Chapter 4: Correlation and Path Coefficient Analyses of Qualitative and Quantitative Traits
4.5 Discussion
Understanding the nature of associations among economically important traits is essential for direct or indirect selection and consequently to improve the efficiency of selection gains in plant breeding programs. In this study, correlation and path coefficient analyses were used to determine associations between qualitative and quantitative traits and consequently to determine the best selection criteria. Simple correlations among qualitative traits showed positive associations between primary fruit colour and secondary fruit colour, fruit texture, degree of neck bending, stem-end fruit shape and fruit neck length (Table 4.5). Secondary fruit colour positively correlated with fruit texture, fruit shape and stem-end fruit shape. Positive correlations were also noted between presence or absence of fruit neck with fruit shape, degree of neck bending and fruit neck length. Further, fruit texture, degree of warts, fruit shape, and degree of neck bending, stem-end fruit shape and fruit neck length were negatively correlated with number of fruits per plant and number of seeds per fruit (Table 4.7) signifying that these traits may negatively limit yield gains.
Results of the present study are supported by Bahraminejad et al. (2011) who reported that different qualitative characteristics such as seeds with light colour and without trichome and leaves without trichome produced high seed yield. These authors suggested that linkages exist between
not been reported in bottle gourd. Therefore, the present estimates may guide targeted breeding of the crop incorporating these valuable traits (Augustina et al., 2013). Further, the lack of correlation between degree of warts and corrugation with other qualitative traits may be of interest for further investigation.
Simple correlation analysis among quantitative traits revealed highly significant (P < 0.001) and positive correlations between number of male flowers with number of female flowers, plant height (r = 0.57), number of branches (r = 0.87), number of aborted fruits (r = 0.42) and number of fruits per plant (r = 0.55) (Table 4.6). This suggests that targeted selection to improve these traits would increase fruit yield (Parhi et al., 1995). Selection for these traits may ultimately improve fruit yield.
Results in this study are in agreement with the report of Narayan et al. (1996), Achigan-Dako et al. (2006), Koffi et al. (2009) and Husna et al. (2011). The authors indicated that several quantitative traits including plant height, number of female flowers per plant and number of branches per plant were important yield components influencing fruit yield in bottle gourd. Other studies in related cucurbits (e.g. bitter gourd and cucumber) also revealed positive correlations between several traits like number of branches and number of female flowers on number of fruits per plant (Srivastava and Srivastava, 1976; Mangal et al., 1983; Cramer and Wehner, 2000).
Number of seeds per fruit significantly and positively correlated plant height (r = 0.64) and, number of male flowers (r = 0.62), number of female flowers (r = 0.47), number of branches (r = 0.59) and fruit weight (r = 0.79), respectively (Table 4.6). Correlation studies on seed yield with related traits in bottle gourd are scanty. The current study further showed that the assessed traits had relatively high heritability estimates of > 60% (Table 4.4) indicating the presence of considerable genetic variation for selection. Characters with high heritability are largely influenced by genetic effects suggesting that their direct selection could yield positive selection gains (Singh et al., 2006; Bhargava et al., 2007; Husna et al., 2011).
Associations among traits as determined by simple correlation coefficient analysis may limit prediction on the success of selection. Therefore, correlation coefficients between various characters were partitioned into direct and indirect effects using path coefficient analysis. Path
Kang et al., 1983; Toebe and Filho, 2013). In this study, positive direct effect was exhibited between degree of warts and number of seeds per fruit. High direct effects were recorded between fruit neck length followed by primary and secondary fruit colour with number of fruits per plant.
However, these traits were not well-correlated with the number of fruits per plant. Several qualitative traits including fruit shape, fruit colour, fruit texture and degree of warts are genetically controlled (Kushwaha and Ram, 1996; Paris and Nelson, 2004; Tiwari and Ram, 2009;
Mladenovic et al., 2013). The poor correlation of fruit neck length, secondary and primary fruit colour with fruit yield suggests that direct selection for these traits may not provide yield improvement.
A relatively high positive direct effect was exhibited between number of female flowers and number of fruits per plant (Table 4.9) suggesting simultaneous selection of the two traits may improve genetic gain of fruit yield in bottle gourd breeding. Number of female flowers was reported to have maximum positive direct effect on number of fruits/plant and fruit yield in bitter gourd (Srivastava and Srivastava, 1976) and bottle gourd (Narayan et al., 1996). In bottle gourd, increased attempt is given towards breeding superior hybrids with high fruit yield, fruit number and high female: male flower ratio (Rakesh and Ram, 2007; Behera et al., 2015). Therefore, to increase fruit yield, more female flowers are desired which is the determinant factor for increased number of fruit yield (Dey et al., 2005). Significant positive correlations between female flowers and number of fruits per plant were also reported in cucumber suggesting that female sex expression has potential for increasing yield through direct selection (Cramer and Wehner, 2000;
Fan et al., 2006). The current analyses showed the presence of high and significant correlation between number of female flowers and number of fruits per plant (r = 0.94) (Table 4.5). Therefore, efforts required in breeding cultivars with a higher fruit set and yield can be achieved through selection of cultivars with increased proportion of female flowers (Arora et al., 1982). Landraces which produced the highest number of female flowers and subsequent fruit set were BG-24, BG- 07, BG-13, BG-67, BG-08, BG-12, BG-37, BG-19, BG-09 and BG-06. These are useful genetic resources for bottle gourd breeding emphasizing fruit yield.
High direct positive effect was exhibited between fruit weight and number of seeds per fruit
4.10). A high path coefficient value indicates that the change will result in a proportional (or inversely proportional) change in another correlated trait, whereas a strong correlation coefficient indicates that the change will have high effect on the second trait (Cramer and Wehner, 2000).
Results in this study are in agreement with Yao et al. (2015) who reported that fruit weight had positive high direct effect on seed yield in bottle gourd. Bottle gourd seeds are rich in essential amino acids, protein, minerals, lipids and fatty acids (Achu et al., 2005; Fokou et al., 2009; Essien et al., 2013). Thus the seed are potentially useful for food or livestock feed (Achu et al., 2005;
Ojiako and Igwe, 2007; Ogunbusola et al., 2010). Landraces which produced the highest fruit weight included: BG-13, BG-67, BG-36, BG-11, BG-17, BG-09, BG-07, BG-06, BG-36 and BG- 67. These are useful genetic resources for bottle gourd breeding emphasizing seed yield.
Knowledge of the associations among qualitative traits is important for simultaneous selections especially for bottle gourd which shows considerable variability in fruit qualitative parameters.