Quantitative Studies On Infection Simulation Of Phytophthora Capsici

We simulated the influence of soil temperature (ST) and soil water content(SW) oninfection of P caPsici in controlled climatic chamber, analyzed epidemic dynamics ofphytophthora blight of pepPer by systematic observation in fields, and bioassayed toxicity ofmetalaxyl, thiram and their mixtUres to P caPsici. The resultS were summarized as fOllows1 Disease index of phytophthora blight of pepper correlated with inoculum sporangiadensity ItS ID-DI curve was described with parobola model: DIso.l090ro.03787 xlD+0.0002794 x ID2.2 Soil tempefatLlfe and soil water content were key factors to influence infection of PcaPsici. For each SW disease index increased up to optimum ST(22C~28C) and thendeclined .On the other hand, fOr each ST,disease index increased up to optimum SW(40%)(soil water-matric pOtential was 0,and soil was near to satUration )and then declined.Quantitative analysis showed that the relationship betWeen incidence(I) and ST, SW wasdescribed with the model: SQRT (I ) =-l.4304-0.03107 X SW+0.l467 X ST-0.0031l2 XT2-0.0003614 x SW'-0.00000005l x T2 x SW'.3 Analyzed MP(soil water-matric potential,Wm) and SW we fOund that the relationshipbetWeen them was described with negative exPOnential model f MP=459.5l6 X exp(-0. l 16 Xsw).The relationship between I and ST, MP was described with the model: SQRT (I)=-0.6908-0.0l544 x MP+0. I 433 x ST-0.003090 x ST2ro.0002083 x MP2.4 Observed epidemic dynamics of phytophthora blight of pepper in fields, resultS showedthat GompertZ model was the best one fOr describing disease progress trend: DI=exp (-5.088X exp(-0.024 X D) ).Used primary incidence(Io), SW ST and T to forecast disease index of pepper blight infields, the forecasting model as follows: Gompit (I ) =-0.04554+0.9526 X Gompit(Io)+0'05484x T+0.00003789 x SW2 x ST-0.00009250 X SW x STSW was key factor on disease. SW was higher in plOt where itrigation was more frequent,which resulted in more serious final incidence. In fieIds, the direction of disease spread wasthe same with the inigation water fiowed, disease distribution was ellipse in shaPe.5 Quantitative bioassay toxicity of metalaxyI, thiram and their mixtUres to P caPsici.Results showed that the mixture of them in 70:30 ratio had the best synergistic interaction, synergistic ratio (SR) was 3.18. The inoculation test also illustrated the mixtures effectively controlled the pepper blight by P. capsici.