RESPONSE OF LEAF SPOT-SENSITIVE AND TOLERANT MUSKMELON (CUCUMIS-MELO L) CELLS TO THE PHYTOTOXIN RORIDIN-E

The response of muskmelon mesophyll and suspension cells to roridin E, a phytotoxin produced by the fungal pathogen Myrothecium roridum, was monitored by measuring changes in the fluorescence of cells stained w ith merocyanine 540, an optical probe for changes in transmembrane ele ctrical potential (PD). The fluorescence emission from leaf spot-sensi tive and tolerant muskmelon mesophyll cells was not affected by roridi n E. However, suspension cells from only the leaf spot-sensitive culti var Iroquois exhibited a significant increase in fluorescence after 5 min of exposure to 10 mu M roridin E. These results suggest that rorid in E may be a good in vitro selective agent for muskmelon suspension c ells and that fluorescence measurements may be useful in screening mus kmelon germplasm for resistance to M. roridum.