The soil-borne pathogen Rhizoctonia solani Kühn (teleomorph, Thanatephorus cucumeris [A.B. Frank] Donk) is worldwide responsible for serious damage of many economically important agricultural and horticultural cr...The soil-borne pathogen Rhizoctonia solani Kühn (teleomorph, Thanatephorus cucumeris [A.B. Frank] Donk) is worldwide responsible for serious damage of many economically important agricultural and horticultural crops. Control of Rhizoctonia diseases is difficult because this pathogen survives for many years as sclerotia in soil or as mycelium in organic matter under numerous environmental conditions. Furthermore, the pathogen has an extremely wide host range. To date, no effective control strategies against Rhizoctonia diseases are available in either organic farming or horticulture. In integrated pest management systems (IPM), mainly fungicides are used as control method. However, the European Union has decided that 60% of the chemical pesticides that were allowed in 1996 should be banned from 2003. Hence, new strategies to control one of the most important soil-borne pathogen R. solani are urgently needed. It is well-documented that an environmentally friendly alternative to protect plants against soil borne pathogens is biological control. Our work is concentrated on the development of a fungal biological control agent (BCA) especially selected against diseases caused by R. solani.. Based on a combination of in vitro and in vivo assays 339 fungal plant-associated strains was evaluated against R. solani. The following characteristics were tested in vitro: antagonistic activity at 20 ℃ and 12 ℃, the ability to produce cell wall-degrading enzymes (chitinase, β-1,3-glucanase, protease), and influence on sclerotia germination. The ability of spore production was also of importance under consideration of formulation of possible candidates. As results of the note characteristics six isolates were selected. Taxonomical characterization using molecular methods like BOX-PCR and sequencing of the 18S rDNA resulted in genetically diverse Trichoderma isolates. The disease suppression effect of the six fungal isolates were tested against bottom rot on lettuce and black scurf on potato in pot experiments in climate chamber. The conditions were favourable for the disease development by R. solani on both crops. All six isolates were able to suppress the disease severity on lettuce and potato. According to their biocontrol effect under field conditions the most efficient isolate will be commercialised as BCA product.展开更多
Three strains of Trichoderma spp. TV112, TX003, TY009 obtained from previous experiments could inhibit the sclerotial formation of two strains of Rhizoctonia salani AG1 (-1A) isolated from the rice paddies in Hanzhou ...Three strains of Trichoderma spp. TV112, TX003, TY009 obtained from previous experiments could inhibit the sclerotial formation of two strains of Rhizoctonia salani AG1 (-1A) isolated from the rice paddies in Hanzhou of China. However, it is unclear if there are the antagonism and mycoparasitism of the Trichoderma strains tested against the mycelial growth of R. solani . The objective of this research was to evaluate the ability of the Trichoderma strains to inhibit the mycelial growth of R. solani in vitro . Dual culture testes showed all the Trichoderma strains tested inhibited the mycelial growth of R. solani. The strains also produced toxic metabolites with activity against R. solani, inhibiting the mycelial growth by 74%, 81.8%, and 53%, repectively. Electron microscopic observations revealed that all the Trichoderma strains interacted with R. solani . The strains TV112 and TX003 grew toward and coiled tightly around the host cells, penetrating and destroying the hyphae. TX009 penetrated the cell wall of R. solani by antagonist directly without formation of appressorium-like structure. Penetration of the Trichoderma strains on host cells was apparently accomplished by mechanical activity. These results demonstrated that all the three strains were effective in inhibiting the mycelial growth of R. solani .展开更多
A field under rice-wheat rotation was selected near Chengdu, China, to study thepopulation of Rhizoctonia solani anastomosis group 1 (AG-1), pathogen causing ricesheath blight disease, in natural soil ecosystem. Inocu...A field under rice-wheat rotation was selected near Chengdu, China, to study thepopulation of Rhizoctonia solani anastomosis group 1 (AG-1), pathogen causing ricesheath blight disease, in natural soil ecosystem. Inocula of the fungus recovered fromthe field were divided into three types, i.e., sclerotia, free mycelium retained in thesoil passed through a 0.355mm sieve, and colonized plant debris which was subdividedinto small colonized debris retained between 2.00 and 0.355mm sieves and large colonizeddebris retained on 2.00mm sieve after wet screening. Quantitative estimation of thethree types of inocula in one year indicated that small colonized debris was the dominantinoculum type for most of the time. The population peaked in March and September at 1210and 480 colonized debris 100g-1 air-dry soil respectively, and fell down in December andAugust to 0 and 177 colonized debris 100g-1 air-dry soil respectively. Free mycelium wasonly detectable in March, September and October with 1209, 7.9 and 14.5g fresh wtmyceliumg-1 air-dry soil respectively, which corresponded to the two peaks and the secondhighest level of small debris density in the year. Viable sclerotia and large colonizeddebris were rare with populations ranging from 0 to 3 for sclerotia and 0 to 14 for largecolonized debris 100g-1 air-dry soil, but were the main structures to survive overwinter. It was expected that soil temperature was the main factor determining populationdynamics of R.solani AG-1 in natural soil. Optimum temperature for population increasingis predicted to be around 15℃, with a range from 10 to 25℃. Viability tests indicatedthat 60.9% sclerotia could survive after 265d being buried in natural sandy loam in fieldconditions in Beijing, while colonized rice straw debris (0.5-1.0cm long) could notyield the fungus on medium plates after 88d of being buried under the same conditions.展开更多
