Monday, November 13, 2006

A Yield Index to Describe Alfalfa Cultivar Resistance to Potato Leafhopper.

R. Mark Sulc, 202 Kottman Hall, 2021 Coffey Rd., Ohio State University - Columbus, Ohio State University, Department of Horticulture & Crop Sciences, Columbus, OH 43210-1086, Edward Brummer, Iowa St. Univ. Dept. Of Agron., Crop and Soil Sciences Dept., 111 Riverbend Road, CAGT, Athens, IA 30602, and Daniel J. Undersander, University of Wisconsin, Department of Agronomy, Madison, WI 53706.

Alfalfa cultivars are characterized for resistance to potato leafhopper (Empoasca fabae Harris) (PLH) using a scoring system to visually identify the percentage of plants within the cultivar population that exhibit little or no damage to PLH under field conditions. Cultivars are described as “highly resistant” if more than 50% of the plants show little damage to PLH. A method based on dry matter yield in the presence of PLH should provide more objective information on cultivar tolerance to PLH. Field experiments were established in spring 2005 in Iowa and Ohio to evaluate yield of alfalfa cultivars in the presence of PLH and under insecticide treatment to control PLH. The cultivar x location interaction was not significant for either insecticide treated (P = 0.26) or untreated (P = 0.16) experiments in 2005, so data were combined across locations. Cultivar differences were not significant (P = 0.20) in the insecticide treated experiment. In the untreated experiment, the PLH resistant cultivars yielded more (+0.81 Mg ha-1, P < 0.01) than the susceptible check cultivars. Using data from growth cycles when PLH populations reduced yield of susceptible check cultivars, an index for alfalfa yield tolerance to PLH was calculated as the percentage yield improvement above the average yield of the susceptible check cultivars. The PLH yield tolerance index ranged from –6 (6% lower yield than susceptible checks) to 50 (50% greater yield than susceptible checks). The cultivars with the lowest (-6) and highest (50) PLH yield tolerance index have both been advertised as being highly resistant to PLH. Thus, our preliminary conclusion is that the PLH yield tolerance index is more discriminating in assessing cultivar response to PLH when compared with the current system of visually rating PLH damage in space-planted nurseries.

Handout (.pdf format, 1249.0 kb)