Selection And Adaptability Of Me3 Virulent Population In The Parthenogenetic Nematode Meloidogyne Incognita

Root-knot nematode (Meloidogyne spp.) is the main pathogens of pepper. Plant resistant cultivars is a effective method for controlling root-knot nematode. Me3 gene which is carried by some resistant pepper cultivars is a dominant gene, confers resistance to the three main species( M. arenaria, M. incognita and M. javanica). However the emergence of virulent biotypes which can overcome this resistance of pepper, severely limits resistant effect of the resistant gene. We got a pair of Me3 near-isogenic lines between virulent and avirulent, studied the fitness cost and specialization of virulent population and so on, the main results were summarized as follows:⑴Selection of Me3 virulent population and construction of near-isogenic lines. 30 plants of HDA149 were inoculated with natural population of M.incognita, 14 virulent egg-masses were obtained, the variation frequency was 2.67×10^-5. After continuous selection of 15 generations of Me3 virulent and avirulent egg-mass, a pair of near-isogenic lines were obtained, and molecular identification results shows both of near-isogenic populations were M.incognita.⑵Analysis on fitness cost of Me3 virulent population. In this experiment each plant was inoculate with 600 nematodes. When Me3 avirulent population was inoculated on resistant pepper HDA149, none root-knots or egg-masses were detected. But when Me3 avirulent population were inoculated on susceptible pepper Qiemen, the average amount of egg-masses was 154 per plant, the average amount of second instar larvae of hatching from egg-mass was 484 strips. The average amount of Me3 virulent nematodes on susceptible pepper was 107 per plant, the average amount of second instar larvae of hatching from egg-mass was 165 strips. Under the Me3 resistance gene selection pressure, the fitness was 83300, but in the absence of this pressure, the fitness was only 17655, the Ch was 76%, means existed fitness cost of Me3 virulent population.⑶Analysis on specialization of Me3 virulent gene. Three tomato cultivars were evaluated, each plant was inoculated with 200 Me3 virulent nematodes,the result shows galls and egg masses were found on the root of susceptible cultivar Lichun, but we didn't get any root-knot or egg-masses on Mogeor and LA2823 which contains resistant gene Mi-1 and Mi-3 respectively. Two pepper cultivars were examined, each plant was inoculate with 600 Me3 virulent nematodes,8 egg-masses per plant were detected on PM217 which containing resistant genes Me1 and Me2, ,101 egg-masses per plant were found on PM687 which containing resistant genes Me3 and Me4. When Me3 avirulent nematodes were inoculated on Mogeor,LA2823,PM217 and PM687,We didn't got any root-knots or egg-masses. These results mean the specialization of Me3 virulent gene.⑷Other adaptability analysis of Me3 virulent population. Two tomato cultivars were evaluated, each plant was inoculated with 500 nematodes. When Me3 avirulent nematodes were inoculated on susceptible tomato MicorTom, 167 root-knots per plant were detected; When Me3 virulent nematodes on MicorTom, 156 root-knots per plant were detected . When Me3 avirulent nematodes were inoculated on Lichun, 154 root-knots per plant were detected , but When Me3 virulent nematodes on Lichun, 112 root-knots per plant were detected The results indicated that the pathogenicity of nematode related to Me3 virulent and tomato cultivars. There was no different between Me3 virulent population and avirulent population, showed that between virulent gene and drug resistant gene, there was no relationshipThe conclusion could have important consequences for the management of resistant cultivars in the field.