Phosphine is the only general use fumigant for the protection of stored grain, though its long-term utility is threatened by the emergence of highly phosphine-resistant pests. Given this precarious situation, it is essential to identify factors, such as stress preconditioning, that interfere with the efficacy of phosphine fumigation. We used Caenorhabditis elegans as a model organism to test the effect of pre-exposure to heat and cold shock, UV and gamma irradiation on phosphine potency. Heat shock significantly increased tolerance to phosphine by 3-fold in wild-type nematodes, a process that was dependent on the master regulator of the heat shock response, HSF-1. Heat shock did not, however, increase the resistance of a strain carrying the phosphine resistance mutation, dld-1(wr4), and cold shock did not alter the response to phosphine of either strain. Pretreatment with the LD50 of UV (18 J cm-2) did not alter phosphine tolerance in wild-type nematodes, but the LD50 (33 J cm-2) of the phosphine resistant strain (dld-1(wr4)) doubled the level of resistance. In addition, exposure to a mild dose of gamma radiation (200 Gy) elevated the phosphine tolerance by ~2-fold in both strains.

Seeds of four local wheat (Triticum aestivum L.) cultivars, namely Hinta, Khaliji, Lokaimy and Qasime collected from different regions of Saudi Arabia were exposed to different doses of gamma rays 50-500 Gy to determine suitable doses for induction of mutation. It was observed that seedling height decreased with the increased dose of radiation in all cultivars. Radiosensitive curve originated from seedling height data resulted in 179, 225, 249 and 256 Gys as LD50 values for the cultivars Hinta, Khaliji, Qasime and Lokaimy, respectively. Based on LD50, as to minimize DNA damage and reduce undesirable mutations, radiation doses which lie between 200 and 250 Gy can be considered suitable for induction of mutation in cultivars Lokaimy, Khaliji and Qasime while between 150 and 200 Gy for cultivar Hinta DOI: http://dx.doi.org/10.3329/bjb.v41i1.11075 Bangladesh J. Bot. 41(1): 1-5, 2012 (June)

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