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Biology And Fitness Of Sexual Hybrids Of Phytophthora Cactorum

Posted on:2001-06-09Degree:DoctorType:Dissertation
Country:ChinaCandidate:C P YouFull Text:PDF
GTID:1103360002452531Subject:Plant pathology
Abstract/Summary:PDF Full Text Request
The biology and fitness of sexual hybrids of different isolates of homothallic Phytophthora cactorum and variability resulting from their sexual hybridization were studied in this paper. 1.. Biology of sexual recombinants of Pkyiopkthora cactorum Fifty sexual hybrids were obtained from 3760 single oospore isolates from pairing of two Phytophthora cactarum isolates ( AP14Mr~l.52 with resistance to metalaxyl and sensitivity to chloroneb, PK9Cnr~2~24 with resistance to chloroneb and sensitivity to metalaxyl) which were incubated on SL media for 36 days. Their biological characteristics randomly selected thirty two were tested in growth rate, sexual and asexual reproduction capacity, oospore and zoospore germination rate, pathogenicity and tolerance towards high temperature. Result was that, 32 hybrids tested grew well on lima bean agar (LBA),, 24 of which were the intermediate between their parents in growth rate; most of hybrids tested produced a great number of oospores on LBA or SL, 37% of hybrids produced much more oospores than their parents on SL; most of hybrids produced a great number of zoosporangia in vitro, 15 hybrids were the intermediate between their parents in production of zoosporangia; oospores or zoospores of hybrids tested may germinate and create effective single oospore or zoospore isolates; the germination rate of oo~pores from 22 hybrids were more than 50%; the tested hybrids inoculated on apple fruits were of pathogenic, 16 of which were of significantly stronger pathogenicity as compared with their parents. Results show that sexual hybrids from homothallic P cactorum were of 72 strong fitness at population level in vitro. Results also indicates that sexual recombination of different isolates might play a important role in enhancing the diversity of P cacborum. 2 .. Comparative variability resuItin~ from selfing and outcrossing in Phytophthora cactorum Self and hybrid oospore progeny, and zoospore progeny of Phytophthora cactorum mutants carrying meralxyi-resistant (Mr)nuclear gene or chloroneb-resistant (Cnr)cytoplasmic gene were compared for variability in growth rate , production of sporangia and oospores, and pathogenicity. Zoospore progeny were relatively uniform whereas oospore progeny resulting from both selfing and outcrossing displayed great dissimilarity in all the traits tested. For pathogenicity both pairs of mutants tested showed greater variation in hybrid progeny than self progeny. For growth rate and oospore production the same is true only for the first pair, but not the second pair. Moreover, the variation in sporangium production displayed by one parental self progeny was greater than that by hybrid progeny in both pairs tested. These results show that isolates and traits selected for study have considerable effect on the variation in hybrid and self progeny, and suggest that different mechanisms may be operating in creation of variation in this two types of progeny. Analysis of hybrid and self progeny reveals that alleles for fast growth, high sporangium production and high pathogenicity were dominant to alleles for slow growth, slow sporangium production and low pathogenicity, respectively. Results on oospore production indicate the additive effects in one pair and heterosis in another pair tested. 3~ Competitive ability of sexual hybrids of Phytopkthora cactorum Zoospores of hybrids (five single oospore cultures) derived from intraspecific outc...
Keywords/Search Tags:Phytophtlwra cactorwn, Honiothalism, Hybrids, Biological characteristics, Fitness, Competitive ability, Genetic diversity
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