Types and frequencies of chlorophyll mutations in Durum wheat induced by radiations and chemicals

Abstract

The comparative effects of X-rays, thermal neutrons, fast neutrons, diethyl sulphate and ethyl methanesulphonate were studied, using dry seeds of the cultivated varieties Aziziah, Cappelli and Russello of durum wheat. Aziziah was found as the most radiation sensitive variety; no statistically significant difference in radiation sensitivity between Cappelli and Russello was ascertained. Excluding the results of two chemical treatments, the three varieties studied did not differ from each other as to frequency and spectrum of chlorophyll mutations in the second generation (M 2). At comparable survival rates, mutation and mutant frequencies in M 2 were two to several times higher after neutron irradiation than after X-rays. In the radiation series, maximum rates of chlorophyll mutations were found in treatments producing a 50 to 80 per cent reduction in the mean number of M 2 seedlings per spike; in the most efficient chemical treatments, the reduction in seedling number per spike comprised between 33 and 42 per cent. Chemically induced spectra of chlorophyll mutations were quite distinct from those resulting from irradiation; they were characterized by a reduced frequency of albina and a greater frequency of xantha and viridis. If the distribution of albina, xantha, chlorina and tigrina was considered in relation to seedling number per spike, they showed a clear accumulation in lower spike fertility classes in the radiation series. In the chemical mutagen series, albina, xantha and chlorina occurred frequently in spike classes with good fertility, whilst tigrina typically accumulated in spikes with clearly reduced fertility. Evidence was found that, in chemically treated materials, the mean size of mutated sectors in M 1 spikes is much smaller than following irradiation. It was estimated that, in several M 1 spikes from chemical treatments, four or possibly more initial cells were to be made responsible for the organization of a spike. Evidence is presented that the deficit of recessives shown in M 3 by individuals heterozygous for radiation-induced chlorophyll mutations can be clearly reduced in the transition from M 3 to M 4. Five out of 1024 induced chlorophyll mutations were found to behave as dominant or semidominant.