Present research investigation was aimed to find out association among different attributing traits using correlation study whereas these association was bifurcated in direct and indirect effect through path coefficient analysis. Comparison of mean between irrigated normal sowing and submergence stress is also presented in this study.
Mean
A comparison of mean values of the morphological data taken from control and submergence on different aspects revealed a drastic decrease in plant height (cm), flag leaf length (cm), flag leaf width (cm), panicle length (cm), filled grains/ panicle, panicle weight (g), 1000-grain weight and grain yield (kg/ha) were recorded. However, a slight increase was found in tiller/ hill and unfilled grains/ panicle. Mean performance in control and submergence is presented in table number 2 and 3, respectively.
Correlation coefficient
Correlation coefficient analysis measures the mutual relationship between different morphological and reproductive characters to determine the component character on which selection can be emphasized for yield improvement. Yield is complex trait that is positively or negatively correlated with other agronomical attributes; selection based on the significant correlation might be increase the effectiveness of selection. The phenotypic (rp) and genotypic (rg) correlation coefficients for control and submergence condition are presented in Table- 4 & Table-5 respectively. In general, the magnitudes of genotypic correlation coefficients were higher than the respective phenotypic correlation coefficient. In case of submergence, survival index was having magnitude opposite to survival %. It means higher the index means lower the survival %. Therefore, negative association of the survival index was important. Here phenotypic correlation of control and submergence is discussed in detail.
In control condition, maximum positive significant phenotypic correlation of grain yield was observed with filled grain/panicle (0.4001**) followed by Days to 50% Flowering (0.2360) and highest negative significant phenotypic correlation was found for grain L/B ratio (-0.4627**) followed by panicle length (-0.2003) Table no 4. Whereas, In submergence condition, filled grain/panicle (0.6091**) and flag leaf length (0.4644), showed positive significant phenotypic correlation with grain yield. Survival index (-0.7899) Days to 50% flowering (-0.3162) showed negative significant association with grain yield. Panicle weight showed negative non-significant association with grain yield (Table-5). All the genotypic correlation in normal irrigated condition and submergence is also presented in table number 4 and 5 and figure number 1 and 2 respectively.
Characters association among other characters In control condition Table (4), Plant Height At Maturity (cm) showed positive and significant phenotypic association with Panicle Weight (g) (0.7114**), and 1000 Grain Weight (g) (0.6168**) and Flag Leaf Width (cm) (0.3026). plant height showed negative significant association with tillers/hill at maturity (-0.375) and Tillers/ m² (-0.3096). Days to 50% flowering showed negative and significant association with panicle length (-0.3728*). Panicle length exhibited significant positively association with only Grain L/B Ratio (0.3027*) (Table- 4.9).
Tillers/hill observed to have significantly negative phenotypic association with panicle weight (-0.4340**), 1000 grain weight (-0.3967), and flag leaf width (-0.3825). Flag Leaf Width (cm) exhibited positive and significant phenotypic correlation with panicle weight (0.4058*) and 1000 Grain Weight (g) (0.3683) while it showed negative significant phenotypic correlation with Days to 50% Flowering (− 0.4120). Panicle weight showed positive and significant phenotypic correlation with 1000 Grain Weight (g) (0.5928**). In submergence condition (Table No. 5), filled grain/panicle (0.6091**) and flag leaf length (0.4644), showed positive significant phenotypic correlation with grain yield. Survival index (-0.7899) Days to 50% flowering (-0.3162) showed negative significant phenotypic association with grain yield.
Survival index recorded in submergence condition had significant role in grain yield and association with other traits. Survival index showed positive and significant phenotypic correlation with Days to 50% Flowering (0.3466) followed by Panicle Weight (g) (0.2046) and 1000 Grain Weight (g) (0.1212) whereas negative and significant phenotypic correlation showed with Filled Grain/ Panicle (-0.5291), followed by Flag Leaf Length (cm) (-0.4656) and Flag Leaf Width (cm) (-0.2667).
In submergence condition, plant height at maturity showed positive and significant correlation with test weight (0.4858**). Tillers/ Hill at Maturity showed positive and significant correlation with Panicle Weight (g) (0.3922). Flag Leaf Length (cm) observed to have positive significant correlation with filled grain/panicle (0.4794**). Flag leaf width showed positive and significant correlation with test weight (0.4093*). Genotypic correlation in control and submergence stress is also presented in table number 4 and 5 respectively.
