| Potato late blight is one of the most serious diseases in potato producing areas throughout the world. Phytophthora infestans (Mont.) de Bary as the pathogen causing potato late blight is badly harmful to potatoes and many planting potato countries suffer from enormous economic losses. Nowadays, study on potato late blight in many countries has already been focused on population genetic structure of pathogens and how to use biological methods to more effectively prevent and control potato late blight, especially how to improve the stability of prevention and control of potato late blight.Pathogenic types (physiological races) and their distributions, population genetic diversity, and SSR genotypes of P. infestans in potato planting areas of Heilongjiang, Jilin, Liaoning and Hebei was investigated in this experiment in order to completely reveal composition and population genetic structure of this pathogen. Also, feasibility, control effect, stability and physicochemical properties of complex fermentation from antagonistic Alternaria alternata (Fr.) Keissl (LH-03) and actinomyces (NB-8) were preliminary researched against P. infestans and on detached potato tissues. The major results are as follows:1. Two hundred and fifty five strains of P. infestans were successfully isolated and purified from 370 leaves specimens with potato late blight collected from Heilongjiang, Jilin, Liaoning and Hebei, in 2009. The average of successful isolation rate was 68.9%.2. Twenty types of physiological races were identified from 150 strains of P. infestans collected from Heilongjiang, Jilin, Liaoning and Hebei from 2008 to 2009. Physiological race 1.2.3.4.5.6.7.8.9.10.11 is dominant, accounting for 34.00%, in 20 types of physiological races.3. All identified virulence genes of P. infestans were found in Heilongjiang, Jilin, Liaoning and Hebei. On other hand, potatoes with resistance gene R11 had been infected by more than 99% P. infestans tested.4. Twelve types of SSR genotypes were identified from 200 strains of P. infestans using two pairs of SSR primers, Pi4B and Pi4G. Among them, Genotype F-01 was a leading genotype and accounted for 72.00%. In addition, Genotypes A-09, F-07, F-08, I-01, J-01, K-01 and L-01 were firstly reported at home and abroad.5. Fourty types of genotypes were identified from 134 strains of P. infestans using 15 pairs of primers. Of them, strains with genotype-III were the most, accounting for 37.31%, in total 134 strains of P. infestans tested.6. Through cluster analysis on the results of SSR amplification, there was no relation between cluster and geographical origin among 134 strains of P. infestans. Also, through population genetic diversity analysis by using POPGENE32 software, genetic difference was minimal among all tested P. infestans populations from Heilongjiang, Jilin, Liaoning and Hebei.7. It was clear that complex fermentation of both Alternaria alternata (LH-03) and actinomyces (NB-8) with evident antagonistic effect on P. infestans was not suitable, but mixed fermentations of them as a certain proportions showed much better effect on direct inhibition to growth of P. infestans and control of late blight on potato detached tissues than that of them individual. The both inhibition rate and control effectivety could increase 10-20% or more.8. Illumination, ultraviolet, temperature, salt ions, protease K and neutral and alkaline pH did not significantly affect the stability of mixed fermentation only extreme acidic condition (pH 2) had evident effect since the inhibitory rate significantly decreased.9. Inhibitory substances in complex fermentation were soluble in chloroform and ethyl acetate and parts of them were soluble in petroleum ether. They can be found from the precipitation by the 85% ammonium sulfate precipitation, whereas found also in supernatants by the ethanol precipitation. So we can deduce that inhibitory substances may be polarity proteins or carbohydrates. |
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