Seasonal Epidemic Dynamics And Crucial Weather Conditions Of The Pathogen-infection Of Potato Early Blight

Potato early blight, one of the important diseases in potato production, occursalmost every year in potato planting regions and causes serious yield loss frequently. Thisstudy was aimed at making clear of the seasional epidemic dynamics of potato earlyblight and the crucial weather conditions of the pathogen-infection by means ofsystematically disease investigation, spore trapping, artificial inoculation andmeterological data analysing. The main results obtained are as follows:1. The seasonal disease progress curve of potato early blight was S-shaped, and theoverall incidence of diseased leaflets and disease index had a linear correlation. InWeichang county of Hebei province, potato early blight occurs generally at mid to late ofJune to early July. The crucial period of disease development from slight to severe wasduring late July to early August. On the three different maturity potato cultivars, thelesions of eary blight firstly appeared at the lower level leaves of the potato plants and atthe same time, then appeared on the middle and higher level ones. Generally speaking,the disease of the eary maturity cultivar was severe than that of the middle and latematurity ones.2. The effective day-degree above7.2℃(DDC) for the first leasion of potato earlyblight appearance in Weichang county were386.6~433.6℃,and that were585.7~611.2℃in Zhangbei county, respectively. Hence, it is required to set up suitablethreshold via disease investigation in order to use DDC to predict the occurring of potatoearly blight in a particular region.3. In the years with heavy disease level of potato early blight, the quantity ofairborne conidia of A. solani in the canopy could be used to estimate the disease index.However, the estimation was accuracy in the early season but failed in late season in theyears with slight disease occurance. The weather conditions had significant effects on thequantities of airborne conidia of A. solani in potato canopy. Generally, a peak of airborneconidia of A. solani would appear in1~2days after a rainfall. The airborne conidia wereremarkably reduced when the daily average temperature (2m above ground) was below 18℃. The amount of airborne conidia of A. solani at5cm from the soil surface wassignificantly higher than that at the35cm and65cm, and there were no significantdifference at the height of35cm and65cm above soil surface.4. The crucial weather conditions (CWC) for the infection of Alternaria solani onpotato leaves in the field were defined as: there is a period with a minimum of21consecutive hours with a relative humidity≧90%, average air temperature (2m aboveground)>17.5℃and, precipitation>1.4mm, in the24hours.