| Research on the Population Genetic Structure of Potato Late Blight Pathogen (Phytophthora infestans) in ChinaDoctoral candidate: Jiehua Zhu Supervisor: Professor Daqun Liu Major: Plant PathologyPotato late blight is a most serious disease in the potato growing areas all over the world. The occurrence and epidemics of this disease are affected by the composition and variation of Phytophthora infestans de Bary population. When the potato late blight emerged again in 1980s, the research on the late blight was focused on the population structure of the pathogen. This paper focuses on the phenotypic and (DNA) genotypic diversity of P. infestans population in areas investigated in China. And the results derived from the paper are of significance to the resistant-breeding as well as to the management of late blight disease.1. One hundred and thirty-five isolates colleted from five provinces i.e. Hebei, Sichuan, Yunnan, Inner Mongolia, and Heilongjiang were tested with 8 potato clones of the international late blight differential hosts containing single dominant resistant gene Rl, R3, R4, R6, R7, R9, R10, and Rll. The result showed that the composition of the physiological races was complex in above five provinces. All tested resistant genes were compatible to the virulent genes of isolates of P. infestans assayed, and 85% of the tested isolates overcome the resistant genes R3, R5 and Rl 1, which indicated that the virulent genes were very common in the tested population of P. infestans. In the 135 isolates tested there were 28 different races. Race 1.3.4.7.9.10.11 showed the highest frequency of 28.1%, followed by 1.3.4.6.7.9.10.11, 3.4.7.9.10.11, 3.4.7.9.11, 1.3.6.7.9.10.11, 1.3.4.7.9.10 with frequencies of 6.7~8.9%. The racial distribution was no correlation with the regions where the isolates came from.2. The metalaxyl-resistant isolates of P. infestans were discovered in potato production areas in Hebei, Sichuan, Yunnan and Heilongjiang provinces. The frequencies of isolates with highly-resistant, resistant, highly-sensitive, and sensitive were 62.5%, 3.8%, 28.7%, and 5.0%, respectively. All of the isolates collected in 2001-2002 from Hebei and Heilongjiang provinces were either highly-resistant or resistant, but the most isolates collected in 1996-1998 from Sichuan, Yunnan and Hebei provinces were metalaxyl-sensitive with the frequencies of 80.0%, 86.7%, and 100%, respectively. The EC50 values of the highly-resistant and the highly-sensitive isolate were 1479.11ug/mL and 0.07244ug/mL, respectively.3. The A2 mating type isolate was discovered in Heilongjiang province. Only 1 from 45 isolates expresses as mating type. The ratio of A2 mating type isolate was only 2.2%.4. An efficient AFLP DNA fingerprinting protocol for P. infestans of potato was modified. The improvement of the protocol could facilitate the research on the genotypic diversity, constructing genetic maps and cloning avirulent genes of the pothogen.5. Fifty P. infestans isolates collected from different provinces were amplified with 25 primer combinations. One thousand five hundred and fifteen DNA bands (fingerprints) were observed. Eight hundreds and fifty-five out of the 1515 DNA bands were polymorphic ones. The rate of polymorphic bands was 56.4%. The result based on the cluster analyse indicated that DNA polymorphism was correlated with the regions where isolates from and metalaxyl-sesitivity, but not with the races and mating types.6. Three specific isolates of the pathogen were discovered in this study. Oospores were produced when these three isolates crossed with any other 210 isolates tested, the amounts of oospores ranged from 2000 to 8000/cm2. The AFLP DNA markers were detected when these 3 isolates were amplified with the primer combinations E19/M8(E+CG/M+CC), E7/M8 (E+AT/M+CC), and E5/M10(E+AC/M+GT).7. Ten single zoospore progenies derived from parent SW98-2 were identical to their parental physiological race through pathogenesis test with the resistant gene. T...
|
PDF Full Text Request