Studies on genetic variability, inheritance and heterosis in pepper (Capsicum annuum L.)

[摘要] English: The knowledge of genetic similarity and dissimilarity among crop cultivars is of vitalimportance for the plant breeder. The genetic variability of 39 pepper (Capsicum annuumL.) genotypes of different varietal groups that were obtained from different geographicalorigins was studied using morphological traits and amplified fragment lengthpolymorph isms (AFLP) markers. Both methods showed moderately high geneticdistances among the different genotypes indicating genetic diversity among the totalgenotypes. However, when a comparison was made between the Ethiopian and the exoticgenotypes, the mean genetic distance among Ethiopian genotypes was lower than thatbetween the Ethiopian and the exotic ones. The dendrogram based on morphological dataclustered the genotypes on the basis of fruit size and was generally consistent withdifferent varietal groups. Similarly, with AFLP data, genotypes with similar fruit sizesclustered together.Combining ability and heterosis estimates are important to determine the direction andgoals of a breeding program. Seven diverse parental lines were selected from the 39genotypes and crossed in a half-diallel method. The parental lines and their 21 FI hybridswere evaluated to estimate the combining abilities and genetic effects determining theheritability of various characters, and to determine heterosis of hybrids over mid-parent,high-parent and standard checks for various characters. Generally, significant general(GCA) and specific (SCA) combining abilities were observed for all measured charactersindicating the presence of both additive and non-additive gene actions. However, additivegene action is more important than non-additive gene action, as the magnitude of GCAeffects was much higher than SCA effects. The estimates of predictability ratios for fruitlength, fruit diameter, fruit weight, pericarp thickness and fruit number were closer tounity, suggesting the possibility of predicting progeny performance based on parentalGCA alone. High heritability both in broad and narrow senses was also recorded for thesecharacters indicating their inheritance is less influenced by the environment.Substantial heterosis over mid-parent, high-parent and the standard check was observed.Many crosses demonstrated high heterosis for fruit yield, fruit diameter, mean fruitweight and pericarp thickness over the standard check. For the traits of earliness (days toflowering, days to maturity and fruit maturation period), the overall mean mid-parent,high-parent and standard heterosis were negative. Thus, it can be suggested that with theproper choice of parents, pepper hybrids that have higher yield potential, good fruitcharacteristics and early maturity can be developed to increase pepper productivity inEthiopia.Genetic diversity between parents may contribute positively to both heterosis andtrangressive segregation. The relationship between genetic diversity of the seven parentallines, and heterosis and hybrid performance was assessed. The genetic diversity wasmeasured using 15 morphological traits and six AFLP primer combinations. Clusteranalysis using the two genetic distance measures generally grouped the seven parentsdifferently. Morphological distance was negatively correlated only with mid-parentheterosis (MPH) for days to flowering and days to maturity. The correlations of AFLPmeasured genetic distances with mid-parent and high-parent heterosis were non significantfor all characters with the exception of fruit diameter and proved to be of nopredictive value.In addition to single crosses, three-way and double crosses can be used to overcome thelow productivity of inbred lines. It is hypothesized that yield stability is high in three-wayand double-cross hybrids owing to higher genetic heterogeneity as compared to singlecross hybrids. Twenty-six genotypes, including six inbred lines, eight single, six threewayand six double crosses were evaluated for yield and other agronomic characters intwo environments using a randomized complete block design with three replications. Thethree categories of hybrids performed differently across the environments and showedhigh variations for the majority of characters studied. Three-way crosses gave the highestmean fruit yield per plant followed by double crosses. The two types of hybrids were alsomore stable than the single crosses. In general, three-way crosses showed promisingperformance for the studied traits. The highest estimates of mid- and high-parentheterosis were also observed in the three-way and double cross hybrids. Therefore, thelow productivity of local pepper cultivars in Ethiopia can be overcome throughdeveloping and utilizing three-way and double cross hybrids.

[发布机构] University of the Free State