfsii
Fusarium crown and root rot
Fusarium oxysporum