The pectin is a backbone of the plant cell wall, its network structure will systemicly resolve when the plant cell splits up and forms. The pectinase produced by Rhizoctonia mainly acts on the pectin of cell wall, and...The pectin is a backbone of the plant cell wall, its network structure will systemicly resolve when the plant cell splits up and forms. The pectinase produced by Rhizoctonia mainly acts on the pectin of cell wall, and causes the maceration of tissue and the death of protoplast. Polygalacturonase (PG) can decompose the galacturonic acid of disease tissue. The research defined the PG activities of extracellular metabolite of the different virulence Rhizoctonia isolates, and testifid the effect of Trichoderma viride to PG activities, and clarified the mechanisms of biocontrol by Trichoderma. The test methods as following: Firstly, to select the isolates of different virulence: WK-47, WK-141 and WK-160 strain of Rhizoctonia AG-D and YW-2 strain of Rhizoctonia AG1-IA and TCS-1 strain of Trichoderma viride. Secondly, to culture TCS-1 on PD, and draw a group of fermented liquid in every 24 hours, and draw 7 times. Thirdly, to culture quietly Rhizoctonia isolates with Czapek-Dox at 25℃ for 15 days, filter and centrifuge (2350 g×30 min), fetch the clear liquid, put it into the ammonium sulfate according to 60% saturation degree, put it quietly for 30 min at 4℃, centrifuge (21000 g×30 min) at 4℃, remove the clear liquid, dissolve the deposit with sodium acetate buffer (25 mmol/L, pH5.5), dialysis for 48 h in the same buffer,and change the buffer every 12 h, Fourthly, to put TCS-1 fermented broth of different times in the tubes, one mL per a tube, add 0.5 mL PG to every tube, react for 4 h in 30 ℃ water, the same time fetch the test tube filled with the same treated liquid that was not dealed in 30℃ water.Finally,to testify PG activities with DNS’s test. In all, PG of Rhizoctonia had high activities and virulence. The conrtrol efficacy of T.viride to PG activities of WK-47, WK-141, WK-160 and YW-2 were 95%,94%,95%,92% separately, fermented time had a great influence to control efficacy, the third fermented broth did the best. Through effect to PG activities T. viride can reduce the virulence of Rhizoctonia, and protect the hosts. The specific mechanism, qualitative and quantitative research of antagonistic substance in the fermented broth will be further carried out.展开更多
文摘The soil-borne pathogen Rhizoctonia solani Kühn (teleomorph, Thanatephorus cucumeris [A.B. Frank] Donk) is worldwide responsible for serious damage of many economically important agricultural and horticultural crops. Control of Rhizoctonia diseases is difficult because this pathogen survives for many years as sclerotia in soil or as mycelium in organic matter under numerous environmental conditions. Furthermore, the pathogen has an extremely wide host range. To date, no effective control strategies against Rhizoctonia diseases are available in either organic farming or horticulture. In integrated pest management systems (IPM), mainly fungicides are used as control method. However, the European Union has decided that 60% of the chemical pesticides that were allowed in 1996 should be banned from 2003. Hence, new strategies to control one of the most important soil-borne pathogen R. solani are urgently needed. It is well-documented that an environmentally friendly alternative to protect plants against soil borne pathogens is biological control. Our work is concentrated on the development of a fungal biological control agent (BCA) especially selected against diseases caused by R. solani.. Based on a combination of in vitro and in vivo assays 339 fungal plant-associated strains was evaluated against R. solani. The following characteristics were tested in vitro: antagonistic activity at 20 ℃ and 12 ℃, the ability to produce cell wall-degrading enzymes (chitinase, β-1,3-glucanase, protease), and influence on sclerotia germination. The ability of spore production was also of importance under consideration of formulation of possible candidates. As results of the note characteristics six isolates were selected. Taxonomical characterization using molecular methods like BOX-PCR and sequencing of the 18S rDNA resulted in genetically diverse Trichoderma isolates. The disease suppression effect of the six fungal isolates were tested against bottom rot on lettuce and black scurf on potato in pot experiments in climate chamber. The conditions were favourable for the disease development by R. solani on both crops. All six isolates were able to suppress the disease severity on lettuce and potato. According to their biocontrol effect under field conditions the most efficient isolate will be commercialised as BCA product.
