Cluster pattern
As per the assumption from D
2 analysis, the 40 bread wheat lines under investigation were grouped into ten clusters (Table 1). The cluster size varies, each comprising one to nine wheat lines. Cluster III emanated with the largest enumerate of components that make up 9 bread wheat lines, specifying comprehensive genetic closeness among them. Clusters II and IV pursued it, constituting 8 lines each, whereas clusters I and X had 6 and 4 entries. The remaining clusters,
i.e., V, VI, VII, VIII and IX, comprise 1 bread wheat strain each, respectively. The framework of the grouping of wheat lines in discrete clusters and vice versa suggested that there was an inclination between geographical and genetic diversity as the wheat lines used in the present study belong to the same geographical region. These results conform with the observations of
Verma et al., (2014), Singh et al., (2014), Vora et al., (2017), Santosh et al., (2019). The clustering arrangement may be exploited in picking the divergent parents by determining suitable cross combinations. It will foster intense feasible variability for several attributes. Thus, the lines with high intra and inter-cluster values can be utilized in the crop improvement programmes for further selection followed by hybridization.
Inter-cluster distances
The results (Table 2) specify that the maximum inter-cluster distances were perceived among VI and X clusters (66.654) followed by clusters IX and X (63.232), VI and IX (62.201), VIII and IX (61.677) and clusters VI and VIII (60.321). On the contrary, the low-lying inter-cluster distance was found between clusters II and III (14.302) followed by clusters I and VI (14.621), clusters II and V (15.321), clusters II and IV (16.111) and clusters I and VIII (16.321), propounded familiarity and the lowest level of genetic diversity among them. Cluster distance (Intra and Inter) is the foremost standard for the identification of diverse lines (parents) using the D
2 statistic
(Rahman et al., 2015). The genotypes which possess the greatest inter-cluster distance are genetically more divergent and hybridization among them may result in the formation of transgressive segregants with more desirable features along with ample variability
(Tewari et al., 2015). Thus, the bread wheat lines fall under VI and X clusters (PBW 343 × CPAN 1796, PBW 343 × HS 420, PBW 343 × VL 892 and PBW 343 × RAJ 4393) will effectuate the possible hybridization among the parents showing broad genetic base/diversity and such crosses could hopefully ensure the blooming of desirable progenies in the F
2 and subsequent segregating generations.
Cluster means
The bread wheat line with respect to their various quantitative/qualitative characters, grouped under 10 clusters, discloses appreciable distinctions concerning their cluster means (Table 3). Based on the average or mean performance, genetically diverse lines with various desirable traits were spotted in each cluster. The findings of the present study designate that cluster I recorded earlier flowering (75.21 days) followed by cluster III (75.41 days), cluster VIII (76.54 days) and cluster IV (77.64 days). The same lines discussed above also mature earlier than the rest. Cluster-I matures in 113.88 days followed by cluster III (114.58 days), cluster VIII (114.87 days) and cluster IV (115.25 days). Such lines can escape the adverse effect of drought, terminal heat stress, disease/insect infestation and at the same time, they can give a better yield than those varieties which come under the adverse effect of terminal heat/drought,
etc. (
Singh, 2015). Thus, these lines can be used in hybridization programmes to transfer their earlier trait into other promising lines that lack such an important trait. The inflated mean value for the number of effective tiller plant
-1 was displayed by cluster VI (10.12) followed by cluster II (9.22) and cluster VIII (8.44), whereas the lowest was recorded in cluster V (6.70). The maximum average value for spike length (8.45 cm) was found in cluster VI followed by cluster I (8.41 cm) and cluster IV (8.33 cm). Cluster VI exhibited a greater cluster mean (40.71) for the number of grains spikes
-1 which was at par with cluster I (40.66), cluster IV (40.23) and cluster VIII (40.09). It is perceived from the present study that maximum cluster means concerning plant height were observed by cluster VI (93.33 cm) followed by cluster II (95.51 cm). Whereas, the lowest plant height was recorded by cluster V (89.54 cm). The mean data of the harvest index indicates that among all the clusters, cluster VI recorded the highest mean value for the harvest index (45.34%) whereas the lowest was recorded by cluster V (38.42%). From the current research, it is comprehended that the highest cluster mean values for 1000 grain weight were recorded in cluster VI (42.75 g) and the lowest in cluster V (37.44 g). Cluster VI observed maximum mean values for protein content (12.22%) and a minimum was observed by cluster X (9.28). The greatest cluster means value for grain yield plant
-1 was displayed by cluster VI (11.25 g) and the lowest by cluster V (9.13 g). Grain yield is not an independent character but a product of a number of the constellation of yield contributing characters such as tillers per plant
-1, which contributes to raising plant population per unit area
(Nazim et al., 2014); spike length, grain per spike
-1 and 1000 grain weight which form the ‘sink’
(Roman et al., 2013) and the harvest index which is the ratio of economic yield to total biological yield. The harvest index is considered an effective parameter to measure yield advancement and is considered directly related to yield (
Abrar et al., 2011). In cereals including wheat, plant height is one of the essential components that is directly linked with lodging resistance and plant canopy (
Singh, 2015). After yield, grain quality especially protein is a very important character and is directly needed by human beings (
Abrar and Ram, 2018). All the above-cited attributes that have been grouped into different clusters under the present study play a pivotal role in the identification of more desirable diverse genotypes/lines within or among the clusters. On that account, hybridization between bread wheat lines grouped in 10 distinct clusters with the highest cluster means values will result in the induction of enormous genetic variability in the F2 and subsequent generations providing an opportunity to encourage the production of desirable transgressive segregants. Thus, ensued genetic improvement in grain yield and yield contributing character as well as protein content either directly or indirectly in wheat. Similar findings were also confirmed by
Kumar et al., (2013);
Kumar et al., (2014a);
Vora et al., (2017);
Tejasvi et al., (2017);
Girnam et al., (2018);
Santosh et al., (2019). They all reported high cluster means for various characters in wheat.
