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Variability and path analysis studies in F 2 population of sorghum ( Sorghum bicolor ( L . ) Moench )

A field experiment was conducted to evaluate Sorghum (Sorghum bicolor (L.) Moench) F2 population of COS 28 x SPV 2308 and COS 28 x SPV 2307. These crosses were raised during Kharif’2018. Variability and path analysis was carried out for ten morphological traits viz., plant height, days to flowering, the number of leaves, flag leaf length, flag leaf width, panicle length, panicle weight, the number of primaries, 100 seed weight and grain yield per plant. The mean value was found to be higher in COS 28 x SPV 2307 for the traits namely plant height and the number of leaves per plant. The mean value was found to be higher in the cross COS 28 x SPV 2308 for the traits viz., flag leaf length, flag leaf width, panicle length, panicle weight, the number of primaries, 100 seed weight and grain yield per plant. Variability studies revealed that the high PCV was observed in both the crosses for all the traits thus showing high environmental influence except days to flowering and the number of leaves. High GCV, heritability and Genetic advance as percentage of mean was found to be high for the traits namely flag leaf length and flag leaf width in COS 28 x SPV 2308 and for the traits panicle length and the number of primaries in COS 28 x SPV 2307. The traits exhibit high GCV, heritability and GAM are additive in nature which could be used as the selection criteria for increasing the yield potential. Path analysis revealed that both the crosses showed high direct effect for grain yield per plant through the traits viz., flag leaf length, panicle length, panicle weight, the number of primaries and 100 grain weight. Flag leaf length, panicle length and the number of primaries exhibited high indirect effect through the trait panicle weight in both the crosses.


INTRODUCTION
Sorghum (Sorghum bicolor (L.) Moench) is the fifth most important cereal in the world, after Wheat, Rice, Maize and Barley. Sorghum belongs to the family Poaceae and tribe Andropogoneae (Harlan and De Wet, (1972)). In India, sorghum is having 5.86 million hectares of area, 4.57 million tonnes of production and 779.6 Kg/ha productivity (FAO STAT, 2017). Studies on variability parameters are essential for a breeder to select the most promising parents for the next generation with high genotypic effect and less environmental influence. The study of heritability suggests the proportion of genotypic variances present in the phenotype that would be carried to the next generation. The study of the GAM suggests the improvement in the mean genotypic values of the progenies over the parental population. The traits that exhibit high heritability and high genetic advance as percent of mean would exhibit an additive gene action hence can be used as selection criteria for improving the yield of the population. The traits that exhibit low heritability and high genetic advance as percent of mean can also be taken as selection criteria since low heritability may be due to the environmental influence. The traits that show low heritability and low genetic advance as percent of mean should not be considered for selection.
The path analysis identifies the direct and indirect effects of different traits on grain yield. The traits that exhibit high direct effects are considered for selection for improving grain yield. The traits that show high indirect effects also contribute to the increased yield of the population via some other traits.

MATERIALS AND METHODS
The study was carried out during Kharif'2018 at Department of Millets, Tamil Nadu Agricultural University, Coimbatore. The seed sources for parents namely COS 28, SPV 2307 and SPV 2308 and their F 1 's were obtained from the Department of Millets, TNAU, Coimbatore. The F 2 of the crosses COS 28 x SPV 2308 and COS 28 x SPV 2307 were raised in 20 rows of 4m length with a spacing of 0.45m between rows and 0.15m between plants. These F 2 segregants were raised along with corresponding parents. During sowing two seeds per hill were sown and later one plant per hill was maintained. All the crop management practices were followed as per recommendation. Observations were recorded for 145 individual F 2 plants in the cross COS 28 x SPV 2308 and 181 F 2 plants in the cross COS 28 x SPV 2307 for 10 biometrical traits viz., plant height (m), days to flowering (days), the number of leaves (no.), flag leaf length (cm), flag leaf width (cm), panicle length (cm), panicle weight (g), the number of primaries, 100 seed weight (g) and grain yield/plant (g). The variability analysis was carried out using MS excel and path analysis studies were carried out in OPSTAT software.

RESULTS AND DISCUSSION
The analysis of variance and genetic parameters for the important traits in the F 2 population of COS 28 x SPV 2308 and the cross COS 28 x SPV 2307 are presented in table 1 and 2 respectively. The analysis of variance revealed the presence of significant differences among the yield related traits.
The F 2 population of COS 28 x SPV 2308 exhibited high PCV (20.58), low GCV (7.48), low heritability (13.22%) and low GAM (5.61%) for the plant height (cm). Moderate PCV (11.62), low GCV (6.69), medium heritability (33.14%) and low GAM (7.93%) were observed for the trait days to flowering (days). Number of leaves per plant (no.) was found to exhibit moderate PCV (12.66), low GCV (5.12), low heritability (16.35%), low GAM (4.27%). PCV, GCV, heritability and GAM were observed to be high for flag leaf length (cm) and flag leaf width (cm). High PCV (23.94), moderate GCV (18.12), medium heritability (57.26%) and high GAM (28.24%) were observed for panicle length (cm). High PCV (83.87), low GCV (8.21), low heritability (0.96%) and low GAM (1.66%) were observed for panicle weight (g). Pedda swamy (2013)  number of leaves. High GCV, heritability and GAM were found to be high for the traits namely flag leaf length and flag leaf width in the cross COS 28 x SPV 2308 and for the traits viz., panicle length and the number of primaries in the cross COS 28 x SPV 2307. The traits that exhibit high GCV, heritability and GAM are additive in nature which could be used as the selection criteria for increasing the yield. The heritability estimates would give the best picture of the extent of advance to be expected by selection. The success of genetic advance depends on the measures viz., genetic variability, heritability and selection intensity of the population.     Hence from the path analysis studies it was adjudged that high direct effect for grain yield per plant was contributed through the traits viz., flag leaf length, panicle length, panicle weight, the number of primaries and 100 grain weight in both the crosses. Therefore the selection based on these traits ultimately leads to increased yield of the plant and the selection criteria based on these traits contribute for the direct improvement of the population yield. Flag leaf length, panicle length and the number of primaries exhibited high indirect effect through the trait panicle weight in both the crosses. Hence the selection based on these traits would further indirectly contribute to increased yield of the population through the panicle weight.