Cucurbit Genetics Cooperative Report 6:49-50 (article 25) 1983
J. D. McCreight
U. S. Department of Agriculture, Agricultural Research Service, P. O. Box 5098, Salinas, CA 93915
Sudden wilt (Pythium ultimum and P. aphanidermatum) of muskmelon has been of increasing importance in California and in Arizona. The disease causes rapid wilting and collapse of the vines just prior to harvest. In the fall of 1981, sudden wilt reached epidemic levels in the Imperial and Palo Verde valleys of California when periods of extremely hot (45°C+) daytime temperatures that induced wilting were followed by short, shallow irrigations.
In 1981, 350 breeding lines, cultivars and plant introductions were planted in mid-July at the U. S. Department of Agriculture, Imperial Valley Conservation Research Center, Brawley, California. Entries were planted in 20-plant plots consisting of 10 hills spaced 0.75 m apart; beds were spaced on 2.4 m centers. Four seeds were planted per hill; hills were thinned to 2 plants at the 1 to 2 leaf stage of growth. Sudden wilt symptoms were rated on a plot basis in September. Most of the entries that did not wilt or wilted only slightly in the 1981 planting were replanted in mid-July, 1982 for sudden wilt observation.
Reaction to sudden wilt varied widely between entries in 1981. Most cultivars and advanced breeding lines were severely wilted and necrotic, but several entries showed little or no wilting. Male sterile breeding lines and various cultivars were moderately wilted. Inbred derivatives and F1 hybrids of PI 125861 and breeding line 61090, F1 hybrid Fla 76-71L (from G. W. Elmstrom, Leesburg, Florida), and breeding line W4 (2), were free of wilt or slightly wilted (Table 1). The highest rated entry in 1981 was 92393, an F1 hybrid between PI 125861 and 61090 (Table 1). Resistance to sudden wilt is available in two muskmelon types (Table 1) following the classification of Naudin (3).
| Table 1. Field ratingsz of potential sources of resistance and standard cultivars of muskmelon; mean of two replications.
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| Entry | 1981 | 1982 | Type | Comment |
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| 92393 | 9 | 9 | inodorus | F1 (PI 125861 x 61090) |
| 92392 | 8 | 5 | inodorus | PI 125861 inbred |
| 92395 | 7 | – | inodorus | F1 (ms-l x PI 125861) |
| W4 | 7 | – | reticulatus | WMVI resistant |
| Fla 76-71L | 7 | 7.5 | reticulatus | F1 |
| 31537 | 7 | – | reticulatus | ms-2 inbred |
| 61090 | 7 | 8.5 | inodorus | powdery mildew resistant honeydew |
| PMR 45 | 1 | 4 | reticulatus | standard cultivar |
| Topmark | 3 | 7 | reticulatus | standard cultivar |
| Green Flesh Honeydew | 2 | 5 | inodorus | standard cultivar |
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| zWilting rating scale: 1=necrosis; 3=severe; 5=moderate; 7=slight; and 9=none. | ||||
Sudden wilt was not as prevalent in 1982; there were virtually no reports of sudden wilt in commercial fields. Wilt was again, however, in epidemic proportions in the breeding trials. That wilt was not as severe as in 1981 was shown by the seasonal differences in ratings of ‘PMR 45’, ‘Topmark’ and ‘Green Flesh Honeydew’. Entries that were most resistant in 1981 were resistant in 1982, with the exception of 92392 (Table 1).
Data from the hybrid 92393 suggest that resistance is conditioned by two or more genes or alleles that combine for higher level of resistance than in the parents. The source of wilt resistance in 61090 is unknown. It’s pedigree is complex and includes ‘PMR45’, commercial honeydew, resistant cantaloupe (1) and PI 124111.
Literature Cited
- Bohn, G. W. 1961. Inheritance and origin of nectarless muskmelon. J. Heredity 52:233–237.
- Thomas, C. E. and R. A. Webb. 1981. W1, W3, W4, W5 and W6 multi-disease-resistant muskmelon breeding lines. HortScience 16:96.
- Whitaker, T. W. and G. N. Davis. 1962. Cucurbits. Interscience Publishers, Inc. New York. 249 pp.