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Pearl millet; Stability; Regression coefficient; Environmental indices; Standard deviation

Pearl millet [Pennisetum glaucum (L.) R. Br.], popularized as bajra (2n = 14) belongs to the family Poaceae (earlier Gramineae) and is highly cross-pollinated crop with protogynous condition [1]. It is heterogenous as well as heterozygous in nature.In India, pearl millet ranks fourth amongst the most widely cultivated food crop after rice, wheat, and maize. Total cultivable area covers 6.93 million ha throughout the nation and secures 8.61 million tons of annual production and 1,243 kgha⁻¹ of productivity [2]. Pearl millet is thought to be originated in West Africa [3]. Although it is grown all over the world, Nigeria, Pakistan, Sudan, and Saudi Arabia contribute as the major pearl millet growing countries throughout the globe. In India, the major pearl millet growing states are Rajasthan, Maharashtra, Gujarat, Uttar Pradesh and Haryana, covering nearly 90% acre.

In agricultural field, study on Genotype X Environment interaction (GXE) is a common phenomenon. When environment changes, gaps between genotypic values may increase or decrease which may cause genotypes to even rank differently between environments.Stability means stable performance of a hybrid in wide range of environmental condition.Usually, no hybridscanperform equally in all environments due to theirparticular genetic barriers. In adverse conditions,unlike the purelines, hybrids show reduced performance rather than total crop failure. Yield is a complicated attribute, influenced by a number of morphological and physiological characteristics, including maturity, panicle length, panicle diameter, test weight, and so on. As those parameters inherit very simply, their exploitation looks so easy. Many scientific reports have already demonstrated a positive association with the final outcome i.e., seed yield.

Plant breeders have long sought to create genotypes with a wide range of adaptability. A huge range of genotype-environment (G x E) interactions, many a times creates complexities while determining the genetic influence on variability. Plant breeding programs strive to create genotypes that are phenotypically stable and adaptable to a variety of settings. Multi-environment testing aids in the selection of genotypes that excel in terms of yield and other traits.This study looked into G x E interactions for ultimate outcomeas well as important yieldcontributing aspects in pearl millet.

For the current study, eighteen hybrids of pearl millet (Table 1) were collected from the Rajasthan Agriculture Research Institute, Durgapura, Jaipur under the supervision of S.K.N.A.U, Jobner. Hybrid seeds werecarefully sownwith proper spacing (45cm × 10cm) in three artificially created environments along with varied doses of fertilizers.

The environments for this study were created using a variety of fertilizer doses in the following manner (Table 2):

Table 1: Hybrids chosen for the current study.

Table 2: Different environments studied under the current investigation

In each replication, hybrid seeds were sown in two rows in a plot of 4.0 x 0.6 m2. Row to row distance was managed at 45 cm, while two adjacent plants were grown at 10 cm apart. From each plot, ten random plants, excluding the border ones were selected for recording the observations. On the field note book, we have recorded grain yield, days to 50% flowering, panicle diameter, ear length and test weight for each and every representative plants.

The importance of variation owing to variations, environments, and varieties x environments interactionwas compared to pooling error.

Statistical analysis

The data on each character for the variations was subjected to standard statistical analysis of variance for each habitat independently [4]. After that, a pooled analysis of variance was run on the data from each group [5].

Earliness is a desirable character in kharif crops where erratic rains or lack of rains, particularly in later part is very common. The early hybrids may escape the adversities and mature before the onset of various stresses. This is the reason why breeders prefer early varieties most,despite of the negative correlation between earliness and the grain yield. In the current study, we found the average values of days to 50% flowering ranging from 44.56 (RHB-177) to 57.11 days (KBH- 108) with the regression coefficient in the range of 0.19 (GHB-558) to 1.64 (HHB-299) (Tables 3-5 and Figure 1) and a wide range of environmental indices (-3.50 to 3.01) (Table 3), which reflectimmense difference between the environments created for this character.The S2di values for all the hybrids were found non-significant (Table 5). Of eighteen hybrids, RHB-177 was found best to perform as an early variety followed by HHB-67 and MARU-TEJ (44.78 days to reach 50% flowering). Grain yield per plant was found to have negative association with days to 50% flowering just alike the expounding of one of the researcher.

Figure 1: bi vs mean value for days to 50% flowering.

