Interaction Of Curvularia Eragrostidis Strain QZ-2000and Target Large Crabgrass And Its Influencing Factors

Curvularia eragrostidis J. A. Meyer, a species of fungi, belongs to family Dematiaceae, Moniliales, Deuteromycetes. Its strain QZ-2000as a key component of Disancu, a newly-developed bioherbicide, has a virulent pathogenicity to Large crabgrass (Digitaria sanguinalis (L.) Scop.).Large crabgrass, one of the worst weeds in dryland agricultural areas, is distributed throughout tropical and temperate regions of the world and is ranked fourth on a list of serious weeds in these regions. The manual, mechanical and chemical control techniques have been developed for this weed, but the successful results was not made yet. The previous studies have involved in biological characteristics, mass-production techniques, formulation, host range and effectiveness bioassay in greenhouse and fields for the strain QZ-2000. The interaction between the strain and host has not been fully studied, which may link to improve the stability and efficacy of this bioherbicide product. Therefore, the interaction of the strain QZ-2000and the target Large crabgrass is studied to provide theoretical basis for a development of Disancu product. Those studies include influencing factors in conidial viability through improvement of the mass-production of conidia of C. eragrostidis strain QZ-2000and storage, and synergy of low-rate herbicide and responses of the host to the inoculum infection.The physiological indexes such as chlorophyll content, soluble protein and MDA and enzymes in large crabgrass were tested after treatment of conidial suspension of C. eragrostidis, low dosage chemical herbicide alone and their mixture. The treatment of C. eragrostidis strain QZ-2000mixtured with low dosage chemical herbicide caused the maximum reduction of chlorophyll content and soluble protein and maximum increase of MDA content. The esterase isozymes demonstrated various activities in treated large crabgrass plants by polyacrylamide gel electrophoresis. The results indicate that C. eragrostidis strain QZ-2000working with low dosage chemical herbicide enhanced inhibition of large crabgrass seedling growth. The fluorescence kinetics parameters demonstrated that treatment of conidial suspension of C. eragrostidis alone or combination with low-rate herbicides caused Large crabgrass to reduce the PHI(PO) of PS Ⅱ and its activity and impede electron transfer and finally to decrease photosynthesis rate.Gene expression profiles of large crabgrass infected by C. eragrostidis strain QZ-2000at the treatment regime at two concentrations of conidia and two dew durations were analyzed by cDNA amplified fragment length polymorphisms (cDNA-AFLP). Inoculum strength was more determinant of gene expression than dew duration. A total of256primer combinations were used for selective amplification and1214transcript-derived fragments (TDFs) were selected for their differential expression. Of these,518up-regulated differentially expressed TDFs were identified. Forty-six differential cDNA fragments were chosen to cloned and35of them were successfully cloned and sequenced, of which25were homologous to genes of known function according to the GenBank database. Only6genes were up-regulated in C. eragrostidis-inoculated large crabgrass, with functions involved in signal transduction, energy metabolism, cell growth and development, stress responses, abscisic acid biosynthesis and response. It appears that a few pathways may be important parts of the pathogenic strategy of C. eragrostidis strain QZ-2000on large crabgrass. Our study provides the fundamentals to further study the pathogenic mechanism, screen for optimal C. eragrostidis strains as potential mycoherbicide and apply this product to control Digitaria sanguinalis.Fungal spore has the advantages of highly virulence and easy to storage. Ingredient of solid substrate had a great effect on the spore quantity of Curvularia eragrostidis strain QZ-2000. Coarse cereals were evaluated as better solid substrates for sporulation of C. eragrostidis compared to sideline products. Sporulation, length of gemma of conidia was increased obviously and germination rate unobviously with improved culture mode. The millet seed as substrate improved the sporulation. Germination rate, length of gemma and pathogenicity of conidia was gradually decreased with the serial passage generation increased in20generation, but the difference was insignificant. The relationship between the DNA and RNA content of C. eragrostidis conidium and its storage duration was studied. During1-8years’ storage, the DNA and RNA content of C. eragrostidis conidium decreased with storage duration extension. The bigger reduction happened in the RNA content than in the DNA content. In20generations of successive transfers of culture, there was a reducing trend in germination rate, tube length and pathogenicity of conidia with a serial passage generation extension despite insignificant difference.Conidia of C. eragrostidis strain QZ-2000stained with aniline blue were observed under a light microscope. The results demonstrated that a conidium was composed of four cells. The bigger two cells with full of protoplasm located in the middle. One cell each pole had a germ pore at end respectively. The protoplast within the bigger cells connected to that with the smaller cells through a thin channel. Germination tube grew out of one or both of the small cells.