Genetic Diversity Studies in Newly Derived Inbred Lines of Maize (Zea Mays L.)  

Udaykumar Kage1 , Deepa Madalageri1 , Laxman Malakannavar2 , Prakash Ganagashetty1
1. Department of Genetics and Plant Breeding, University of Agricultural Sciences, Dharwad, Karnataka-05, India
2. Department of Genetics and Plant Breeding, University of Agricultural Sciences, GKVK Bangaluru, Karnataka-05, India
Author    Correspondence author
Molecular Plant Breeding, 2013, Vol. 4, No. 9   doi: 10.5376/mpb.2013.04.0009
Received: 28 Jan., 2013    Accepted: 13 Feb., 2013    Published: 15 Feb., 2013
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This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Udaykumar K., et al., 2013, Genetic Diversity Studies in Newly Derived Inbred Lines of Maize (Zea Mays L.), Molecular Plant Breeding, Vol.4, No.9 77-83 (doi: 10.5376/mpb.2013.04.0009)

Abstract

The present investigation was carried out to know the genetic diversity among the new inbred lines of maize during Kharif 2011. In this experiment, seventy nine inbred lines and three checks were evaluated and observations were recorded for thirteen quantitative traits. Analysis of variance revealed that highly significant difference among all inbred lines. Inbred lines were grouped into fourteen clusters, indicating the presence of genetic diversity. The cluster I is having highest number of genotypes (67). The maximum inter cluster distance was observed between clusters II and XII (22.41) and highest intra cluster distance was in cluster XII (5.46) and also wide range of variation was observed in cluster mean performance for the characters studied. These genetically diverse inbred lines can be further used for developing superior hybrids and can also be utilized in developing synthetics and composites.

Keywords
Genetic diversity; Variance; Inbred lines; Cluster; Maize

Maize (Zea mays L.) is the third most important cereal crop in the world after rice and wheat. It is cultivated in a wider range of environments than wheat and rice because of its greater adaptability. India is the fifth largest producer of maize in the world contributing three per cent of the global production. In India, it is grown over an area of 8.55 million hectares with total production of 21.73 million tones (Anon, 2011). Karnataka stands first in area (1.287 m ha), it stands second with respect to production (4.44 mt) and productivity (3633 kg/ha) of maize next to Andhra Pradesh (Anon, 2011).

Different methodologies have been used to characterize genetic diversity in the maize germplasm, which are morphological characters, pedigree analysis, heterosis and the detection of variation at the DNA level using markers. In present study we did based on morphological characters.
Germplasm, which is a prerequisite for any breeding programme, serves as a valuable source material as it provides scope for building of genetic variability. Study of variability heritability and genetic advance in the germplasm will help to ascertain the real potential value of the genotype. Mahalanobis D2 statistical analysis is very useful tool in studying the nature and cause of diversity prevalent in the available germplasm. Genetic diversity plays an important role in plant breeding because hybrids between lines of diverse origin display a greater heterosis than those between closely related strains. For example in maize, increased genetic difference between inbred lines resulted in a greater heterosis in their hybrids. However, the maximum heterosis generally occurs at an optimal or intermediate level of diversity.
Results and Discussion
For crop like maize, the strategy of developing superior hybrids depends on genetic diversity present in the available inbred lines has immense value on crop improvement for trait of interest. For development of superior hybrids, one needs to select superior inbreds which possess higher directional dominance, genetic diversity and allelic differentiation for most of the traits. The genetic divergence can be estimated by using an effective statistical tool, Mahalanobis D2 statistics, which gives clear idea about the diverse nature of the population. The analysis of variance carried out for the yield and its component characters among 82 inbred lines was presented in Table 1. The results revealed that all the genotypes differed highly significant for all characters.

 
Table 1 ANOVA for yield and yield related characters in 82 inbred lines

The knowledge of genetic diversity among the genotypes is essential for selecting parents for hybridization programme, especially in a cross pollinated crop like maize. Genetic diversity considered to be an important tool for realizing heterotic response in F1 and a broad spectrum of variability in segregating generations.
The D2 analysis carried out involving 82 inbreds for 13 characters revealed that altogether 14 clusters have been formed (Table 2, Figure 1), wherein cluster I had a maximum of sixty seven genotypes, cluster XII have three genotypes and remaining clusters II, III, IV, V, VI, VII, VIII, IX, X, XI, XIII and XIV were all monogenotypic. The genotypes which are within the clusters by and large exhibit a narrow range of genetic variability.
 
