Production, survival and infectivity of oospores ofPhytophthora infestans

Abstract

The formation of oospores of Phytophthora infestans was studied in tomato and potato crops and volunteer plants under field conditions, and in laboratory tests with leaf discs of potato cultivars differing in their level of racenonspecific resistance. Oospores were readily detected in blight-affected tomato leaflets and fruits, and in leaflets of field crops and volunteer potato plants. Oospores extracted from blighted potato leaflets yielded 13 oospore-derived progeny. Oospores were also produced following inoculation of leaf discs of eight potato cultivars expressing different levels of race-nonspecific resistance with a mixture of sporangia of A1 and A2 isolates. The highest numbers of oospores were produced in cvs Bintje (susceptible) and Pimpernel (resistant), and the lowest in Nicola (intermediate resistance). The relationship between lesions per leaflet and oospore incidence, affected by varying A1 : A2 ratios, was explored using a simple mathematical model, and validated by comparing actual oospore production in leaflets with multiple lesions of the race-nonspecific-resistant potato clone Lan 22-21 with the predictions generated by the model. Survival of oospores was investigated after their incorporation in either a sandy or a light clay soil in buried clay pots exposed to the local weather conditions. Over 6 years these soils were regularly assessed for their infection potential using floating leaflets in a spore-baiting bioassay. Sandy and clay soils contaminated with oospores remained infectious for 48 and 34 months, respectively, when flooded. Infections of floating potato leaflets occurred within 84±92 h and ceased after 11 days. Soil samples remained infective if dried and re-flooded on two, but not more, occasions.

Reducing Severity of Late Blight (Phytophthora infestans) and Improving Potato (Solanum tuberosum L.) Tuber Yield with Pre-Harvest Application of Calcium Nutrients

“…Latently infected seed tubers, infected tubers (cull piles and volunteer potatoes), and closely related weed hosts are a primary source of inoculum. Late blight disease can be airborne [3], soil-borne, and seed-borne [4], and latently infected seed tubers are the most important source of primary inoculums leading to epidemic disease development. In Ethiopia, potato seed tubers are commonly produced through field multiplication of vegetatively produced seed tubers.…”

The Role of Oospores in the Epidemiology of Potato Late Blight

“…The soil was put into pots, which were buried in a field. Survival of the oospores was checked with a leaf baiting method developed by Drenth et al (1995) which showed a survival of up to 4 years (Turkensteen et al, 2000). Using the same method Fernandez-Pavia et al (2004) reported a survival of two years in Mexico, but observed a decline in vitality and infectivity in the oospores over time.…”

“…There are however, some characteristics of epidemics that indicate that oospores serve as primary inoculum of P. infestans. Such indications are that the spatial distribution of infection foci in a field corresponds with infections in the previous potato crop ( Andersson et al, 1998;Turkensteen et al, 2000), both mating types are present within a field early in the epidemic (Drenth, 1995) or first lesions appear low in the crop, particularly on leaves touching the soil (Lehtinen and Hannukkala, 2004).…”

Evaluation of PCR markers for Phytophthora infestans mating type determination

“…The thick-walled and robust oospores can survive dry and cold conditions in the soil without a host for years. Turkensteen et al (2000) demonstrated that in the Netherlands the oospores have been able to survive in the soil up to 4 years. Fernández-Pavía et al (2004) have showed the survival of oospores for 2 years in dry weather conditions in Mexico.…”