INHERITANCE OF RESISTANCE TO WATERMELON MOSAIC-VIRUS IN THE CUCUMBER LINE TMG-1 - TISSUE-SPECIFIC EXPRESSION AND RELATIONSHIP TO ZUCCHINI YELLOW MOSAIC-VIRUS RESISTANCE

The inbred cucumber (Cucumis sativus L.) line TMG-1 is resistant to th ree potyviruses: zucchini yellow mosaic virus (ZYMV), watermelon mosai c virus (WMV), and the watermelon strain of papaya ringspot virus (PRS V-W). The genetics of resistance to WMV and the relationship of WMV re sistance to ZYMV resistance were examined. TMG-1 was crossed with WI-2 757, a susceptible inbred line. F-1, F-2 and backcross progeny populat ions were screened for resistance to WMV and/or ZYMV. Two independentl y asserting factors conferred resistance to WMV. One resistance was co nferred by a single recessive gene from TMG-1 (wmv-2). The second resi stance was conferred by an epistatic interaction between a second rece ssive gene from TMG-1 (wmv-3) and either a dominant gene from WI-2757 (Wmv-4) or a third recessive gene from TMG-1 (wmv-4) located 20-30 cM from wmv3. The two resistances exhibited tissue-specific expression. R esistance conferred by wmv-2 was expressed in the cotyledons and throu ghout the plant. Resistance conferred by wmv-3 + Wmv-4 (or wmv-4) was expressed only in true leaves. The gene conferring resistance to ZYMV appeared to be the same as, or tightly linked to one of the WMV resist ance genes, wmv-3.