Manifestation of heterosis and inbreeding depression in Indian mustard (Brassica juncea L.)

Y.P. Singh , Anil Kumar , V.K. Dhangrah

School of Agricultural Sciences & Engineering, IFTM University, Moradabad, Uttar Pradesh–(244 102), India

Corresponding Author Email: vinod.dhangrah@gmail.com

DOI : https://doi.org/10.51470/ABF.2024.4.2.16

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INTRODUCTION

Since ancient times, Indian mustard (B. juncea (L.)) has been farmed, accounting for over 80% of the entire planted area for rapeseed mustard and providing around 27% of India’s edible oil pool. Mustard oil is mostly used for human consumption in Northern India [18]. India’s mustard yield for the past ten years has been essentially stagnant, averaging about 1.1 to 1.2 tons/ha, far less than the global average of 1.98 tons/ha. When the productivity of mustard in India is compared to 4.3 tons/ha in Germany, 3.8 tons/ha in France, and 3.4 tons/ha in the UK, there is a significantly larger yield disparity [20]. Population density, the number of pods per plant, the number of seeds per pod, and the weight of each individual seed multiply to produce yield per area [4]. Therefore, as [6] points out, yield may not reflect the expression of any one gene per se. If better germplasm lines are successfully used to create high-yielding genotypes or hybrids, a greater yield can be attained. Heterosis is a phenomena that may be used to increase agricultural plant yields and provides an explanation for how this process can be used more financially and efficiently. Hybrid vigor has often been recognized as a primary component of heterosis in plants [2,12].As the phenotypic manifestation of heterosis, which is a genetic phenomena, hybrid vigor is described as the heterosis evident. This occurrence occurs often in plants, in both self-pollinated and cross-pollinated crops. Heterosis has been economically used in a variety of extremely different brassica crops [7,9,13]. There is a considerable amount of heterosis in mustard in terms of seed production and other traits.Since the environment has a significant impact on how heterosis manifests, it is vital to examine this expression across a variety of climates and seasons [8].While inbreeding can help retain favorable traits or eliminate unwanted genes, it frequently leads in children that are smaller, less vigorous, and less fertile due to the combined effects of deleterious genes that were recessive in both parents. Plant vigor is reduced as a result of ongoing inbreeding, a condition known as inbreeding depression.The F₁ to F₂ generation is when inbreeding depression peaks. In order to generate high-yielding genotypes of mustard, early selection of favorable heterotic crosses is crucial.Therefore, the main goal of mustard breeding in recent years has been to effectively use heterosis to produce high-yielding hybrids and analyze the depression caused by inbreeding in the F₂ generation [19]. The goal of the current study was to examine inbreeding depression and heterosis in Indian mustard.

MATERIALS AND METHODS

The experimental material comprising the ten  diverse genotypes of Indian mustard, NRCHB – 101, DRMR- IJ- 31, Kanti,  Urvashi, Pusa mustard- 25 (NPJ-112), Pusa mustard-26 (NPJ-113),  Pusa mustard 27 (EJ-17), CS 54, RH 406, RH 749. These parents maintained as pure lines by selfing for several generations were crossed in half diallel fashion at Agriculture Research Farm of R. B. (PG) College, Agra, (U.P.), India. Hundred treatments consistingof 10 parents, 45 F₁s and 45 F₂s were evaluated in a Randomized Block Design with three replications during Rabi season of 2017-20 at the Agriculture Research Farm of School of Agricultural Sciences and Engineering, IFTM University, Moradabad (U.P.), India. Each parents and F₁s were grown in a single row and each F₂s in two rows of five meter length spaced at 45 cm×15 cm apart. All recommended agronomic practices were adopted for raising a good crop. Fifteen plants each from parents and F₁s and thirty plants from F₂s were randomly selected for recording the observations on ten characters. The mean of three replications for parents and F1 crosses for all traits were subjected to statistical analysis of variance suggested by [11] was used to test the significance. Heterosis was estimated in relation to better parent (heterobeltiosis) and standard check (standard heterosis) as per the standard procedure. Inbreeding depression was measured in F₂ plants for eachcharacter through inbreeding of F₁ hybrids. Heterobeltiosis was calculated following the formulae given by [5].

