Interrelationship, direct and indirect Effect of Different Component Characters on Grain Yield in Amaranth Genotypes (Amaranthus hypochondriacus) under Varied Plant Densities

In grain amaranthus (Amaranthus hypochondriacus L.) ten genotypes were evaluated for twelve characters under four plant density levels viz., very high (D1), high (D2), normal (D3) and low plant density (D4) levels to study the relationship of different characters on yield and their direct and indirect effects. The study was conducted at College Orchard, Department of Horticulture, Pandit Jawaharlal Nehru College of Agriculture and Research Institute, TNAU, Karaikal during kharif 2007. The results revealed that the correlation and direct effect of component traits on grain yield were, in general, highly influenced by the plant densities both in direction and magnitude. The fresh weight of the inflorescence, length of the primary inflorescence and number of secondary branches per inflorescence recorded strong positive correlation with grain yield as well as strong intercorrelations among themselves, indicating that improvement of grain yield in amaranthus could be achieved by exercising selection for these component traits. The path analysis indicated that fresh weight of the inflorescence, leaf area at 50 per cent flowering, length of the primary inflorescence and number of secondary branches per inflorescence had direct positive effects on grain yield. Therefore, these parameters should be kept in mind for better planning of any improvement programme in amaranth.


Introduction
Amaranthus species are being cultivated since centuries as a leafy vegetable, as well as an important subsidiary food grain crop in many parts of the world (Tucker, 1986). Grain amaranth serves as an alternative source of nutrition for people in developing countries since it is a rich and inexpensive source of protein, vitamins and dietary fibre (Prakash and Pal, 1991;. Unlike other vegetables, grain amaranth is cultivated during hot summer months when no green vegetables are available (Singh and Whitehead, 1996). Besides immense nutritional importance, it can also be successfully grown under varied soil and agro climatic conditions (Katiyar et al., 2000;Shukla and Singh, 2000). Recently, current interest in grain amaranth resides in the fact that it has a great amount of genetic diversity and phenotypic plasticity. Grain amaranths is extremely adaptable to adverse growing conditions, resist heat and drought, has no major disease problem and is among the easiest of plants to grow. Improvement of grain yield is the main target of breeding program to develop amaranthus varieties for diverse ecosystems. Population density is a major environmental factor influencing the genetic parameters like variability and association among the characters. Study of the extent of such influence of different plant density levels in these genetic parameters is required to formulate appropriate breeding strategies. However, grain yield is a complex trait, controlled by many genes and highly affected by Plant Gene and Trait, 2013, Vol.4, No.3, 9-16 http://pgt.sophiapublisher.com environment. In addition, grain yield also related with other characters such as plant type, growth duration and yield components. The low heritability of grain yield characters made selection for high yielding varieties usually use secondary traits associated with yield. Thus, information on contribution of each plant character to grain yield is important to make selection process more efficient. Causal relatio-nship between predictor variables and response variable can be defined by path analysis. Using path analysis, correlation coefficient is partitioned into two components, which are direct effect of a predictor variable on its response variable and indirect effect of that predictor variable on the response variable through other related variables. Path analysis has been intensively used to estimate contribution of yield related traits to grain yield of rice and assisted breeders to determine selection criteria to improve yield. However, information on relationship of agronomic traits and grain yield in the breeding program for specific environment particularly for different plant density levels is very limited.  (Goulden, 1952). The variance and covariance components were utilized to calculate genotypic correlation coefficient as outlined by Al -Jibour et al. (1958). Path analysis was adopted to partition the genotypic correlation coefficient into direct and indirect effects as suggested by Dewey and Lu (1959).

Materials and methods
The path coefficients were ranked on the scales given below (Lenka and Misra, 1973).

Results and discussion
Information on the strength and direction of component characters with seed yield and also interco rrelation among themselves would be very useful in formulating an effective selection criteria for improvement of yield. A simple measure of correlation of characters with yield is inadequate, as it will not reflect the direct influence of component characters on the yield. Thus, it is necessary to split the correlation coefficients into direct and indirect effects (Dewey and Lu, 1959). This would help to identify with certainty the component traits to be relied upon during selection to improve seed yield. Such an attempt was made in the present study. Genotypic correlation coefficients were calculated through variance and      The genotypic correlation coefficients of component traits with grain yield per plot were partitioned into direct and indirect effects through path coefficient analysis (Tables 5~8). In the present study the direct effects of all the component traits on grain yield showed high fluctuation in direction as well as in magnitude under four plant density levels. The traits viz., fresh weight of the inflorescence, length of the primary inflorescence and number of secondary branches per inflorescence which were identified as yield attributing traits based on correlation and intercorrelation studies, fresh weight of the inflorescence was found to be the most important contributing trait as it significantly improves the grain yield per plant in all the four plant density levels. In path analysis, as in case of correlation studies, these traits had very high positive direct effects on grain yield in all the plant density levels (Figure 2). In addition to that, leaf area at 50 per cent flowering, length of the primary inflorescence and number of secondary branches per inflorescence also identified as the most important yield contributing traits from the path analysis in all the four plant density levels.
The length of the rachis per inflorescence had high positive direct effect on grain yield per plant in all the density levels except very high density. These results confirm that the fresh weight of the inflorescence should be given prime importance in selection programme for improvement of grain yield in grain amaranthus irrespective of plant density levels. The positive direct effect was exhibited by plant height in high and normal plant densities, whereas in very high and low plant density levels this trait showed high and very high negative direct effects. The other yield contributing trait diameter of the inflorescence had direct positive effect on grain yield in all density levels except high density level (D 2 ). Total carbohydrates and protein content showed high positive direct effects on grain yield in very high density and also protein content recorded low positive direct effect under low plant density. In the present study, days to 50 per cent flowering and number of rachis per inflorescence recorded negative direct effects in all the density levels. Total carbohydrates recorded high and     negligible negative direct effects on grain yield in normal, high and low plant density levels respectively. Protein content showed high negative direct effects in normal density, whereas in high plant density this trait recorded negligible negative direct effects grain yield. The estimate of residual effect reflects the adequacy and appropriateness of the characters chosen for the path analysis. In the present study, the residual effect was low in all the four plant density levels indicating the adequacy of characters chosen for the study to reflect the grain yield.

Authors' Contributions
Dr. S. Ramesh Kumar conceived the overall study, performed the experiment designs and drafted the manuscript. Dr. G.
Mohamed Yassin and Dr. R. Govin-darasu took part in the experiment as chairman of the advisory committee. The above scientists read the manuscript and revised it. All authors had read and consent the final text.
handing the grain amaranth germplasm and varieties to the corresponding author.