Phytoparasitica (1997) 25, p. 249 (Rekah et al.)

Yael Rekah, D. Shtienberg and J. Katan (1997)
Dissemination in space and survival in time of Fusarium oxysporum f.sp. radicis-lycopersici
Phytoparasitica 25 (3), 249-249
18th Congress of the Israeli Phytopathological Society, February 3-4, 1997, Bet Dagan, Israel, lecture
Abstract: Tomato crown and root-rot, caused by Fusarium oxysporum f.sp. radicis-lycopersici (F.o.r.l.), is a potentially severely destructive disease. The purpose of this study was to determine whether F.o.r.l. is a polycyclic pathogen, namely, if it has the ability to complete several disease cycles per growing season, or is it a monocyclic pathogen, namely, has one cycle per growing season. It is currently assumed that most soilborne pathogens are monocyclic in nature, whereas foliar pathogens are polycyclic. Such characterization of pathogens has important epidemiological consequences for disease management. The development of the disease caused by F.o.r.l. was followed in a naturally infested field in the years 1995 and 1996. The data were analyzed statistically using geostatistics, in order to determine the probability that disease in one plant is related to infection of neighboring plants. Variogram functions, by which the changes in variance around the focus of the disease were quantified, provided evidence that during the season the disease spreads in the field to a distance of a few meters. In another set of experiments, inocula of nit mutants of F.o.r.l., which are resistant to chlorate (KClO₃), were buried near tomato plant roots. These mutants can grow on chlorate media and therefore can be identified specifically. This technique enabled us to follow the pathogen's movement in time and space under natural conditions. The F.o.r.l. mutant succeeded in infecting plants at a distance of 1.5 m along the row from the inoculum source, resulting in typical disease symptoms. The spread of the pathogen along the rows was via root-to-root contact. Our results suggest that F.o.r.l. is a polycyclic pathogen. This is a deviation from the classic pattern of nonzoosporic soilborne pathogens, which are considered to be monocyclic. F.o.r.l. produces macroconidia on the surface of infested plants. These conidia may provide another mechanism of dispersal, contributing to the polycyclic behavior of the pathogen. The dissemination mechanisms, including aerial dispersal of macroconidia, are being studied.
Database assignments for author(s): Dani Shtienberg, Jaacov Katan

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

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Fusarium crown and root rot	Tomato (Solanum lycopersicum)	Israel
	Fusarium oxysporum