The Roles Of Extracellular Esterase Of Pathogen And Epicuticular Waxes Of Plant During The Specific Invasion Of Digitaria Sanguinalis By Crvularia Eragrostidis

Large crabgrass (Digitaria sanguinalis (L.) Scop), a malignant weed in drylandagricultural areas, is distributed throughout tropical and temperate regions of the worldand is ranked fourth on a list of serious weeds in these regions. It is the major weed inmaize, soybean, cotton and turf field in China. The strain QZ-2000 of Curvulariaeragrostidis, isolated from infected D. sanguinalis, has a great potential as amycoherbicide for biocontrol of D. sanguinalis. In this paper, the specific invasionmechanism of C. eragrostidis on D. sanguinalis was studied to attempted to make sure ofthe factors involved in the fungus- the plant selective relationship.The turf grass Festuca arundinacea that could not be infected by the fungus was usedas non-host plant control.The observation of the invasion process on the two plants by C. eragrostidis to showedthat the fungi could achieve invasion to the leaves of D. sanguinalis, and the brown andtransparent spots formatted subsequently around invasive site, however the leaves of F.arundinacea were impervious to the fungal appressoria.Aider inoculation of C. eragrostidis on leaves of plants, the activities of SOD, POD andPAL increased slowly in D. sanguinalis, while the activity of SOD and POD were stableand a sharp PAL increasing wasshowed in F. arundinacea. These results indicated that theconidia of C eragrostidis could not interrupt the leaves of F. arundinacea and couldinduce partially defensive response in it.Different extracelluar esterase isoenzyme profiles were found in saprophytic andparasitical phase of the fungi. For this fungus, the epicuticular waxes of host plant (D.sanguinalis) and a component, 16-hydroxyhexadecanoic acid, were more efficient toinduce the secretion of esterase from the fungi than waxes of the non-host plant (F.arundinacea) and palmitic acid.The effects of epicuticular waxes of D. sanguinalis and F. arundinacea on invasion of C. eragrostidis to its host and nonhost plants were studied. The results showed that thewaxes of host plant D. sanguinalis facilitated the growth of germ tube of C. eragrostidisconidia significantly, but did not influence the appressoria formation. The waxes ofnon-host plant F. arundinacea, however, inhibited the extension of germ tube and theappressoria differentiation significantly. The wax layer of D. sanguinalis was morefacilitate the adhesion of germinating conidia of C. eragrostidis to plant surface than thatof F. arundinacea.Crude extracellular esterase extracted from conidia of C. eragrostidis degraded thewaxes of D. sanguinalis completely, but hydrolyzed that of F. arundinacea only partially.GC-MS analysis showed that there were 24 components in the waxes of D. sanguinalisand 23 in that of F. arundinacea, but only a few presented in both waxes. D. sanguinaliswaxes particularly owned 9,12-Octadecadien-l-ol, (Z,Z)- that had 54.3ï¼…of total waxes,and F. arundinacea waxes particularly owned 9-Tricosene that had 49.8ï¼…of total waxes.Our results indicated that the epicuticular waxes of plants and the extracellular esterasecontributed to the selective invasion of C. eragrostidi to D. sanguinalis.