Studies On Sporulation And Sensitivity To Azoxystrobin Of Alternaria Solani9and Resistance Of Potato Cultivars To Early Blight

Early blight (EB), which is caused by Alternaria solani, is a foliar fungal disease. A.solani produced little or a small amount of conidia in vitro. Conidia were used asinoculums to screen plants for resistance to the fungus. Azoxystrobin is an effectivechemical agent to control early blight, but there is an inherent risk for fungicideresistance after frequent usage of azoxystrobin. Breeding resistant varieties is the mainmethod of prevention and treatment of potato early blight. However, screening resistantcultivar is a key component for breeding resistant varieties. Field trials require an entiregrowing season for screening plants with EB resistance. In addition, plants beingevaluated for early blight resistance in the field may be affected by environmentalcondilions and other factors that may either increase or decrease susceptibilily to earlyblight. Because of these problems, research was conducted to study three aspects out ofsporulation of A. solani, sensitivity to azoxystrobin, and detection of EB resistance ofpotato cultivars. It was designed to establish the theoretical basis for making an intensivestudy of fundamental research and developing control strategy of EB. The main resultswere listed as follows:1. The current paper deals with the effects of media, mycelial wounding, ultravioletlight treatment, and temperature alteration on conidial production of7strains. It is foundthat all these treatments had significant effects on sporulation. The optimum condition forlarge amount sporulation of A. solani was determined. For maximum sporulation, strainsrequired tomato juice agar dedium, mycelium wounding,10min ultra-violet treatmentand altered temprature to20℃.2. Totally160strains of A. solani isolated from various locations were investigatedfor sporulation by using optimizing sporulation conditions in vitro. The results showedthat120strains(75%) could produce a large number of conidia, ranged from1.26×104conidia/cm2to5.0×104conidia/cm2. Germination rate of the120strains was alsoinvestigated.97.5%strains were germinated ranging from96%to100%. A total of40%strains were germinated in100%. 3. Evaluation of azoxystrobin sensitivity in vitro of117A. solani isolates weredeterminated. The isolates were collected from twenty regions of seven provinces inChina. It was found that distribution of sensitive frequency of these strains presented anunimodal curve. EC50values ranged from0.01μg/mL to0.09μg/mL, and the mean valuewas0.04μg/mL. Azoxystrobin-resistant strains or strains with reduced sensitivity toazoxystrobin were not found. In addition, azoxystrobin sensitivity of strains collected in2009(EC50=0.03μg/mL) was higher than in2010and2011. There were differences inazoxystrobin sensitivity among isolates from distinct regions.4. In current research, EB resistance in32potato varieties was evaluated byauxins-treated and isolated leaf assay. The results showed that there were six immunevarieties, two highly resistant varieties, eight resistant varieties, seven susceptiblevarieties and nine highly susceptible varieties.