The watermelon strain of papaya ringspot virus (PRSV-W) and zucchini yellow mosaic virus (ZYMV) are potyviruses that cause significant disease losses in cucumber. Resistances have been identified primarily in exotic germplasm that require transfer to elite cultivated backgrounds. In order to select more efficiently for virus resistances, we identified molecular markers tightly linked to PRSV-W and ZYMV resistances in cucumber. We generated F6 recombinant inbred lines from a cross between Straight 8 and TMG1 (susceptible and resistant, respectively, to both viruses) and studied the segregations of amplified fragment length polymorphisms (AFLPs), randomly amplified polymorphic DNAs, restriction fragment length polymorphisms, and resistances to PRSV-W and ZYMV. A 353-point map of cucumber was generated and resistances to PRSV-W and ZYMV were tightly linked (2.2 cM), mapping to the end of one linkage group. The 5-kb genomic region carrying an AFLP cosegregating with resistance to ZYMV was cloned and sequenced. This region possesses many single nucleotide polymorphisms and small insertion/deletion events; however all polymorphisms were unique to the susceptible parent (Straight 8). We are screening a Melon BAC library to assess the synteny between cucumber and melon across this region and to identify polymorphisms unique to the resistance TMG1 parent.

The cucumber mitochondrial genome is paternally transmitted. There is no information regarding genetic variability for organellar DNA transfer in cucumber. MSC 16, a cucumber line possessing a severe mosaic phenotype due to mitochondrial, is resistant to scab. In this project, we are using scab resistance and the MSC phenotype to evaluate for maternal or biparental Mt transmission in cucumber. This research will provide a phenotypic data on the reaction of cucumber plant introductions to scab and a first step towards the potential genetic improvement of this important organellar genome.