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Résumé :
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Five genotypes of wheat, Triticum aestivum L. ('Arapahoe', 'Halt', PI 137739, PI 225245, and PI 262660), were compared for their antixenotic effects on the Russian wheat aphid, Diuraphis noxia (Mordvilko). Comparisons were made by host plant choice tests, diurnal and nocturnal probing behavior of D. noxia, and examination of leaf trichome and epicuticular wax structure. The choice test showed that PI 137739 and PI 225245 were the least preferred hosts among the 5 genotypes evaluated. Electronic monitoring of D. noxia probing behavior showed that the aphids fed differently among the 5 wheat genotypes, and aphid probing behavior was different between diurnal and nocturnal periods. Although the number of probes per aphid was not different among the 5 genotypes either diurnally or nocturnally, the accumulative probing duration per aphid during the 8-h recording period was different. The least probing duration per aphid was on PI 137739 diurnally, but no differences were found among the 5 genotypes nocturnally. Furthermore, aphid piercing duration per probe was significantly longer on PI 137739 than on Arapahoe. D. noxia probing (i.e., salivation and ingestion) duration per probe was significantly different among the 5 wheat genotypes and between diurnal and nocturnal periods. The aphids had the shortest probing duration on PI 137739 among the 5 genotypes diurnally and nocturnally. Irrespective of genotype differences, total probing duration per aphid was significantly longer nocturnally than diurnally. Aphids made numerous short probes diurnally and fewer long probes nocturnally. Adaxial leaf surface examination showed that PI 137739 dad the longest trichomes and medium density, whereas Arapahoe and Halt had the shortest trichomes and the highest density. Examination of adaxial leaf epicuticular wax showed that its ultrastructure was similar among the 5 wheat genotypes, although the density of wax flakes varied among the genotypes. We concluded that Halt and PI 262660 were not antixenotic to D. noxia, but the PI 137739 and PI 225245 were antixenotic to D. noxia based on the host choice test, aphid probing behavior, and examination of leaf surface structure.
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