Cucurbit Genetics Cooperative Report 1:38 (article 34) 1978
E. Kowalewski3 and R. W. Robinson
New York State Agricultural Experiment Station, Geneva, NY 14456
Cucumis species were evaluated for resistance to natural infestation with white flies in the greenhouse. Scanning electron and stereoscope microscope studies were made to determine if white fly resistance is related to morphology or density of leaf trichomes. White fly resistance was compared to cucurbitacin content as determined by ultraviolet fluorescence of chloroform leaf extracts treated with antimony trichloride.
The three species with the greatest density of trichomes, C. dinteri, C. angolensis and C. asper, were the species most resistant to white flies (Table 1). Overall, trichome density was inversely correlated with frequency of adults (r = -.89), pupae (r = -.39), larvae (r = -.61), and eggs (r = -.53) of the white fly, but this relationship was not evident among species having trichomes spaced further apart than the size of the white flies. White fly resistance did not appear to be related to any morphological feature of the trichomes, and none of the species had glandular trichomes. No correlation was noted between cucurbitacin content and white fly infestation.
Table 1. Number of Trichomes and Different Stages of the White Fly on Leaves of Cucumis species.
Species |
Trichomes¹ |
Eggs¹ |
Larvae¹ |
Pupae¹ |
Adults² |
| C. prophetarum | 34 | 108 | 199 | 12 | 9.0 |
| C. trigonus | 24 | 175 | 236 | 148 | 9.0 |
| C. sativus | 33 | 151 | 177 | 168 | 8.8 |
| C. heptadactylus | 14 | 257 | 197 | 18 | 8.5 |
| C. ficifolius | 18 | 64 | 119 | 10 | 8.5 |
| C. leptodermis | 34 | 173 | 144 | 98 | 8.5 |
| C. longipes | 38 | 160 | 166 | 133 | 8.2 |
| C. metuliferus | 26 | 82 | 119 | 63 | 8.0 |
| C. hookeri | 40 | 102 | 144 | 72 | 8.0 |
| C. dipsaceus | 62 | 123 | 99 | 28 | 7 5 |
| C. anguria | 45 | 234 | 226 | 74 | 7.5 |
| C. zeyheri | 43 | 106 | 121 | 40 | 7.1 |
| C. pustulatus | 30 | 46 | 70 | 19 | 7.0 |
| C. myriocarpus | 32 | 52 | 36 | 35 | 6.5 |
| C. africanus | 52 | 107 | 103 | 38 | 5 8 |
| C. melo | 56 | 88 | 77 | 17 | 5.0 |
| C. asper | 110 | 44 | 44 | 2 | 2.0 |
| C. angolensis | 117 | 44 | 86 | 13 | 2.0 |
| C. dinteri | 200 | 12 | 4 | 0 | 1.5 |
¹ Mean number per unit area of lower leaf surface.
² Subjectively rated from 1 (resistant) to 9 (susceptible).