| Dingxi,Gansu Province,is the breeding base of potato seed and one of the four major potato producing areas in China.Long term continuous cropping led to the aggravation of soil borne Fusarium Wilt in this area.Therefore,it is urgent to clarify the pathogenesis of potato Fusarium wilt under continuous cropping,and then seek the control measures of potato Fusariumwilt.In this paper,the pathogenicity of Fusarium oxysporum,the dominant pathogen of potato soil borne Fusarium wilt,was systematically studied by long-term experiment in Dingxi,Gansu Province,and the control measures of potato soil borne Fusarium wilt were preliminarily studied.The main results are as follows:1.Isolation and identification of dominant pathogen of potato Fusarium wilt under continuous croppingCompared with rotation,potato blight did not show significant difference under short-term continuous cropping(1?2 years).However,after potato continuous cropping for more than 3 years,the incidence rate of Fusarium wilt increased significantly with the extension of continuous cropping years,and the incidence rate of Fusarium Wilt in the serious plots reached over 80%.The standard samples were isolated and purified by tissue isolation method,and the isolates were identified by morphological identification and molecular identification(r DNA and EF sequence).The pathogenicity of the pathogen was determined according to Koch's law.The results showed that F.oxysporum and F.solani were the dominant pathogens causing potato wilt in dryland of Gansu Province.2.Effects of different continuous cropping years on fungal community structure in potato rhizosphere soilBased on Illumina PE250 platform,the fungal diversity of potato rhizosphere soil samples with different continuous cropping years was sequenced.The results showed that there were five phyla in the rhizosphere soil fungal community of different continuous cropping years,among which Ascomycota was the main phyla(accounting for 86.17%of the total abundance).The relative abundance of F.oxysporum and F.solani increased with the extension of potato continuous cropping years.This indicated that the accumulation of F.oxysporum and F.solani in continuous cropping soil increased their abundance,which may be one of the main reasons for the aggravation of soil borne Fusarium wilt disease in continuous cropping potato.3.Effects of Fusarium oxysporum infection on Photosynthetic Physiology and agronomic traits of potato plantsThe results of culture experiment showed that the top of potato plants began to wilt15 days after inoculation with Fusarium oxysporum,and root tissue browning 30 days after inoculation,showing typical symptoms of Fusarium wilt.Photosynthetic pigment,photosynthetic and fluorescence parameters were measured at flowering stage of potato.Photosynthetic pigment,photosynthetic and fluorescence parameters were measured at flowering stage of potato.The results showed that the infection of Fusarium oxysporum significantly reduced the chlorophyll content of potato leaves.At the same time,The decrease of photosynthetic pigment content led to the decrease of light harvesting ability of PSII reaction center,especially the decrease of chlorophyll a led to the decrease of photochemical conversion efficiency.Therefore,the net photosynthetic rate of potato decreased and the economic yield of diseased plants significantly decreased.After the infection of Fusarium oxysporum,the economic yield of potatosignificantly reduced by54.63%-64.57%.4.Isolation and identification of autotoxic substances from root exudates of continuous cropping potatoThe comprehensive allelopathic indexes of root exudates of RT(rotation potato),CP5(continuous cropping for 5 years)and CP10(continuous cropping for 10 years)of potato seedlings were 13.20%,32.12%and 48.33%,respectively.With the increase of continuous cropping years,the inhibition degree of root exudates on seedling root growth gradually increased.GC-TOF-MS was used to isolate and identify root exudates collected from hydroponic and long-term field experiments.The results showed that 30 kinds of organic acids were detected in 48 kinds of substances secreted by potato roots.Comparing the relative contents of organic acids in root exudates of potato in RT,CP5 and CP10,it was found that malic acid and palmitic acid varied significantly.The allelopathic effects of malic acid and palmitic acid on potato plants were studied by exogenous addition method.The results showed that malic acid and palmitic acid had autotoxic effect on potato growth,and the autotoxic effect increased with an increase in the concentration.5.Effects of autotoxic substances on growth and pathogenicity of Fusarium oxysporumThe root exudates collected from potato continuous cropping could significantly enhance the development of F.oxysporum and aggravate the occurrence of potato Fusarium wilt.Compared with CK,RT,CP5 and CP10 significantly promoted the mycelial growth and spore germination of Fusarium oxysporum.With the extension of continuous cropping years,the mycelial growth and spore germination rate of F.oxysporum significantly increased.The allelopathic effects of malic acid and palmitic acid on F.oxysporum were studied by exogenous addition method.The results showed that malic acid had a strong promoting effect at high concentration.Palmitic acid had a promoting effect on the growth of F.oxysporum at low concentration,but had a significant inhibitory effect at high concentration.Pot experiment showed that malic acid and palmitic acid at the concentration of 0.05-0.50 mmol·L-1 significantly increased the incidence level and disease index of Fusariumwilt.The incidence level and disease index increase with an increase in the concentration of the acids.These results indicated that malic acid and palmitic acid were allelochemicals secreted by potato roots,and their effect on Fusariumoxysporum was the main cause of potato Fusarium wilt.6.Study on control measures of soil borne Fusarium Wilt of potatoAn experiment was conducted on a potato field continuously cropped for 4 years,to assess the effect of different soil amendment measures on soil water relationships,microbial community structure and incidence of blight disease and tuber yield.The experiment was laid out in a randomized complete block design with three replicates.Five soil amendment treatments were tested:oxalazine,pentachloronitro benzene,Trichoderma harzianum,microbial soil amendment and conventional practice(control).It was found that the use of the oxalazine and T.harzianum in a continuously cropped potato field stimulated soil microbial biomass,bacteria:fungi ratio,tuber yield as well as reduced the incidence of Fusarium wilt and Rhizoctonia solani diseases of potatoes in dry land cultivation.In conclusion,malic acid and palmitic acid in the root exudates of continuous cropping potato can significantly promote the growth,reproduction and pathogenicity of the dominant pathogen Fusarium oxysporum.This chemotaxis makes Fusarium oxysporum and other pathogenic fungi become the dominant population in the soil and infect potato roots.This may be the main cause of potato wilt. |
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