Genetic Divergence in Maize (Zea mays L.)

MATERIALS AND METHODS

Twenty-five genotypes of Maize (Zea mays L) were grown in randomized complete design with three replication at Regional Agricultural Research Institute, Rhamatpur, Barisal during rabi 1999-2000. The seeds of each entry were sown in two rows of 5 m long with spacing 25 x 20 cm. One plant was kept per hill after thinning. Fertilizers were applied @ 250:120:120:40:5 kg ha^–1 of N, P₂O₅, K₂O, S and Zn, respectively.

The other intercultural operations were done timely to rise the crop uniformly. Observation were recorded from 10 randomly selected plants of the each row for plant height, Ear height, Days to 50% silking, Days to maturity, Number of grains/Ear, 1000 grain weight and Yield (t ha^–1). The data were then subjected to Mahalanabis D² analysis using GENSTAT 5.0 program.

RESULTS AND DISCUSSION

The analysis of variance on the basis of mean value revealed significant differences among the genotypes for all characters. Diversity analysis for all characters were carried out.

Twenty five genotypes were grouped into seven different clusters using clustering techniques. The clustering patterns and genotype distribution are presented in Table 1. The distribution pattern indicate that maximum number of genotypes were inclined in cluster III (5) and the minimum in cluster I (3) and cluster V (2). Cluster II, IV and VI, VII included to 4 and 3 genotypes respectively. Genetic diversity is generally associated with geographical diversity, but the former is not necessarily directly related with geographic distribution. The genotypes within the same clusters were originated from different geographical regions of the world, which indicated the geographical distribution and genetic divergence did not follow the same trend which might be due to continuous exchange of genetic material among the countries of the world. Similar results was reported by Sheriffa and Shivarhankar (1992) and Shewe et al. (1972). The Intra and Intercluster values among the seven cluster are presented in Table 2. The table revealed that the inter cluster distance in most of the cases was larger than the intracluster distance. The highest inter cluster distance was observed between cluster II and III and that of lowest between cluster II and VI.

Table 1:	Distribution of 25 genotypes of maize in seven clusters

Table 2:	Average Intra and Inter cluster distances (D2) for 25 maize genotypes

Table 3:	Cluster Means for 9 characters 25 genotypes in maize
DS= Days to silking, PH = Plant height, EH = Ear height, EL = Ear length DM= Days to maturity, G/E = Grain per year. GW = Grain weight and YH= Yield per hectare

Table 4:	Relative contribution of eight characters to the total divergence in maize

The highest intra cluster distance was noticed for cluster II, III IV were far diverged from those of cluster I, VI, VII. Somayagullu et al. (1970) reported that the clustering revealed instability due to relatively lesser divergence, where as the widely diverged cluster remained distinct in different environment. This result was also supported by Raut et al. (1985). In the cluster II, III and IV were highly diverge. So, they would be more stable. Therefore the genotypes belonging to the distant cluster may be used in hybridization program for obtaining a variation.

The cluster means of eight characters are presented in Table 3. Cluster III showed highest mean values for number of grain/ear and 1000 grain weight. In case of days to 50% silking, cluster IV had higher mean values. In case of days to maturity cluster VII was earlier. High mean values of plant height were recorded in cluster I and lowest in cluster V. Cluster V had lowest mean values for plant height and ear height. Endang et al. (1971) stated that clustering pattern could be utilize in choosing parents for cross combination which likely to be generate the highest possible variability for the effective selection of various economic traits.

Contribution of the characters towards divergence are presented in Table 4. The Canonical variate analysis revealed that, the vectors (vector I and II) for plant height and days to maturity were positive. Such results indicated that these two characters contributed maximum towards diversity of the genotypes. So, It is encouraging that the divergence in the present materials due to these two characters will offer a good scope for improvement through rational selection.