Journal of Science. GS Sanghera*, V Tyagi, R Kumar, KS Thind and B Sharma

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1 Journal of Science e ISSN Print ISSN Agriculture GENETIC VARIABILITY, ASSOCIATION AND THEIR DISSECTION THROUGH PATH ANALYSIS FOR CANE YIELD AND ITS COMPONENT TRAITS IN EARLY MATURING SUGARCANE CLONES GS Sanghera*, V Tyagi, R Kumar, KS Thind and B Sharma Punjab Agricultural University, Regional Research Station, Kapurthala , Punjab, India. ABSTRACT Genetic variability, correlations and path coefficients were studied in thirteen phenotypically diverse early maturing sugarcane clones, which were planted in randomized block design. The study revealed highly significant differences among the 13 clones for all the characters studied, indicated the ample variation. High phenotypic and genotypic coefficient of variation were observed for number of shoots at 240 followed by cane diameter and number of tiller at 120 and single cane weight. High heritability estimates were recorded for stalk diameter (80.69%) and moderate for cane yield (74.42%) and number of millable canes (NMC) at 10 months (72.49%) implying simple selection for these traits would be effective. Maximum genetic gain (as percent of mean) was observed for stalk length (37.09%) followed by number of shoots (34.31%) indicating that there exist a scope to improve cane yield through this trait. Moderate heritability coupled with high genetic advance observed for number of shoots and cane length indicated the presence of additive gene action. Correlation coefficient revealed that cane yield was found to be significantly and positively correlated with NMC at10 months, stalk length, single cane weight, cane diameter and germination percentage at 45 indicating the importance of these traits to be involved in selection criteria. Partioning of association into their direct and indirect effects showed that highest positive direct effect on cane yield is exerted by growth characters like no. of shoots 240, number millable canes, single cane weight and stalk diameter in this study so be taken into consideration in clonal selection programme for evolving improved sugarcane genotypes. Keywords: Sugarcane, genetic variability, heritability, correlation and path analysis. Abbreviations: PCV-phenotypic coefficient of variation, GCV- genotypic coefficient of variation, GA- genetic advance, NMC-number of millable canes, GMgrand mean, h 2 (bs)- heritability broad sense. INTRODUCTION Sugarcane (Saccharum spp. hybrids) is an important agro industrial crop and knowledge of heritability of agronomic traits is important in breeding programmes worldwide. It is an important agro-industrial crop in India, plays a pivotal role in national economy by contributing 1.9% to gross domestic product. However, plateauing yield level, declining factor productivity, increasing production cost, slashing sugar prices in international market and decreasing profitability in recent years indeed pose the real concerns before cane researchers, growers and mill owners. In India, sugar industry being the second largest agro-based industry next to textile. Sugarcane varieties in commercial cultivation are complex polyploids, the heterozygous and polyploid nature of this crop has resulted in generation of sufficient genetic variability. Genetic improvement in cane yield may be achieved by targeting traits closely associated with cane yield. A number of characteristics have been proposed as indirect selection criteria for genetic improvement of yield in plant breeding programmes [1]. Corresponding Author:- G S Sanghera - sangheragulzar@pau.edu 28

2 Understanding the associations between traits is of great importance in breeding and selection studies especially for low heritability or difficult to measure traits [3,4]. Consideration of genetic relationships between important attributes in exploiting genetic populations through breeding and directed selection is essential, primarily to understand how changes made by selecting one character may cause changes in others [5,6]. This knowledge can be used when devising appropriate selection strategies for particular traits in a sugarcane breeding programme [7]. Since, the crop is grown in diverse climatic conditions in the country, breeding objectives vary accordingly. The subtropical region for sugarcane cultivation occupies about 50 per cent of the national area [8]. To improve the productivity and efficiency of the sugarcane production system, new varieties and technologies were introduced in Punjab state to shift the productivity horizon. The extent of variability present in the genetic material in any crop and the information on the nature and magnitude of correlations are of prime importance for a breeder to initiate effective selection programme for identification and development of new varieties. Genotypic coefficient of variation (GCV) is another measure of relative genetic variation of a trait in a population [9]. Traits exhibiting relatively high GCV estimates may respond favorably to selection. Further, heritability estimates, together with expected genetic gain, are more useful than the heritability values alone in predicting the effects of selecting the best genotypes. In this crop, varietal improvement by using newly developed scientific concepts to bring out the maximum expression of yield potential possessed