Soilborne Oospores of Phytophthora infestans in Central Mexico Survive Winter Fallow and Infect Potato Plants in the Field

Abstract

Survival and infectivity of oospores in soils naturally infested with P. infestans oospores were studied in central Mexico. Sporangia were selectively eliminated from soil samples to determine infectivity attributable to the presence of oospores. Selective elimination of sporangia was achieved by two cycles of wetting and drying the soil. Oospore concentration, viability, and infectivity varied among soils collected during the winter fallow in different locations of central Mexico. In some soils, oospores were infective regardless of the time at which they were collected during the winter fallow. However, oospore viability and infectivity decreased following 2 years of intercropping. The number of stem lesions and initial disease severity were significantly higher in soils with moderate (20 to 39 oospores g-1 soil) oospore infestation compared with soils with low (0 to 19 oospores g-1 soil) infestation. Our study confirms that oospores can survive winter fallow and serve as a source of primary inoculum in the central highlands of Mexico. Oospore survival appeared lower in the Toluca Valley soil, which may be an indication of soil suppressiveness.

Lineage, Temperature, and Host Species have Interacting Effects on Lesion Development in Phytophthora ramorum

“…Second, the interactions of host with pathogen lineage and temperature docu mented in this study indicate that rates of spread may differ de pending on lineage and host available in natural ecosystems. For example, oospores of P. infestans at its center of origin are thought to serve as the species' primary inoculum and survival structures (22,30). Currently, no regulations are enforced within the 14 infested California counties to prevent the introduction of NA2, EU1, and EU2 isolates (2).…”

Concerted evolution of a tandemly arrayed family of mating-specific genes in Phytophthora analyzed through inter- and intraspecific comparisons

“…As a mating-specific gene, it is therefore, reasonable to propose that M96 forms a structural element such as an adhesive between gametangia. Perhaps more likely based on the timing of M96 expression, it may form part of the protein-rich oospore wall; features such as tyrosine cross-linking and O-linked glycosylation would help the wall maintain integrity through freeze-thaw cycles and during attack by enzymes from the plant or microbes (Fernandez-Pavia et al 2004). Due to the current primitive state of gene silencing technologies in Phytophthora and the presence of a large family, testing such functions genetically is not presently feasible (our attempts at silencing have been unsuccessful so far).…”

“…Oospores are also made in single cultures of homothallic members of the genus, such as P. phaseoli. In both heterothallic and homothallic species, oospores are important since they serve as long-lived inoculum for disease outbreaks, and enable exchanges of important traits such as host specificity, aggressiveness, and fungicide resistance (Fernandez-Pavia et al 2004).…”

Development of a quantitative real‐time PCR assay for Phytophthora infestans and its applicability to leaf, tuber and soil samples

“…Four sets of infested soil samples were constructed and subjected to various treatments used to eliminate mycelial fragments and sporangia, namely the use of lysing enzymes, soil drying (Fernández‐Pavía et al. , 2004) and soil freezing (Lehtinen & Hannukkala, 2004).…”