RESULTS

Analysis of variance for Parents+F₁+F₂ of Indian mustard

            Analysis of variance was carried out for ten characters in parents, F₁and F₂generation, and the results are presented in Table 2. The results revealed that there was significant variation among all genotypes including parents and F₁ hybrids for the characters studied except oil content (%).The variance due to parents vs.F₁ hybrids was significant for all the charactersstudied indicating the parents were distant related to each other.Similarly, variance due to parents vs. F₂ hybrids was significant for most of the characters except test weight, oil (%) and seed yield.

Per se performance, heterosis,and inbreeding depression in hybrids

The performance of hybrids in heterosis breeding is generally assessed by mean performance, better parent heterosis and standard heterosis.In addition, assessment of inbreeding depression is essential for effective selection of segregants.Therefore, mean values of hybrids per se performance, better parent heterosis, standard heterosis and inbreeding depression are kepttogether in Table 3a and Table 3b.

Days to maturity

The mean performance for days to maturity was lowest i.e. 109.67 days in hybrids from the crosses, PM 27×RH 406,Kanti×Urvashi and Kanti×PM 25. Since early maturity was considered as desirable character, negative heterosis was taken as beneficial. The hybrids from crosses,Kanti×Urvashi and PM 27×RH 406 exhibited the highest negative significant heterobeltiosis (better-parent) and standard heterosis, respectively.Significantly lowest inbreeding depression was estimated in the hybrid from the cross, Urvashi×PM-25 (0.95%) and followed by NRCHB 101×PM-25 (1.16%).

Plant height (cm)

In hybrids, it varied from 180.33 (Kanti× PM 27) to 251.00 (DRMRIJ 31×Urvashi).Thehybrid from cross, Kanti×PM 25 had highest significant positive heterobeltiosis followed by PM 26×PM 27 (26.02%)and DRMRIJ 31×Urvashi. The highest significant standard heterosis was observed in the hybrid form the cross DRMRIJ 31×Urvashi (28.72%), followed by Kanti×PM 25 and Urvashi×RH 749.Significantly lowest inbreeding depression was estimated in the hybrid from cross, PM-27×CS-54 (0.43%) and followed by Uravshi×RH-749 (0.63%).

Primary branches per plant

The hybrid from the cross, PM 27×CS 54 exhibited the highest number of primary branches per plant (11.0). In accordance with per se performance, this hybrid showed the highest significant positive heterobeltiosis (83.33%), followed by PM 25×RH 749 (52.38%), PM 27×RH 406 (52.38%), PM 25×PM 27 (50.0%), PM 26×PM 27 (41.67%). The hybrid from the cross, PM 27×CS 54 exhibited highest significant positive standard heterosis (83.33%) followed by PM 25×RH 749 (77.78%), PM 27×RH 406 (77.78%), PM 27×RH 749 (44.45%) and DRMRIJ 31×PM 27 (38.88%).Significantly lowest inbreeding depression was estimated in the hybrid from the cross, PM-27×RH-406 (6.25%).

Secondary branches per plant

The hybrid from the cross, PM 26×CS 54 gave rise tothe highest number of secondary branches (65.67). The hybrid from the cross, PM 25×PM 26 exhibited highest significant positive heterobeltiosis (165.0%), followed by PM 26×CS 54 (134.52%), Kanti×PM 26 (80.0%). The maximum significant standard heterosis was observed in the cross, PM 26×CS 54 (152.57%), followed by RH 406×RH 749 (107.69%) and PM 25×PM 26 (103.85%).Significantly lowest inbreeding depression was estimated in the hybrid from the cross, PM-25×PM-26 (2.57%) and followed by DRMRIJ31×PM-25 (2.83%).