文摘Three strains of Trichoderma spp. TV112, TX003, TY009 obtained from previous experiments could inhibit the sclerotial formation of two strains of Rhizoctonia salani AG1 (-1A) isolated from the rice paddies in Hanzhou of China. However, it is unclear if there are the antagonism and mycoparasitism of the Trichoderma strains tested against the mycelial growth of R. solani . The objective of this research was to evaluate the ability of the Trichoderma strains to inhibit the mycelial growth of R. solani in vitro . Dual culture testes showed all the Trichoderma strains tested inhibited the mycelial growth of R. solani. The strains also produced toxic metabolites with activity against R. solani, inhibiting the mycelial growth by 74%, 81.8%, and 53%, repectively. Electron microscopic observations revealed that all the Trichoderma strains interacted with R. solani . The strains TV112 and TX003 grew toward and coiled tightly around the host cells, penetrating and destroying the hyphae. TX009 penetrated the cell wall of R. solani by antagonist directly without formation of appressorium-like structure. Penetration of the Trichoderma strains on host cells was apparently accomplished by mechanical activity. These results demonstrated that all the three strains were effective in inhibiting the mycelial growth of R. solani .
文摘A field under rice-wheat rotation was selected near Chengdu, China, to study thepopulation of Rhizoctonia solani anastomosis group 1 (AG-1), pathogen causing ricesheath blight disease, in natural soil ecosystem. Inocula of the fungus recovered fromthe field were divided into three types, i.e., sclerotia, free mycelium retained in thesoil passed through a 0.355mm sieve, and colonized plant debris which was subdividedinto small colonized debris retained between 2.00 and 0.355mm sieves and large colonizeddebris retained on 2.00mm sieve after wet screening. Quantitative estimation of thethree types of inocula in one year indicated that small colonized debris was the dominantinoculum type for most of the time. The population peaked in March and September at 1210and 480 colonized debris 100g-1 air-dry soil respectively, and fell down in December andAugust to 0 and 177 colonized debris 100g-1 air-dry soil respectively. Free mycelium wasonly detectable in March, September and October with 1209, 7.9 and 14.5g fresh wtmyceliumg-1 air-dry soil respectively, which corresponded to the two peaks and the secondhighest level of small debris density in the year. Viable sclerotia and large colonizeddebris were rare with populations ranging from 0 to 3 for sclerotia and 0 to 14 for largecolonized debris 100g-1 air-dry soil, but were the main structures to survive overwinter. It was expected that soil temperature was the main factor determining populationdynamics of R.solani AG-1 in natural soil. Optimum temperature for population increasingis predicted to be around 15℃, with a range from 10 to 25℃. Viability tests indicatedthat 60.9% sclerotia could survive after 265d being buried in natural sandy loam in fieldconditions in Beijing, while colonized rice straw debris (0.5-1.0cm long) could notyield the fungus on medium plates after 88d of being buried under the same conditions.
文摘The pectin is a backbone of the plant cell wall, its network structure will systemicly resolve when the plant cell splits up and forms. The pectinase produced by Rhizoctonia mainly acts on the pectin of cell wall, and causes the maceration of tissue and the death of protoplast. Polygalacturonase (PG) can decompose the galacturonic acid of disease tissue. The research defined the PG activities of extracellular metabolite of the different virulence Rhizoctonia isolates, and testifid the effect of Trichoderma viride to PG activities, and clarified the mechanisms of biocontrol by Trichoderma. The test methods as following: Firstly, to select the isolates of different virulence: WK-47, WK-141 and WK-160 strain of Rhizoctonia AG-D and YW-2 strain of Rhizoctonia AG1-IA and TCS-1 strain of Trichoderma viride. Secondly, to culture TCS-1 on PD, and draw a group of fermented liquid in every 24 hours, and draw 7 times. Thirdly, to culture quietly Rhizoctonia isolates with Czapek-Dox at 25℃ for 15 days, filter and centrifuge (2350 g×30 min), fetch the clear liquid, put it into the ammonium sulfate according to 60% saturation degree, put it quietly for 30 min at 4℃, centrifuge (21000 g×30 min) at 4℃, remove the clear liquid, dissolve the deposit with sodium acetate buffer (25 mmol/L, pH5.5), dialysis for 48 h in the same buffer,and change the buffer every 12 h, Fourthly, to put TCS-1 fermented broth of different times in the tubes, one mL per a tube, add 0.5 mL PG to every tube, react for 4 h in 30 ℃ water, the same time fetch the test tube filled with the same treated liquid that was not dealed in 30℃ water.Finally,to testify PG activities with DNS’s test. In all, PG of Rhizoctonia had high activities and virulence. The conrtrol efficacy of T.viride to PG activities of WK-47, WK-141, WK-160 and YW-2 were 95%,94%,95%,92% separately, fermented time had a great influence to control efficacy, the third fermented broth did the best. Through effect to PG activities T. viride can reduce the virulence of Rhizoctonia, and protect the hosts. The specific mechanism, qualitative and quantitative research of antagonistic substance in the fermented broth will be further carried out.
