Effect of induced awn mutations on yield in wheat

Abstract

From comparisons between sister lines of the same parental derivation segregating in awn character and from experiments using backcrosses, awns have been found to have a positive function as regards grain yield in varieties of bread wheat. A spontaneous awned mutant isolated by Mackey in the variety JScandia III outyielded the parent strain in trials carried out over a period of 5 years. Awns have been supposed to influence yield by increasing assimilation and transpiration and thereby the size of the grains. Fully awned mutants frequently occur when varieties belonging to the tipped 1 class of Watkins and Elleron (that is, awns 1-2 cm. in length and confined to the uppermost spikelets) are treated with both ionizing radiations and chemical mutagens. Several such mutants were found by us in the M₂ progenies of the varieties N.P. 799 and N.P. 809 treated with phosphorus-32 and sulphur-35 (both 5 μc. per seed), X-rays (16,000 and 22,000 r.) and different dosages of fast and thermal neutrons. Both these varieties have the dominant epistatic gene B1 on chromosome 5A (nomenclature of Sears) and the established awn mutations behaved as monogenic changes in genetic studies. The mutants had the somatic chromosome number 42 and no prominent change could be detected in their karyotypes.