Genetic Diversity Analysis Of Colletotrichum Gloeosporioides From Stylo And Anthracnose Resistant Breeding

Stylosanthes spp, a native legume in South America, is the most important and commercial forage legume in tropical area around the world. It is widely used for forage, green manure, cover crops, erosion control, hay and meal commercial production. However stylo anthracnose, mainly caused by Colletotrichum gloeosporioides(sometimes called Glomerella cingulata), had been a global severe disease in stylo production since 1970s. It causes stylo leaves yellow, necrotic and fallen, stem and leaf stalk wilted, flower fallen and seedless. In serious cases, the disease can cause seedlings or whole plant dead, reduce forge and seed production in large quantity, sometimes even seedless. It has caused stylo serious damage in China in the past 20 years. More than 3 good productive varieties have ceased because of anthracnose.Total 703 isolates of Colletotrichum gloeosporioides have been collected from Hainan, Guangxi, Guangdong, Yunnan and Sichuan provinces by disease investigation, sample collection,pure-culture and single sporing in this research. 181 isolates were selected for AFLP analysis and 43 for RAPD which were clustered and compared with 276 isolates from other countries. Both two mollecular markers showed a significant DNA polymorphism and genetic diversity among the tested isolates.Total 43 isolates collected in China were grouped in clusters â…¡ ,â…¢ and â…¥ with the majority in cluster A/I based on six clusters of isolates from South America, the centre of origin of Stylosanthes genus. Three Chinese isolates in cluster â…¡, five isolates in cluster â…¢ and 35 in cluster â…¥ which was formed by 4 subgroups. However 181siolate were grouped in four clusters with the majority in cluster â…  and â…¡ which were formed by 4 subgroups each.This indicated that a genetic variation of Colletotrichum gloeosporioides on stylo existed in China.The results also showed the genetic variation in the Chinese population was very limited compared with that in South America, the centre of host -pathogen diversity. Asimilar situation also was detected for pathogen variation in China from this study. The genetic variation in the population of Guangdong and Guangxi was more limited than that in Hainan which also has highist virulence, specially in CATAS forage experiment station,Changjiang and Dongfang. This could be linked to a long history of growing stylo and introduction in Hainan. Some isolates from the same geographic origin and host species or genotypes were grouped in same cluster or subcluster. This indicated that different pathgen types or genotypes had their own parasitic specialization on genetic basis and pathogens from different countries or areas evolved in their own way relatively.112 isolates(47 with biotype A,57 with biotype B) were selected for race typing based on virulence and pathogenic variation determination by using a set of host differientials.The results showed different virulence in different isolates.Total 47 of type A isolates were grouped in 3 races and 57 of type B in 2 races.The hosts of type A isolates were S.scabra and S.hamata in this research. However type B for S.gianensis. In Hainan, all the three races of type A and type B existed and race A-3 only were found in Hainan with most serious virulence, but in Guangdong only race A-2 presented.For both type A and type B, the most virulent isolates were from A-3 ,B-2 in races and CATAS,Changjiang and Dongfang in sites. The results from race typing also showed that this a wide pathegenic variation in type B. It may produce more new races in the future with evolution.This is similar to the result from RAPD and AFLP analysis. Thus more attention should be paid to the monitoring and evaluation.An on-station observation on epidemyology for three years showed the severity and incidence of stylo anthracnose were significantly correlated with air humidity (r=0.44037,Pr=0.0457) .There were two peaks of disease incidence in a year.The main peak was in August and September,the other in Jannuary which followed the rainfall.22 accessions from S.guianensis were evaluated and compared based on the anthracnose resistance from 2001 to 2003. Lines 24, 12, 81, 55 and 89 were selected with higher anthracnose resistance and godd yield performance. 14 acessiones from S.Seabmna...