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082			_a630.28 _bJOS/GE
100			_aJoseph C A
245			_aGenetic Studies in Sweet Potato (Ipomoea Batatas(L.)Lam.) A Biometric Approach
260			_aVellayani _bDepartment of Agricultural Botany, College of Agriculture _c1979
502			_bPhD
520	3		_aIn a varietal evaluation of 40 varieties of sweet potato all the 15 characters studied showed highly significant differences among the varieties. This was also expressed in the higher phenotypic and genotypic coefficients of variation. The high degree of variability especially in tuber characters offers scope for recombining desirable genes from different varieties. Tuber yield showed significant positive correlation with number of tubers, tuber diameter and harvest index, and significant negative correlation with internode length, vine length and top weight. Path-coefficient analysis revealed that among the first order components of tuber yield, tuber diameter, length and number and top weight had high positive direct effects while leaf area index had a negative direct effect. A comparison of the direct and indirect effects of first and second order components revealed that while selecting for high yielding types, a balanced approach may be adopted with regard to the different yield attributes. Genetic divergence in the available germ plasm was estimated using the Mahalanobis' D2 statistic and based on this the 40 varieties were grouped into 12 clusters. The number of verities in each cluster ranged from one to eight. The divergence between different clusters was not always due to divergence in the same set of characters but a combination of different sets of characters. Out of the fifteen characters studied seven viz., tuber diameter, vine length, number of branches, number of tubers, tuber yield, top weight and number of leaves accounted for more than 80 per cent of the divergence in the material. Canonical analysis also more or less confirmed the grouping of the verities made by Tocher's method. Eight varieties selected on the basis of genetic divergence were used for progeny studies. All these varieties were found to be completely self-incompatible. It is observed that time of pollination markedly affected fruit and seed set. Maximum fruit and seed set was obtained between 7 and 7.30 a.m. And it progressively decreased as time passes. The weather conditions prevailing during the period of anthesis and pollination also influenced fruit and seed set. Maximum, minimum and mean temperature had significant negative correlation with both fruit and seed set. Path-coefficient anaysis revealed that most of the weather elements studied had negative direct effect on fruit and seed set. The total contribution of weather elements alone on fruit and seed set worked out to 40 and 32.5 percent respectively and hence any study on incompatibility and sterility in sweet potato may be conducted under controlled environmental conditions for reliable results. Genetic analysis of quantitative characters was done utilising line x tester and open pollinated progenies of the eight selected varieties. In the open pollinated progenies, existence of non- additive and environmental effects were observed in top weight, vine length, tuber diameter and leaf area index, and additive effects in number of leaves, number of tubers and tuber yield. In the line x tester progenies, additive variance was high compared to non- additive components in all the characters except the number of branches. The regression coefficients of progenies on male and mid- parental values were significant in seven out of ten characters in the line x teater progenies and in four characters on female parental values in the open pollinated progenies. The standardised regression coefficients reduced the magnitude and variability in the regression coefficients to some extent. The estimates of broad sense heritability from the varietal evaluation was higher in magnitude for most of the characters than the estimates of narrow sense heritability obtained from components of variance in open pollinated and line x tester progenies. Tuber yield showed 70.61 and 43.65 per cent heritability from the components of variance analyses in the open pollinated and line x tester progenies respectively, while number of tubers showed 82.75 and 70.07 per cent heritability. The variance between males was significant in respect of top weight, vine length, number of leaves, number of tubers, tuber diameter, leaf area index and harvest index, while the variance between females was significant only in tuber length. Significant reciprocal differences were observed in top weight, number of tubers, leaf area index and harvest index. With respect to general combining ability significant positive effects were observed in number of tubers in the varieties J.29 and H.42, tuber length in Palchakram and H.42, tuber diamter in IB.40 and Chakkaravalli and harvest index in J.29 and Palchakram. Significant heterotic effects were observed in a number of vine and tuber characters in both hybrid and open pollinated progenies. Seven hybrid progenies showed significant increase in tuber yield which ranged from 31.25 to 84.63 per cent over the higher parental values. Both hybrid and open pollinated progenies gave heterotic combinations for economic characters. The varieties which gave heterotic progenies by open pollination have performed well in certain hybrid combinations also. Considering the difficulties in the large scale hybridization and production of hybrid seedling, it is suggested that open pollination in selected varieties especially good combiners can be adopted as a quick and efficient method for varietal improvement in sweet potato.
700			_aMary George K (Guide)
856			_uhttps://krishikosh.egranth.ac.in/handle/1/5810159551
942			_2ddc _cTH