Improving Culture Efficiency of Cucumis metuliferus Protoplasts

Although we have made great progress in developing resistance to root – knot nematodes in cucumber, no source has been created or screened to resistance to M. incognita, the main species affecting cucumber (9, 10). Resistance to M. incognita exists in horned cucumber (Cucumis metuliferus), but efforts by many research groups (including our own) to make crosses of Cucumis species with cucumber have failed. Somatic hybridization using protoplast fusion is an alternative for utilizing C. metuliferus germplasm. Plants have been regenerated from protoplasts isolated from C. sativus (2, 4, 7), but not from C. metuliferus. To apply protoplast fusion, a reliable technique for isolating and culturing C. metuliferus protoplasts is often a prerequisite. Several reports suggest that large improvements in plating efficiency can be made by culturing protoplasts in a medium solidified with agarose (2, 3, 8).