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Title: First report of the occurrence of the A2 mating type of Phytophthora infestans on tomato crops in Taiwan, Republic of China

Author
item Deahl, Kenneth
item Jones, Richard
item BLACK, L
item WANG, T
item COOKE, L

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2008
Publication Date: 6/1/2008
Citation: Deahl, K.L., Jones, R.W., Black, L.L., Wang, T.C., Cooke, L.R. 2008. First report of the occurrence of the A2 mating type of Phytophthora infestans on tomato crops in Taiwan, Republic of China. Plant Disease. 92:978.

Interpretive Summary: Late blight poses a significant threat to potato and tomato production throughout Taiwan. To understand why the causal agent has caused such severe epidemics of late blight in Taiwan, diseased plant samples were collected from the major growing areas of Taiwan from the 1997 outbreak to 2006. We analyzed the entire group of isolates looking for distinctive features that would allow this population to successfully compete and maintain or increase its numbers in succeeding generations. A rare mating ability was discovered in a few individuals that may provide insight into mechanisms of variation in this potent pathogen. This information will be used by plant breeders and pathologists in their attempts to develop an integrated management strategy for this damaging disease.

Technical Abstract: Late blight caused by Phytophthora infestans is one of the most destructive diseases of tomato in Taiwan. A total of 655 isolates of P. infestans, including 29 isolates from potato, were collected from the major tomato and potato production areas during 1991 to 2006 in Taiwan. Isolates were characterized on their pathogenicity, mating type, in vitro metalaxyl sensitivity, and molecular genotype, which includes allozyme pattern, mitochondrial genomic haplotype, and DNA fingerprint analyses for monitoring the population shift of P. infestans. Results show that the population of P. infestans in Taiwan underwent a significant genetic shift in 1997-1998 growth seasons. Metalaxyl sensitivities were changed from sensitive/intermediate to resistant since 1998. Similarly, the isolates obtained before 1997 were all US-1 clonal lineage, including variants US-1, US-1.1, US-1.2, US-1.3, and US-1.4; however, new US-11 clonal lineage, including variants US-11, US-11.1, and US-11v, appeared during the 1997-1998 growth season possibly introduced on imported table potatoes. Moreover, a few isolates were A2 mating types. This was the first report of the A2 mating type in Taiwan and the first reported A2 in the US-11genotype. Although sexual recombination was not yet detected, increasing percentage (up to 42.3% in 2006) of the US-11 variants implied that genomic diversity of the pathogen is changing quickly. Therefore, it is important to monitor the population shift of the P. infestans continuously and develop the integrated management strategy for the disease control.