Physiological and Molecular Characterization of Kenyan Barley Lines (<em>Hordeum vulgare</em> L.) for Abiotic Stress Tolerance and Malting Attributes

Abstract

Abiotic stresses such as drought, salinity agriculturally poor soils, and inappropriate fertilizer usage as factors of production determining yield and quality of barley for various end uses challenges the production of barley in Kenya. In order to develop appropriate breeding strategies there is a need to understand the physiological, biochemical and molecular processes that lead to observed phenotypes. The effect of increasing salt stress for 3 and 6 days was determined in 14 barley lines used as breeding lines (MN-3, MN-4, MN-5, MN-6, MN-7, MN-8, MN-12, MN-23 and MN-24), those in commercial production (Nguzo, Karne, Sabini) as well as wild progenitors of barley (Hs 2698, HOR 3301) at seedling stage. Changes in important physiological parameters ionic membrane leakage, lipid peroxidation, chlorophyll, and sucrose and GB contents in response to stress showed that reduced ion leakage and MDA and increased chlorophyll, proline, sucrose and GB contents. A reconciled physiological screening clustered Nguzo, MN-24, MN-8, MN-3 as tolerant while Karne, MN-12, MN-7, MN-4 and MN-5 as susceptible cultivars. Expression profiles of dehydrins (Dhn) in roots and leaf tissues of Nguzo, Morex, MN-24, Karne, MN-8 and MN-12 in response to dehydration and salt stress indicated that gene induction depends on the genotype, type of stress, level of stress and the type of tissue targeted. Dhn1 and Dhn9 were exclusively induced by dehydration stress and could be used as potential markers for screening for drought tolerance depending on the choice of tissue. Immunoblot analysis using anti dehydrin anti-sera confirmed the accumulation of low molecular weight DHN which was induced during dehydration and increased salt stress. <br /> Malting quality was determined by evaluating the effect of N regimes and seeding rates on yield parameters, starch content, grain protein, hordein polypetide fractions and hordein transcript profiles. There was genotype variation in yield ton/ha under field conditions in response to N treatment. HKBL 1385 recorded the highest yield of 5.1 ton/ha while Nguzo and HKBL 1512 had 3.7 and 3.8 ton/ha respectively. Starch analysis showed that HKBL 1385 recorded 278 mg/g DW while Nguzo and HKBL 1512 recorded 240 and 225 mg/g DW respectively. Grain protein analysis indicated HKBL 1512 exhibited the highest (10.4%), while Nguzo and HKBL 1385 recorded 9.7 and 9.8% respectively. N treatment caused variations in intensities in the hordein subclasses mainly C and B fractions in a genotype-dependent manner. Expression analysis of storage protein genes showed that the D, C and B hordeins genes were down-regulated irrespective of genotype or level of N treatment in the desiccated seeds, while actin the house keeping gene was constitutively expressed. Expression analysis of AMY1, BAMY1 and BG1 genes in the different physiological stages was found to be dependent on germination stage and the genotype. Increased expression of AMY1, BAMY1 and BG1 was highest in HKBL 1385 suggesting a high efficiency of starch modification of starch. Genotype variations in root morphological parameters like root mass, lateral root length and number of lateral root in response to N and P deprivation in pot grown and in vitro propagated seedling in Morex, Nguzo, MN-24, Karne, HKBL 1385 and MN-12 was evaluated. Genotype and treatment had a significant effect on the evaluated parameters. N deficiency promoted root elongation and intensive lateral formation in Nguzo and HKBL 1385. On the other hand P deficiency promoted lateral root formation in genotype-dependent manner. Cultivars tolerant to nutrient stress can better assimilate and accumulate nutrients efficiently compared to susceptible cultivars.