Number of siliquae per plant

The hybrid from the cross, RH 406×RH 749 resultsa highest number of siliquae per plant (2485.33).The highest significant positive heterobeltiosis was estimated from the crossviz. Kanti×PM 25 (385.17%).In accordance with per se performance, the hybrid from the cross, RH 406×RH 749 exhibited highest heterosis over economic parent (260.19%). Significantly lowest inbreeding depression was estimated in the hybrid from cross, PM-27×CS-54 (0.66%) and followed by CS-54×RH-406 (1.09%).

Siliqua length (cm)   

The mean length of siliqua in hybrid from the cross, PM 27×RH 749 was highest recorded as 7.17 cm.Out of 12 crosses exhibiting positive heterobeltiosis, the highest magnitude of heterosis (16.67%) over better parent was expressed by NRCHB 101×NPJ 112(PM25), followed by Urvashi×PM 27 (9.09%).Followingper se performance, the hybrid from the cross, PM 27×RH 749 exhibited maximum significant standard heterosis (30.31%).Significantly lowest inbreeding depression was estimated in the hybrid from cross, NRCHB 101×PM-27 (3.67%) and followed by Kanti×PM-25 (4.00%).

Seeds per Siliqua

Highest number of seeds per siliquae was recorded as 20.67 in the hybrid from the cross, DRMRIJ 31×RH 406.The hybrid from the cross, DRMRIJ 31×PM 26 exhibited highest significant positive heterobeltiosis(60.56%), followed by DRMRIJ 31×Kanti (55.56%), DRMRIJ 31×RH 406(47.62%). Likeper se performance, thehybrid from the cross, DRMRIJ 31×RH 406 exhibited the highest significant positive standard heterosis (87.88%).Significantly lowest inbreeding depression was estimated in the hybrid from the cross, NRCHB 101×DRMRIJ31 (1.75%) and followed by NRCHB 101×PM-27 (2.19%).

Test weight (g)

The hybrid from the cross, DRMRIJ 31×RH 406gave 7.46 g test weight.The highest heterobeltiosis was observed in the cross PM 26×PM 27 (49.67%)and followed by DRMRIJ 31×RH 406 (48.31%).Like per se performance, the hybrid from the cross DRMRIJ 31×RH 406 exhibited highest significant positive standard heterosis (48.61%).Significantly lowest inbreeding depression was estimated in the hybrid from cross, DRMRIJ 31×Urvashi (3.08%) and followed by DRMRIJ 31×RH406 (3.35%).

Seed yield per plant

The hybrid from the cross, RH 406×RH 749 gave the highest yield per plant (83.60g).The estimate of better-parent heterosis showed that 15 crosses exhibited positive heterosis over the better parent. In accordance with per se performance, the hybrid from the cross, RH 406×RH 749 exhibited maximum heterobeltiosis (51.99%).Similarly, significant positive standard heterosis was highest in the cross RH 406×RH 749 (103.80%). Significantly lowest inbreeding depression was estimated in the hybrid from cross, DRMRIJ 31×RH-406 (4.57%) and followed by DRMRIJ 31×Kanti (4.66%).

Oil content (%)

Highest oil content (42.91%) was recorded in hybrid from the cross DRMRIJ 31×Urvashi. The highest magnitude of heterosis over better parents was expressed by Urvashi×PM 25 (4.74%). Like per se performance, the hybrid from the cross DRMRIJ 31×URVASHI exhibited maximum significant heterosis for oil content (2.09%). No inbreeding depression was found in the hybrid from crosses, NRCHB 101×DRMRIJ 31, NRCHB 101×PM-27, DRMRIJ 31×PM-27 and DRMRIJ 31×RH-749.

