IDENTIFICATION OF DROUGHT TOLERANT KENYAN BRACHIARIA ECOTYPES USING DROUGHT TOLERANCE INDICES

Abstract

Drought is one of the major abiotic stress factors limiting agricultural productivity globally. Brachiaria also known as signal grass is a native of sub-tropical and tropical Africa and important in livestock production. The grass has many advantages including; high biomass, high nutritional value, adaptation to drought and low fertility soils, sequestration of carbon, enhanced nitrogen uses efficiency and low greenhouse gas emissions. Emergence of climate change with increased global temperatures has led to prolonged drought which has adversely affected the improved Brachiaria hybrids. Locally available ecotypes are a rich source of unique genes and characteristics that could be key in developing drought resilient hybrids. The objectives of this study were to i) assess the effectiveness of various indices in selection of drought tolerant Kenyan Brachiaria ecotypes, ii) evaluate the relationship between the indices and iii) to identify high yielding and stable ecotypes under stressed condition. The design of the experiment was completely randomized design (CRD) with three replications in a factorial arrangement (3 x 25). A total of 11drought tolerance indices; tolerance (TOL), stress Tolerance Index (STI), mean productivity (MP), yield stability index (YSI), Geometric Mean Productivity (GMP), stress susceptibility index (SSI), Yield Index (YI), harmonic Mean (HM), drought intensity index (DII), modified stress tolerance k1 and modified stress tolerance k2 were calculated based on shoot biomass production under non-stressed (YP) and stressed (YS) conditions. Rank means, rank sum and standard deviation were also used to identify the tolerant materials. In the previous experiment, various physiological parameters were scored which included; leaf relative water content, relative chlorophyll content using SPAD -502 Chlorophyll meter (Minota Co), leaf fresh weight, leaf dry weight and leaf relative water content. Relative water content was also estimated and comparative scores were done between control, medium and extreme or water deficit experiments. Based on all the indices and ranking, BrK 1, BrK 6, BrK 7, BrK13 and BrK 18 were the most tolerant in stressed condition. These ecotypes can be recommended for planting in areas prone to drought. More studies on the identified tolerant ecotypes are essential to ascertain whether the materials hold unique genes that could later be introgressed into various breeding schemes to confer tolerance.