Characterization of isolates of Glomerella cingulata causal agent of Glomerella leaf spot and bitter rot of apples based on morphology and genetic, molecular, and pathogenicity tests
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2003-11-17
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Abstract
Isolates of Glomerella cingulata, Colletotrichum gloeosporioides and C. acutatum, obtained from symptomatic fruit and leaves collected from apple orchards in the US and Brazil, were characterized based on morphological and cultural characteristics, vegetative compatibility groups (VCGs), mtDNA RFLP haplotypes, and the sequence analysis of a 200 bp intron of the glyceraldehyde 3-phosphate dehydrogenase (GDPH) gene. The isolates were also tested for pathogenicity on leaves and fruit. The population structure of the species associated with bitter rot of apples in two orchards of cv. Granny Smith was also studied. Multiple VCGs and mtDNA RFLP haplotypes were found within each of the species tested. Phylogenetic trees constructed based on Neighboring-Joining and Maximum Parsimony methods, using the intron sequence, produced similar topologies. Each species was separated into distinct groups. All isolates tested were pathogenic on fruit. Only isolates with haplotypes G1, G1.1, G3, and G4 and VCGs 1, 4, and 5 were capable of causing Glomerella leaf spot (GLS). G. cingulata was the predominant species associated with bitter rot in the two orchards of cv. Granny Smith. Vegetative compatibility was a better indicator than molecular characterization for distinguishing isolates of G. cingulata pathogenic on both leaves and fruit from the ones pathogenic only on fruit. Isolates of G. cingulata from the US and Brazil which cause GLS were included in different haplotypes and phylogenetic groups. Therefore, our results suggest that isolates of G. cingulata from the US capable of causing both GLS and bitter rot arose independently of Brazilian isolates of G. cingulata, and may have arisen from isolates of G. cingulata from the US that originally were capable of causing bitter rot only. Slower growth, lower optimum growth temperature, and less sensitivity to benomyl distinguished isolates of C. acutatum from isolates of G. cingulata and C. gloeosporioides.
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fungal genetics, plant pathology
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PhD
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Plant Pathology
