Njoroge Janet Wamuyu^1,, Wamalwa Mercy Nasimiyu², Muga Charles Ope¹

Wheat is ranked second as the most consumed and produced food across the globe. Over the years, wheat production has been faced with biotic and abiotic factors, leading to low wheat production and quality. As a result, it has attracted many researchers aiming to improve productivity and quality through mutation breeding. Although there is significant literature on morphological, biological and chemical properties of wheat under the influence of gamma radiations as physical mutagens, a gap exists on how gamma radiations influences strength of the wheat stem, a mechanical property. Njoro BW 11 wheat seeds were irradiated with dosages of 80, 100, 120, 150, 200, 250 and 300 Gy from a Cobalt 60 gamma source. Seeds were then sown, and at the maturity stage, samples of wheat straw from four randomly selected plants were cut from the second internode for the first and second mutant generations. Using the universal testing machine, the samples were subjected to tension force, where the stress-strain curves, stress, ultimate force, elongation percent and break distance were obtained automatically. S-shaped stress-strain curves were obtained. Analysis of variance showed statistical significance between ultimate force and treatments (p = 0.00478), and an interaction effect exists between treatment, mutant generations and ultimate force (p = 0.01456). Stress-strain curves showed wheat straws are elastic in nature with little or no plastic deformation. In conclusion, wheat straw mimics collagen fibers and structurally resembles biological tissues. Gamma radiations have significant effect on straw strength, where dosages of 150 and 200 Gy produced straws with high ultimate force and stress. Therefore, mutations by gamma radiation should maintain moderate dosages (150-200 Gy) to prevent the development of weak wheat stems in Njoro BW11, which may potentially predispose wheat plants to lodging.

Gamma radiations, mechanical properties, wheat (Triticum aestivum L.), ultimate force, stress-strain curves