The correlation among traits under study indicated that the short period to heading will provide more time to increase the number of panicle per plant and 1000 grain weight, and full-grain number per panicle will be improved by increasing of panicle length or panicle number per plant, as well as any increase in panicle number per plant will cause an increase in 1000 grain weight which leads to improvement of the final grain yield which was correlated positively to yield traits. These results agree with the results of Kumar et al. (2011), Khush (2013), Karim et al. (2014), Kumar et al. (2017), Lakshmi et al. (2017), Bhutta et al. (2019), Chhangte and Devi, (2019), and Panda et al. (2019). Current knowledge about trait relationships helps in the appropriate selection process due to the increased share of crop improvement (Gonçalves et al., 2017).
Breeding programs aim to increase rice production by using more genetic types and applying effective selection methods to increase yield through yield traits. Identifying the relationship between yield and yield traits via correlation analysis is an essential step (Akhtar et al., 2011), but dividing the influence of traits into direct and indirect effects by path analysis is more essential for the selection of yield traits (Ahmadizadeh et al., 2011, Dhavaleshvar et al., 2019).
The total effect in path analysis represents correlation value between targeted trait and grain yield, the direct effect of days to heading reflects the real relationship with grain yield, while the indirect effect of days to heading via other traits especially 1000 grain weight then panicle number per plant were the causes of the negative correlation. The same result was indicated for plant height, in which the direct effect was positive and equal to the negative correlation because of its indirect effects on grain yield via other studied traits. Although the direct effect of panicle length was neglected, its indirect effects via panicle number per plant and full-grain number per panicle were the reason for the strong and positive total effect. Our results are in agreement with the results of Herawati et al. (2019) which indicated that direct effect of plant height was positive and neglected (0.06), the direct effect of panicle length was positive and neglected, and the direct effect of full-grain number per panicle was positive and strong (0.4); these agree with Chhangte and Devi (2019) who found that the direct effect of 1000 grain weight on grain yield was positive and strong, the total effect of panicle number per plant was positive and high (0.68), and indirect effect on grain yield via plant height was negative, while positive and weak via the grain number per panicle (0.11).
The positive total effect of panicle number per plant was mainly due to the strong and positive direct effect of panicle number per plant which indicated that this trait could be the selection criteria for improvement of grain yield of rice, with similar results for full-grain number per panicles and 1000 grain weight which their direct effects reflected about half or more of the total effect on grain yield, in addition to their indirect effects via panicle number per plant, and for that these three traits (1000 grain weight, panicle number per plant, and full-grain number per panicle) are considered as important indices to increase grain yield. These agree with the findings of other researchers (Hairmansis et al., 2013, Sarwar et al., 2015). Harish et al. (2019) study resulted that the indirect effect of plant height on grain yield via each of the panicle length and grain per panicle was negative and neglected, and indirect effect of panicle length via plant height was negative and neglected, while the indirect effect of grain per panicle via panicle length was positive on grain yield.
Our results of path analysis are in agreement with the findings of Bhutta et al. (2019), who revealed that the indirect effect of panicle length via plant height on grain yield was negative and neglected, and the direct effect of plant height on grain yield was positive and neglected as well as an indirect effect of plant height via panicle length was negative, and with Babu et al. (2012), who defined a positive and neglected direct effect of plant height on grain yield, as well as with Panda et al. (2019) who indicated that the direct effect of panicle length on grain yield is positive and neglected (0.08) and the direct effect of 1000 grain weight was positive on grain yield, with other scientists (Harish et al., 2019, Mohammad et al., 2013).
In the present study, the rice genotypes had sufficient genetic variability for all studied traits. A significant negative association was found between days to heading and both of panicle number per plant and 1000 grain weight; panicle length and full-grain number per panicle were significantly positively associated. A highly significant and positive association was found between panicle number per plant and each of full grain number per panicle and 1000 grain weight; a highly significant association was found between grain yield per plant and three traits (panicle number per plant, full-grain number per panicle, and 1000 grain weight). Enhanced attention in the breeding program on 1000 grain weight, panicle number per plant, and full-grain number per panicle as selection criteria is crucial to improve rice grain yield.