Studies On Asexual Recombination, Construction Of Genetic Linkage Map And Localization Of Avirulence Genes In Magnaporthe Grisea

Vegetative compatibility, asexual recombination and several biological characteristics of asexual recombinants in Magnaporthe grisea were studied and aimed to validate the role of recombination in genetic variation of M. grisea: variation of pathogenicity in sexual progeny and composition of avirulence genes from the cross between M. grisea isolates CH63 and TH16 were analyzed; and genetic linkage map and avirulence genes from the cross between M. grisea isolates CH63 and TH16 were constructed and localized primarily for aiding to the cloning and study of the avirulence genes.Vegetative compatibility and asexual recombination in M. grisea from Jiangsu province, China were studies. Vegetative compatibility among isolates of M. grisea collected from different areas of Jiangsu province and asexual recombination among compatible isolates by anastomosis were determined. Twenty isolates involving seven races from diseased rice plants were paired on polished rice rose bengal medium and incubated at 25癈in darkness for 18 days. Out of 173 pairings tested, solid hyphal fusion lines formed by anastomosis between 124 pairings indicated that these isolates were vegetative compatible with each other. The result showed that most M. grisea isolates were vegetative compatible. Furthermore, 17 vegetative compatible pairings between monoconidial isolates with IPTrMBCs marker and isolates with IPTsMBCr marker were selected to detect the asexual recombination between the paired isolates of different races. The asexual recombinants with MBCrIPTr marker were detected in single hyphal fragment progenies in thirteen out of the seventeen pairings. The percentage of recombinants detected was about 0.6 % - 11.3 %. Results showed that vegetative compatibility was prevailing among isolates of M grisea in Jiangsu province in vitro. These results also suggest that asexual recombination may be an important mechanism for M. grisea to produce and maintain genetic diversity in nature.Several other biological characteristics of asexual recombinants of M grisea were mensurated. The vegetative compatible isolates between races of M. grisea with differentchemical resistant markers were paired on plates containing polished rice rose bengal agar and incubated at 25C in darkness for 18 days. The populations of single hyphal fragment isolates were established from the hyphal fusion line formed between the interracial isolates paired. The 75 asexual recombinants were obtained from 1132 single hyphal fragment isolates of 5 interracial pairings, from which 20 stable asexual recombinants carried stable MBCrIPTr marker after storage at - 20C for 3 months were selected and their biological characteristics were tested in growth rate, sporulation, spore germination rate and virulence. The results showed that all of asexual recombinants grew well on the five kinds of common fungal media, part of which were higher significantly than their parents in growth rate. The sporulation capacity of asexual recombinants was strong with amount of spore production at 1.08 x 105~8.18 x 106/ disc ( d =60 mm), and some recombinants produced much more conidia than their parents on the medium containing corn and rice stalk juice. The spore germination rate of asexual recombinants tested was 65 % - 97 %, which was similar with the parents. After inoculated on 13 Japanese rice cultivars harboring known resistance genes, most of recombinants shared different virulence spectrums compared with their parents, which indicated that complicate interaction might occur between the genetic materials from their parents in asexual recombinants. These results showed that the asexual recombinants were of strong fitness in vitro, indicating that the asexual recombination might be an important role in producing and maintaining the genetic diversity in the wild population of M. grisea.A cross was made between two isolates of Magnaporthe grisea, CH63 and TH16. A total of 78 ascospore isolates were tested for pathogenicity on 36 rice varieties. There were 71 pathotypes were clearly o...