New approaches to detecting Phytophthora
O'Brien, P.A. (2010) New approaches to detecting Phytophthora. In: 6th Australasian Soilborne Diseases Symposium, 9 - 11 August, Twin Waters, Queensland, Australia.
Phytophthora comprises a genus of devastating plant pathogenic microorganisms. They have been responsible for some of the most extensive disease epidemics and continue to pose problems with agricultural and horticultural crops worldwide. Taxonomically Phytophthora are classified with the Stramenophiles and are quite distant from the true fungi. Unlike the fungi they have diploid vegetative cells and cellulose cell walls (Hardham 2005). Their closest relatives are the alveotates, such as Plasmodium, Toxoplasma and Cryptosporidium.
Genetic variation arises by mating between A1 and A2 mating types although some species are self fertile and do not require the opposite mating type. Importation of strains of the opposite mating type can stimulate a burst of sexual recombination leading to the emergence of new genotypes. The importation of new genotypes of the potato late blight pathogen P. infestans into the USA from Mexico in the late 1980’s led to an almost complete change in the genetic structure of the resident P. infestans population (Goodwin et al. 1998). New species also arise by hybridisation between two species. P. alni a new species that is causing extensive damage to stands of Alder trees throughout Europe is a hybrid of P. cambivora and an unknown taxon similar to P. fragariae (Brasier et al. 1999). New species are continually being described and may represent new hybrid species (Man In't Veld et al. 2007).
Traditionally detection is by baiting of infested soil, or by plating diseased tissue on selective agar (O'Brien et al. 2009). More recently a number of DNA tests have been developed for detection (O'Brien et al. 2009). Progress is being made towards the development of on-site DNA identification tests. On-site antibody tests have been developed and are used extensively in the UK to screen nurseries for Phytophthora pathogens.
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