Control Of Chill Pepper Phytophthora Disease By Biofumigation With Rapeseed Meal As Soil Amendments

Soil-borne diseases of chilli peppers, caused by single or complexed infection by pathogens, such as Pytophthora capsici, Pythium aphanidermatum, Fusarium oxysporum, Rhizoctonia solani. The diseases have great influence on cultivation of chilli peppers, caused serious economic losses. Phyophthora root rot occurred in China universally ever year.It has been difficult to control it since disease cycle short and spread fast. Methyl bromide is most commonly used fumigant in soil treatment to control soil-borne disease for a long time. But it will be forbidden to be used after2015, the alternatives to methyl bromide in soil disinfestation have received much attention in all over the world.In this research, we used rapeseed meal (RSM) as soil amendments to control chilli pepper disease caused by Phytophthora capsici, and compared with synthetic isothiocyanates (ITCs) for inhibitory activity to plant pathogens in vitro and in vivo trials. We carried out some research works as inhibitory activities in vitro, simulative biofumigation, pot experiments and field trails. At last, PCR-DGGE technique was adopted to study the effects of soil treatment on the population structure and diversity of soil fungi.Inhibitory activity of synthetic isothiocyanates(ITCs) dazomet, mustard oil and phenyl isothiocyanate to mycelial growth and spores germination of pathogens was tested in vitro. The results showed that the fungicidal and fungistatic effect varied based on the volatile and involatile of isothiocyanates. The volatile toxicity ranked as mustard oil> dazomet> phenyl isothiocyanate, while the involatile toxicity of phenyl isothiocyanate was stronger than mustard oil. Aromatic ITCs were less volatile toxic than aliphatic ITCs, but were more toxic than the aliphatic ITCs when they were dissolved in the agar. The inhibitory activity of isothiocyanates against spore germination was much stronger than that against mycelial growth. The pathogens differed in sensitivity to the isothiocyanates.Inhibition of mycelium growth and spore germination of pathogens by hydrolytic compounds release by different rapeseed meal varieties was tested. The results showed that antifungal activities of RSM2was stronger than that of RSM1. It can be presumed that spores is more susceptible to volatile hydrolytic compounds than mycelium, but to water soluble hydrolytic compounds, mycelium is more susceptible than spores.In simulative biofumigation test, using0.4%(w/w) of RSM2as soil amendments can inhibit the growth of fungi mycelium as dazomet. The fungistatic function of rapeseed meal was best at35℃and at soil water contents of70%. Rapeseed meal were fungicidal when extension of biofumigation time.Studies on the control effect of the different cultivars and amount of rapeseed meal on chilli pepper caused by Phytophthora capsici. The pot trial results showed that used0.2%(w/w) of RSM2as soil amendments was the best method of biofumigation. Optimized the condition of biofumigation, the results showed that incorporate rapeseed meal into soil, keep soil water contents of70%, at35℃above for20days, control efficacy get to90%The field trial showed that RSM amendment elevated populations of fungi and actinomycosis, but suppressed bacteria numbers. Efficacy of RSM controlling pepper phytophthora blight was excellent and yield of chilli peppers was increased.Couting culture method and PCR-DGGE technique were adopted to study the effects of soil treatment on the population structure and diversity of soil microbes. The result of plate count showed that P. capsici, fungi, bacteria were suppressed by chemical fumigation.RSM-amended soils did not appear to have a significant role in the suppression of P. capsici, it elevated populations of fungi. DGGE analysis showed that the fungal community was temporarily altered by biofumigation treatment and more persistently by the dazomet treatment. The fungal diversities were higher after RSM-amended soils, while, dazomet application had a deleterious effect on the structure of the microbial community. Our findings indicate that RSM-amended soils induces changes on the structure of the soil microbial community that are mostly related to microbial substrate availability changes derived from the soil amendment with fresh organic materials. It needs further studies on mechanism of control diseases.RSM have ability in inhibiting plant pathogens in vitro, and the pot trial showed that RSM efficient in controlling pepper phytophthora blight. In the field, Efficacy of RSM controlling pepper phytophthora blight was excellent and yield of chilli peppers was increased. RSM not only can control diseases but have the efficacy of organic fertilizer. It has a promising application prospect in the agriculture industry.