Contribution of the characters toward total divergence
The involvement/contribution of the characters in connection with the manifestation of the entire genetic divergence (Table 4) indicated that the greatest per cent of the contribution comes from grain yield plant
-1 (23.17%) followed by spike length (20.75%), effective tiller plant
-1 (19.42), 1000 grain weight (14.33%), plant height (14.21%), harvest index (10.44%) and the number of grains spike
-1 (8.42%). These results conform with
(Lal et al., 2009; Kolakar et al., 2014; Kumar et al., 2014a; Vora et al., 2017 and
Girnam et al., 2018). The characters with a maximum percent of contribution concerning the assertion of genetic divergence shall be acquired as an indicator in the selection of diverse parents from each cluster and utilized the same in the hybridization programmes for the development of desirable segregants which ultimately may result in the selection and release of new elite cultivars from the segregating population.
Heritability
Heritability is one of the important biometrical techniques, a reliable and excellent indicator aids in determining how much percentage of a trait is transmitted from parent to their offspring. In the ongoing investigation apart from focalizing the genetic diversity, heritability in the broad sense (the ratio of genotypic variance to the total or phenotypic variance) was also evaluated in all the 10 attributes under study. The values of heritability as per
Johnson et al., (1955a) were classified as low (less than 30%, moderate (30-60%) and high (greater than 60%). It was seen that all the 10 characters considered under the current research showed more than a 60% heritability estimate thus observing a high heritability percentage (Table 5). Amongst the 10 attributes, the highest heritability percentage in a broad sense was heeded by spike length (85.41%) ensued by 1000 grain weight (84.88%), harvest index (81.72%), number grains spike
-1 (80.22%), number of effective tillers plant
-1 (79.26%), plant height (74.56%), protein content (72.63%), grain yield plant
-1 (69.45%), days to maturity (67.59%) and days to 50% flowering (65.41%). The findings of
Yadav et al., (2011);
Abrar et al., (2018);
Pavan et al., (2018);
Abrar et al., (2020) and
Patil et al., (2023) are consistent with our results. A high heritability percentage for the aforementioned components shows that a portion of phenotypic variance has been linked to genotypic variance and hence credible selection for these traits based on phenotypic expression could be made. Characters with high heritability are wealthier for a plant breeder than those with low heritability since the traits with low heritability are more subject to environmental change and selection of such traits would result in misleading the findings. In addition to heritability, one more important biometric tool is the genetic advance which refers to the enhancement in the average genotypic value of selected genotypes over the original population (parental population) before selection. Howerver, as per
Johnson et al., (1955a), heritable estimate combined with genetic advance expressed as per cent of mean is more useful than heritability alone in forecasting the eventual effect of selection and according to
Johanson et al., (1955a) the range of genetic advance as per cent of mean is classified as low (less than 10%), moderate (10-20%) and high (more than 20). The number of effective tillers plant
-1 (64.37%), spike length (51.88%) harvest index (45.05%),1000 grain weight (41.03%), number of grains spike
-1 (39.64%) and protein content (34.55%) were all considered to be highly encouraging because of recording high genetic advance as percent of mean along with high heritability estimates. Consequently, these traits may also exhibit the least genotype x environment interaction as they are the least affected by environmental factors. Similar findings were also corroborated by (
Yadav et al., 2011;
Abrar et al., 2018;
Pavan et al., 2018;
Abrar et al., 2020 and
Patil et al., 2023).