Studies On Screening Alfalfa Germplasm Resources For Rust Resistance

Alfalfa rust is one of the most common and serious disease on alfalfa, and threatening the product of alfalfa. For learning and controlling alfalfa rust further and screening out resistant alfalfa germplasm, biological character of urediospore and teleutospore of Uromyces striatus was studied primarily; regulation of occurence of alfalfa rust was researched and an improvement on identification method of screening of alfalfa germplasm for alfalfa rust resistance was made; at the meantime85alfalfa germplasm was identified in resistance to alfalfa rust, and some plants with hypersensitive necrosis reaction to Uromyces striatus were screened out.The main results:1. The formation of urediospore appressorium and germ tube lateral branch was observed on the surface of glass slide, but not on the surface of water agar. But the germ tube grew faster on water agar than on glass slides. Urediospore generated beneath from another urediospore continuously, rather than generating separately. The germination rate decreased significantly as the concentration of suspension was increased from1.5×104spores/ml to1.5×106spores/ml. CoCl2and CuSO4inhabited the germination of urediospore strongly; ZnSO4inhabited that less; and NaCl, KCl, CaCl2, MgSO4, MnSO4had the weakest inhabitant effect.2.The inoculation efficiency was higher when0.1%tween-20solution was used as a dispersant of spore suspension than petroleum ether. Effects of leaf wetness duration and temperature on severity of disease and effects of temperature after inoculation on latent period of alfalfa rust were investigated respectively by growth chamber and greenhouse experiments. Number of pustules per square centimeter under the12h,24h,36h and48h leaf wetness period treatment was significantly higher than under the4h and8h leaf wetness period treatment. As the temperature during the initial24h period of leaf wetness was increased, the density of pustule increased to the summit at19℃, and then it decreased gradually as the temperature continued to increase. The seedlings were cultured at15℃,20℃,25℃,30℃and35℃respectively after they were inoculated at19℃during24period of leaf wetness, then the results showed the seedlings cultured at35℃did not appear any symptom of alfalfa rust; and under the other temperature after inoculation treatments(15℃,20℃,25℃and30℃), the latent period was11d,10d,7d and7d respectively; and the density of pustule was significantly higher when the temperature after inoculation was25℃or30℃than that was15℃or20℃; And there was no significant relationship between temperature after inoculation and time of pustule appearance.3. There were differences between alfalfa germplasms on alfalfa rust resistance by screening of54domestic materials and31foreign materials. Disease index distributed between29.25%～70.65%. There were11materials of which the disease index was less than40%, including4domestic materials and7foreign materials. Disease index of87%materials were more than40%. Disease index of18domestic materials and1foreign material was more than50%. Medicago lupulina L.Longdong presented the lowest resistance to alfalfa rust among all the collected materials. And hypersensitive response was found on alfalfa, which was classified into4levels.