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Genetic variability, genetic gain and relationships of yield and yield components in castor (Ricinus communis L.)

A.D.Halilu, D.A.Aba, J.O.Ogunwole

Thirty (30) castor accessions were evaluated in 3 locations in 2011 and 5 locations in 2012 wet seasons in the Nigerian savannas. Data were collected for yield and the yield components: Peduncle length (PL), Number of nodes to the first raceme (NFR), Number of capsules in the first raceme (Noc), Number of secondary branching (NSB), Number of spikes/plant and Plant height at harvest (H@H). Analysis of the data showed that the GCV was low for all the yield components but moderate for yield. The PCV was also low for PL, NFR and height, while it was moderate for NOC, NOSB, No.S/p and Yield.Amongst the yield components height at harvest had the highest difference between GCV and PCV (RD=71.4%) while all the others were also high except No.S/p (RD=36%). These indicate that the observed variations for the traits were mostly due to environment factors. Moderate broad sense heritability coupled with moderate Genetic gain (GA) were observed for NOSB, No.S/p and Yield indicating that these traits are mainly controlled by additive type of genes and that direct selection for these traits could be effective. However, moderate heritability coupled with low GA was observed for PL. Thus this character is controlled by non-additive genes (dominance and epistasis). Low heritability with low GA observed in height and NFR indicates environmental control on the expression of these traits. Location by traits biplot revealed that NOC, NFR, Height at harvest, PL and yield had stronger association. The Trait Association by Environment (TAE) biplot grouped the eight environments into three distinct groups: the first group consisted of three environments, Kadawa, Talata mafara and Bakura in the Sudano-sahelian savanna, the second group consisted of Samaru2012 in the northern guinea savanna and Minjibir of the sudan savanna, the third group consisted of Geshere and Samaru kataf in the southern guinea savanna and Samaru2011 of the northern guinea. The first group sites were characterized by strong positive associations of NFR vs. No.S/p, NFR vs. NOC and height vs. yield. This implied that accessions with higher number of nodes to first racemes had higher yield at these sites. The second group were characterized by strong positive associations of NOC vs. Yield, height at harvest vs. yield. Therefore, at these locations, taller genotypes and those with more number of capsules in first raceme tended to give higher yields. The third group were characterised by strong positive associations for NFR vs. NOSB and NOC vs. Yield implying that genotypes with higher NFR, NOC and NOSB tended to have higher yields in these sites.