导致南方梨早期落叶的果生炭疽菌致病力分化分析

【目的】明确我国南方梨产区造成早期落叶的果生炭疽菌(Colletotrichum fructicola)的致病力分化状况并建立其室内快速测定方法。【方法】以梨的枝条、叶片和果实为材料,采用不同方法造成伤口后接种果生炭疽菌的强致病力菌株PAFQ32,通过比较各处理的测定效果筛选其室内快速测定方法,并对供试菌株的致病力进行观测和致病类型划分,分析不同菌株致病力分化与其地理来源之间的相关性。【结果】采用梨枝条、叶片和果实对果生炭疽菌致病力的观测结果显示,梨叶片经针刺后接种菌丝块的测定效果明显优于其他处理。供试菌株致病力的测定结果表明,来源于我国南方梨产区的111个果生炭疽菌菌株其致病力可划分为强、中、弱3个类型,其中强致病力菌株17个(15.3%);中等致病力菌株89个(80.2%);弱致病力菌株5个(4.5%)。不同地理来源的果生炭疽菌菌株,其致病类型的分布比例有异。【结论】果生炭疽菌的菌丝块针刺接种梨叶片的方法,可用于其致病力的室内快速测定。来源于我国南方梨产区导致早期落叶的果生炭疽菌存在明显的致病力分化,以中等致病力菌株为优势群体。

Pathogenicity differentiation of Colletotrichum fructicola causing precocious defoliation in pear in southern China

【Objective】In recent years,precocious defoliation of pear,mainly caused by Colletotrichum fruticola in southern China has become serious and resulted in large losses of fruit production in these areas.The aim of this study is to determine the pathogenicity differentiation of C.fruticola and establish the laboratory methods determining virulence of this pathogen.【Methods】The strain PAFQ32 of C.fruticola,which has strong virulence,was isolated from diseased leaves of Pryus pyrifolia cv.Cuiguan in Fujian.Mycelial discs(5 mm in diameter)were taken from the colony margins of 5-d-old cultures on PDA medium,and fresh PDA discs were used as controls.Isolates were cultured on SNA(synthetic nutrient-poor agar)medium for 3 days at 28℃.Conidia were harvested and put into a 2.0 mL sterilized Eppendorf tube,and the conidial suspension was diluted with sterile water to a final concentration of 1×10^6 conidia per mL.The strong pathogenic strain PAFQ32 of C.fructicola was inoculated from the twigs(P.pyrifolia‘Cuiguan’),leaves(P.pyrifolia‘Cuiguan’),and fruit(P.bretschneideri‘Huangguan’)wounded with various methods.Inoculation of detached twigs was performed by using 1-yearold twigs(10.0 cm in length)with mycelial plugs on wounds and incubated at 25℃in plastic contain-ers covered with plastic film.The lesion lengths were recorded at 9 dpi.Inoculation of detached mature pear fruit was performed by placing mycelium plugs or dropping an aliquot of 6.0μL conidial suspension(106 conidia per mL)on wounds.Fresh PDA discs(5 mm in diameter)and sterile water were used as the controls,respectively.The lesion lengths were recorded at 7 dpi.Inoculation of detached leaves was performed by placing mycelium plugs or dropping a 6.0μL aliquot of conidial suspension on the left side of a leaf after wounding.The lesion lengths were recorded at 4 dpi.The results of each treatment were compared,and then chose a laboratory method to determine the pathogenicity of 111 strains of C.fruticola that were isolated from the leaves and fruits of P.pyrifolia and P.bretschneideri in 7 orchards in Anhui,Fujian,Guangxi,Hubei,Jiangsu,Jiangxi,and Zhejiang.The pathogenicity of strains from different sources were observed and divided into different pathogenic types,and the relationship between the pathogenicity differentiation of the strains and their sources were analyzed.【Results】Laboratory determination of virulence showed that,on inoculated twigs,the incidence rate was 100%by scald holing and holing,80%by girdling,40%by puncturing with 10 needles,and 20%by puncturing with 3 needles after three days of inoculation.The average diameters of lesions treated with scald holing were significantly bigger than the latter four wounding treatments,but it varied greatly.On inoculated fruit,the average diameters of lesions produced by inoculating with mycelium plugs were larger than by inoculating with conidial suspensions under the same wound treatment,and there was no significant difference among the average diameters of lesions produced by inoculating mycelial plugs with different wounding treatments.On inoculated leaves,the average diameters of lesions produced by puncturing with 3 needles were significantly larger than with 1 needle on the right and the back side of the leaves.Under the same wound treatment,the expansion of the lesions produced by inoculating with mycelial plugs was faster than that by inoculating with conidial suspensions.The results showed that the method of inoculating with mycelial plugs on punctured pear leaves had good material uniformity and significant effect,and took less time,and thus was better than the other inoculation treatments.The pathogenicity of 111 strains were determined by this treatment.The results showed that there were significant differences in pathogenicity among C.fructicola strains from different provinces in southern China.According to cluster analysis,the strains could be divided into three types including 17 strains with strong pathogenicity(15.3%),89 strains with middle pathogenicity(80.2%)and 5 strains with weak pathogenicity(4.5%).There was a significant difference in the proportions of the pathogenic types of the strains from different areas.This difference was related to climate differences.【Conclusion】It was suggested that rapid laboratory determining the virulence of C.fruticola could be carried out by inoculating with mycelial plugs on leaves wounded by puncturing.There was significant pathogenicity differentiation in C.fructicola causing leaf early defoliation in pear in southern China,and the strains with middle pathogenicity were the dominant group.