Genetic divergence, Cluster analysis, Mono-genotypic, Inter and intra cluster distance.

Linseed (Linum usitatissimum L.) chromosome number, 2n = 30, is one of the most important Rabi oilseed crops and belongs to genus Linum, which is a Latin term that means "very beneficial" (Naik et al., 2020). It is an annual plant belonging to family Linaceae and order Malphigiales, commonly known as "Alsi". It is presumed to have originated in South West Asia, particularly in India. Linum usitatissimum is the sole cultivated species grown by man, having 6000-7000 years of planting history and is one of the oldest crops under cultivation (Paul et al., 2020). Every part of the linseed has extensive and varied uses; linseed oil content varies from 33 to 45 per cent (Jaishri, 2021) and it is richest plant source of omega-3 (36-57 per cent) and omega-6 (18-24 per cent) that are nutritionally significant (Paul et al., 2020). It has been found that consumption of 25 g linseed on daily basis reduces risk of breast cancer (Kaur et al., 2023). For normal growth and development of linseed, cool climatic conditions are considered most suitable. The minimum and maximum temperature regimes should be 10ºC and 38ºC, respectively; therefore, October to November is suitable for sowing. Linseed is cultivated in most of the countries in the world. In India, linseed occupies about 219.86 thousand hectares with a production of 158.64 thousand tonnes and productivity of 979 kg/ha (Annual Report of AICRP Linseed, 2022-2023). In Rajasthan, linseed is being cultivated in an area of 22.5 thousand hectares with a production of 24.2 thousand tonnes and productivity of 1070 kg/ha (Directorate of Economics and Statistics, DAC & FW, GOI, 2022-23). To thrive in any crop improvement programme, the pivotal factor is the analysis of the genetic diversity present, especially in the primary gene pool. It also plays an important role in effectively managing gene pool thereby conserving it. Among the different methods for evaluating genetic diversity, multivariate analysis, such as D2 statistics, has proven useful in various breeding applications, notably in selecting the most diverse genotypes suitable for hybridization. Hence, this investigation was conducted to estimate the magnitude of genetic diversity available in 33 linseed genotypes. 

The experiment material consisting of 33 genotypes of linseed including three checks and was evaluated in Randomized Block Design (RBD) with three replications during Rabi 2023-2024 at Agriculture Research Station, Kota. Each genotype was laid in plot size of 4 × 1.2 m2 with a spacing of 30 × 10 cm. All the recommended agronomic practices and plant protection measures were timely adapted to raise a healthy plant population.  

All the observations were recorded on ten randomly selected plants of each genotype for eleven characters viz., plant height, number of primary branches per plant, number of capsules per plant, number of seeds per capsule, biological yield, harvest index, test weight and seed yield per plant in each replication except for phonological characters i.e., days to 50 per cent flowering, days to maturity and plant stand. These three characters were recorded on plot basis. These collected data were used to analyze genetic diversity using Mahalanobis’s D2 estimates and cluster genotypes were clustered using Tocher’s method. The data analysis and diagram construction was done using Windostat (9.3 version) and R 4.30.

In culmination to genetic relationship, based on relative magnitude of D2 estimates the thirty three linseed genotypes were grouped into 8 distinct non-overlapping clusters and presented in Table 1. The discrimination of genotypes into discrete clusters suggested presence of high degree of genetic diversity in the material evaluated. Out of all the clusters, cluster I had maximum number of genotypes i.e.,15 namely RCRL-21-2, JSL 95, RL 18105, LCK 2109, RL 18114, BRLS 109-2, DLV-24, BRLS 109-5, SLS 142, LMS-2019-I-11, LCK 2037, RLC-190, RL 15580, LSL 93, and Pratap Alsi-2, followed by cluster II i.e., 8 which includes genotypes RLC 192, T-397, RL-189, BRLS 109-2-1, RLC-191, LCK 2132, RLC 92, and LMS 9-2K and cluster VI consists of 5 genotypes viz., LCK 2107, LMS-2019-I-4, Kota Alsi-6, RLC 184 and BAU-2021-06.While other five clusters comprised of only one genotype viz., cluster III (BRLS 111-2), cluster IV (SLS 133), cluster V (DLV-23), cluster VII (RCRL-21-1) and cluster VIII (SLS 141). The average inter and intra cluster distances based on D2 values is presented in the Table 2 and diagrammatically represented in Fig. 1. The intra cluster distance had ranged from 0 to 56.26. The maximum intra cluster distance was recorded for cluster VI (56.26), followed by cluster II (35.92) and cluster I (35.86) while cluster III, cluster IV, cluster V, cluster VI, and cluster VIII had least intra cluster values viz., zero as these clusters comprises of only one genotype each. The inter cluster distances ranged from 18.06 to 218.51. Samantara et al. (2020) reported the similar results in their respective studies.

The maximum inter cluster distance was recorded between cluster IV and VIII (218.51), followed by cluster V and VIII (204.56), cluster VII and VIII (167.2), cluster III and VIII (152.42), cluster II and IV (144.24), cluster II and V (135.81), cluster VI and VIII (135.29), cluster VII and VI (129.62), cluster II and VI (116.01), cluster III and V (111.38), cluster I and VIII (109.38), cluster III and VI (97.75), cluster II and VI (96.28), cluster II and III (93.72), cluster II and VIII (89.15), cluster V and VI (87.78), cluster III and VI (87.37), cluster IV and VI (80.78), cluster III and IV (79.33), cluster I and II (74.4), cluster I and VI (71.76), cluster I and V (61.28), cluster I and VII (58.17), cluster I and IV (57.5), cluster I and III (54.12), cluster IV and VII (52.19) and cluster V and VII (40.16). These findings were in agreement with the findings of Chand et al. (2022); Thakur et al. (2021) ; Sharma et al. (2018).

The cluster mean values for 11 different characters for eight clusters are presented in Table 3. Cluster IV consists of genotype (SLS 133) with a higher cluster mean for test weight, harvest index, and plant stand while cluster VI consists of genotypes (LCK 2107, LMS-2019-I-4, Kota Alsi-6, RLC 184, and BAU-2021-06) with higher cluster mean for seed yield per plant, biological yield, number of seeds per capsule and number of capsules per plant and genotypes included in these clusters could be utilized in hybridization programme for yield improvement. Cluster III (BRLS 111-2) was found earliest for days to 50 per cent flowering and days to maturity and the genotype included in it can be used as a donor for early maturing variety development programmes. Therefore, it is essential for a breeder to wisely combine all the targeted traits for a specific hybridization programme including selected genotypes from divergent clusters. These results are in conform with the results of Kumar et al. (2022); Meena et al. (2021); Ankit et al. (2019).

Fig. 1. Diagrammatic representation of cluster distances.

Table 1: List of thirty three linseed genotypes groupedin to eight different clusters by Tocher’s method.

Table 2: Intra and inter cluster distances based on D2 analysis.

Table 3: Cluster mean values of seed yield and its contributing traits.

By conforming the above results at varied locations might help validate the unambiguousness of conclusions at its best. The study on genetic divergence lays out foundation for further hybridization programmes for improving varieties in respect of resilience against adverse climate and pathogens or insects hence stabilizing and increasing the yield of linseed crop.