COMBINATION AND EXPRESSION OF 2 VIRUS-RESISTANCE MECHANISMS IN INTERSPECIFIC SOMATIC HYBRIDS OF POTATO

Solanum tuberosum cv. Pentland Dell expresses single gene-mediated hyp ersensitive resistance (HR) to potato virus Y (strain group PVY0), A ( PVA(1)) and X (PVX3) and is resistant to cucumber mosaic Virus (Fny-CM V). S. brevidens is resistant to these viruses, too, but resistance is functional through slow virus cell-to-cell movement. These two virus resistance mechanisms were combined by symmetric somatic hybridization . Six hybrid plants were regenerated from a single fusion callus and t ested for virus resistance by graft-inoculation. Titers of PVY and PVA in the hybrids were higher than in S. brevidens. Only limited necrosi s developed following infection with PVY and chlorotic lesions develop ed following infection with PVA in the hybrids, whereas top necrosis a nd necrotic lesions, respectively, developed in P. Dell. No virus or s ymptoms were observed in one hybrid inoculated with PVX and three hybr ids inoculated with CMV. Other hybrids developed lethal necrosis follo wing infection with PVX, and stunting, necrosis and yellow mosaic symp toms following infection with CMV, which was similar to P. Dell. S. br evidens contained moderate titers of PVX and CMV. It developed no symp toms following infection with PVX and only mild mosaic symptoms follow ing infection with CMV. Altered resistance expression in the hybrids m ay be attributable to simultaneous expression of the two resistance me chanisms, interference in the expression of either resistance mechanis m caused by the genes of the heterologous genome, and/or somaclonal va riation. (C) 1998 Elsevier Science Ireland Ltd.