Résumé :
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In Montpellier, France, the effects of wheat cultivar and irrigation level on damage symptoms and Diuraphis noxia (Mordvilko) abundance were tested in screenhouse and field experiments. Four cultivars were used: 'Mondur' and 'Arcour', which are drought susceptible, and 'Agathe' and 'Ardente', which are drought tolerant. Previous preliminary observations had also indicated that 'Arcour' might be more susceptible to D. noxia than 'Ardente'. Each cultivar was irrigated at three levels in the screenhouse (25, 50, and 75% soil saturation) and in the held (sheltered from rain, rainfall, and irrigation plus rainfall). In the screenhouse, D. noxia density increased throughout the experiment, but did not vary with cultivar. In the field, although D. noxia density increased initially densities were much lower than in the screenhouse, perhaps because of natural enemy impact. 'Arcour' and 'Agathe' tended to have higher densities in the fia:ld than 'Mondur' and 'Ardente'. Although aphid densities were lower with lowest level of irrigation in the screenhouse, irrigation level did not affect aphid density in the field. Irrigation level did not significantly affect damage symptoms in the screenhouse or field. Although cultivar did not affect leaf streaking in the screenhouse or field, 'Ardente' and 'Agathe' showed significantly greater leaf rolling than 'Mondur' and 'Arcour' in the screenhouse, despite lack of differences in aphid density. Tile results of these experiments suggest that neither irrigation nor drought tolerance directly reduce density or impact of D. noxia, and one must look at other mechanisms to explain the negative correlation between high rainfall and D. noxia abundance.
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