Cucurbit Genetics Cooperative Report 6:43-44 (article 20) 1983
Richard N. McArdle and Stephen A. Kendall
Department of Horticulture, University of Maryland, College Park, Maryland 20742
Greenhouse tests for Fusarium resistance in muskmelon typically involve inoculation by dipping young melon plants into spore suspensions (2, 3) or growing in infested soil (1). These methods are time-intensive, cumbersome, and often injurious to the seedlings. If the plants were inoculated in their seedling containers, then a minimal amount of time and labor would be required to screen for Fusarium in progeny trials. The seedlings would also sustain less damage.
Jiffy-7 peat pellets (Jiffy Products, Ltd., Shippegan, Michigan) are commonly used for melon transplants. Our objective was to determine if they could absorb and hold sufficient Fusarium inoculum to induce infection.
Spore suspensions of Fusarium oxysporum f. sp. melonis Race 1, isolated from a Maryland melon growing area, were prepared by inoculating flasks containing Richard’s solution (5); these flasks were agitated for three weeks. The contents of the flasks were strained through four layers of cheesecloth to separate out all but the conidia. The concentration of the spore suspension used in this study was 135,000 spore/ml.
In early March, seeds of each of 11 muskmelon cultivars and lines were planted in moist, expanded Jiffy-7 peat pellets, 2 seeds per pellet. After seedling emergence, the pellets were thinned to one plant each. Each treatment combination consisted of six pellets in a plastic “market pack” container. Two replicates were used for both inoculated and control treatments for each entry.
When the plants reached the first true-leaf stage, the pellets were allowed to dry for 48 hours. A small piece of polyethylene film was placed under the pellets in each container. Fifty ml of the spore suspension was poured into the middle of each of the treated containers so that the pellets would absorb approximately equal amounts. Fifty ml of tap water was similarly applied to each control container.
The plants were rated for disease reaction seven days later, using a scale where 0= completely resistant, and 3= completely susceptible. The rating for analysis of variance was the difference between the mean ratings of the inoculated and control units for each rep of each entry.
Analysis of variance indicated significant differences between cultivars and lines at the 5% level of significance. The ranking of reaction ratings (Table 1) corresponds to a pattern expected from other reports of disease resistance and our own experience. Resistance to Fusarium is complicated, involving both genetic and environmental factors. For instance, temperature is known to affect the level of resistance in muskmelon (4). In our study, a nearly constant daily temperature of 30°C permitted optimum disease development, making the rating of reaction to disease more accurate.
| Table 1. Disease reaction ratings of 11 muskmelon entries.z
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| Entry | Rating | Entry | Rating |
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| Perlita | 0.05 | Golden Beauty Casaba | 1.80 |
| Saticoy | 0.33 | Hale’s Best 36 | 1.82 |
| Star Trek | 0.75 | Hearts of Gold | 1.92 |
| Summett | 1.00 | Tamdew | 2.00 |
| Harvest Queen | 1.67 | K 11 | 2.17 |
| MD 6353 | 1.67 | ||
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| z LSD 5% = 1.17 | |||
For these reasons, we do not suggest this method or modifications of it will be a panacea for those breeding for Fusarium resistance. However, we believe that eventually this system could be used in a breeding program where the breeder wants to eliminate progeny from a population expected to be largely susceptible. Extension of this method might permit the screening of large numbers of seedlings, perhaps by dipping seedling flats into spore suspensions. In addition, this procedure could have value in screening for other soil-borne pathogens. The time saved using this method could be enormous.
Literature Cited
- Douglass, D.R. 1970. The effect of inoculum concentration on the apparent resistance of muskmelons to Fusarium oxysporum f. sp. melonis. Can. J. Bot. 48:687–693.
- Gubler, W.D., and R.G. Grogan. 1976. Fusarium wilt of muskmelon in the San Joaquin Valley of California. Plt. Dis. Rept. 60:742–744.
- Leary, J.V. and W.D. Wilbur. 1976. Identification of the races of Fusarium oxysporum f. sp. melonis causing wilt of muskmelon in Canada. Phytopath. 66:15–16.
- Mortensen, J.A. 1959. The inheritance of Fusarium resistance in muskmelon. Diss. Abstr. 19:2209.
- Sourcebook Committee of the American Phytopathological Society. 1967. Sourcebook of laboratory exercises in plant pathology. W.H. Freeman and Company, San Francisco.