Identification Of Physiological Races Of Phytophthora Parasitica Var. Nicotianae In Hubei

Tobacco Black Shank is one of the most important pathogen causing huge damage to yield and quality of tobacco in recent years. Phytophthora parasitica var. nicotianae which cause tobacco black shank pathogen can infect all the tobacco cultivars and bring powerful destroy and serious loss. This research identified the physiological races of 0 and 1 with PCR-RFLP for the first time, which provides a new method for the rapid identification of physiological races of Phytophthora parasitica var. nicotianae.30 strains were isolated and purified from 111 samples collected from the area planting tobacco in Hubei province. All isolates were obtained from the main planting tobacco areas which contain Xiangfan, Enshi, Lichuan, Badong, Xuanen, Xianfeng, Laifen and Hefeng in Hubei province. All these isolates were colorless colony without mycelial dissepiments, and the sporangia were mostly spherical orsubspherical with conspicuously papillate, asymmetry and short pedicel. All isolates were identified as Phytophthora parasitica var. nicotianae by rDNA analysis.The physiological races of 30 Phytophthora parasitica var. nicotianae strains were identified by zoospore suspension inoculation and TTZ (2,3,5-tripheny ltetrazolium chloride) color reaction. The results showed that all these 30 strains were presented red reaction in TTZ medium. And according to the reaction on the differential host, 24 strains belonged to physiological race 1 and were the Dominant race, which take up 80 percent in all strains. The other 6 stains showed different pathogenicity to L8 and NC1071: 1 strain was resisted by L8 and NC1071; 1 strain had high pathogenicity to NC1071 and was middle resisted by L8; 1 strain had high pathogenicity to L8 and middle resisted by NC1071; 3 strains had middle high pathogenicity to NC1071 and were middle resisted by L8, which needs further study to make sure their races.As to 2 physiological races, primers of ITS₁ and ITS₄ were used to amplify a 900bp fragment from both their genomic DNA. After digestion with DpnI and MboI, 3 PCR-RFLP fragments were acquired, which can distinguish the 2 races.