Path coefficient analysis
The direct and indirect effects at phenotypic and genotypic levels of the studied characters on grain yield in control are presented in Table- 6. For submergence condition, these effects for genotypic and phenotypic levels are presented in Table- 7. phenotypic path coefficient analysis has been discussed in detail following the classification given by Lenka and Mishra (1973). Genotypic path in control and submergence is also presented in Figs. 3 and 4 respectively. In path coefficient also, survival index in case of submergence has opposite magnitude to that of survival% and therefore, where survival index is showing negative effects on other traits, actually it means that survival% is having positive effects on the concerned trait.
Phenotypic path coefficient analysis In control Table- 6, filled grain/panicle (0.2468) and days to 50% flowering (0.2277) showed moderate positive direct effect on grain yield and panicle weight (0.1390) had positive but low positive direct effect whereas flag leaf length (0.0329), panicle length (0.0528), 1000-grain weight (g) (0.0185), had positive but negligible direct effect on grain yield. Whereas, plant height (-0.4236), grain L/B ratio (-0.3783) showed high but negative direct effect on grain yield. Flag leaf width (-0.0621) exhibited a low negligible direct effect on grain yield.
Plant height at maturity showed positive and indirect phenotypic effect on grain yield via Tillers/ Hill at Maturity (0.1589), Tillers/ m² (0.1312) and Grain L/B Ratio (0.0295). similarly, 1000 Grain Weight (g) shown positive low and indirect phenotypic effect on grain yield via Plant Height At Maturity (cm) (0.1578) and Panicle Weight (g) (0.1517); Grain L/B Ratio shown positive and indirect phenotypic effect on grain yield via Filled Grain/ Panicle (0.1321). Whereas negative and indirect phenotypic effect of Plant Height At Maturity (cm) on grain yield shown via Panicle Weight (g) (-0.3014), 1000 Grain Weight (g) (-0.2613), 1000 Grain Weight (g) via Tillers/ Hill At Maturity (-0.1015) and Grain L/B Ratio via Panicle Lenth (cm) (-0.1145).
Whereas in submergence condition Table- 7, Plant height at Maturity (cm) (0.2293) and Filled Grain/ Panicle (0.2663) showed positive and moderate direct phenotypic effect on grain yield and 1000 Grain Weight (g) (0.1787) showed positive and low direct phenotypic effect on grain yield whereas, Survival index % (-0.7045) showed negative and high direct phenotypic effect on grain yield, and Flag Leaf Length (cm) (-0.1572) shown negative and low direct phenotypic effect on grain yield. Positive and indirect phenotypic effect of survival index on grain yield shown via Filled Grain/ Panicle (0.3728), Flag Leaf Length (cm) (0.3280) and Flag Leaf Width (cm) (0.1879) and negative and indirect phenotypic effect of survival index on grain yield shown via Days to 50% Flowering (-0.2442) and Panicle Weight (g) (-0.1441). similarly, positive and indirect phenotypic effect on grain yield was shown by plant height at maturity via 1000 Grain Weight (g) (0.1114), Filled Grain/ Panicle via Flag Leaf Length (cm) (0.1277). Whereas, negative and indirect phenotypic effect on grain yield was shown by Filled Grain/ Panicle via Survival index % (-0.1409). Present research is in-lined with Parte et al 2022 reported that panicle weight per plant, filled spikelets per panicle, harvest index, and biological yield per plant are having a high direct effect and significant correlation with grain yield per plant by conducting an experiment with 58 rice genotypes. Similarly, Manasa et al 2022, characterised the correlation and path analysis for yield and yield attributing traits and findout most positive and significant correlation between the number of panicles per plant and the number of filled grains per panicle. Number of panicles per plant and number of filled grains per panicle reported the strongest positive direct effect on grain yield per plant. Swapnil et al 2020 also reported that seed yield per plant was positively and significantly correlated with number of tillers per plant, number of panicles per plant, number of spikelets per plant, number of grains per plant, number of spikelets per panicle, number of grains per panicle and path analysis indicated that number of panicles per plant, number of spikelets per plant and number of grains per plant exhibited high and positive direct effects in F2 population of the cross Sahbhagidhan and BPT-5204 Sub-1. Kulsum et al 2019 evaluated 46 submergence tolerant rice genotypes and find out similar result for correlation and path analysis; significant correlations at both phenotypic and genotypic level between yield per plant and panicle weight, thousand grain weight. In Path coefficient analysis, they reported that panicle weight, spikelet fertility percentage, days to maturity and thousand grain weight had direct positive effect on yield. Genotypes under evaluation having submergence tolerance gene such as the advanced lines taken from IRRI, Phillipines and Swarna sub1 showed comparatively better performance in submergence stress environment. Similar results reported by Kumari et al 2019 evaluated 240 mutant lines developed from three rice varieties i.e FR13A, FR13B and Labella along with three untreated checks (FR13A, FR13B and Labella). These were evaluated for their survival percentage under submerged condition for yield potential. Association study revealed that number of tillers per plant and survival percentage showed significant positive direct association with grain yield per plant under submergence environment. Thus, these traits may be used as selection criteria in further crop improvement programmes for submergence tolerance. Traits showed significant and positive association with yield might be used for selection criteria for yield improvement in submergence stress condition. Present research study was also supported by Kumar, et al 2018; Saketh et al 2023; Priya et al 2024 and Pradhan et al. (2015).
