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straw yield per plot, harvest index, dry straw weight, panicle length and plant height showed high heritability estimates indicating the least influence of environment on these characters.
These findings were in agreement with the reports made earlier in rice by (Okelola, Adebisi, Kehinde, & Oluwole, 2016) for days to 50% early flowering, plant height, grain yield per plot, Atanu and Sabesan (2010) for days to 50 percent early flowering, days to maturity, plant height, grain yield per plot, Jayasudha and Deepak (2010) for days to 50 percent early flowering, spikelets per panicles, grain yield per plot, and harvest index, Karthikeyan et al.(2010) for days to maturity, plant height, panicle length, 1000 grain weight, grain yield per plot, dry straw yield per plot and harvest index, Naresh et al. (2012) for days to 50 percent early flowering, days to maturity, plant height, 1000 grain weight and grain yield per plot and Devi and Kamireddy, (2015) for days to 50 percent early flowering, days to maturity, plant height, panicle length, spikelets per panicle, 1000 grain weight and harvest index. Heritability estimates are generally influenced by; the type of genetic material, sample size, method of sampling, the way the experiment is conducted, method of calculation and effect of linkage etc., therefore, their scope was restricted (Lal and Chauhan, 2011).
Heritability values coupled with genetic advance would be more reliable and useful in predicting the gain under selection than heritability estimates alone. The characters such as yield per plot, harvest index, days to maturity and days to early flowering exhibited high heritability coupled with high genetic advance, indicating that most likely heritability was due to additive gene effects and selection may be effective for these characters. Rita et al. (2009) and Jayasudha and Sharma, (2010) observed similar results for days to maturity, and Devi and Kamireddy, (2015)for harvest index and yield per plot. High heritability coupled with moderate genetic advance are normally classified as indicating that additive gene action were present. In this study all the characters which showed high heritability coupled with high genetic advance such as days to maturity, spikelets per panicles and days to early flowering indicated high genetic control. Since in self-pollinated crop homozygous lines are developed, the dominance component will not contribute to the phenotype of homozygous lines derived from a population. Consequently, in such cases additive and genetic variance are important for variation.
Earlier reports also indicated high genetic advance for days to maturity (Jayasudha & Sharma, 2010) and Karthikeyan et al., 2010), 1000 grain weight (Subudhi and Dikshit, 2009;
Karthikeyan et al., 2010 and (Devi and Kamireddy, 2015) and grain yield per plot (Karthikeyan et al., 2010 and (Vanniarajan et al., 2012). High heritability coupled with high genetic advance as percent of mean was recorded for grain length, grain width, dry straw weight, and yield per plot and harvest index indicating that most likely the heritability is due to additive gene effects,
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which might cause variations among varieties / genotypes, and selection may be effective for these characters. Similar kind of observations were reported by Sinha et al. (2004) for yield per plot, Karthikeyan et al. (2010) dry straw weight and harvest index, (Prajapati et al., 2011) for grain length and grain width, Venkata et al. (2011) for harvest index, and Parikh et al.
(2012) for yield per plot and dry straw weight.
The characters early vigour and bacterial leaf blight exhibited moderate heritability and moderate genetic advance as percent of mean suggesting that both additive and non-additive gene effects were involved for variations of these characters, so selection and heterosis breeding both may be effective for improvement of these traits. These results were in agreement with the earlier findings of Sinha et al. (2004) for early vigour, Karthikeyan et al.
(2010) for early vigour.
3.5.2 Efficiency of indirect selection for grain yield
According to Falconer, (1960) RSE of greater than unity (1) would permit use of a secondary trait for indirect selection for a primary trait such as grain yield. In this study, no trait had an RSE greater than 1. However, harvest index had an RSE of 0.83, which is close to unity. This trait (harvest index) seems promising and should be given top priority during selection for grain yield improvement. Other traits influencing grain yield but with moderate RSE should not be ignored during selection for grain yield improvement; these traits include days to maturity (0.59), days to early flowering (0.53) and dry straw weight (0.50).
3.5.3 Diversity and grouping
The amount of diversity available in the crop decides the success of any crop improvement programme. Assemblage and assessment of diversity in the germplasm is thus essential to know. In the present investigation, 30 genotypes of rice were studied for their diversity with respect to 16 important quantitative characters.
The eight clusters that were observed in this study indicate the existence of high level of diversity among the genotypes. Cluster I consisted of six accessions, cluster II consisted of two genotypes, cluster III consisted of two genotypes, cluster IV had one genotype, cluster V consisted of 10 genotypes, cluster VI –five genotypes, cluster VII- three genotypes and cluster VIII- one genotype.The genetic distances and the dendrogram showed that G14 and G19were the most similar pair, followed by G6 and G9 which were also highly similar to each other;
while the dissimilar genotypes were G30 and G28 followed by G28 and G13. The dissimilar genotypes can be used for hybridization to bring heterosis among the genotypes. Similar genotypes such as G14 and G16 could be sharing common parents in their pedigrees. A
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breeding programme may be initiated in which individuals in different clusters are crossed and significant heterosis would be expected.