Sexual Genetic Characteristics Of Colletotrichum Fructicola

Glomerella leaf spot(GLS)is a new disease on apple in China.Colletotrichum fructicola is the dominant pathogen,and it can produce ascospores in nature.Ascospores can launch into the air and spread with the air.These will contribute to rapid spread of GLS.So the investigation of genetic characters of the pathogen is significant to understand the ocuurrence and spreading of Glomerella leaf spot.In this study,the isolates of C.fructicola producing ascospores were isolated from diseased leaves.Further we conducted researches on the genetics,cultural characters,pathogenicity of the C.fructicola.The main results are as follows:1)The mating tests between monoascospore isolates showed that the strains of C.fructicola were divided into two type: Fertile strain and Semi-fertile strain.The Fertile strains were self-fertile(homothallism),and it could produce perithecia,asci and ascospores.The Semi-fertile strains were partial homothallism.They could produce perithecia,a few asci,but no ascospores.We supposed that C.fructicola is atypical homothallism.2)The Fertile strains and Semi-fertile strains showed differences on characters of colony,size of conidia,the capability and speed of producing fruiting body,fertility of progeny and the pathogenicity.The colonies of Fertile strains on PDA were white,becoming grey and lividity in the center with rage.The aerial mycelia were thick and felty.It could produce 10-20 perithecia clumps after cultivated 15 days,with 70-100 perithecia in it.The sexual productions all showed the characters of Fertile strains.Inoculated the leaves of Gala,Fertile strains could cause 0.7cm spot,and the morbidity was 92%.The colonies of Semi-fertile strains on PDA are lividity and black,with sparse aerial mycelium tiling on the surface of medium.The strains could produce scattered perithecia embedding in PDA after about 13 days,20 per square millimeter.The perithecia are mature but without or a few mature asci and ascospores.Inoculated the leaves of Gala,Fertile strainscould cause 0.4cm spot,and the morbidity was 77%.3)The cross between Fertile and Semi-fertile strains could come up in very short time,usually about 7days.Nigrescent line appeared in the contact area after about 3 days of contact,and then extended to about 5mm.There were a lot perithecia clumps and scattered perithecia,and the number was about 50 per square millimeter.Sexual reproduction contained both Fertile and Semi-fertile strains,and the numbers of two types are nearly equal.4)The analysis of MAT genes illustrated that the mating types of Fertile and Semi-fertile have no differences.Both types contain MAT1-2(HMG),without MAT1-1gene(?).So we speculate that C.fructicola may have unique MAT1-1 gene.5)Different factors such as temperature,nutrition and pH influenced the develop of two type strains.Fertile trains were more sensitive to temperature,and the growth was inhibited when temperature was lower than 20? or higher than 30?.There were no significant differences in sensitive to nutrition and pH.6)Simple sequence repeat PCR were used to analysis genetic differences of Fertile and Semi-fertile strains.Primer 889 had a feature amplification witch is about 1000 bp.The results showed that two type strains have differences in genetic.Primer 889 is a molecular mark of Fertile and Semi-fertile strains.