Studies On The Genetic Diversity Of Thanatephorus Cucumeris And Magnaporthe Oryzae From South China Crop Breeding Area

South China Crop Breeding Area, located in Hainan Island, is the important base of crop reproduction and breeding in our country, and plays a prominent role in the reproduction and breeding of crops including rice. However, with the rapid development of South China crop breeding work and the frequently increasing of rice seeds transportation between the mainland and Hainan island, it is inevitable that the seed-borne pathogens have a potential damage on rice of Hainan island and the mainland. In order to understand the genetic diversity of Thanatephorus cucumeris(Frank) Donk [anamorph: Rhizoctonia solani Kühn], the causal agent of rice sheath blight, and Magnaporthe oryzae(Hebert) Barr [anamorph: Pyricularia oryzae Cav.], the causal agent of rice blast, The morphological characteristics, cultural characters, pathogenicity differentiation and AFLP polymorphisms of DNAs of Thanatephorus cucumeris and Magnaporthe oryzae collected from the core area(Sanya, Ledong, Lingshui) and non-core area(Qiongzhong, Tunchang, Ding'an) of South China Crop Breeding Area, respectively were comparatively analyzed so as to clarify their differences in these aspects, and provide evidence for the control of rice diseases. The main results are reported as follows:1. The diversity of morphological characteristics and cultural characters of Thanatephorus cucumeris. Their cultural characters of 56 and 51 isolates collected from the core area and the non-core area respectively were not completely consistent, showing a certain diversity. The determination of anastomosis group(AG) and cell nuclear staining showed that these isolates all belong to multi-nuclear Rhizoctonia and R. solani AG 1-IA. The results of pathogenicity test showed that there were some differences in these isolates, but no correlation between their growth rates and the pathotypes.2. The AFLP polymorphisms of DNA of Thanatephorus cucumeris. Eight primer combinations with rich and high polymorphism were selected from 64 primer combinations. A total of 366 DNA fragments were produced, 331 of which were polymorphic with a polymorphism percentage of 90.44%. The value of PPL, I, H in the core populations was 82.24%, 0.3062, 0.1932, respectively, which were higher than that of non-core populations whose value of PPL, I, H was 67.49%, 0.2447, 0.1535, respectively. These results indicated that the core populations showed greater genetic diversity. 60 isolates were classified as 9 AFLP lineages by the cluster analysis with the core isolates distributing in 9 lineages and non-core isolates distributing in 4 lineages, indicating that the core populations showed greater genetic diversity, which was basically the same as the result by the principal coordinate analysis. In addition, there was no correlation between AFLP lineages and pathogenicity.3. The genetic structure of Thanatephorus cucumeris. The value of GST in core and non-core populations was 0.1633 and 0.3481 respectively and the value of Nm in core populations and non-core populations was 2.5627 and 0.9365 respectively, indicating that the genetic variation was mainly within the populations and there were normal gene flows among core populations, but gene flow was difficult among non-core populations. The clustering analysis based on genetic uniformity among six populations indicated a high concordance between core populations and non-core populations.4. The molecular identification and diversity of cultural characters of Magnaporthe oryzae. 60 isolates of rice blast fungus from South China Crop Breeding Area were identified as Magnaporthe oryzae by ITS-PCR, which had little difference in the cultural characters on PDA medium, showing a certain diversity; the morphology of their conidia was down-pear-shaped.5. The diversity of avirulence genes of Magnaporthe oryzae. The results of PCR amplification showed that except the avirulence gene Avr-Pik, the distribution of other 5 avirulence genes ACEI, Avr-Pia, Avr-Pita, Avr-Piz-t and PWL2 showed a certain difference in core and non-core populations; in the meantime, except the avirulence gene Avr-Pia, the distribution rate of other 5 avirulence genes ACEI, Avr-Pik, Avr-Pita, Avr-Piz-t and PWL2 were high in both the core and non-core populations, indicating that the genetic structure of Magnaporthe oryzae was relatively simple.6. The AFLP polymorphisms of DNA of Magnaporthe oryzae. Night primer combinations with rich and high polymorphisms were selected from 64 primer combinations. A total of 413 DNA fragments were produced, 411 of which were polymorphic with a polymorphism percentage of 99.52%. The value of PPL, I in the core populations was 87.89%, 0.2738, higher than that of non-core populations whose value of PPL, I was 81.37%, 0.2703, respectively. But the value of H in the core populations was 0.1657, lower than that of non-core populations whose value of H was 0.1662. These results indicated that the core and non-core populations showed consistent level of genetic diversity. Cluster analysis showed that almost every isolate become an independently group, and there was no obvious cluster subgroup, indicating the core and non-core populations showed rich genetic diversity, which was basically the same as the result revealed by the principal coordinate analysis.7. The genetic structure of Magnaporthe oryzae. The value of GST in core and non-core populations was 0.1044 and 0.1223 respectively and the value of Nm in core and non-core populations was 4.2897 and 3.5892 respectively, indicating that the genetic variation was mainly within the populations and there were wide gene flows among core and non-core populations. The clustering analysis based on genetic uniformity among 6 populations indicated that a quite high concordance between core populations and non-core populations was existed.