ADH Specific Enzymatic Activity
In our study, ADH specific enzymatic activity was carried out before (i.e. 0 day of) submergence; 5th day, 10th day, 15th day and 18th day of submergence; and 5th day of de-submergence. The ADH enzymatic activity was found to be negligible before the start (i.e. at 0 day) of submergence. The same trend was recorded up to 5th day. However, at 10th day of submergence, a sudden increment in the ADH enzymatic activity was recorded in the positive control Swarn Sub 1 and test genotypes namely Rajendra Sweta, RYC-743, IR 96321-315-402-B-1, IR 96321-1686-199-B-3 and Purnendu. Magnitude of ADH enzymatic activity was recorded high at 15th day of submergence for almost all the genotypes, however, it was found to be maximum for positive control Swaran Sub1 and the test genotypes namely Rajendra Sweta, RYC-743, IR 96321-315-402-B-1, IR 96321-1686-199-B-3, Purnendu that were close to positive control Swarna sub1. A sharp and gradual reduction for ADH enzymatic activity was recorded after 15th day of submergence and it was found to be very less at 18th day of submergence. Genotypes viz. Rajendra Sweta, RYC-743, IR 96321-315-402-B-1, IR 96321-1686-199-B-3 and Purnendu were found to be close to Swarna Sub1. At 5th day de-submergence, ADH enzymatic activity was found to be sharply declined for all the genotypes (Fig. 5). Genotypes showing high ADH enzymatic activity at 15th day of submergence were found to be having very good survival percentage under submergence. Therefore, it is clear that ADH enzymatic activity is directly responsible for the survival of genotypes under complete submergence. The activity shoots up after 10th day of submergence and reaches its maximum level followed by sharp decline. ADH specific enzymatic activity was found to be responsible for better survival of rice under complete submergence (Kumar et al., 2021; Pradhan et al., 2016; Goswami et al., 2017). A significant and positive correlation was recorded between ADH enzymatic activity and survival percentage after complete submergence (Kato-Noguchi and Kugimiya T, 2003; Bui et al., 2015). In our study, the same trend was found for almost all the genotypes. Genotypes showing high ADH enzymatic activity at 15th day of submergence were found to be having good survival percentage under submergence. Pradhan et al., 2019 also reported that the variety showed gradually increase in alcohol dehydrogenase activity during submergence period than the normal aerial condition also performed well than others, they found that well established sub 1 incorporated rice mega varieties like IR64 sub 1 and Swarna sub 1 showed comparatively high ADH enzyme activity among fifty diverse paddy genotypes in the submergence experiment. While rice genotypes like Mahananda, Sabita and Purnendu showed high ADH units from the FR43B tolerant check genotypes and below the other tolerant check genotypes. Similarly, prasad et al., 2011 also reported the three group of studies genotypes based on survival percentage and ADH activity in submergence condition (I) Submergence tolerant (FR13A, Jalashree and Jalkunwari), (II) Moderately submergence tolerant (Bahadur and Ranjit), (III) Submergence susceptible (Luit, Keteki, Lachit, chilarai and Mahsuri). According to earlier report of (Das et al., 2011), the ADH specific enzymatic activity under submerged condition was found to be increased as the duration of submergence enhanced and it undergoes towards a plateau followed by decline at later stage.