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Title: Potential Sources of Resistance to Broad Mites (Polyphagotarsonemus latus) in Watermelon Germplasm

item Kousik, Chandrasekar - Shaker
item Levi, Amnon
item Simmons, Alvin

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/19/2007
Publication Date: 12/20/2007
Citation: Kousik, C.S., Shepard, B.M., Hassell, R., Levi, A., Simmons, A.M. 2007. Potential Sources of Resistance to Broad Mites (Polyphagotarsonemus latus) in Watermelon Germplasm. HortScience. 42(7):1539-1544.

Interpretive Summary: Watermelon is an important crop grown in forty-four states in the USA. Many different pests and diseases attack watermelon plants causing extensive damage. Broad mites are a serious pest of many cucurbit crops such as melons and cucumbers that belong to the same family as watermelons. During the summer of 2006, we observed a severe natural infestation of broad mites in our watermelon fields in Charleston, SC. The tender leaves and the growing tips of watermelon plants were severely injured by broad mites. Therefore broad mites have the potential to become a serious pest of watermelons in the US. In this study, we evaluated many wild watermelons from different regions of the world and identified several that had no visible damage and very few broad mites on them. These wild watermelons may be useful as a source of resistance for developing good watermelon varieties that are resistant to broad mites.

Technical Abstract: Two hundred and nineteen United States plant introductions (PI) belonging to the watermelon core collection were evaluated for broad mite, Polyphagotarsonemus latus (Banks) infestation and injury that occurred naturally in a field planting. Of the 219 PI, nine (4%) had no visible broad mite injury in the field compared with a commercial cultivar ‘Mickey Lee’ which was severely injured. Injury was mainly observed on the growing terminals including the tender apical leaves. The growing terminals and the apical leaves were bronzed, grew poorly and in some cases were distorted and curled upwards. Broad mites were extracted by washing the growing terminals of twenty two select PI with boiling water and counting the mites under a stereomicroscope. Mickey Lee had more broad mites on growing terminals compared with some of the PI with no visible injury. Fourteen select PI were further evaluated in the greenhouse to confirm their resistance by artificially infesting them with broad mites that had been cultured on susceptible watermelon plants. PI in accessions belonging to Citrullus lanatus var. lanatus (PI 357708, PI 368526), C. lanatus var. citroides (PI 500354), C. colocynthis (PI 386015, PI 386016, PI 525082) and Parecitrullus fistulosus (PI 449332) had significantly lower broad mite injury ratings and counts compared with Mickey Lee and other susceptible PI. Broad mites have not been reported on watermelons in the US before, however, it can emerge as a serious pest. The above mentioned accessions can serve as a potential source of broad mite resistance that can be used in breeding programs aimed at enhancing disease and pest resistance in watermelon.