Preliminary Studies On The Screening Methods In Vitro For Resitance (Tolerance) To Sclerotinia Sclerotiorum In Brassica Napus L.

Sclerotinia sclerotiorum is the main disease on oilseed rape (Brassica ssp), which has caused 30 millions directed damages to the rapeseed production in China every year and the sourse of resistance to Sclerotinia sclerotiorum has not been found so far. In order to acquiring some new disease-restance materials, premiliminary studies on induced mutation with -raysand sreening in vitro were done with Brassica napus .The results were summarised below:1. The dry rapeseeds were treated with y -rays dose ranging from 160 to 320 Krad and then were seeded in B5 medium added oxalic acid(OA) with concentration ranging from 0 to 6.0 mM.The results showed the effects on the germination capacity of seeds, hypocotyl length, root length and the survial rate of the seedlings after the seeds were treated with V -rays and OA. Following were the conclusions.A. The germination percentage of the seeds was rapidly decreased with the increase of the concentration of OA added in medium. When the concentration reached to 3.0 mM, the germination rate reduced by half and the seeds almost cant germinate in 65 medium. The seed germination also deduced after the rapeseeds were irradiated by the Y -rays and the tolerant of seeds to the OA became weak. Correlation analysis revealed that negative relation between the seed germination pecentage and the concentration of OA added in the medium reached significant level(r=0.9543).B. The hypocotyl length were significant shorter than that of controls. When seeds were treated with 160 Krad Y -rays, the average length of hypocotyl was 26.3 mm in OA-added medium,which was only 50.9% compared with that of controls.When the OA's the concentration varied from 0 to 4.0 mM,the hypocotyl length hardly reduced by 30 pecent while the concentration rised every one mM. Test usfng Duncan's method indicated that the difference of hypocotyl length between the OA's congcentration- and between dose of Y -rays were significant.C. The effect on growth stage of main root was similar to that on the hypocotyl length. The primary root's length of seedling was shorter and shorter gradually with the increase of OA's concentration and dose of Y -rays.But test using Duncan's method demostrated that the difference was significant only between the dose of Y -rays.D. A test about culture in vitro with apical buds along with cotyledons cut from the seedlings was done.The results showed that the survial rate of seedling was 99.2%,91.8% and 90.1% respectively when the dry seeds had been exposed with 0,80 and 120 Krad Y -rays.But the survial rate was only 7.3% when the dose of Y -rays was 160 Krad. Result showed that the LD5 o of Huashuang No.3 was between 120 and 160 Krad. Because meristematic cells of the seed had suffered from irradiation injury and died ,the germination of seeds were only the straight growth of corculum and embrynonal and the extension of cotyledon.So there were no euphylis to be grown when the apical buds were translated into medium. Even if there were one or two euphylises to be form, they would not grow any more and die after a period. The same result had been gained when the seedling were derectly translateded into the Bs medium.2. A culture in vitro in OA-added medium seedlings at one-leaf stage,two-leaf stage and three-leaf stage were done. The results showed that the seedlings' capacity of tolerance to OA were not significant between the seedling at different stage. When the concentration of OA reached to 3.0 mM, the stem of 98.4% of seedlings rot away and the seedlings died after one month. This also demostrated that the seedlings' capacity of tolerance to OA toxin were inferior to that of seeds.3. Identification for the seedlings' resistance to Sclerotinia sclerotiorum by detached-leaves inoculated with mycelium were done. The results showed that the seedlings screened with OA-added medium at seed-stage all had suffered the disease, but there were significant difference between the seedlings from different medium and negative relation between the...