EVALUATION OF NEW-ZEALAND BARLEYS FOR RESISTANCE TO MAYETIOLA-DESTRUCTOR AND M-HORDEI (DIPTERA, CECIDOMYIIDAE) AND THE EFFECT OF TEMPERATURE ON RESISTANCE EXPRESSION TO HESSIAN FLY

Six New Zealand barleys were evaluated for resistance to biotype L of the Hessian fly, Mayetiola destructor (Say), the most virulent biotype that infests wheat ill the United States. Three of the barleys,'Gwyla n', 'WPBS 316/80', and 'Fleet', were found to be resistant to biotype L and were tested to Hessian fly and the stem gall midge M. hordei Kei ffer in Morocco. Because high temperature may affect the expression of resistance to Hessian fly, the temperature sensitivity of resistance to biotype L also was assessed at constant temperatures of 18, 24, and 30 degrees C. Resistance tests demonstrated that Gwylan, WPBS 316/80, and Fleet were highly resistant to biotype L and Moroccan Hessian fly , but were susceptible to stem gall midge larvae. Resistance was expre ssed mainly as antibiosis, with Ist instars dying after feeding on res istant plants. Small numbers of larvae survived on resistant plants an d appeared to develop normally, indicating that a tolerance mechanism also may be involved. Neither plant resistance nor the level of antibi osis expressed in the three cultivars was affected by increasing tempe rature up to 30 degrees C. The results indicate that the New Zealand b arleys carry resistance genes different than those preciously identifi ed in barley and would be excellent sources for breeding Hessian fly-r esistant cultivars in the United States and Morocco.