Biological Characteristics And Infection Process Of Colletotrichum Sublineolum And Its Chemical Control

With the increasing acreage of sorghum,sorghum anthracnose has become the main disease of the sorghum production in Heilongjiang province,which seriously affects the yield and quality of sorghum in recent years.At present,spraying chemicals is still the most effective way to control sorghum anthracnose,because most sorghum varieties planted in large areas are susceptible cultivars.To clarify the biological characteristics and infection process of Colletotrichum sublineolum,and to screen out single and combined fungicides with higher efficacy against C.sublineolum through laboratory biological determination and field control experiments.It would be lay a foundation for further study on disease prevalence,interaction mechanism between pathogen and host,and effective control of sorghum anthracnose.The research results are as follows:1.The growth rate method was used to study the mycelial growth conditions of C.sublineolum.The results showed that the suitable medium for pathogen growth was the agar medium of sorghum leaf decoction.The suitable temperature range for the growth of the pathogen was 20℃～35℃,the optimum temperature was 28℃,and the lethal temperature was54℃ for 10 min.The suitable p H range was 8～10,and the optimum p H was 9.The suitable carbon source was maltose.The suitable nitrogen source were peptone and yeast powder.All dark conditions was beneficial to mycelial growth.2.According to the types of the culture medium,culture conditions and so on research of conidia production conditions of C.sublineolum.The results showed that the spore production of the strain was low in the selected 10 kinds of natural media.The sporulation rate was 1.20×10⁷conidium/m L in oatmeal liquid medium（p H 8）,which was kept under shaken（130 r/min）for 10days at 25℃ in full darkness.Decreasing the carbon source promoted sporulation of the strain in the potato broth liquid medium.The optimum sporulation was 1.36×10⁶conidium/m L at a glucose concentration of 0.2%.The best sporulation was 1.36×10⁸conidium/m L when the strain was incubated in agar oatmeal culture medium for 5 days at 30℃ in total darkness,scraped off the mycelium and incubated for 5 days at 30℃ under continuous fluorescent lighting.3.The germination conditions of conidia were studied by agar surface germination method and slide droplet germination method.The results showed that the conidia germinated at single or multiple sites.The optimal germination temperature of conidia was 25℃～30℃ and the optimum temperature was 30℃,and the lethal temperature was 43℃ for 10 min.The optimum p H was 10;In the condition of continuous light,the germination rate was the highest.Ultraviolet light had an inhibitory effect on conidia germination.Low concentrations of glucose solution or peptone solution could promote conidia germination in water droplets.4.The infection process of susceptible cultivars of Sorghum by C.sublineolum was conducted by light microscopy.Conidia began germinating at 4～6 h post inoculation（hpi）.At6～12 hpi appressoria formed directly or at the ends of germ-tubes.Appressoria direct penetration of host tissue had begun from the intercellular space or stomatas.Infection pegs formed at 20 h after hpi.Infection vesicles and hyphae formed in epidermal cells by 24 hpi.At36～120 hpi hyphae grew extensively inter-and intracellularly.After 72 hpi light red lesions appeared on the leaves.Acervuli with one or two melanized setae and falcate conidia were visible on lesions by 96～168 hpi.Typical anthracnose disease spots could be found on the leaves 192 hpi.5.The susceptibility of C.sublineolum to 23 different fungicides and 6 kinds of combined fungicides were determined by the mycelial growth rate method and the conidia germination inhibition method,respectively.The results showed that pyraclostrobin 250 g/L EC had the strongest virulence against C.sublineolum,with an EC₅₀of 0.0029 mg/L for mycelium and an EC₅₀of 0.0039 mg/L for conidial germination.The combined virulence results showed that pyraclostrobin 250 g/L EC and carbendazim 50%WP with the ratio of 7:3 and 1:9,pyraclostrobin 250 g/L EC and mancozeb 80%WP with the ratio of 2:8,prochloraz 45%ME and carbendazim 50%WP with the ratio of 8:2,7:3,6:4,5:5 and 1:9 were showed synergistic effect on mycelium and conidia.6.The control efficiency of seven fungicides in the field was determined by the conventional spray method.The results showed that pyraclostrobin 250 g/L EC,the mixture of pyraclostrobin 250 g/L EC and carbendazim 50%WP（1:9）had higher control effects on sorghum leaf anthracnose,and the control effects for 10 days after the third application were 91.00%and81.37%,respectively.The treatment of pyraclostrobin 250 g/L EC,the mixture of pyraclostrobin250 g/L EC and carbendazim 50%WP（1:9）could improve the quality of the broom and increase the grain yield of 4.80%and 11.75%,respectively.