by varieties are the factors desiring more attention of the researchers [10]. Various traits are accounted for variations in cane yields. Many of these character components are quantitatively inherited and inter-related with each other. Knowledge of interrelationship among the various characters is considered to be important in devising proper selection strategies in a sugarcane breeding (In this crop, varietal improvement by using newly developed scientific concepts to bring out the maximum expression of yield potential possessed by varieties are the factors desiring more attention of the researchers. Various traits are accounted for variations in cane yields. Many of these character components are quantitatively inherited and inter-related with each other. Knowledge of interrelationship among the various characters is considered to be important in devising proper selection strategies in sugarcane breeding [11]. Therefore, to identify the different factors responsible for the productivity growth, this study was undertaken to estimate heritability of sugarcane yield and some of its components, and to determine phenotypic and genetic correlations among sugarcane yield and path analysis for enhancing productivity of sugarcane production system of the state. MATERIALS AND METHODS Experimental material and its layout The experimental material comprised of thirteen clones, eleven new clones viz. Co 10035, CoH 10261, CoS 10231, CoH 09262, CoH 09263, CoLk 09202, CoPb 09181, CoH 09246, CoPb 08211, CoPb 08212, COS and two standards viz. CoJ 64 and CoPant The experiment was planned to evaluate these elite sugarcane clones belonging to early maturity group under subtropical conditions at Punjab Agricultural University, Regional Research Station, Kapurthala, during in randomized block design having a plot size of 36 m 2 with four replications. Three budded sets of each genotype at the rate of 12 buds per meter were planted in 6 rows of 6m length with inter-row spacing of 75 cm. The data from different clones were recorded for various growth and cane yield parameter viz. cane yield (t/ha), number of millable canes 10 months (000/ha), cane length (m), cane diameter (cm), single cane weight (kg), no. of shoots (000/ha) 240, no. of tillers (000/ha) and germination % 45 under subtropical conation of India. Cane yield (t/ha) was recorded from final harvested crop, number of millable canes were counted after 10 months duration of crop per plot and converted in to MNC (000/ha). Cane length of five plants was marked from each genotype to measure cane length. The cane length was measured from base to the tip of cane at the time of harvesting when plant attained maximum growth. Same five canes were used for measurement of cane diameter with help of vernier caliper. Single cane weight was recorded from the same set of five cane used for length and diameter. The mean data of five plants was used for statistical analysis. No. of shoots (000/ha) were recorded at the 240 old crop and same for no. of tillers (000/ha). Germination (%) was calculated with help of following standard method at 45 from the date of sowing. Total no. of plants/plot Germination (%) = 100 No. of sown buds/plot Statistical analysis The genotypes were evaluated for components of genetic variability [12], genotypic and phenotypic associations of cane yield with its contributing traits [13] and their portioning in to direct and indirect effects using path analysis [14]. RESULTS AND DISCUSSION The analysis of variance revealed significant differences among the clones for all the traits studied. Thus the clones were genetically divergent. The significant genotypic effects indicated genetic variability among the genotypes and the possibility of genetic improvement in most of the traits studied through 29

3 selection [15,16]. The relatively large genotypic mean squares indicated that clones differed in their potential for the traits. Genetic variance is important as it describes the amount of genetic variation present for the trait. High genetic variance relative to environmental variance for number of millable cane and stalk weight in the plant cane and for stalk diameter and stalk weight indicates that these traits were affected less by environmental effects. The estimates for phenotypic coefficient of variation (PCV) were higher than for genotypic coefficient of variation (GCV) in all the traits, suggesting that the apparent variation is not only due to genetics but also due to environmental influences. However, the differences between PCV and GCV for most of the traits were small indicating high prospects for genetic progress through selection under the conditions of this investigation [17]. The highest phenotypic coefficient of variation (PCV) were observed for no. of shoots at 240 (22.75%) followed by cane diameter (22.31%) and no. of tiller at 120 (22.24%) (Table 1). Genetic variance is important as it describes the amount of genetic variation present for the trait. Highest genotypic coefficient of variation were observed for cane diameter cm (20.04%) followed by no. of shoots at 240 (19.46%) and no. of tiller at 120 (18.90%). High genotypic and phenotypic coefficients of variation for cane diameter were reported earlier by Singh and Sangwan [18]. Traits exhibiting relatively high GCV estimates may respond favourably to selection. The success of a variety