REACTION OF KENYAN BARLEY (Hordeum vulgare) CULTIVARS TO SCALD (Rhynchosporium secalis) AND ITS EFFECT ON YIELD AND SEED QUALITY

Abstract

Scald caused by Rhynchosporium secalis (Oudem), is an important disease in Kenya.Three experiments were conducted to determine the effect of scald on the yield, grain and seed quality of barley as well as the role of seed borne inoculums in the transmission of the disease. In the first experiment, 143 barley genotypes were planted in a nursery and evaluated for resistance or susceptibility to scald at Mau Narok and Timau during the 2012/2013 barley growing season. Data on disease reaction was taken during the crop growth stages and grain yield for each entry taken at maturity. The data was analyzed to relate the effect of scald infection on grain yield and quality of the grain. Approximately 36 percent of the test lines were resistant to moderately resistant to scald. Cultivar Nguzo, HKBL 1512-5, Steptoe and QSMO005 were among those evaluated as resistant to scald. The genotypes that were resistant to scald gave higher grain and thousand kernel weights per plot in comparison to genotypes that were susceptible. In experiment two,12 barley varieties with diverse field resistances to scald were investigated in a field trial at the two sites, each in small plot in a randomized complete block design in a split plot layout (sprayed with fungicide and unsprayed). Grain yield of each of the two sub plots of the twelve varieties was taken at maturity and analyzed to assess the yield losses due to scald. Susceptible varieties gave a reduced grain yield and a significant yield loss per plot when not protected with fungicide spray. Cultivar Sabini, evaluated as susceptible, recorded the highest yield loss of 18.1 percent. Scald resistant Cultivar Nguzo and HKBL 1512-5 had the lowest yield losses of 3.81 and 3.22 percent respectively when not protected with fungicide spray. Finally, a seed-seedling transmission experiment was carried out in a greenhouse at KALRO-Njoro to determine the potential role of seed borne R. secalis as primary inoculum in the transmission and spread of scald. Seed infected with R.secalis at four levels of seed borne infection (nil, 20, 50 and >75 percent) was planted in plastic pots on sterile soil in a completely randomized design in two sub samples: seed-treated and not seed-treated with fungicide each in two replicates. Data on seed-seedling transmission was taken between plant growth stages 21 and 31. The rate of seed borne-seedling infection increased as the level of seed borne infection increased for the untreated seed category. The >75 percent seed infection category gave the highest rate of seed-seedling transmission. Seed treatment resulted in reduced rates of seed-seedling transmission except for the > 75 percent seed infection category. On conclusion of these experiments, some scald resistant barley genotypes were identified. The amount of yield losses and seed and grain quality decline to barley due to scald depends on the resistance or the susceptibility of the variety. Scald resistant varieties suffer little yield losses when attacked by the disease. Seed borne inoculums of R. secalis may act as a major source of infection of scald in the field. Seed dressing with appropriate fungicide is only beneficial for moderately infected seed.