Heterosis and combining ability for morphological, yield and quality characters in coffee (Coffea arabica L.) Hybrids

Abstract

Increasing coffee productivity is one of the highest national priorities of the rural development policy of Ethiopia; and thus, the choice of promising genotypes from diverse genetic base and subsequent utilization of hybrids is one of strategies of improving productivity. A half diallel analysis involving five parents, ten F1 hybrids and one check hybrid was studied for several quantitative and quality traits to generate information on heterosis and combining ability. The genotypes were evaluated in a randomized complete block design (RCBD) with three replications at Melko, Metu and Tepi research centers. The analysis of variance revealed highly significant difference among genotypes at (p<0.01) for almost all characters. This consistent significant difference for different traits suggests the presence of genotypic difference among parental lines and hybrids evaluated. There was consistently high overall mean of the hybrids compared to the parental mean value for yield and other morphological characters. In contrast, the mean value of hybrids was less than the mean value of parental lines for quality characters. Heterosis over mid parent (MP) and over better parent (BP) for yield ranged 12.8 to 57.8 and 12.1 to 41.8% respectively. Cross combinations P1XP2, P1XP3, P2XP4 and P3XP5 showed relatively high positive heterosis MP and BP for most important favorable characteristics. Hybrids P2XP4 and P1XP5 had comparable yield result with the commercially released check hybrid showing respective positive heterosis of 11.5% and 5.1 % over check hybrid. Even though the heterosis over check hybrid was not significant, these two hybrids do have better yield and can be used as candidate after repeated performance evaluation across locations for quality and resistance to CBD and CWD. The BP and MP heterosis for the majority of quality characters was negative. This result may give a clue for the dominance of unfavorable quality character over favorable characteristics. Yet this calls for further study of quality inheritance by crossing between known top quality parents with that of known poor quality parents. Both GCA and SCA mean squares were highly significant for yield indicating both additive and non-additive gene actions are important for the inheritance of this economic trait; however the higher the percentage relative contribution of SCA over GCA indicates the predominance of nonadditive gene action. Both the additive and non-additive gene actions were involved in the control of the characters studied for fruit length, fruit width, fruit thickness, bean length, bean width, bean thickness and 100-bean weight similar to aforementioned trait. Parental line P4 found to be the best combiner for stem girth, length of first primary branch and internode length showing significant and positive GCA effects for these traits; this parent may contribute favorable additive genes to its progenies for the synthesis of vigorous hybrids. Parental lines P4 and P5 were found good general combiners for important economic trait yield showing highly significant GCA effects in across locations GCA effects. These parental lines may have good prospect for the inclusion in the breeding program for yield improvement in synthesis of new high yielding hybrid varieties. Parental line P3 showed highly significant and positive GCA effect for flavor and overall quality; higher positive value for body and physical quality character shape & make. This gives an indication for the possible contribution of this parent in crossing for quality breeding program. Nearly 90% of the crosses showed positive SCA effects for yield out of which five crosses: P3XP5, P1XP5, P2XP5, P2XP4 and P3XP4 showed positive and significant SCA values for yield indicating that these crosses were good combinations. Crosses with higher values of SCA effects also showed higher value of mean yield performance, indicating good correspondence between SCA effects and mean yield. Hence such cross combinations could effectively be exploited in hybrid coffee breeding program