Evaluations of melon germplasm reported to exhibit host plant resistance to sweetpotato whitefly

Sweetpotato whitefly (MEAM1 cryptic species of Bemisia tabaci; SPWF) displaced B. tabaci biotype A in 1991 in the lower desert area of southern California and the adjoining areas of Arizona and western Mexico. The search for high-level host plant resistance to this devastating insect has been ongoing since that time. Cucurbit yellow stunting disorder virus (CYSDV) appeared in these areas in fall 2006, and in combination with SPWF has nearly eliminated fall season melon production in these areas. High-level resistance to CYSDV has been identified and is being introgressed to elite adapted western U.S. shipper type melon germplasm. CYSDV resistance alone will not, however, ensure economical production of high quality melons, but must be coupled with a timely regimen of insecticides. Five melon accessions  have been reported resistant to MEAM1 and MED cryptic species of B. tabaci: PI 313970, TGR-1551, PI 161375, PI 414723, PI 523841. Five unique melon accessions expressed in an open field test potentially higher levels of resistance to MEAM1 in fall 2012 based on ad hoc comparisons with PI 313970, TGR-1551, ‘Top Mark’, and ‘Impac’. Replicated field studies in fall 2013, spring and spring 2014 demonstrated few consistent differences among PI 313970, TGR-1551, and susceptible ‘Top Mark’ and the putative new sources of resistance through 7-week sampling periods. PI 116482 had consistently high numbers of adults per leaf, though not always the highest. PI 145594 consistently had lower adults per leaf than most of the other entries though it was not always significantly lower than all the other entries or different from the lowest in either year. In an open field test in fall 2014, PI 122847, a putative CYSDV resistant melon, exhibited potentially high-level resistance to MEAM1, based on numbers of adults and plant condition ratings. Open field and controlled greenhouse tests are underway to compare PI 122847 with the previously reported resistant accessions.