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Caractérisation et bioécologie du complexe parasitaire du genre Pratylenchus (Nemata : Pratylenchidae) présent sur caféiers (Coffea spp.) au Guatemala

Villain L.. 2000. Rennes : ENSAR, 312 p.. Thèse de doctorat -- Biologie et agronomie.

The first purpose of this work was to characterize four isolates of Pratylenchus that were morphologically similar to P. coffeae, taken from coffee trees at four different geographical sites in Guatemala. The obligatory amphimictic reproduction method of these isolates was confirmed. Observation of reproductive isolation between these isolates suggested they belonged to different species. The characterization tools used revealed two levels of diversity. Detailed observation under a scanning electron microscope enabled separation of the four isolates into two groups. Among these isolates, three were studied more thoroughly. The morphological dichotomy tallied with the differences seen in the reproductive fitness of these isolates on in vitro carrot disks depending on the temperature with a thermal optimum of between 27°C and 30°C or between 24°C and 27°C. A multivariate analysis of various morphometric descriptors enabled differentiation of the three isolates studied. Biologically, on C. arabica, each of the three isolates revealed a different parasitic fitness directly linked to its infestation capacity and its reproductive fitness on this host. For each of the isolates, the amount of damage caused to the host was directly linked to its parasitic fitness. The ability to cause damage seemed to be identical for the three isolates. This study suggests the polyspecific Pratylenchus spp. parasite complex on Coffea spp. in Guatemala presents a substantial diversity which needs to be studied on a Meso-American scale in the different coffee producing regions. At the same time, studies conducted in plantations have revealed seasonal fluctuations in wild Pratylenchus populations in relation with the phenological rhythms of C. arabica and climatic factors depending on altitude. The rapid and severe outbreaks seen in these populations indicate the considerable ability of the parasite to colonize coffee orchards under the study conditions. The degree of damage observed in the field on C. arabica is in line with the strong parastic fitness seen in pots for certain isolates. This study reveals the existence of partial resistance factors in C. canepora on a pre- and post-infectious level, thereby confirming the merits of this germplasm for selecting rootstocks with resistance to Pratylenchus spp. The efficacy of grafting on C. canephora in the field and the low impact of chemicals in controlling Pratylenchus populations are also demonstrated.

Mots-clés : coffea; coffea arabica; coffea canephora; pratylenchus; pratylenchus coffeae; provenance; conformation animale; performance de reproduction; pouvoir pathogène; nématodose; facteur du milieu; température; résistance aux organismes nuisibles; variation génétique; dégât; facteur lié au site; dynamique des populations; variation saisonnière; guatemala

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