Interactions of the fungicide 2-aminobutane with potato tubers
A synthetic route to 2-aminobutane (2-AB) was developed, which enabled the synthesis of specifically and uniformly 14C labelled 2-AB to be carried out. 14C labelling was employed as a means of detecting 2-aminobutane in tuber tissue samples. An analytical technique, based on acid extraction and scintillation counting, was developed for the determination of 2-AB residues in potato tubers. This allowed studies to be carried out on various factors influencing the efficiency of fumigation of potato tubers with 2-aminobutane.Using C 2-AB and a specially constructed small scale fumigation chamber, an investigation into the absorption and penetration of 2-AB into tubers was undertaken. The rate and extent of 2-AB absorption were studied, and also the effect of initial fumigant concentration and length of exposure period, on the final 2-AB residues in tubers. The depth of penetration was shown to be limited to the first 1 cm of tissue indicating that after initial absorption, the amine is firmly bound at or near the tuber surface. Thin layer chromatography of extracts from fumigated tubers,provided evidence which suggested that 2-AB is not metabolised by the tubers during the storage period.Damaged tubers were shown to absorb higher levels of 2-AB, and the effect of wound healing at different temperatures, prior to fumigation, was demonstrated. The preferential uptake of 2-aminobutane through tuberlenticels was highlighted as a possible cause of tuberto tuber variation in 2-AB residues. Studies showed that there was no appreciable loss of 2-AB from fumigated tubers during the storage period, and that transfer of 2-AB from tuber to tuber during air recirculation was very limited.The absorption of 2-AB by soil, straw and wood,was examined and identified as a likely sink for the amine fumigant, and this could contribute to the low 2-AB residues recorded for some commercial fumigations.A comparison of the antifungal activity of the optical isomers of 2-aminobutane, confirmed that the R-(-)- enantiomer was more active than the corresponding S-(+)- isomer, or racemic mixture, against the fungi responsible for gangrene and skin spot in potato tubers.