Genetic diversity and post flowering drought tolerance analysis of Eritrean sorghum [sorghum bicolour (L) Moench] landraces using morpho-physiological and molecular markers

Abstract

Sorghum (Sorghum bicolour (L.) Moench) is the most important staple food crop in Eritrea, mainly used for home consumption in the form of injera, bread, porridge and local alcoholic beverages. Sorghum grown under rain-fed conditions is usually affected by drought stress at different stages resulting in negative effect on yield. The assessment and quantification of morpho-physiological diversity for the traits contributing towards drought tolerance at these stages is of critical importance. The aim of this current study was to evaluate and identify sorghum landraces for post flowering drought stress tolerance and assess Eritrean sorghum landraces for diversity.The study was done in two parts: A two year field experiment on evaluation of sorghum landraces for post flowering drought tolerance in Eritrea, and a laboratory study on sorghum genetic diversity using SSR markers in Kenya. In a randomized field design experiment a total of 100 sorghum genotypes (96 landraces and 4 checks) were evaluated off-season (February – June, 2013) for drought tolerance and variation in morpho-physiological traits. Twenty genotypes selected from this rapid screening were proceeded to a replicated field evaluation trial at the Hamelmalo College field station, Eritrea in the off-season of March – June, 2014 using a split plot design and irrigation levels as the main plots and genotypes as the sub plots. Data collected on 16 different morpho-physiological traits were analysed using the analysis of variance, drought tolerance indices, estimation of genetic variability and heritability and principal component analysis. In the laboratory experiments the genetic diversity analysis of 98 Eritrean and 42 regional sorghum landraces was conducted using SSR markers. Observation showed that the treatments under stress and irrigated conditions had significant genotypic differences at P<0.05 - <0.001. Based on grain yield, positive and significant correlations were recorded between yield under irrigated (Yi) and each of the parameters yield under drought stressed (Yr) conditions, mean productivity (MP), geometric mean productivity (GMP), and stress tolerance index (STI). The biplot and cluster analysis also grouped clearly the tolerant and susceptible landraces based on drought tolerance indices. High magnitude of phenotypic and genotypic coefficient of variations for plant height, harvest index and biomass as well as high heritability for days to flowering, panicle length, days to maturity and over all agronomic score were recorded.. Principal component (PC) analysis showed that the first 4 PCs having eigen values >1 explained 74.6% of the total variation. Based on these analyses and drought indices, seven (7) accessions namely, EG 885, EG 469, EG 481, EG 849, Hamelmalo, EG 836 and EG 711 were identified as promising genotypes for post-flowering drought tolerance that could be used by breeders in sorghum improvement programmes and small scale farmers. The SSR genotyping analysis also revealed high genetic variation among the landraces, especially among individual populations. Besides this, the results indicated that the landraces had unique alleles and higher levels of allelic richness with close genetic distance and isolated clustering that could indicate the Eritrean germplasm have not been introgressed with foreign genes and are a valuable resource for future breeding programmes.

Key words: Biplot analysis, Drought stress, Genetic diversity, Principal Component Analysis, Sorghum, SSR markers