Study On Biological Characteristics Of Phytophthora Sojae And Screening Of Germplasm For Resistance To The Pathogen

Phytophthora root rot of soybean caused by Phytophthora sojae is one of the most dangerous soybean disease.The disease was first found in Hei longj iang province of China in 1991 and then it has been a serious disease which has severe latent damage of soybean production in Hei longjiang Province. This study served as a basic research for resistance breeding,a study of factors which infleunced the growth of myceliuni of Phytophthora sojae and its zoospores production was carried out basedon R25 of? sojae.By using R25 and H4 of the pathogen, 956 varieties(or lines) from Hei longjiang, Ji un, Liao ning Province were evaluated for screening resistant germplasm, which can provide resistant germplasm and parents for disease-resistant breeding programme as well as provide basic materials for basic research of resistant genetics, resistant mechnism etc.The results of this study showed that suitable temperature for mycelium growth ranged from 240C to 320(2 and the optimum temperature were 280C. The pathogen could grow in medium with pH value ranging from 2 to 9, but acid condition was favourable to the growth of pathogen which developed much fast when pH value was from 4 to 5. The mycelium grew faster while it was incubated in the dark. The pathogen was not particular about carbon sources, it could utilize both monosaccharide and polysaccharide. The optimum nitrogen sources were beef, typetone and asparagine, it couldn utilize ammoniuni nitrogen veiy well.Under 250(2 the myceliuni of 8 days were incubated in the distilled water for 72 hours, suspicion solution of zoospore with high concentration could be produced.Young mycelium produced more zoospores than the old, and acid condition was favourable to the production of zoospore. Temperature was an important factor which influenced the production of zoospore, but there was no zoospore produced under 00C. 350C . The appropriate temperature for the production of zoospore ranged from 200(2 to 300(2 and the optimum temperature was 250C.The soybean germplasm from the three Northeast Provinces were evaluated for resistance to? sojae, 23 varieties(or lines) ,2.54% of the tested varieties(or lines)were resistant to both R25 and H4, Furthermore, 68 varieties(or lines) were resistant to R25 as well as 251 varieties(or lines) were resistant to H4, the percentages were 7.48% and 27.77% respectively.The results of repeated inoculation experiments showed that it was feasible to screen germplasm for resistance by using the method of inoculating on hypocotyl wound and its reliability was high.Postgraduate:Huiymg Lu,Supervisor:Qmgkai Yang,Major:Crop Genetics and Breeding...