Rejuvenation, Preservation, Drug Resistance Of Phytophthora Capsici And Genetic Analysis Of Resistance In Resistant Sources

Pepper blight is caused by Phytophthora capsici, the whole growth period of pepper canbe infected by this fungi. This disease can severely damage pepper production. Thisexperiment was conducted to study the methods of sporangia inducing and rejuvenation of P.capsici and the effect of rejuvenation, volume of medium, cell age of mycelium andphysiological races on colony growth and morphology; P. capsici couldn’t maintainlong-term survival by artificial preservation, so the methods of short-term preservation andlong-term preservation were studied. We also studied P. capsici’s sensitivity tometalaxyl-mancozeb, dimethomorph and azoxystrobin and the inheritance regularity ofCM334and PI201234. The main results showed that:1. The sporangia of different physiological races were induced by water soaking ofmycelial plugs and irradiating the whole colony; the rejuvenation of P. capsici was backinoculated by two different methods i.e. stem and leaf segments. The effect of rejuvenation,volume of medium, cell age of mycelium and physiological races on colony growth andmorphology were also studied. The results showed that the sporangium which were inducedby water soaking of mycelial plugs were more and appeared earlier than the sporangium thatwere induced by irradiating the whole colony; the efficiency of stem segments’ backinoculation was higher than the leaf segments and mycelium easily grew out from thediseased and health tissue at the junction of the stem; growth rate of Ph1and Ph3except Ph2had no significant differences pre-and post-rejuvenation but the colony of differentphysiological races all became compact and pathogenicity recovered after rejuvenation; thevolume of medium had effect on the growth of colony and the best volume was10-15mL; thecell age of mycelium had no effect on the growth of colony; the growth rate of5strainsslowed as their pathogenicity enhanced.2. The short-term preservation of different physiological races on solid plate mediumwas conducted at4℃,16℃and27℃, the long-term preservation of five strains was by twodifferent methods of preservation on slant solid medium and preservation by liquid paraffinsealing at4℃and16℃. The results showed that the short-term preservation effect of Ph2 and Ph3on solid plate medium at16℃was best, Ph1at27℃was best; P. capsici shouldn’tbe preserved at4℃on solid plate medium because three strains lost viability when they werepreserved at4℃for45d. The long-term preservation effect on slant solid medium at4℃wasbest, the contamination rate at4℃was lower than16℃and the preservation time was six toten months, the strains lost viability was because of water loss of the medium. The long-termpreservation effect by liquid paraffin sealing at16℃was best which was also the bestlong-term preservation method, five strains didn’t be contaminated and they all had viabilitywhen they were preserved for10months, the colony morphology of five strains didn’t changeand they all had pathogenicity when they were transferred.3. We studied the effect of three reagents on mycelial growth of Ph1and their controleffect on Ph1in vivo by plate growth rate method and floating leaf disc test, we alsoresearched the effect of dimethomorph on mycelial growth of Ph2and Ph3and the myceliumrecovery growth condition after removing dimethomorph inhibition. The results showed thatdimethomorph had the strongest inhibition effect on mycelial growth of three physiologicalraces and the best control effect on Ph1in vivo; three physiological races all can recovergrowth after removing dimethomorph inhibition which showed that the inhibition effect ofdimethomorph can be reversed.4. The inheritance of the variety CM334and PI201234of hot pepper from America,resistant to P. capsici, was studied by the traditional genetic analysis method. In the presentstudy, the F1, F2, and reciprocal cross (BC1) populations were developed by two phytophthorablight resistant varieties hybridization with highly susceptible inbred line Early Calwonder,respectively. The resistance of plants of each population was evaluated by vitro leavesmethod using Ph1and Ph3of P. capsici as inoculum. The segregation ratios of the resistantto susceptible leaves in F2and BC1populations were analyzed by χ2test. The results showedthat oligogene or polygene controlled the resistance to Ph1in CM334; a single pair ofincomplete dominant gene controlled the resistance to Ph3in PI201234but the resistance toPh1in PI201234was not accord with this control mode, this showed that there wasinteraction between resistance material and strains.