Study On Biology Characteristics Of Didymella Bryoniae And Screening Of Resistance Germplasm Of Cucumber

Gummy stem blight is a serious disease causing by D. bryoniae that affects the middleand late product of cucurbitaceous crops.This pathogen had been found in most of thecountries and regions, including America, Canada, Northerland, India, and so on. In China,gummy stem blight was becoming worse and worse in Zhejiang, Shanghai, Gansu andXinjiang.But there was a little systemic reports about the pathogen.This paper studied thebiology characteristics of A strain from Nanjing and B-la strain from Hainan.Because Astrain distributed abroad and couldn't produce spores in the normal incubation, sporulationcondition of this strain was researched elementarily to get abundant conidium spores forinoculation.To provide germplasm resistanct to gummy stem blight, through artificialinoculation at different growth stages,we got 4 materials of cucumber that had high level ofresistance from 26 varieties (lines).1 Identification and biology characteristics of A strain of D. bryoniae Acooeding to Qiu's classification, the isolates from Nanjing were identified as A strainof D. bryoniae. The effects of different media, carbon sources, nitrogen sources, pH value,illumination and temperatures on the A strain of D. bryoniae were tested. In the 10 kinds oftested medium, diameter of colony was longest on the potato dextrose agar media and dryweight of mycelial was heaviest on the yeast extract media. It had different mycelialgrowth on different kinds of carbon or nitrogen sources media. Potato solid media withmaltose and NH₄H₂PO₄ was propitious to diameter of colony; and potato liquid media withdextrose and L-Cysteine was best for dry weight of mycelial. The fungus grew best with anoptimum of pH 4.0.The mycelial growth was enhanced by ultraviolet. The optimumtemperature for mycelial growth and conidia germination was 25℃, and the lethaltemperature of conidia was 50℃10min.2 Fruiting-body isolation of D.bryoniae and sporulation condition of its A stainUsing a single fruiting-body of D. bryoniae from infected melon stems could yield purecultures effectively, avoiding contamination with Fusarium oxysporum. Dark and UV light(12h UV and 12h darkness) treatment of the A stain of D. bryoniae yielded abundantconidia. 12h fluorescent and 12h darkness produced sterile mycelia. Media compositionaffected the amount of conidia produced. Among the 11 carbon sources combined withpotato agar, lactose gave the best results while no conidia were produced on potato agarwith fructose. Of the nitrogen sources, NH₄H₂PO₄ generated the most conidia and noconidia were produced on (NH₄)₂SO₄. Conidia could be produced within the pH range5.0-11.0, best results were obtained at pH 6.0 on PDA. Only plus NH₄H₂PO₄ in potato agar,7 d darkness and 4 d UV at 25℃were the ideal conditions for sporulation.3 Biology characteristics of B-la strain of D. bryoniaeThe effects of different media, carbon sources, nitrogen sources, pH value, illuminationand temperatures on the mycelial growth, sporulation and conidial germination of B-laswain of D. bryoniae were tested. The results showed that in the tested 10 media, mycelialgrowth was the fastest on the PDA, and the amount of conidia was the largest onhalf-composition agar. In the tested 12 carbon sources, maltose is an optimum carbon formycelial growth and sporulation. In the tested 11 nitrogen sources, mycelial growth was thefastest on the medium using yeast extract as nitrogen source; mycelial dry weight was thehighest on the medium using DL-asparagine as nitrogen source; and the amount of conidiawas the largest on the medium using niter as nitrogen source. The pH values for themycelial growth and sporulation were 3.0-10.0, with an optimum of pH 4.0.Illuminationhad no effect on the linear growth of mycelium, but contious ultraviolet could increase themycelial growth and the amount of conidia. The optimum temperature is 25℃for mycelialgrowth, sporulation and conidia germination, and the lethal temperature of conidia was55℃10min.4 Identification of cucumber cultivars and lines resistance to D. bryoniaeThe fast and reliable methods for identifying resistance of cucumber to D. bryoniae byartificial inoculation of the plant seedlings and screening of resistant plant seedlings andscreening the resistant plant varieties and lines were reported. The critical technique ofthese methods included inoculation of seedlings at 1 true leaf stage with a spore suspensionof 1×10⁶ spores·mL^-1 or at 3true leaf stage with 2×10⁶ spores·mL^-1, and incubation of the inoculated plants in the controlled condition (25℃, RH100ï¼…,darkness) for 72h, respectively,followed by examination of resistance levels. Resistance identify by these methods wasconsistent with mature plants (8 true leaves) in the field. Using these methods, 4matefialsof 26 cultivars and lines were high resistant (disease index＜30ï¼…) to D. bryoniae.