|Grunwald, Niklaus - Nik|
Submitted to: Agrociencia Magazine
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/3/2005
Publication Date: 4/1/2006
Citation: Lozoya-Saldana, H., Guzman-Galindo, L., Fernandez-Pavia, S., Grunwald, N.J., Mcelhinny, E. 2006. Phytophthora infestans (mont.) de bary. i. host-pathogen specificity and resistance components. Agrociencia. 40:205. Interpretive Summary: Phytophthora infestans is the causal agent of potato late blight disease that caused the Irish potato famine. It is well known that there exists a high degree of genetic diversity among Phytophthora infestans strains infecting potato in central Mexico. However, a relationship between P. infestans genotypes and potato host genotype has not been established. Isolates of P. infestans were obtained from five potato varieties with differing levels of disease resistance. Isolates were compared and characterized for genotype using isozymes. Isolates were also analyzed for sensitivity to the well-studied fungicide metalaxyl. A relationship between pathogen genotype and host resistance or genotype was not observed.
Technical Abstract: The molecular identity of Phytophthora infestans strains infecting potatoes in the Toluca Valley has been documented. Nevertheless, the relationship of the P. infestans genotypes to the host’s genetic resistance is unclear. In order to identify potential host-pathogen specificity, isolates of the oomycete obtained from five potato varieties with differing levels of disease resistance were compared regarding mating type (MT), isozyme genotype for glucose-6- phosphate isomerase (Gpi) and peptidase (Pep), and sensitivity to metalaxyl. Also, host resistance components and specificity on the host-pathogen interaction were assessed twice in detached leaves in the laboratory and once in attached leaves in the greenhouse for three of the varieties. No mating type predominated relative to host genetic resistance (frequency of A1:A2; Alpha, susceptible: 1:1.6; Rosita, resistant: 1:0.75; Norteña, resistant: 1:0.9; Monserrat, resistant: 1:2; Michoacán, resistant: 1:0.20). Eighteen MT-isozyme combinations were identified from 97 isolates. All of them have been previously reported. The most common multilocus genotypes (MT, Gpi, and Pep) were A1, 86/100, 100/100 (37% of the whole population) and A2, 86/100, 100/100 (14%). Both genotypes represented 66% of the P. infestans population obtained from cvs. Michoacán and Monserrat. The level of metalaxyl sensitivity was lower relative to the levels reported in previous studies. A relationship between frequency of pathogen genotypes and level of host genetic resistance was not observed. The isolate from Rosita was the most aggressive. It resulted in the largest lesion area in the laboratory and in the greenhouse, and showed the highest sporulation in the greenhouse. The isolate from Alpha, which showed the highest sporulation in the laboratory, was second in sporulation under greenhouse conditions. Aggressiveness was higher in isolates obtained from resistant varieties and only limited host-pathogen specificity was observed in cvs. Alpha and Rosita. Suppression of lesion area and sporulation were the host resistance components identified only for the variety Norteña.