Table 3: Environment indices for different characters of pearl millet hybrids

Table 4: Joint regression analysis for the parameters tested in three different environments

Table 5: Mean values and stability parameters (bi and S2di) of the Pearl millet hybrids for days to 50%  flowering

Harer PN and Karad SR, reported positive association between panicle length (cm) and seed yield per plant (g) in pearl millet. In the present study, mean value of panicle length ranging from 18.95 (MARUTEJ) to 25.26 cm (RHB-233) with the regression coefficient in the range of -0.29 (MPMH-17) to 2.28 (RHB-233) (Table 6) and (Figure 2) and a wide range of environment indices (-1.25 to 1.95) (Table 3), indicating a remarkable distinction among the all environments created. The S2di estimates of all the hybrids were found non-significant except of HHB-299, GHB-558, 9450, 9001 and KBH-108 (Table 6). Many of the hybridshave shown non-significant deviation from regression line for panicle length. Based on mean and regression coefficient, 9001, RHB- 173 and GHB-538 were found most stable among all the hybrids, whereas GHB-905, HHB-67, HHB-197 being found with below average stability looked congruent for improved management practices like high fertility and proper irrigation. High mean and regression coefficient less than 1 in RHB-233, RHB-234 indicate their stability indices exceeding the average value.

The mean panicle diameter ranged from 1.89 (MARU-TEJ) to 2.93 cm (86-M-86). The regression coefficient ranged from -1.21 (MARUTEJ) to 3.02 (9001). The S2di estimates were non-significant for most of the hybrids except HHB-67, HHB-299, 9450, MARU-TEJ (Table 6) and (Figure 3). The environmental indices varied from -0.16 to 0.09 panicle diameter wasfound maximum in 86-M-86 (2.94 cm) followed by HHB-299 (2.59 cm), RHB-233 (2.55 cm), and GHB-744 (2.27 cm) where the bi values were obtained close to 1, indicating their stable performance (Table 6).

Figure 2: bi vs mean value for Panicle Length (cm)/Plant.

Figure 3: bi vs mean value for Panicle Diameter (mm).

Table 6: Mean values and stability parameters (bi andS2di) of the pearl millet hybrids for panicle diameter and panicle length (cm)

The test weight ranged from 8.69 (RHB-173) to 10.62 (GHB-744). The regression coefficient ranged from -0.55 (9001) to 2.61(RHB-223). The S2di estimates were all the hybrids were non- significant (Table 7 and Figure 4). The environmental indices ranged from -0.57 to 0.84 (Table 3), indicating differences among the environments. Irshad-ulhaq M [7] reported positive correlation between test weight and seed yield per plant, hence high mean of test weight is desirable. The S2di estimates of most of the hybrids for test weight were non- significant. Because of high mean in 86-M-86 (10.51), RHB-538 (10.31 g), and RHB-234 (9.43 g) along with regression coefficient close to 1, these have been considered as stable for test weight.

The average seed yield per five plants ranged from 23.17 (RHB-173) to 30.73 g (KHB-108). The regression coefficient ranged from -0.49 (RHB- 173) to 2.14 (86-M-86) (Table 7 and Figure 5). The environment indices ranged from -2.85 to 1.76 (Table 3), reflecting noticeable differences among the environments created. The S2d_i associated with most of the hybrids were non-significant barring HHB-67, GHB-744, RHB-538 (Table 7).

Figure 4: bi vs mean value.

Figure 5: bi vs mean value for Grain yield per plant (g).

Table 7: Mean values and stability parameters (bi and S2di) of the pearl millet hybrids for test weight (g) and seed yield (g)

For all parameters, an environment-by-environment analysis of variance revealed substantial differences between hybrids in each environment. For all of the characters, the pooled analysis revealed substantial differences across the hybrids, demonstrating that actual differences exist between hybrids. For all of the qualities that are comparable to the vast range of environmental indicators, the environmental influence was likewise extremely significant. This suggested that the surroundings had a significant impact on hybrid performance. Except for days to 50% blooming and panicle length, genotype x environment interactions were significant for the majority of the characteristics, hence stability parameters were determined for all of them. Except for plant height, panicle length, and panicle diameter, the environment plus genotype x environment interactions were significant for the majority of the traits (Table 4). The linear component of the G x E interaction was significant for test weight and seed yield per plant, indicating that hybrids had divergent linear responses to environmental changes for these characters, according to stability analysis by joint regression analysis [8]. The pooled deviations for panicle length, panicle diameter, and seed yield per plant were found so significant (Table 4), that indicate that departures from linear regression also contributed significantly to the variations in hybrid stability for these traits.

The hybrids RHB-177, HHB-197, and MPMH-17 were found to be stable for the majority of the traits, making them suited for everchanging environmental circumstances.

A stable genotype according to Eberhart and Russell [8] is one which has the regression coefficient (b) equal to unity (bi = 1.0) and deviation not significantly different from zero (S2di =0).

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