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Project description

Resistance of alfalfa against silverleaf whitefly: breeding and mechanisms of resistance. (01XA010)
Program Exotic Pests and Diseases Research Program
G.P. Walker, Entomology, UC Riverside
L.R. Teuber, Agronomy and Range Science, UC Davis
Host/habitat Alfalfa
Pest Silverleaf Whitefly Bemisia argentifolii
Discipline Entomology
Agricultural Systems
Start year (duration)  2001 (Two Years)
Objectives Determine the mechanism of resistance in alfalfa clones selected for resistance against silverleaf whitefly.

Evaluate material identified as resistant in previous laboratory assays in the field (Imperial Valley) under natural infestation conditions.

Further improve the silverleaf whitefly resistance of advanced genetic materials currently being selected for improved agronomic characteristics and resistance to other economically important pests and diseases.

Objective 1. We have systematically narrowed down the mechanisms of resistance in the resistant alfalfa genotypes in accordance with our original planned research approach. We have ruled out difficulty of the whiteflies penetrating the plant tissue with their stylets and difficulty penetrating a phloem sieve element (the type of plant cell that whiteflies upon) as possible mechanisms of resistance. Resistance is expressed AFTER a sieve element is penetrated, and results in the whitefly spending significantly less time in ingestion behavior and a greatly reduced (one fifth) volume of plant sap ingested, and eventually death.

Objective 2. We made the first year evaluation of our alfalfa clones under field conditions in Imperial Valley. Due to high mortality of transplants, we did not get as many individual plants established as we had hoped, so we will fill in the missing plants this spring and repeat the evaluation this summer. Nonetheless, several of the clonal lines that looked good in our greenhouse evaluations performed excellently in the field trial and considerably better than the recently released alfalfa cultivar UC-Impalo-WF with moderate resistance against whiteflies. This means we have identified germplasm that can improve whitefly resistance over what is currently available.

Objective 3. We are continuing to use our greenhouse/laboratory evaluations to screen the potential parent clones for the next generation of whitefly resistant alfalfa. We have conducted at least one replicate on 30 of the potential parent alfalfa clonal lines.

We are preparing our field plots for this year's field evaluation of different clonal lines of alfalfa for resistance against silverleaf whitefly.

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