Study On Plant Endophytic Bacteria Inducing Resistance Of Pepper To Meloidogyne Incognita And Phytophthora Capsici

Endophytic bacteria can establish a harmonious symbiosis with host plants.They exist in plants,being protected by plants,have stable living environments.At the same time,they also can protect plants by killing or inhibiting pathogens or reduce the influence of adversities on plants through the effects of induced systemic resistance(ISR).Literatures showed that endophytic bacteria which can produce ACC deaminase can promote plant growth,improve plants' resistance to biotic and abiotic stresses significantly.Root knot nematode(M.incognita)and Phytophthora capsici are two threats to Capsicum annuum.There is no good bio-control measures for them at present.The effects of two endophytic bacteria DLJ1,pseudomanas fluorescens isolated from pepper fruits and SZ5,Bacillus cereus isolated from fruits of ripe persimmon,on pepper germination,seeding growth and on resistance to M.incognita and P.capsici were studied in this pepper.1.Effects of treatments of DLJ1 and SZ5 on seed germination and seedling growth of pepper.Treatment with bacteria suspensions during germination could not promote seed germination,but could promote seedling growth in a short time.Contents of secondary metabolite as flavonoids and polyphenols,and activities of antioxidant enzymes represented by CAT in seedlings were still higher than the control significantly after the plant-growth promoting effect disappeared.The effect of DLJ1 was higher than those of SZ5.This suggested that although the plant-growth promoting effect disappeared,other effects still existed.2.Preliminary analysis of pepper plants for resistance to M.incognita by DLJ1 and SZ5.The biocontrol effect of DLJ1 and SZ5 on plants to M.incognita was analyzed through inoculations at germination stage and transplanting stage.Results showed that the two bacteria increased the response sensitivity of plant immune system to adversity.The increase ranges of POD,CAT,PAL activity,total flavonoids and total phenol content in plants from the treatment groups were higher than those of the control.Inoculation of DLJ1 and SZ5 decreased the disease degree,improved the yield.Effect of inoculation at germination stage was higher than those of inoculation at transplanting stage,there is no obvious difference between inoculation once and many times,and effect of DLJ1 was better than those of SZ5.All the above results showed that inoculation once at germination stage could promote the resistance of pepper plants to root knot nematodes for a long-term.3.Analysis of pepper plants for resistance to M.incognita by DLJ1 and SZ5 once again.Based on the previous results,the biocontrol effect of DLJ1 and SZ5 on plants to M.incognita was analyzed again with seeds being inoculated with DLJ1 and SZ5 at the germination stage and root knot nematode being inoculated after transplanting into the field,and avermectin being used a control.The results confirmed again that,inoculation once at germination stage with DLJ1 and SZ5 can reduce the infection rate of root knot nematode,improve the pepper yield without reducing the pepper quality;effects of DLJ1I was better than those of SZ5 and avermectin,and effects of SZ5 was lower than those of avermectin.Inoculation of DLJ1 and SZ5 not only can increase contents of total flavonoids and polyphenols,but also can improve the activities of Pathogenesis-related protein(PR)?-1,3-glucanase and chitinase,and the increase magnitude of DLJ1 treatment was greater.So,the resistance of pepper plants to M.incognita was improved by DLJ1 and SZ5 through ISR effect which included improving antioxidant capacity,secondary metabolite content and PR activity etc.4.Effects of DLJ1 and SZ5 treatment on pepper seedlings resistance to Phytophthora capsiciThe biocontrol effect of DLJ1 and SZ5 on plants to P.capsici was analyzed through inoculation of DLJ1 and SZ5 at germination stage and defiantly inoculation with P.capsici at 5-6 leaf stage.Results showed that DLJ1 treatment significantly increased plants' resistance to P.capsici,while SZ5 treatment was just the opposite.Further analysis showed that DLJ1 cannot kill P.capsici,or inhibit its growth through secreting siderophores.SZ5 also could improve antioxidant capacity,secondary metabolite content and PR activity etc.,but promote plant disease at the same time.These results suggest that the mechanism above is not the key mechanism of pepper plants against P.capsici.To sum up,inoculation of DLJ1 and SZ5 at germination stage could inhibit the germination of pepper seeds,promote the growth of pepper seedlings,and enhance the immune activity of pepper plants,and the effect of DLJ1 is better than that of SZ5.Inoculation once at germination stage could significantly improve the resistance of plants to M.incognita,could improve pepper yield without reducing its quality.Inoculation with DLJ1 at germination stage can improve plants' resistance to P.capsici,while SZ5 can't.The mechanism of DLJ1 improved plants' resistance to P.capsici need to be explored.