ACCUMULATION OF MANSONONES IN CALLUS-CULTURES OF ULMUS-AMERICANA L INTHE ABSENCE OF A FUNGAL-DERIVED ELICITOR

The Dutch elm disease pathogens Ophiostoma ulmi (Buism.) Nannf. and Op hiostoma novo-ulmi Brasier elicit the production of phytoalexins calle d mansonones in the American elm (Ulmus americana L.). As part of a la rger investigation, it was revealed that mansonone elicitation in call us culture does not require the Dutch elm disease pathogens, as has be en reported in other studies. The objective of this study was to deter mine the nature and timing of the nonfungal elicited mansonone accumul ation in U. americana callus. Initially, 7-week-old calli were subject ed to inoculations with various fungal growth medium components. Manso none production occurred in all treatments, indicating that it was sti mulated prior to the addition of the medium components. Next, cotyledo ns and calli at various stages of development were analysed for the pr oduction of mansonones to determine the timing of its production. Mans onone production appeared to be correlated with the initiation of call us production and may be related to the callus wound reaction. As the callus aged, its colour changed from white-green to brown possibly as a result of phytoalexin accumulation. Additional experiments in which the cotyledon source, agar source, and type of plant tissue culture me dia were modified resulted in no change to the mansonone accumulation ability of the callus. The discrepancy between our results and those o f other researchers could be due to differences in the method of manso none quantification, namely, that our method is more sensitive and led to the detection of mansonones where previously none had been found. Further research must be done in this area to investigate this mansono ne accumulation.