Résumé
A comparative study of penetration dynamics of two reproductively isolated Pratylenchus isolates was carried out on hypocotyledonar stage seedlings of C. arabica cv. Catuai and C. canephora rootstock cv. Nemaya. Roots were stained with acid fuschine, 24, 48 and 96 hours after the inoculation of 300 nematodes/plant. Stained nematodes were counted in situ. For both isolates, a high penetration rate was observed on C. arabica while very few nematodes infested Nemaya's roots. Complementary histological studies of roots showed no noticeable structural differences between these two coffee species. On the other hand, the presence of high amount of polyphenols was observed on Nemaya's roots even before nematode penetration, suggesting the existence of constitutive factors of resistance. In contrast, polyphenols were not observed on Catuai roots, whether they were infested or not by nematodes. One of the Pratylenchus isolates was inoculated on 3 months coffee seedlings of cv Catuai and a progeny of a Nemaya parent plant. Nematode population densities in root, stem height and fresh root and shoot weights were measured 50, 100 and 150 days after the inoculation of 200 nematodes/plant. The reproductive fitness of this isolate was significantly lower on C. canephora progeny than it was on Catuai. Therefore there is some evidence of existence in C. canephora of pre- and postinfectious factors of partial resistance to Pratylenchus spp. The nature of these factors of resistance must be specified. (Texte intégral)