Accumulation of mansonones in callus cultures of Ulmus americana L. in the absence of a fungal-derived elicitor

Abstract

The Dutch elm disease pathogens Ophiostoma ulmi (Buism.) Nannf. and Ophiostoma novo-ulmi Brasier elicit the production of phytoalexins called mansonones in the American elm (Ulmus americana L.). As part of a larger investigation, it was revealed that mansonone elicitation in callus culture does not require the Dutch elm disease pathogens, as has been reported in other studies. The objective of this study was to determine the nature and timing of the nonfungal elicited mansonone accumulation in U. americana callus. Initially, 7-week-old calli were subjected to inoculations with various fungal growth medium components. Mansonone production occurred in all treatments, indicating that it was stimulated prior to the addition of the medium components. Next, cotyledons and calli at various stages of development were analysed for the production of mansonones to determine the timing of its production. Mansonone production appeared to be correlated with the initiation of callus 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 media were modified resulted in no change to the mansonone accumulation ability of the callus. The discrepancy between our results and those of other researchers could be due to differences in the method of mansonone 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 mansonone accumulation. Key words: phytoalexin, Dutch elm disease, mansonone, Ulmus americana, callus.