DISCUSSION

ANOVA revealed that all F₁ hybrids showed significant variation for most of the characters. Significant variance due to parents vs. F₁ hybrids and parents vs. F₂ hybrids may be helpful in opting better hybrids and desirable segregants, respectively. Early maturity is a desirable characteristic in most plant species especially Brassica where delayed maturity cause losses in yield and quality of oil due to high temperature [17]. Also, it fetches good returns from the markets by avoiding glut production during main season. The hybrids from the crosses, Kanti×Urvashi and PM 27×RH 406 were found early maturing hybrids. They also showed high negative heterobeltiosis for days to maturity. The hybrid from the cross, Urvashi×PM-25 exhibited lowest inbreeding depression. It is suitable for the development of early lines/variety. Low inbreeding depression could be due to additive gene action. Our findings were similar to those reported by several researchers [9, 10, 20].[1] reported heterosis for days to maturity.

Short and medium plant stature less vulnerable to lodging due to heavy winds is also preferred in Brassica. In hybrids, plant height varied from 180.33 cm (Kanti×PM 27) to 251.00 cm (DRMRIJ 31×Urvashi). The hybrid from the cross, Kanti×PM 25 exhibited the highest significant positive heterobeltiosis and standard heterosis for plant height. Low inbreeding depression in the hybrid from cross, PM-27×CS-54 could be attributed to poor combining ability of the parents and low heterosis. Per se performance revealed that this hybrid could be utilized to develop the variety with medium plant height. [9] reported high heterosis for dwarf plant height.

The presence of significantly positive heterosis for branches per plant in F₁ crosses indicates the potential of their use for developing high-yielding genotypes. Per se performance revealed that the hybrids having either of parent as CS 54 had the highest number of primary and secondary branches per plant. Followingper se performance, the hybrid, PM 27×CS 54 exhibited highest significant positive heterobeltiosis and standard heterosis for primary branches per plant. In case of secondary branches, per se performance had no linear relation with heterosis over better parent. However, the maximum significant standard heterosis was observed from the cross, PM 26×CS 54 for this trait. Significant positive heterosis for a number of primary and secondary branches were earlier reported by [17,10]. Due tothe lowest inbreeding depression in the hybrid from crosses, PM-27×RH-406 and PM-25×PM-26 for primary and secondary branches, respectively which could be is suitable to isolate the pure inbred lines with profuse branches with vigorous stature. 

Promising cross combinations identified on the basis of heterotic effects (standard heterosis) for various traits are RH 406×RH 749 for a number of siliquae per plant, and DRMRIJ 31×RH 406 for a number of seeds per siliquae and for test weight. These two crosses also performed best on the basis of per se performance for said traits. Significantly lowest inbreeding depression in the cross NRCHB 101×PM-27 for a number of siliquae per plant, NRCHB 101×DRMRIJ 31 for seeds per siliqua and DRMRIJ 31×Urvashi for test weight.Therefore, these above new cross combinations are useful populations for obtaining heterotic hybrids and transgressive segregants.

In accordance with per se performance, significant positive heterobeltiosis and standard heterosis in the hybrid from the cross, RH 406×RH 749 for seed yield per plant could be attributed with high heterosis for number of siliquae per plant and/or dominant effect of either of the parent in expressing the trait during F₁ generation. Significantly lowest inbreeding depression in the hybrid from the cross, DRMRIJ 31×RH-406 indicates that the parental line RH-406 could be a poor combiner for seed yield with additive gene effect.Considerable heterosis for seed yield in Brassica was also observed by [9, 13]. Similarly, the hybrid from the cross DRMRIJ 31×URVASHI exhibited maximum significant heterosis for oil content. No inbreeding depression for this trait in the hybrids from crosses, NRCHB 101×DRMRIJ 31, NRCHB 101×PM-27, DRMRIJ 31×PM-27 and DRMRIJ 31×RH-749 might be due to additive variance and poor combining ability of parents resulting low heterosis. More or less similar results have been reported by [14].

CONCLUSION

Present findings conclude that commercial exploitation of the cross/hybrid with high seed output and early maturation is possible, while the selection of appropriate seggregants in Indian mustard is facilitated by reduced inbreeding depression.

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