Mating Type And Physiological Race Of Phytophthora Nicotianae In Chongqing

The distribution of tobacco black shank was very extensive in China,and it was found in almost all the provinces where were planting tobacco including Taiwan,except Heilongjiang.Phytophthora nicotianae,the casual agent of tobacco black shank, infected all the tobacco cultivars including flue-cured tobacco,air-cured tobacco, sun-cured tobacco,burley tobacco,oriental tobacco and brought powerful destroy.1.The source of isolatesThe samples with typical symptom of tobacco black shank were collected from the area planting tobacco in Chongqing and were brought to the laboratory for isolation, purification and identification of the pathogen.We obtained 12 isolates from 54 samples by tissue isolateion method and medulla plate method.At the same time,we were provided 50 isolates which were provided by Institute of Plant Ecology &Pathology, Southwest University.All isolates were collected from the main eight planting tobacco areas which contain Youyang,Qianjiang,Shizhu,Wulong,Fuling,Pengshui,Wanzhou and Wushan in Chongqing.2.Identification of isolatesIsolating isolates that were obtained from diseased tobacco stems were studied systematically in vitro,respectively.The results showed all of these isolates were colorless colony,without mycelial dissepiment.The sporangia were mostly spherical or subspherical,caduceus,and conspicuously papillate,with narrow pore and short pedicel, and the asymmetry shape ones unfrequently appeared.The rDNA ITS sequences of the eight isolates that came from different areas were gained by PCR.The number of the sequence was mostly 892.After BLAST,the results indicated those isolates were Phytophthora nicotianae with a percentage of identical homology of 99%.The results of identification of pathogen,the characteristics of morphology and molecular biological methods showed those isolates were Phytophthora nicotianae Breda de Haan var.nicotianae Waterhouse(equal to Phytophthora parasitica Dustur var.nicotianae Waterhouse).3.The determination of mating typeMating types of the sixty two isolates were investigated by the method of partnership culture in vitro on 10%Vs medium.The results showed that A₂ mating type of P.nicotianae var.nicotianae was the predominant in Chongqing,next was A₀ mating type.Among the sixty two isolates tested,thirty six isolates were the A₂ mating type, twenty six isolates were A₀ mating type,A₁ and other mating types were not observed.It was suggested that sexual reproduction of P.nicotianae var.nicotianae might not take place frequently,and Chongqing might not be original center of P.nicotianae var. nicotianae.The results also indicated that mating type geographical distribution of P. nicotianae var.nicotianae in Chongqing was in line with that in China.4.Identification of physiological raceAll isolates were inoculated on the oat medium with 2,3,5-triphenyl tetrazolium chloride(TTZ) and in TTZ liquid medium,and the medium color showed that those isolates were race 0 or 1 except 3.According identification hosts,physiological races of P.nicotianae were identified by normal identification technology.The result showed that fifty-four isolates were identified to race 1,in proportion of 87.10%,eight isolates were identified to race 0,in proportion of 12.90%.Both Race 0 and Race 1 existed in all the tobacco planting areas of Chongqing,and their distributions were different. However,Race 1 was the predominant race type.