improvement programme depends largely on the amount of genetic variability present in the population. Genetic coefficients of variation along with heritability estimates give a better indication of the amount of genetic variation for a trait than either parameter alone. In present study, high heritability (broad sense) estimates were recorded for stalk diameter (80.69%), cane yield (74.42%) and NMC at 10 months (72.49%). This suggests that a large proportion of the total variance is heritable and selection of these traits would be effective. Chaudhary [19] also reported high heritability estimates for stalk diameter while Nair et al. [20] and Singh et al [21] recorded high heritability estimates for single stalk weight. In this study medium heritability estimate has been for recorded stalk length (64.67%) indicating that selection for these traits would not be as effective as for the other traits. These findings agree with Chaudhary, who reported similar values in clonal genotypes of sugarcane. Selection for characters with low heritability (less than 40.0%) can be considerably difficult or virtually impracticable because of the masking effects of environment on genotypic expression [22]. Knowledge of variability and heritability of characters is essential for identifying those amenable to genetic improvement through selection [23]. Results of the current study indicate that use of the traits with high heritability as selection criteria together with cane yield could lead to genetic improvement in cane yield. The effectiveness of selection depends not only on heritability but also on genetic advance [24]. The high genetic gain (GA %) observed for single stalk weight (34.0%) followed by no. of shoots 240 (34.31%), number of millable cane (29.22%), cane yield t/ha (27.33%) and moderate for stalk length (19.02%) and single cane weight (11.73) (Table 2) was the result of high broad sense heritability and high GCV for these traits. The results suggest existence of considerable scope for improvement of these cane yield components. High genetic advance has also been reported for single stalk weight and number of millable cane [25,26]. The high broad sense heritability coupled with high genetic advance for single stalk weight and number of millable canes indicates these traits are under the control of additive genetic effects and highlights the usefulness of selection based on phenotypic performance [27,28]. Breeding for high yielding crop varieties requires information on association of component characters with yield and among themselves. This knowledge helps in designing suitable criteria for selection of genotypes having high yield potential because correlations among phenotypic traits may reflect biological processes that are of considerable evolutionary interest and can be the result of genetic, functional and physiological or developmental nature [29,30]. The r values obtained at phenotypic and genotypic levels for the inter se combinations between cane yield and its components are presented in Table 3. A perusal of the table 2 revealed that there were highly positive and significant correlation between NMC at 10 months with stalk length (0.484), no. of shoots 240 (0.893), no. of tillers 120 (0.900), germination 45 (0.439) and cane yield (0.834). Stalk length was highly and positive associated with stalk diameter (0.626), no. of shoots 240 (0.710), no. of tillers 120 (0.688), germination 45 Days (0.735) and cane yield (0.556). Skinner (1972) reported that stalk diameter, number of millable cane and stalk height are by far the main cane yield components. These two traits were positively correlated with cane yield and might dictated for higher cane yield. Germination 45 Days (0.735) was significant associated with stalk diameter (0.591), no. of shoots 240 (0.589) and no. of tillers 120 (0.567). In this study, all the traits had positive association at phenotypic and genotypic levels with cane yield. Positive and highly significant associations of cane yield with no. of shoots 240 (0.834), no. of tillers 120 (0.841) and germination 45 (0.513) were also recorded. Character association between cane yield and number of millable stalks, stalk height, single stalks weight have been reported by [31] indicated improvement of one of these character may resulted in positive response of the other character. High and positive correlation between number of millable cane and cane yield was also reported by James [32]. 30

4 Table 1. Genetic components of variability in early maturing clones of sugarcane grown under subtropical conditions S. No. Traits h 2 bs (%) GA % GA PCV (%) GCV (%) GM CV (%) 1 NMC at 10 months (000/ha) Stalk length (m) Stalk diameter (cm) Single cane weight (kg) No. of shoots (000/ha) No. of tillers (000/ha) Germination % 45 Days Cane yield t/ha Table 2. Correlations coefficients phenotypic (above diagonal) genotypic (below diagonal) among cane yield and component traits in early maturing clones of sugarcane grown under subtropical conditions No. of No. of Germin NMC at Stalk Single Stalk shoots) tillers ation Cane Traits 10 diamete cane length % 45 yield months r weight) Days - NMC at 10 months (000/ha) 0.380** ** 0.740** ** 0.477** Stalk length (m) 0.484** ** 0.513** 0.496** 0.502** 0.440** Stalk diameter (cm) ** ** 0.343* Single cane weight (kg) ** * * No. of shoots (000/ha) ** 0.310* ** ** No. of