Combined analysis of variance
The result of combine analysis of variance (Tables 3 and 4) revealed that highly significant differences were observed among location to location for plant height, tiller number, panicle number, panicle length, flag leaf length, flag leaf width, leaf area index, harvest index, total dry weight, total grain weight, 1000 seed weight, filled grains, unfilled grains and grain yield. The significant difference among the phenological traits of the three environments helped to find out the best genotype for the locations. This result is the same as finding of
Vange (2009). While few of the phenotypic traits like flag leaf length, harvest index, total dry weight, total grain weight and filled grains had a significant difference among genotypes to genotypes. There were significant differences among harvest index, total dry weight and total grain weight of the genotype to location sites. Various environmental phenomenon such as, rainfall, temperature, humidity and soil types might have a great influence on the genotypes.
Mean comparison for phenotypic parameters
Tables 5 and 6 showed the mean comparison for the phenotypic traits of the genotypes that Nahng Kian had highest value for grain yield (6234.11 kg ha
-1). Khao/ Trai genotype for 1000 seed weight (23 g), total dry weight (44.60 g) and flag leaf width (1.99 cm). Dawk Kahm showed a highest value for plant height (131.46 cm) and filled grain (689.67 no.). Dawk Pa-yawm showed a highest value for total grain weight (19.22 g).
Genetic Variability
In Table 7, the maximum genotypic variabilities were found in grain yield (7735.3333), followed by filled grain (6854.0000), unfilled grains (67.3333), total dry weight (24.4444) and plant height (13.6811). Similarly, the highest phenotypic variabilities were found in grain yield (112167.4444), followed by filled grain (8764.8889), unfilled grains (424.5556), total dry weight (68.6778) and plant height (21.4556). High variability in grains yield and plant height was also reported by
Sumanth et al., (2017) and
Girma et al., (2018).
Values more than 15% of genotypic and phenotypic coefficients of variation were considered as high, 9% to 14% as moderate and less than 9% as low. Moderate to low genotypic and phenotypic coefficients of variation were obtained for tiller number, panicle number, leaf area index and unfilled grain. The small differences observed for plant height, flag leaf length, harvest index, 1000 seed weight and filled grains indicated the presence of enough genetic variability for these traits which might facilitated selection
(Yadav, 2000). The high to low differences observed only for total grain weight indicated the high influence of the environments on this trait.
Broad sense heritability
Johnson et al., (1955) classified broad sense heritability as low (<10%), medium (10 to 30%) and high (>30 %) showed most of the traits easily modified over selection. High heritability was observed (Table 7) for plant height (63.76), flag leaf length (55.95), leaf area index (44.04), harvest index (60.40), total dry weight (35.59) and filled grains (78.20) indicating the possibility of genetic improvement of these traits through selection. This outcome showed the similarities with the findings of
Sarawgi et al., (2000) and
Sao (2002). The medium heritability in panicle number (28.71) and unfilled grains (15.86) showed the more influence of environment on these traits. The low broad sense heritability observed for the tiller number (1.68), total grain weight (8.17), 1000 seed weight (8.55) and grain yield (6.90). The low heritability recorded for these traits showed direct selection for these traits was not effective.
Genetic advance
Johnson et al., (1955) also stated that measuring only heritability does not indicate genetic improvement. They also classified genetic advance (GA) as low (<10%), medium (10% to 20%) and high (>20%). In this study the range of GA varied from 0.34% to 25.30%. High percentage of GA was accounted for harvest index (25.27%) and filled grains (25.30%). Flag leaf length (11.09%), leaf area index (13.47%) and total dry weight (16.75%) achieved the medium percentages of GA. On the other hand, plant height (4.86%), tiller number (0.34%), panicle number (7.22%), total grain weight (4.40%), 1000 seed weight (1.01%) and unfilled grains (4.21%) had low percentages of GA. High heritability and genetic advance were seen in harvest index and filled grains in Table 7 which indicated these traits were less influenced by the environment
(Sumanth et al., 2017). For better result heritability in addition with genetic advance will be more useful for the selection
(Ali et al., 2002).
Cluster analysis
Based on the agronomic traits, the average, maximum and minimum distances between clusters were 417.13, 978.70 and 73.74 respectively (Fig 1). Group I comprised with three genotypes (Dawk Pa-yawm, Mai Tahk and Dawk Kha 50), group II four genotypes (Nahng Kian, Hawm Jet Ban, Dawk Kahm and Nahng Dum) and Group III three genotypes (Nual Hawm, Bow Leb Nahng and Khao/ Trai). Each group consisted genotypes were collected from several provinces, represented the usefulness of the cluster analysis. Dendogram showed that average, maximum and minimum distances between clusters had diverged genetic materials. Group I showed the highest mean values of yield contributing traits such as flag leaf length (38.18 cm), leaf area index (2.66) and total grain weight (19.22 g). Group II achieved plant height (131.46 cm), tiller number (7.89 no.), panicle length (26.19 cm), harvest index (0.57), filled grains (764.33 no.), unfilled grain (188.76 no.) and grain yield (6234.11 kg ha-1). Group III showed the maximum value of panicle number (6.81), total dry weight (44.60 g) and 1000 seed weight (23.00 g). Similar results also reported by
Khare et al., (2014), Girma et al., (2018) and
Iqbal et al., (2018). These results might assist the investigator for their selection strategies to improve grain yield for breeding program. Thus, present results concluded that traits such as flag leaf length, harvest index, total dry weight, total grain weight and filled grains were useful for higher grain yield. Some genotypes such as Dawk Pa-yawm, Dawk Kha 50, Nahng Kian and Khao/ Trai should be used for crossing to develop new upland rice varieties of southern Thailand.