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M. MANJUBHARGAVI*, M. SHANTHI PRIYA, D. MOHAN REDDY AND B. RAVINDRA REDDY
S.V. Agricultural College Tirupati-517502, Andhra Pradesh, India
Fourty four genotypes of groundnut were used to study the correlation and path analysis for yield, quality and their contributing characters under two fertilizer managements viz., organic and conventional. Correlation analysis revealed that kernel yield per plant was significantly and positively correlated with days to 50 % flowering, primary branches per plant, total number of pods per plant, number of mature pods per plant, pod yield per plant, harvest index, 100 seed weight and protein content under both the managements. When both direct and indirect positive contributions were considered, pod yield per plant and shelling percentage influenced kernel yield per plant under both managements signifying the importance of these traits in the improvement of kernel yield.
Correlation, Groundnut, Path analysis
Groundnut (Arachis hypogaea L.) is important oilseed crop of the world. It is a segmental allotetraploid (2n=40), self-pollinating annual legume and it is grown throughout the tropical, sub-tropical and warm temperate regions of the world. Its seeds are valued both for its oil and protein contents. The production of oilseed crops was much higher after 1980’s and it brought yellow revolution in oilseed crops in India. But our traditional agro system suffered a great setback, especially owing to the indiscriminate use of fertilizers that created the problem of serious environmental consequences. It is believed that organic farming can solve many of these problems as this system is believed to maintain soil productivity and pest control by enhancing natural processes and cycles in harmony with the environment. Organic agriculture is continuously growing worldwide on land and farms in more than 160 countries.
There is a growing demand for the varieties suitable to organic and / or low input farming. The major constraint in organic farming is the lack of suitable varieties specifically bred for optimal production in organically managed systems (Dawson et al., 2011). In the words of Murphy et al. (2007) with crop cultivars bred in and adapted to the unique conditions inherent in organic systems, organic agriculture will be better able to realize its full potential as a high-yielding alternative to conventional agriculture. In several circumstances varieties that perform well in organic systems have different yield rankings under conventional management. Hence it would be a challenge for the breeders to develop cultivar for that condition. In organic agriculture, the immediate need is to make available greater quantity of organically produced seed. Hence there is essential need to encourage breeding programmes, designed in concert with organic farming.
The main objective of any breeding programme is the improvement of yield. Yield being a complex character and are the result of interaction of a number of components. It is essential to identify the component characters through which yield can be improved. Correlation which is the primary tool of breeding programme only provides the amount of association of characters, while path coefficient analysis measures the direct influence of one variable upon another and facilitates the separation of correlation coefficients into components of direct and indirect effects (Dewey and Lu, 1959). Thus, correlation in conjunction with path analysis would provide a better picture of cause and effect relationship between character pairs. Keeping this in view, the present study was carried out to formulate the selection strategies for improvement of pod yield in groundnut under organic and conventional fertilizer managements.
The material for the present investigation comprised of fourty four genotypes of groundnut evaluated in two separate contiguous trials that differ only in fertilizers managements using a Randomized Block Design with three replications, during kharif, 2014 at dryland Farm of S.V. Agricultural College, Tirupati. Each genotype was sown in single row of 3 m length adopting recommended spacing of 30 × 10 cm. In organic fertilizer management trial, FYM at the rate of 20 t ha-1 at the time of field preparation and at fifteen days interval Jeevamrutha was applied. The seed of groundnut was treated with bijamrutha. No inorganic chemicals were used. In order to encounter biotic stresses biopesticides (neemasthram, bramhastram, Gobanam) were used.
In conventional fertilizer management trial, FYM at the rate of 10 t ha-1 at the time of field preparation and recommended dose of chemical fertilizers at the rate of 20 kg N, 40 kg P2O5 and 40 kg K2O per hectare in the form of urea, single super phosphate and murate of potash were used. Seed treatment was done with Bavistin at the rate of 3 g kg-1. The crop was raised with protective irrigation and 500 kg of gypsum ha-1 was applied at peak flowering stage. Cultural practices like weeding and irrigation were followed in common for both trials to maintain good crop growth. Apart from these need based plant protection measures were adopted during the crop season for controlling diseases and pests.
The biometrical observations were recorded on five randomly selected plants per genotype per replication for twelve traits viz., days to 50 % flowering, plant height, primary branches per plant, number of pods per plant, pod yield per plant, mature pods per plant, kernel yield per plant, shelling percentage, harvest index, 100 seed weight, oil content and protein content. The genotypic and phenotypic correlation coefficients were calculated using the method given by Johnson et al. (1955) and path coefficient analysis were carried out as suggested by Dewey and Lu (1959).
Analysis of variance of twelve quantitative characters revealed highly significant differences among the genotypes for all the characters under both the fertilizer managements except shelling percentage, which showed non- significant difference under organic fertilizer management and significance under conventional
fertilizer management. The data on all the twelve characters were subjected to statistical analysis. Estimation of correlation coefficients at phenotypic and genotypic levels under both organic and conventional fertilizer managements were presented in Tables 1 and 2.
Higher values of genotypic coefficients than phenotypic coefficients revealed the influence of environment on phenotypic expression of characters under both fertilizer managements. Under organic fertilizer management pod yield per plant showed highly significant and positive correlation with kernel yield per plant (rp = 0.927**, rg = 0.978), followed by mature pods per plant (rp = 0.728**, rg = 0.833), number of pods per plant (rp = 0.687**, rg = 0.813), harvest index (rp = 0.458**, rg = 0.520), primary branches per plant (rp = 0.368**, rg = 0.395), days to 50 % flowering (rp = 0.357**, rg = 0.442), protein content (rp = 0.333**, rg = 0.456) and 100-seed weight (rp = 0.297**, rg
= 0.312), at both phenotypic and genotypic levels, indicating that increase in these traits would result in an increase in the pod yield.
