Genetic Diversity Of Phytophthora Sojae And Disease Resistance Of Soybean Germplasm In China

Phytophthora root rot (PRR) of soybean caused by Phytophthora sojae is adestructive soybean disease. Since it was first found in the Northeast China in1991, the area subjected to the disease and the loss has rapidly increased inHeilongjiang Province. It is becoming a major threat to soybean production inthis province.In this study, the method of isolation of P sojae from soil through baiting wasmodified. By the improved method, the distribution of P sojae was surveyed inChina and the pathogen was isolated from soil in which soybean grew. Thegenetic diversity in population of P sojae in China was evaluated by theanalysis of virulence and random amplified polymorphic DNA (RAPD)fingerprint. In the same time, soybean cultivars or lines from three provinceswere identified for resistance to P sojae. The followings are the main resultsand conclusions of the study:1.By the study of the factors affected oospore germination in soil, theoptimum condition of the leaf disc baiting method for production of sporangiawas in 25%?0% soil moisture and at 24 C for 7--8d. Comparing severalprocedures, a new method has been established. By this method Pyhium wasextremely reduced in combination of the chemicals and the soybean hostselections. Using the method the distribution of P sojae in China was surveyed.The result showed that P sojae exists in Yangtze River Basin, Yellow River andHuaihe River Basins as well as in the Northeast.2.The races of isolates obtained from plant and soil were identified indifferential host. Extensive diversity of virulence was found in isolates collectedin China. In 83 isolates, all of them are new virulence type expect one isolateidentified as race 1. There was more abundant diversity of virulence in soilisolates than those isolated from soybean plants. In general, the virulence ofisolates from Yangtze River Basin, Yellow River and Huaihe River Basins wasstronger than that from Northeast.3.Genetic variation in 86 isolates of P sojae, including 75 from China andii from United States, was analyzed by RAPD assay. Using 14 oligonucleotideprimers, fingerprint patterns were generated for each isolate. Of RAPD markers,74 were polymorphic. The percent disagreement coefficient among 86 isolatesVIwas O.047~0.390. Isolates from China were greater polymorphic than isolatesfrom Unite States. The results showed that substantial genetic diversity existedamong isolates. No relation between virulence and RAPD markers amplifiedwith 14 primers was detected.4.236 soybean cultivars and lines collected from Anhui, Henan andHeilongjiang provinces were evaluated for resistance to Phytophthora root rot.The result showed that the resistance to isolates of P sojae was extensivelyexited in soybean cultivars and lines from three provinces. There wasconsiderable difference of resistance to special isolates among soybean cultivarsfrom difference provinces. The evaluation of resistance of soybean cultivarsfrom Henan and Heilongjiang provinces showed that the cultivars of multi-resistance to isolates with different virulence were also abundant, especially inHenan's cultivars. By the analysis of resistance reaction to 5 isolates, it was found that some new resistant genes probably existed in 67 soybean cultivars from China.