APS Homepage

Poster: Biology & Disease Mgmt: Oomycetes


Phenotypic variation between two clades of Phytophthora cinnamomi isolated from avocado fields in California
R. BELISLE (1), B. McKee (2), W. Hao (2), P. Manosalva (2) (1) University of California, Riverside, U.S.A.; (2) University of California Riverside, U.S.A.

Phytophthora cinnamomi (Pc) is the causal agent of Phytophthora root rot (PRR), the most serious disease of avocado worldwide. Pagliaccia et al. (2013) first assessed the genetic diversity of this pathogen in California and identified 16 genotypes corresponding to two distinct clades of A2 mating type isolates. Additionally, differences in virulence were observed between these two clades after infecting avocado rootstocks with different levels of tolerance to Pc. To reveal additional phenotypic differences in these specific genotypes, three representative isolates from clade I and clade II were characterized for: i) mycelial growth rate at different temperatures, ii) zoospore production, iii) zoospore germination, and iv) fungicide sensitivity. More virulent Pc isolates of clade II showed slower growth but an earlier release of zoospores. The molecular interaction between these Pc isolates and their hosts are being studied using lupin and avocado plants. Pc nuclear and mitochondrial genes will be used to study the genetic relationship among isolates from these two clades. Our data suggests that the isolates representing clade II differ in most of the phenotypic traits assessed. Fungicide efficacy among these isolates is being tested under greenhouse conditions using avocado seedlings. This work represents an integrated approach to study the molecular interaction of P. cinnamomi with its host and provide practical solutions to manage this pathogen in the field.