The assessment of the genetic diversity present in Jatropha curcas L germplasm cultivated in Kenya as a potential biofuel feedstock
Jatropha curcas L has the potential of becoming an important feedstock for biodiesel and bioenergy in Kenya. There has been a concerted effort in collaboration from the sector industry to promote large scale farming of jatropha. However, to date thti'e has been no program to improve J. curcas traits and thus its full potential has not been realized. Hence knowledge on the presence of genetic diversity and genotype x environment (GxE) interactions of J.curcas germplasm are vital source for the genetic improvement of seed yield, seed oil quality and quantity as well as other agronomic traits for viable commercial exploitation of the plant. The objective of this study was to assess genetic diversity and evaluate the effects of genotype-environment (GxE) interaction of the currently grown genotypes. A field trial consisting of 49 genotypes was laid out in a lattice design of two replications in two contrasting agro-ecological environments, namely Thika and Kibwezi for two years. Based on the multivariate Mahalanobis D2 statistics, the genotypes were grouped into four clusters: III, IV, I and II comprised 20, 14, 9 and 6 genotypes, respectively. The analysis further indicated that the genotypes of common geographical origin or same location were grouped into different clusters, suggesting a lack of relationship between genetic and geographical diversity. The highest inter-cluster distance was observed between II and IV followed by I and III which may serve as potential parents for new gene combination. It has been shown that leaf type (22.12%), branching (19.24%) and days to flowering (12.10%) contributed most to the genetic divergence among the genotypes. The Eberhart and Russell stability method was used to measure the performance of yield components of the 49 genotypes. Environmental variance influenced the performance of genotypes for all the traits measured and genotype x environment interactions was important in determining their performance. The environmental parameters that were important in influencing performance were minimum temperature and soil pH while the stability parameters that were important for adaptation were height and leaf type for ~i= I; leaf type, days to flowering and oil content for ~i> I; while height, leaf type, days to flowering, seed yield and oil content for ~i<l. Genotypes KJI, KJ2, KJ5, KJ7, KJlO, KJIl, KJ15, KJ18, KJ20, K22, KJ23, KJ24, KJ27, KJ28,KJ3l, KJ34, K36, KJ39,KJ40, KJ44, K47 and KJ49 showed high mean values , regression coefficients close to unity and least mean square deviation from regression for oil content in high responsive environments, whereas genotypes KJ4, KJ12, KJ16, KJ17, KJ25, KJ29, KJ32, KJ 33 and KJ 41 would be stable and have high mean oil yields under low-responsive environments such as the Kibwezi site. Keywords: Genetic diversity, Jatropha curcas, multivariate analysis, Stability method.