Combining ability for yield and yield contributing traits in hybrid rice

INTRODUCTION

Rice is a staple food for a significant portion of the world’s population, particularly in Asia. It provides a major source of dietary calories and nutrition, meeting the energy requirements of millions of people.Rice plays a vital role in global food security, contributing to stable food supplies and mitigating hunger and malnutrition risks, especially in regions heavily reliant on rice as a primary food source.Rice production has witnessed substantial growth over the years, keeping pace with the increasing demand. Despite progress, challenges remain in achieving optimal productivity.The development of hybrid rice has been a significant milestone in rice breeding, providing enhanced productivity and other desirable traits.

Combining ability analysis is a valuable approach in plant breeding that helps assess the genetic potential of parental lines and predict the performance of their hybrids. The concept of combining ability was developed by Sprague and Tatum in 1942 [17] through preliminary studies with maize.This analysis involves the evaluation of both general combining ability (GCA) and specific combining ability (SCA) effects, which provide insights into the additive and non-additive genetic components contributing to important traits in rice.In the case of rice (Oryza sativa), combining ability analysis plays a crucial role in identifying superior combinations for developing high-yielding and desirable rice varieties and hybrids.

With this background present research problem was conducted in three locations to identify the best parents and hybrid combinations suitable for Telangana state.

MATERIAL AND METHODS: Experimental material for this investigation comprised four WA-based cytoplasmic male sterile (CMS) lines and ten elite proven restorer lines.During Kharif, 2020 four CMS lines and ten testers were planted in a crossing block with a spacing of 20 cm × 15 cm and crosses were performed in Line × Tester mating design to produce 40  hybrids. Three staggered sowings of the parents (females and males) were undertaken at an interval of 10 days to ensure synchronous flowering to make crosses.

            A total of 40 hybrids along with 10 restorers, 4 ‘B’ lines of corresponding male sterile lines and 2 checks were sown at three locations viz.,Regional Agricultural Research Station (RARS), Polasa, Jagtial (NTZ), Regional Sugarcane & Rice Research Station, Rudrur, Nizamabad (NTZ) and Rice Research Center ARI, Rajendranagar, (STZ)during Rabi, 2020-21 for estimation of per se performance, combining abilityand heterosis.

A completely randomized block design with three replications was followed. Top dressing was given with urea and need-based plant protection measures were undertaken for raising healthy seedlings. Each entry was planted in two rows of three meters in length with a spacing of 20 cm × 15 cm in three replications and all the package of practices were followed to raise a healthy crop.

            Five plants were selected at random from each entry in each replication to record plant height, number of productive tillers per plant and panicle length. Observations were recorded for yield and yield-attributing traits at three locations. However 1000 grain weight were recorded on the random sample in each plot, whereas for days to 50% flowering the data was recorded on a whole plot basis. In the case of CMS lines, the observations were recorded on their respective maintainer (B) lines.

RESULTS AND DISCUSSIONS:

1 Analysis of variance for combining ability

The material comprising 54 genotypes (4 CMS lines, 10 restorer lines and 40 hybrids) was evaluated during rabi2020-21 at three locations viz., Jagtial, Rudrur, and Rajendranagar for combining ability analysis. The pooled analysis of variance for combining ability over locations revealed the presence of significant differences among thelocations, genotypes, parents and crosses for all the characters studied (Table 1). Researchers like, [12]and [8] reported the significance of parents and crosses for all the characters studied. For parents vs crosses except panicle length, spikelet fertility, kernel breadth and kernel length breadth ratio all the characters were significant. The variance due to lines was significant for plant height, panicle length, head rice recovery, kernel length, kernel breadth and kernel length breadth ratio whereas, the variance due to testers was significant for plant height, panicle length, test weight, head rice recovery, kernel length, kernel breadth traits. The variance due to lines × testers was significant for the all characters studied. Parents × hybrids showed significant variance for nine characters viz., indicating the superiority of hybrids and the presence of heterosis for the majority of the traits studied, [12]and [8] also noticed significant variances of line × tester effects for all the characters studied.

Interaction effects of lines × testers × locations recorded significant differences for the characters days to 50% flowering, plant height, panicle length, number of productive tillers per plant, spikelet fertility, 1000 grain weight and grain yield per plant. Earlier researchers like, [12]and [8] also reported significant variances of lines × testers × locations for grain yield per plant and its attributes.This indicates the existence of wide variability within the material studied and there is a good scope for identifying promising parents and hybrid combinations.

