Phytoparasitica (2002) 30 (3) - Population dynamics of ...

Y. Cohen (2002)
Population dynamics of Phytophthora infestans in Israel: A 20-year perspective
Phytoparasitica 30 (3)
The 23rd Congress of the Israeli Phytopathological Society - February 11-12, 2002
Abstract: During the years 1983–2001, 820 isolates of Phytophthora infestans collected from potato crops in Israel were analyzed for mating type and sensitivity to metalaxyl and 324 isolates were analyzed for race structure. The A₂ mating type, first recorded in 1983, fully dominated the pathogen population from 1983 until 1991 (9 years). It was thereafter replaced by the A₁ mating type, which strongly dominated the population during 1993–2001 (except in 1999). Metalaxyl-resistant isolates were first recorded in 1982. During 1983–1991 the majority of the isolates were resistant. Isolates with intermediate sensitivity (I) to this fungicide were first observed in 1993, when both A₁ and A₂ mating types occurred in the population. The proportion of I isolates increased gradually, reaching 39–41% in 1997–98 and then declined to approximately 15–22% in 1999–2001. Pathogenicity to eight potato differential cultivars was determined for 80 potato isolates collected in 1983–91, to 11 potato differentials in 173 isolates collected in 1993–98 and in 71 isolates collected in 1999-2000. The first population was composed of five races with race 1,3,4,7,8,10 predominating (76%); the second population was composed of 19 races with race 1,3,4,7,8,10,11 predominating (63%); and the third population exhibited 42 (34 new) races with no single predominating race. RG-57 DNA fingerprinting and allozymes loci assays of 23 isolates revealed that isolates collected during 1984–86 belonged to the PO-57 lineage whereas those collected during 1997–99 belonged to the RFO-39 lineage. Among isolates collected during 1993–95, two unreported DNA fingerprinting patterns were found. Severe late blight epidemics occurred in tomato crops during 1998–2000. Of 35 tomato isolates, 28 were A₁ and only 7 were A₂. Ninety-four percent of the tomato isolates were sensitive to metalaxyl. Almost every isolate had a different race structure on the 11 potato differentials. When inoculated onto three tomato differential cultivars, tomato isolates showed a more enhanced virulence than potato isolates. The data suggest that the Israeli population of P. infestans has passed three major genetic changes during the past 19 years: in 1983, 1993 and 1999. The most recent change included host specialization to tomato.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
Database assignments for author(s): Yigal R. Cohen

Research topic(s) for pests/diseases/weeds:
surveys/sampling/distribution
pesticide resistance of pest

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Phytophthora infestans	Potato (Solanum tuberosum)	Israel
	Phytophthora infestans	Tomato (Solanum lycopersicum)	Israel