Screening of Melons for Silverleaf Whitefly Resistance: 1994

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Cucurbit Genetics Cooperative Report 18:45-47 (article 22) 1995

James D. McCreight
U.S. Department of Agriculture, Agricultural Research Service, U.S. Agricultural Research Station, 1636 East Alisal Street, Salinas, CA 93905

Sweetpotato whitefly, Bemisa tabaci Genn. (SPWF) B strain, virtually destroyed the Fall 1991 melon crop in the lower desert valleys of Arizona and California (8). This whitefly strain was re-designated silverleaf whitely (SLWF), but no without controversy (1, 2, 9, 10, 11, 12).

From 1991-1993, approximately 530 melon plant introductions (PI) were evaluated in naturally-infested field tests in Imperial Valley, California for resistance to SLWF. In 1991, 17 of 150 PIs from India appeared to have some level of resistance to SLWF (5). In 1992, these 17 PIs were re-tested for SLWF resistance along with 108 previously untested PIs from India plus 27 standard cultivars, breeding lines, and F1 – F2 backcross families from crosses of susceptible parents with lines identified as potentially resistant to lettuce infectious yellows virus (transmitted by SPWF strain A) or SLWF (6). None of the entries was superior for whitefly resistance. In 1993, 276 melons from Afghanistan and Pakistan were evaluated for whitefly resistance in a naturally-infested field test (7). Also included in the 1993 test were: three cultivars (PMR 45, Top Mark, GF Honeydew), breeding line WMR 29, Snakemelon from the Middle East, and progenies 28479 (an F1 from the cross Top Mark FR x Snakemelon), 28478 (a backcross from the series Top Mark FR (Snakemelon (Freeman Cucumber x Snakemelon))), and 28481 and 28482 which are backcrosses from the series PMR Honeydew (Snakemelon (Freeman Cucumber x Snakemelon )). Nine of the entries in the 1993 test showed potential resistance four weeks post-planting, but by eight weeks post-planting all entries were dead. None of the entries tested to date appears to be highly resistant to SLWF. It is, therefore, necessary to continue field testing PI for resistance to SLWF.

In 1994, a field test to evaluate SLWF resistance was planted on 26 August at the University of Arizona, Yuma Agricultural Center. This site is also in the northern portion of the Sonoran Desert and is approximately 120 km from Brawley, California the site of the three previous tests. This test included 266 wild melons from Afghanistan, India and Turkey plus six cultivars (PMR 45, Top Mark, FG Honeydew, Primo, Perlita, Mainstream), breeding lines WMR 29 and PMR Honeydew, and progeny 28481 from the backcross series PMR HD (Snakemelon (Freeman Cucumber x Snakemelon)). Plots were planted on 80 inch centers and consisted of five two-plant hills spaced 30 inches apart. The test was evaluated on a plot basis four weeks and eight weeks post-planting for number of live plants, plant size, plant condition, yellowing, leaf burn and flowering. As in previous years, plots were not treated with any pesticides.

There were statistically significant differences among the entries for SLWF resistance in the field four and eight weeks post-planting for plant size, condition, leaf burn and leaf yellowing. Eight weeks post-planting, mean plant condition ranged from 2.5 to 7.5 (Table 1). This is in stark contrast to 1993 when all plants were dead eight weeks post-planting. Top Mark had a mean plant condition rating of 5.3. PMR 45 and Mainstream which were slightly better than Top Mark,; and Perlita which was slightly worse than Top Mark did not differ significantly from Top Mark. GF Honeydew was significantly worse than Top Mark. In contrast, PMR Honeydew was significantly better than Top Mark. Eight (PI 116915, PI 125861, PI 125890, PO 125918, Pi 125951, PI 126966, PI 125997, PI 126165) of the nine best lines four weeks post-planting in 1993 had mean plant condition ratings lower than Top Mark. Progeny 28481 had a higher rating for plant condition but it was not significantly better than Top Mark. Only PI 237257 was significantly better than Top Mark.

Eighteen entries were noted in one of the replications during the evaluation to have some merit for further evaluation (entries in Table 1 noted with the x). An additional eight entries were noted in both replications to have some merit for further evaluation (entries in Table I denoted with the y).

Table 1. Mean plant condition eight weeks post-planting in response to whitefly feeding, 1994.z

Mean

Entries
7.5 237257y
7.0 PMR HDy 532841y 179248x 167266x
6.5 344342y 183675 177362 172381x 164852x 164662
124433x
6.0 344318 344316 182951 179907x 176930y 175682
175675x 175668 174157 171598x 171594x 164680x
124105 117162x 28481x
5.5 PMR-45 Mainstream 532840 344346y 344069 277280
179900 179898x 179675 179251 176955 176949
175678 175676 172833 172825x 172821x 169320
167221 164855 164637 109479
5.3 Top Mark
5.0 Primo 503324 344334 344320 344307 293922
210076 183676 183674 183302 183046 182944
180428y 179914 179897 177355 177341 176935
176506 174165 174148 174133 172827 172813
171599 169379 169360 169355 169348 169322
169318 169312 169305 167044 166966 165031
165025 164976 164820 164611x 164584 125997
124207 116915
4.5 490995 344341 344335 344322 344309 183301
183047 183034 182954 182186 179257 179247
177353 177348 177347 177345 177336 176507
176505 175684 174162 174138 173672 172819
169374 169371 169367 169331 169327 169323
169317 169313 169309 169307 169303 167057x
166190 165232 165022 164996 134822 164610
164609 164432 164357 164328 124093 123688
117158 116666 18100
4.0 Perlita 344345 344344 344338 344317 344308
344306 344305 245735 231130 204691 183304
183042 183027 182955 182950 179254 179245
177388 177335 177334 176948 176942 176940
176929 176510 176504 176503 176502 175674
174168 174144 174137 174136 174134 173673
172828 172822 172816 172814 169370 169366
169347 169336 169329 169325 169321 169310
169302 165003 164974 164664 164364 164313
164269 136181 136180 125966 124445 124435
124432 124430
3.5 344337 344333 334330 344321 344315 344311
344303 258353 210768 182958 182956 182187
179908 178880 177351 176937 176511 174176
174175 174156 174150 172836 172834 172826
169368 169362 169343 169333 139330 169311
167058 167032 164395 126165 125951 125890
124104 124099
3.2 .344302 183053 174151 125918
3.0 GF HD 490997 344343 344339 344326 344323
344314 344310 176941 175673 174140 171593
169349 169344 169314 169306 164990 125861
2.5 503325 183039 176946 169364

zCondition was rated on a 1 (dead) to 9 (vigorous, flowers) scale; LSD0.05 = 1.7; LSD0.01 = 2.2
y Entry was notable in both replications.
x Entry was notable in one replication.

Literature Cited

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