tillers (000/ha) ** ** 0.281* 0.614** Germination % ** 0.735** 0.591** ** 0.567** 0.320* Cane yield t/ha 0.834** 0.556** 0.314* 0.320* 0.834** 0.841** 0.513** *, ** Significant at 5% and 1% level, respectively Table 3. Genotypic path analysis for cane yield and component traits in early maturing clones of sugarcane grown under subtropical conditions Direct (diagonal) and indirect (above and below diagonal) effects NMC at Stalk Single No. of No. of r value Variable Stalk Germina 10 diamet cane shoots tillers with length tion % months er weight (000/ha) (000/ha) cane (m) 45 (000/ha) (cm) (kg) yield NMC at 10 months (000/ha) ** Stalk length (m) ** Stalk diameter (cm) * Single cane weight (kg) * No. of shoots (000/ha) ** No. of tillers (000/ha) ** Germination % ** Proportional contribution of variables Explained variation =0.986, Unexplained variation = 0.014; *, ** Significant at 5 and 1% level, respectively Simple correlations between yield components are less informative with respect to determining the functional relation between components from diverse hierarchy. In this regard, path analysis helps us in identifying the most important characters affecting directly and indirectly through other characters. In the present study, the path coefficient analysis was performed for cane yield as a dependent variate (Tables 3 and 4). 31

5 Table 4. Phenotypic path analysis for cane yield and component traits in early maturing clones of sugarcane grown under subtropical conditions Direct (diagonal) and indirect (above and below diagonal) effects Variable NMC at Single No. of No. of Germin r value Stalk Stalk 10 cane shoots tillers ation 45 with cane length diameter months weight yield NMC at 10 months (000/ha) ** Stalk length (m) ** Stalk diameter (cm) Single cane weight (kg) * No. of shoots (000/ha) ** No. of tillers (000/ha) ** Germination % * Proportional contribution of variables Explained variation = 0.982, Unexplained variation = 0.018; *, ** Significant at 5 and 1% level, respectively High positive and direct contribution to the cane yield was recorded for growth characters like no. of shoots 240, number millable canes, single cane weight and stalk diameter in this study. This observation indicated that these growth parameters are strong contributors to cane yield which confirms the earlier report by Milligan et al [33] and Guddadamath et al [34] who reported stalk number and stalk girth as the most important determinant of cane yield. The indirect effect of number of shoots was positive through number of millable canes and stalk length. However, its negative indirect effect was observed through stalk diameter. Number of millable cane showed higher direct effect on cane yield. On the other hand, it had negative effect on the cane yield through germination, stalk diameter and stalk weight. Stalk diameter exerted direct effect on cane yield which was positive and markedly high. The indirect effect of stalk diameter on cane yield through stalk weight was positive which was counter balanced by its negative effect through number of shoots, number of millable canes and stalk length. Xie et al [35] found stalk number and stalk girth to be the most useful traits when selecting for sugarcane and sugar yields in their path analysis studies. Stalk length was found to have positively direct effect on cane yield. Germination was found to have negative and considerably low direct effect on cane yield. The direct effect was counter balanced by the positive indirect effect through number of millable canes, stalk length, stalk diameter and stalk weight. The single cane weight also showed indirect and positive effect on cane yield through stalk length and stalk diameter. These results are in agreement with earlier findings of Kumar and Singh [36], Thippeswamy et al [37] and Madhavi et al [38]. Thus, on the basis of above analysis it may be stated that number of millable canes and stalk weight are most important characters for cane yield. Further, the percentage contribution of cane yield parameters shown that the number of millable canes made the highest individual percentage contribution followed by single cane weight and stalk diameter. Present study revealed that cane yield is associated with its various components genetically and phenotypically in various magnitudes of variability, correlations among cane yield traits, their heritability, expected genetic advance that could be encountered within the sugarcane breeding programme. Path coefficient results showed the amount of contribution either directly or indirectly and also the percentage contribution of each parameter to the cane yield. It can be concluded that number of millable canes, single cane weight and cane girth gave the highest contribution to cane yield. Therefore, these parameters are very important to be considered when selecting for sugarcane yields especially in determining possibility of obtaining optimal yield from millable sugarcane particularly for this subtropical ecology. REFERENCES 1. Skinner JC. Selection in sugarcane, A review. In, the Proceeding of International Society for Sugarane Technol, 14, 1972, Rebettzke GJ, Condon AG, Richards RA and Farquhar GD. Selection of carbon isotope discrimination increases aerial biomass and grain yield of rainfed bread wheat. Crop Sci, 42(3), 2002,

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