|Miller, M. - TEXAS A&M UNIVERSITY|
|Isakeit, T. - TEXAS A&M UNIVERSITY|
Submitted to: American Phytopathological Society
Publication Type: Abstract Only
Publication Acceptance Date: May 19, 1998
Publication Date: N/A
Technical Abstract: Muskmelon fruit rot caused by Didymella bryoniae can be severe when environmental conditions and fruit developmental stage are favorable for infection. Inoculation of muskmelon fruit at different developmental stages with five D. bryoniae isolates exhibited the greatest (P = 0.05) amount of decay on 10-day old fruit as compared to 20-, 30-, 40- or 50-day old fruit. There was no difference (P = 0.05) in lesion size between 30-, 40-, or 50-day old fruit, although they were significantly larger than those on 20-day fruit. All 5 fungal isolates produced the highest polygalacturonase (PG) activity in inoculated 10-day old fruit, and the least in 20-day old fruit. There was a positive correlation (r = 0.7226, P = 0.0001) between lesion size and total fungal PG activity in decayed tissue. At least nine PG isozymes (pI 4.6 to 8.3) were produced both in shake culture and decayed fruit tissue by a representative isolate. The activity of D. bryoniae PG from in vitro and in vivo was optimum at pH 6, and showed a primary endo-mode of action.