Identification Of Root-knot Nematodes Of Melon And Vegetable In Hainan Province And Determination Of Resistance To Three Nematicides

Root-knot nematode（RKN）,Meloidogyne spp.,are important plant pathogenic nematodes.It causes serious economic losses to agricultural production every year.Using nematicide is one of the main methods to control RKN,but the abuse of nematicide will aggravate the resistance of RKN.At present,there is a lack of systematic research on the resistance analysis of RKN in Hainan province.The investigation and identification of RKN in different cities and counties were carried out.And the resistance of different RKN populations to abamectin 3%ME,fluopyram41.70%SC and fosthiazate 20%EW were analyzed.At the same time,in order to determine the effects of these three nematicides on Meloidogyne enterolobii（Me）,the embryonic development and egg hatching of Me were treated by dipping method with different concentrations of these nematicides.The results have important reference value for the control of RKN in Hainan province.A systemic investigation of RKN（Meloidogyne spp.）occurring in the 11 cities and counties of Haikou,Lingshui,Sanya,Ledong,Chengmai,Wuzhishan,Danzhou,Dongfang,Wenchang,Tunchang,and Ding’an was conducted from November 2018 to February 2021.The results showed that,RKN occurred in 45 planting areas out of 97sites,with a positive rate of 46.39%.A total of 24 RKN samples were collected and identified as M.incognita and M.enterolobii by morphology and molecular biology.The proportion of Me was 29.17%.The toxicity of three nematicides to the second instar larvae（J₂）of RKN populations in different cities and counties was compared.Different RKN populations showed different levels of resistance to the three nematicides.The RKN populations in Haikou,Wenchang,Danzhou,and Lingshui counties were all low-resistant or sensitive to the three nematicides;The cowpea and coriander RKN populations in Chengmai,and the cowpea,pepper,cabbage and water spinach nematode populations in Ledong all showed high resistance to fosthiazate 20%EW;The Hami melon population in Dongfang showed high resistance to fluopyram 41.70%SC,while Chengmai cowpea,coriander and Ledong pepper showed moderate resistance;the rest of the nematode populations were low resistance or sensitivity.In general,the resistance of nematode populations in southern Hainan province was more serious than that in northern areas,and the resistance of nematode populations to fosthiazate 20%EW was the most serious.Among them,the resistance of nematode populations in long-term planting areas of cowpea,pepper and Hami melon was significantly higher.The effect of three nematicides on egg hatching and embryo development of Me showed that,abamectin 3%ME showed the best toxicity to the eggs hatching and the inhibition rate reached 100%treated by 0.16 mg/L of abamectin within 24 hours.The next to abamectin 3%ME was fluopyram 41.70%SC,with inhibition rate reached92.47%treated by 2.5 mg/L.While the toxicity of fosthiazate 20%EW was the lowest,with 65.54%inhibition rate treated by 2.5 mg/L.All three nematicides could affect the embryonic development.The proportion of dead eggs was positively correlated with nematicides concentration and treated time.The nematicides made most embryos suspend at the stage of single cell and first stage juveniles.These results demonstrated that three tested nematicides have certain inhibitory effects on eggs of Me,and the inhibitory effect was abamectin 3%ME>fluopyram 41.70%SC>fosthiazate 20%EW in order.