 
Table 2 Distribution of 82 inbred lines into different cluster


 
Figure 1 Dendrogram showing clustering by Tocher’s method

While studying contribution of individual characters towards divergence among 13 characters studied (Table 3), plant height (30.65%), days to 75% brown husk maturity (22.55%) and ear height (16.65%) contributed high for divergence, so these characters should be given weightage, for selecting diverse parents for breeding programme.

 
Table 3 Per cent contribution of character towards divergence in 82 inbred lines

Whereas, other characters like grain yield per hectare (8.7%), number of kernels per row (6.14%), days to 50% tasseling (5.03%), 100-grain weight (2.11%), number of kernel rows per ear (1.96%), ear girth (1.6 %), shelling percentage (1.6%), ear length (1.48%), fodder yield per hectare (1.39%) and days 50% silking (0.15%) contributed very little for divergence. More et al (2006) reported that leaf area per plant, plant height and days to 50% flowering were the major contributors towards divergence, while studying forage maize and more than 90% contribution to divergence was from days to 50% flowering, plant height and number of kernels per row. This contradicted the present investigation.
Based on the intra and inter cluster distances using D2 values (Table 4), the maximum intra cluster distance was recorded within cluster XII (5.46), while it was lowest for the genotype of cluster I (4.73) indicating that the genotypes of these clusters might be differing marginally in their genetic architecture and it can be considered that the genotypes belonging to clusters II and XII (22.4) having highest inter cluster distances followed by cluster IV and XII (22.2), clusters IX and XII (21.9) and cluster III and XII (21.57), suggesting that hybridization between divergent groups may lead to higher magnitude of heterosis for the characters concerned. However, many earlier studies are of the opinion that crosses between too divergent groups of parents are less successful in achieving required magnitude of heterosis (Arunachalam et al., 1984). On the other hand, the crosses between genotypes exhibiting a narrow range of variability as revealed by short inter cluster distances may not be worthwhile to get desired extent of heterosis. This is probably because of parents with similarity may possess common alleles governing the characters and may not help in complementation in the hybrid combination. Similarly, parents exhibiting greater divergence may also lack nick well ability. This is specially being observed in distant crosses (interspecific) for yield related traits. However, many studies are on the record that whenever parents with moderate divergence are used for crossing, throw out significant level of desired heterosis (Arunachalam et al.,1984; Singh et al., 2005).

 
Table 4 Average intra and inter cluster distance values of inbred lines

Different characters as revealed by cluster mean analysis (Table 5) indicate that the contrasting genotypes for days to 50% tasseling and for days to 50% silking are being grouped in clusters III, IV, VII and XII, for plant height in clusters II and XII, for ear height in clusters XI and XII, for days to 75% brown husk maturity in clusters III and XII, for ear length character in clusters IX and VIIII, for ear girth in clusters IV and XII, for no of kernel rows per ear in clusters IV and XIII, for no of kernels per ear in clusters XIII and VIII, for 100-grain weight in clusters IV and X, XIII, for grain yield per hectare in clusters VII and VIII, for shelling percentage in clusters IX and V and for fodder yield in clusters VII and IV.

 
Table 5 Cluster means of inbred lines for 13 characters

However, it is always desirable to look for genotypes having more than one desirable trait and belonging to different clusters as in case of clusters XII, which is being grouped with genotypes for days to 50% tasseling, days to 50% silking, plant height, ear height, days to 75% brown husk maturity, ear girth. Whereas, cluster VIII possessed genotypes with high no. of kernel rows per ear, no of kernels per row and grain yield per hectare.
Materials and Methods
The present investigation was carried out at All India Co-ordinated Maize Improvement Project, Agricultural Research Station, Arabhavi during the Kharif 2011. The experiment comprised of newly derived 79 inbred lines of tropical origin which were available in All India Co-ordinated Maize Improvement Project. These new inbred lines were derived from different source populations by continuous inbreeding. These 79 inbred lines were used along with three testers viz., KDMI-10, KDMI-16 and CI-5 to study the genetic diversity. All 82 inbred lines were grown and experiment was irrigated throughout the growing season and cultural operations, fertilization and weed control were accomplished according to normal field practices. The experiment was replicated twice in a randomized complete block design. The experimental unit was two rows for each entry, 4 m row length and 75 cm apart, with intra row distance of 20 cm. The observations were recorded from ten plants randomly selected from each plot for 13 quantitative traits viz., days to 50% tasseling, days to 50% silking, plant height, ear height, days to 75% brown husk maturity, ear length, ear girth, number of kernel rows per ear, number of kernels per row, 100-grain weight, grain yield per hectare, shelling percentage and fodder yield per hectare. Diversity analysis was done using Mahalanobis D2 statistics and inter cluster distance was calculated by the formulae described by Singh and Chaudhary (1977).
Reference
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