Optical conditions of chemical fumigation with Methyle-iodide for biological collections

Abstract

Methyl bromide has been widely used for the fumigation of herbarium specimens, but will be banned by January 2005 under the Montreal Protocol. We recently reported that methyl iodide (CH_3I), as an alternative fumigant, exerted small influence on DNA contained in biological specimens. In order to determine the optimum condition of fumigation against herbarium specimens, seven treatments, combinations of different concentration of CH_3I, temperature and fumigation time in 65% relative humidity, were performed. Fumigation with CH_3I did not produce double-strand breaks of the purified DNA. A main effect of CH_3I on specimen DNA is that the extraction of high-molecular DNAs is obstructed by denatured proteins. Therefore, proteinases added to extract solutions and chloroform extraction facilitate the efficient purification of DNA from fumigated specimens. In all CH_3I treatments, fragments larger than 1,000 bases were amplified using isolated DNAs from fumigated specimens, and they were applicable to molecular phylogenetic analyses. Fumigation of specimens under the condition of 40g/m^3 CH_3I for 24 hours at 25℃ exhibited 100% insecticidal, ovicidal and fungicidal effects and the least influence on specimen DNA. CH_3I exerted little influence on specimen DNA, when fumigation was performed only for insecticidal and ovicidal effects, 20-40g/m^3 CH_3I for 24 hours at 10℃.