2. Combining ability variances and gene action

The estimates of GCA and SCA variances in pooled analysis are presented inTable 2.General combining ability is associated with additive gene action, while specific combining ability is due to dominance and epistasis. In the present investigation SCA variances were higher than GCA variances in pooled analysis for most of the traits indicating the predominance of non-additive gene action.

A comparison of the magnitude of variance components due to GCA and SCA confirmed the nature of gene action in controlling the expression of traits. In the present investigation, it was found that SCA variances were higher than GCA variances for most of the characteristics like duration of 50% flowering, plant height (cm), panicle length (cm), productive tillers per plant, spikelet fertility (%), test weight (g) and grain yield per plant which indicated the predominance of non-additive gene action. It is evident from different studies, that predominance of non-additive gene action over the additive component is ideal for exploitation through heterosis breeding.

Similar to the present findings, certain workers reported the importance of non-additive components in rice for duration of 50% flowering, [9], plant height [ 8, 10and 22], panicle length [8, and 22], spikelet fertility per cent [22], 1000-grain weight [8, 9, 10, 22, 4,7 and 20], number of productive tillers per plant [8, 10, 7 and 20], and grain yield per plant [1, 8, 15, 9, 21, 10, 22, 4, 7 and 22 ] as in case of present study.

Contrary to present findings, non-additive gene action was reported by some researchers for grain yield per plant [11 and 4]. The discrepancy among the results reported may be due to the differences in the material used for the studyand the environment tested.

The contribution of lines was recorded high for four traits viz., plant height, panicle length, test weight, and kernel breadth while the contribution of testers was high for characters i.e., days to 50 per cent flowering, number of productive tillers, spikelet fertility, and grain yield per plant. The contribution of line × tester interaction was moderate for plant height, spikelet fertility, number of productive tillers per plant and grain yield per plant indicating the importance of these traits in determining the potentiality of the hybrids.

3. General and specific combining ability effects

The estimates of general combining ability (4 lines and 10 testers) and specific combining ability effects (40 hybrids) for different characters at three locations and pooled analysis are presented character-wise below.

1. Days to 50% flowering

a) GCA-GCA effects

In rice, genotypes with dominant genes having negative effects tend to be early in duration which is desirable. Among the four lines, CMS 23B recorded significant negative GCA effects at all locations and pooled over locations.Whereas CMS 46B showed significant positive GCA effects at all the locations and pooled analysis(Table 3). Among the testers, JGL 35126 and RNR 28411 recorded significant negative GCA effects at all the three locations and pooled. RNR 26085, RNR 28359 and JGL 34551 recorded significant positive GCA effects at all three locations and also in pooled data.

b) SCA–SCA effects

Out of the 40 hybrids studied desirable significant negative specific combining ability effects were exhibited by five crosses at Jagtial, Rudrur and Rajendranagar and seventeen crosses in pooled analysis. Five crosses viz., JMS 13A × RNR 26085, CMS 23A × RNR 26085, CMS 23A × RNR 2354,CMS 46A × RNR 28359 and CMS 59A × JGL 35047 exhibited a negative significant effect at all the three locations and pooled analysis.The significant negative GCA and SCA effects were also reported by [8, 19, 7 and 15] for days to 50 % flowering.

2. Plant height (cm)

a) GCA effects

For the character plant height, GCA effects on negative side is more desirable in order to develop non-lodging and semi dwarf genotypes in rice. The line, JMS 13B and CMS 23B recorded significant negative GCA effect at all locations and pooled over locations (Table 3). Among the testers, RNR 2354, RNR 28359, IR 72 and JGL 35047 exhibited significant negative GCA effect at all the three locations as well as in pooled over locations. Significant positive GCA effects were observed in testers RNR 26085,JGL 34551 and RNR 28411 at all the three locations and when pooled over locations.

b) SCA effects

Out of the 40 crosses studied significant negative specific combining ability effects were exhibited by 13 crosses at Jagtial, 12 crosses at Rudrur, 13 crosses at Rajendranagar and 14 crosses in pooled analysis. Seven crosses that registered significant negative SCA effect at all the three locations and pooled over locations includes,JMS 13A × RNR 21571,JMS 13A × IR 72,JMS 13A × JGL 35047, CMS 23A × ZGY 1,CMS 23A × RNR 2354, CMS 23A × JGL 35126 and CMS 59A × RNR 28411.Significant negative GCA and SCA results were supported by [8, 3 and 7] for this trait.