SCREENING FOR RESISTANCE TO RUSSIAN WHEAT APHID IN TRITICALE

Resistance to Russian wheat aphid (Diuraphis noxia Mordvilko) (RWA) remains scarce in hexaploid wheat (Triticum aestivum L. em. Thell.) and has been identified only in unadapted wheats. Introduction of resistance from related species is a viable alternative. A greenhouse study was conducted to identify possible sources of resistance to RWA, and to examine RWA screening techniques. After screening 133 triticale (X Triticosecale Wittmack) lines in replicated flat screening tests, 11 resistant lines were identified and evaluated along with 3 susceptible lines and 1 susceptible wheat for antibiosis, antixenosis, and tolerance. In preliminary screening trials, correlations of 0.50 (P less-than-or-equal-to 0.05) to 0.58 (P less-than-or-equal-to 0.01) were found between plant damage ratings and plant heights. Plant damage ratings and antibiosis values also were correlated (r = 0.55, P less-than-or-equal-to 0.05). Antixenosis time periods of 24, 48, and 72 h were compared. There were significant differences between resistant and susceptible lines for antibiosis and tolerance, but not for antixenosis. Number of nymphs per adult ranged from 0 to 9 in antibiosis tests. Plant stunting ranged from 0 to 16.5 cm among resistant lines and from 8 to 21.5 cm among susceptible lines in tolerance tests. Correlations among all three antixenosis evaluation times were significant. We concluded that excellent sources of RWA resistance exist in triticale, and that resistance is expressed primarily as antibiosis and tolerance.