Dispersal and establishment of Phytophthora infestans: Biology and modeling

Sporangia germination of P. infestans isolates belonging to the US-1, US-7 and US-8 clonal lineages was assessed at temperatures ranging from 10 to 25C. At 10C there were no significant differences in germination percentages among lineages. At 18 or 20C US-7 and US-8 had significantly lower germination percentages than US-1. At 21, 24 or 25C all lineages had low germination percentages. Sporangia of US-7 and US-8 germinated more quickly at 15C than did the US-1 lineage. The incubation period (IP), lesion area (LA) and sporulation per unit area (SPU) of the isolates were assessed on detached potato leaflets at 10, 15, 20 or 25C. The IP declined and LA increased with temperature. SPU had a quadratic shape with maximum at 15C. The US-7 lineage had the shortest IP. The US-8 lineage had larger LA than US-1. There was no significant difference between US-7 and US-1 for LA. There were no significant differences among lineages for SPU.; The effect of solar irradiance on the viability of sporangia of P. infestans was assessed. Exposures during a three-hour period on sunny days reduced germination. The effective time necessary to inactivate 95% of the sporangia (ET{dollar}sb{lcub}95{rcub}){dollar} was 1.1 h. The effective solar irradiance dose (ED{dollar}sb{lcub}95{rcub}){dollar} to inactivate 95% of the sporangia was 2.6 MJ/m{dollar}sp2.{dollar} On overcast days the ET{dollar}sb{lcub}95{rcub}{dollar} was 8.2 h and the average ED{dollar}sb{lcub}95{rcub}{dollar} was 8.0 MJ/m{dollar}sp2.{dollar} The ET{dollar}sb{lcub}95{rcub}{dollar} for non-exposed sporangia was 16.8 h.; A model to estimate the number of viable sporangia of P. infestans arriving at a field was constructed. The number of sporangia deposited in a target field 10 km away from a source field was three orders of magnitude higher on a cloudy compared to a sunny day. Simulations of the effectiveness of a small source of inoculum located 100 m away from the target field suggested that such a source is as important as larger sources of inoculum located farther away. The model can be used for disease management in area-wide basis when combined with late blight forecast systems.