Cucurbit Genetics Cooperative Report 7:61-62 (article 27) 1984

A Preliminary Report on Screening Watermelons for Resistance to Watermelon Mosaic Viruses 1 and 2

Munger, H.M., T.A. More, and S. Awni

Cornell University, Ithaca, NY 14853.

About 150 watermelon seed lots planted in November, 1982, were inoculated as 3-week seedlings with WMV-1 and WMV-2. Except for about 10 entries, all were PI's supplied by the Regional Plant Introduction Station at Experiment, Georgia. For most entries 5 or 6 seedlings were inoculated with each virus.

Following inoculation mottling appeared on the leaves of nearly all the seedlings and differences were not readily apparent initially. In a few weeks certain entries showed much greater growth and diminished mottling. The best plant in each of the best entries was selected for transfer to a pot and carried through the winter. Most selected plants survived until May, 1983, when they were rated for resistance and several cuttings of each rooted. The surviving entries and their ratings are shown in Table 1.

Table 1. Watermelons planted Nov. 10, 1982, 6 plants inoculated with WMV1 and 6 with WMV2 on Dec. 2. Best plant saved from each entry below and held for field planting in 1983.
Cornell test no.	Entry	Origin	Resistance rating (May 1983)		O.P. seed from WMV2 isolation	Edibility
			WMV1	WMV2
83	PI 179662	India	High	Med.	-
80	PI 179878	India	High	-
74	PI 179884	India	-	Med.	+	Red flesh1
63	PI 182934	India	-	Med.-High	+	Red flesh
51	PI 183398	India	-	Med.	+	Red flesh
133	PI 234603	New Zeal.	Med.	-
20	PI 295848	S. Africa	Highest	High	++	Tasteless
123	PI 381703	India	Med.	-
100	PI 381731	India	-	Med.	-
94	PI 381740	India	-	High	++	Good2
86	PI 381751	India	-	Med.	+
151	Wild citron	Egypt	High3	-		Bitter
152	WM5-4 (Webb's sel. from Egon)	Nigeria	High	High	+	Tasteless
1Rotted but flesh color suggested a commercial variety.
212% soluble solids. Field assistant took it home to eat.
3Only seed produced in WMV1 isolation.

From 1 to 4 cuttings from each plant selected in the WMV-1 test were planted in one isolated field, and from the WMV-2 test in another, in single long rows. Plants were allowed to open- pollinate with the thought that natural crossing might lead to greater resistance through transgressive segregation. Unfortunately, the WMV-1 selections were in an unfavorable location and most did not survive transplanting in a hot, dry period. Most of the WMV-2 selections grew and set fruit normally, showing little evidence of virus disease. Part of the seed from each selection will go to Egypt for testing since virus diseases are limiting watermelon production there. There is adequate seed to share with other watermelon breeders interested in evaluating virus resistance.

These are highly preliminary results; larger samples of the more promising entries should be re-tested and more care given to getting seed, particularly from survivors of WMV-1 inoculation. In the collection tested, 75 entries came from India, 15 from Japan, 15 from South Africa, 10 from USSR, 10 from Central and South America, and 7 from tropical parts of Africa. The survivors from India had the best horticultural features but none had high resistance to both viruses. Entries with the best combined resistance to the 2 viruses came from Africa, but none was really edible.