EFFECT OF SCREENING METHODS ON EXPRESSION OF ROMAINE LETTUCE RESISTANCE TO ADULT BANDED CUCUMBER BEETLE, DIABROTICA BALTEATA (COLEOPTERA: CHRYSOMELIDAE)

Juan Huang, Gregg S. Nuessly, Heather J. McAuslane and Russell T. Nagata

Abstract


Resistance in lettuce, Lactuca sativa L., to feeding by adult banded cucumber beetle, Diabrotica balteata (LeConte), was evaluated using three screening methods: leaf disks, excised leaves and intact leaves attached to plants. Dual-choice and no-choice bioassays were used to evaluate each method based on leaf area consumption. Methods of testing had a significant effect on the level of feeding damage by D. balteata on two lettuce cultivars, Tall Guzmaine and Valmaine. Valmaine expressed a significant degree of resistance to D. balteata damage when intact leaf and excised leaf methods were used in dual-choice bioassays between Tall Guzmaine and Valmaine, but the latter failed to show resistant characteristics in no-choice tests when excised leaves were used. Furthermore, there was no significant difference in D. balteata feeding between Tall Guzmaine and Valmaine in the leaf disk tests. Therefore, whole plants are the best method to evaluate lettuce cultivars for resistance to D. balteata. Reduction or cessation of resistance characters in excised Valmaine whole leaves and disks are discussed with references to potential changes in concentration of feeding stimulants and deterrents and changes in latex pressure.

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