Inventaire,distribution et agressivité des espèces ou variétés deFusarium rencontrées sur la pomme de terre ou dans son environnement dans différentes zones agroécologiques du Pérou

Résumé L'inventaire et la distribution de la flore fusarienne dans les 3 zones agroécologiques du Pérou (C?te, Sierra, Haute-Selva) sont étudiés.F. oxysporum est l'espèce la plus fréquemment isolée puis, en ordre décroissant,F. solani etF. roseum (et ce, aussi bien à partir de plantes présentant des sympt?mes qu'à partir du sol). Cette flore s'est révélée très stable d'une région à l'autre. L'inoculation sur tubercules, des souches des différentes espèces ou variétés deFusarium isolées à partir des plantes et du sol entra?ne très fréquemment des pourritures importantes.

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Summary A survey was carried out ofFusarium species in three agroecological zones in Peru (Coast, Sierra and High Selva) (Table 1). Information was obtained on the characteristics of PeruvianFusarium flora, the distribution of isolates and their aggressivity (Tables 2 and 3). TheFusarium flora is characterised by its stability and the absence of diversity. Thus, it is stable in all three agrochemical zones of Peru (Fig. 1):F. oxysporium is by far the most common species followed byF. solani andF. roseum isolated from both diseased plants and the soil. Qualitative or quantitative differences inFusarium populations were not found between regions in spite of widely different climatic conditions, crop rotation systems and land preparation practices. It is notable that a close relationship was found between the plant and soil populations: the proportions ofFusarium species or varieties present in the soil and in the plant were similar. Furthermore, aggressivity on tubers of the differentFusarium species or varieties whether isolated from plants or the soil indicated that the risks of crop contamination and the subsequent development of rots were closely related to the health status of the soil and possibly of the plant (Table 4). Finally, this study shows that the biology ofFusarium is a complex problem which involves the soil, the plant and the tuber. It should be examined by studying factors affecting fungal wilt symptom expression and populations ofFusarium isolates during tuber storage.