Under conventional fertilizer management the trait pod yield per plant showed highly significant and positive correlation with kernel yield per plant (rp = 0.938**, rg = 0.987), followed by 100-seed weight (rp = 0.458**, rg =
0.622), mature pods per plant (rp = 0.432**, rg = 0.451), number of pods per plant (rp = 0.416**, rg = 0.333), harvest index (rp = 0.412**, rg = 0.601), primary branches per plant (rp = 0.298**, rg = 0.420) and days to 50 % flowering (rp = 0.180*, rg = 0.512) at both phenotypic and genotypic levels, showing that increase in these traits would result in increase in the pod yield. Similar kind of significant positive association of kernel yield per plant with pod yield per plant was reported by John et al. (2008), Kumar et al. (2012), Narasimhulu et al. (2012) and Rao et al. (2014). Significant and positive association of pod yield per plant with mature pods per plant were reported by Manoharan et al. (1988), Venkateswarlu et al. (2007), Kumar et al. (2012), and Vasanthi et al. (2015), with number of pods per plant by Kumar et al. (2012) and Rao et al. (2014), with harvest index and 100-seed weight by Korat et al. (2010), Suneetha et al. (2007) and Golakia et al. (2005) with primary branches per plant by Vasanthi et al. (2015) and days to 50 % flowering by Mahalakshmi et al. (2005).
Identification of important yield components and information about the association with yield and also with each other are necessary in developing efficient breeding
strategy for evolving improved genotypes in any crop species. Under both fertilizer managements significant and positive correlation was observed for days to 50 % flowering with kernel yield per plant and primary branches per plant; primary branches per plant with number of pods per plant, mature pods per plant and kernel yield per plant; number of pods per plant with mature pods per plant and kernel yield per plant; mature pods per plant with kernel yield per plant; kernel yield per plant with shelling percentage, harvest index, 100 seed weight and protein content; Shelling percentage with harvest index and 100 seed weight; harvest index with 100 seed weight and 100 seed weight with protein content. Where as under organic fertilizer management significant and positive association was observed for days to 50 % flowering with number of pods per plant, mature pods per plant and harvest index; plant height with protein content; number of pods per plant with harvest index; mature pods per plant with harvest index and protein content.
Hence these characters could be emphasized during selection process to bring about improvement in the yield potential as well as quality of groundnut cultivars under organic and conventional fertilizer management. Selection of easily observable traits among these would ultimately enhance the mean performance of all concerned inter dependent characters and hence would be helpful in order to get improved pod yield under organic and conventional fertilizer management.
Oil content displayed significant negative association with pod yield under both organic and conventional fertilizer managements. Hence judicious selection programme might be formulated by repeated intermating to break the negative correlation between oil content and pod yield per plant for simultaneous improvement of these characters under organic and conventional fertilizer management.
Path coefficient analysis was conducted using pod yield per plant as dependent variable and characters which exhibited significant correlation with pod yield as independent variables under both organic and conventional fertilizer managements and the results are presented in Tables 3 and 4. Under organic fertilizer management the trait kernel yield per plant recorded high positive direct effect (0.688) and mature pods per plant recorded moderate positive direct effect (0.2502) on pod yield per plant. On the other hand harvest index (-0.0565) and oil content (-0.0136) recorded negligible direct effect on pod yield per plant. Days to 50 % flowering (0.2422) and 100 seed weight (0.2780) displayed moderate positive indirect effect through kernel yield per plant. The traits number of pods per plant (0.3963), mature pods per plant (0.4280) and harvest index (0.3965) showed high positive indirect effect on pod yield through kernel yield per plant. Number of pods per plant recorded moderate positive indirect effect (0.2369) through mature pods per plant. Kernel yield per plant displayed low positive indirect effect (0.1556) through mature pods per plant. Oil content recorded moderate negative indirect effect (-0.2628) through kernel yield per plant.
Under conventional fertilizer management the traits kernel yield per plant (0.8691) and number of pods per plant (0.2507) exhibited high and moderate positive direct effects on pod yield per plant respectively. Days to 50 % flowering exhibited low positive indirect effect (0.1947) through kernel yield per plant. Primary branches per plant (0.2034) and number of pods per plant (0.2720) recorded moderate positive indirect effect through kernel yield per plant. The traits mature pods per plant (0.3068), harvest index (0.4284) and 100 seed weight (0.4502) displayed high positive indirect effect through kernel yield per plant. Oil content recorded moderate negative indirect effect (-0.2851) through kernel yield per plant. Mature pods per plant showed moderate positive indirect effect (0.2371) through number of pods per plant.
High direct effects of kernel yield per plant with pod yield per plant was reported by Reddy et al. (1986), Vijayasekhar et al. (2002), Dhaliwal et al. (2003), Lakshmidevamma et al. (2004), Venkateswarlu et al. (2007), Sudhir et al. (2008) and Kumar et al. (2012). High positive indirect effect of harvest index through kernel yield per plant was reported by Vijayasekhar (2002). Negative direct effect of mature pods per plant on pod yield per plant was reported by Sumathi and Muralidharan (2007). High indirect positive effect of mature pods per plant through kernel yield per plant on pod yield per plant was reported by Ahamad (1995) and Kumar et al. (2012).
Hence from the foregoing discussion, it could be inferred that kernel yield per plant, and mature pods per plant were the major contributing characters in groundnut under organic fertilizer management where as the traits kernel yield per plant and number of pods per plant were the major contributing characters in groundnut under conventional fertilizer management. Due weightage to these traits in the respective fertilizer management could
be highly beneficial. Therefore, these traits should be given due consideration for indirect selection to improve yield to obtain superior genotypes under the respective management conditions.