Penetration, development and emigration of juveniles of the nematode Meloidogyne arenaria in Myrobalan plum (Prunus cerasifera) clones bearing the Maresistance genes

Penetration, development and emigration of M. arenaria in the roots of thre e Myrobalan plum (Prunus cerasifera) clones genetically characterized for t heir resistance to root-knot nematodes (RKN) were studied during the 10 (pe netration) and 15 (emigration) days following the date of inoculation (D) o f 2500 juveniles (J2s) per plant into the soil. Miniaturized tests were con ducted on the two resistant clones P.2175 (Ma1 gene) and P.1079 (Ma2 gene) and the susceptible clone P.2032 (recessive for both genes), obtained from micropropagated plantlets and grown in mini-containers under controlled con ditions at 25 degrees C in a growth chamber. For penetration and developmen t studies, nematodes in the roots were recovered by the acid fuchsin-lactop henol staining technique. Equivalent numbers of J2s were recovered in all t he clones at D + 1 and D + 2. Subsequently, the numbers increased rapidly i n P.2032 and were significantly different from those in P.1079 and P.2175 t hat remained at a low level. No swollen larvae were observed in the resista nt clones. In P.2032, the first swollen larvae were observed at D + 4, the first females were observed at D + 12, whereas the first females with attac hed egg sacs and the first new-generation J2s were obtained between D + 21 and D + 28. Our data suggest that the resistance phenomenon does not act on the very early nematode penetration but acts later by preventing feeding-s ite induction and development into the third-stage. For emigration studies, plants in which J2s had been allowed to penetrate for two days (from D to D + 2) were washed free of soil, reported and then, after various periods o f growth, soil-free roots were placed under a mistifier to evaluate the num bers of emigrating individuals. Emigration of J2s from the roots occured ma inly from D + 2 to D + 4 in all the genotypes and was very limited from D 4 to D + 10. There was no significant differences in the number of emigrat ed juveniles between the resistant and susceptible clones, indicating that emigration cannot explain the difference in the numbers of nematodes recove red in the roots.