Estimation of Heterosis and Inbreeding Depression for Yield and Yield Related Traits in Rice (Oryza sativa L.)  

S.K. Sharma , S.K. Singh , R. Nandan , Amita Sharma , Ravindra Kumar , V. Kumar , M.K. Singh
Department of Genetics & Plant Breeding, Institute of Agricultural Sciences Banaras Hindu University, Varanasi (U.P.), 221005, India
Author    Correspondence author
Molecular Plant Breeding, 2013, Vol. 4, No. 29   doi: 10.5376/mpb.2013.04.0029
Received: 09 Jul., 2013    Accepted: 22 Sep., 2013    Published: 25 Sep., 2013
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This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Preferred citation for this article:

Sharma et al., Estimation of Heterosis and Inbreeding Depression for Yield and Yield Related Traits in Rice (Oryza sativa L.), Molecular Plant Breeding, Vol.4, No.29 238-246 (doi: 10.5376/mpb.2013.04.0029)

Abstract
The present investigation inrice (Oryza sativa L.) was undertaken for studying the magnitude of heterosis of 48 hybrids (F1s) made by involving sixteen restorer lines and 3 cytoplasmic male sterile (CMS) lines following line×tester mating design. The result indicated that the magnitude of heterobeltiosis for grain yield was significantly superior in 28 hybrids ranging from 10.85 to 66.35% and only in 2 hybrids (IR58025A×Sarju-52; IR58025A×BPT5204) over the standard hybrid (Arize-6444) with the magnitude of 11.87 and 20.60% respectively. These crosses also exhibited significant heterosis for days to maturity, number of spikelets panicle-1, number of grains panicle-1. The most promising combinations (IR58025A×Sarju-52 and IR58025A×BPT5204) for grain yield and other traits need to be tested on larger scale for their commercial values. Besides these, few other crosses viz; Pusa6A×BPT5204, IR68897A×BPT 5204 and Pusa6A×Krishna Hansa expressed more than 40% heterobeltiosis for grain yield alongwith other desirable yield components may be considered for commercial expliotation.  
Keywords
Heterosis; Oryza sativa L.; Rice; WA-CMS

Hybrid rice has established its superiority over high yielding varieties in respect of growth, yield and tolerance to stresses. The first commercially usable Cytoplasmic Male Sterile (CMS) line was developed in China during 1973 from a spontaneous male sterile plant isolated in a population of the wild rice Oryza sativa f. Spontanea in Hainan Island (Cheng, 2012). The discovery of this source, designated as Wild Abortive (WA) type is considered a landmark in the history of hybrid rice. With the availability of effective seed production through CMS-fertility restorer system, commercial utilization of heterosis has become practically feasible in rice. Following the success of hybrid rice in China, the International Rice Research Institute (IRRI), Philippines in 1979 augmented research to evolve hybrid ideally suited to tropical environment. IRRI Developed stable male sterile lines including, IR 58025 A, IR 62829 A, IR 68888 A, IR 68897 A and many others in the background of indica rice varieties suited for tropical conditions and has facilitated intensive hybrid breeding research in many countries. Recognizing the potential of this technology, the Indian Council of Agricultural Research (ICAR) launched a mission mode project on hybrid rice during 1989. As a result of concerted efforts for more than 2 decades, a total of 59 rice hybridshave been released up to 2012 for commercial cultivation in India (Viraktamath et al., 2012). However, for development of region and situation specific hybrids to enhance the area under hybrid rice cultivation, it is important to estimate the magnitude of heterosis in number of hybrid combinations. Identification of superior hybrid combinations is prerequisite for development of new hybrids. As rice is being cultivated in varying land and agro-climatic conditions, baskets of choice of hybrids are required to fulfill the need of the stakeholders. Variable types of restorer lines may be tested with different CMS lines for studying the magnitude of yield heterosis along-with heterosis for other yield attributing traits for searching suitable hybrids to meet the region specific requirements. Keeping these points in view the present investigation was formulated to study the heterosis in rice.

Results and Discussion
The analysis of variance (Table 1) revealed that highly significant differences among lines (female) for several traits under study except for 50 % flowering, days to maturity, plant height (cm), number of effective tillers plant-1, number of spikelet panicle-1, number of grains panicle-1, 1000 grains weight (g), while variance among males (testers) were highly significant for almost all the traits. The variance among crosses due to males and females (lines×testers) interaction component were highly significant for all the traits. The present findings confirming the earlier findings of Saravanan et al (2008) and Tiwari et al (2011).


Table 1 ANOVA for L×T analysis for eighteen characters in rice

Heterosis was estimated as percent increase or decrease of F1 values over better parent (BP) and standard hybrid (SH); Pro Agro-6444. The nature and magnitude of heterosis are presented in Table 2.


Table 2 Estimates of heterosis based on better parent (BP) and standard hybrid check, Arize 6444 (SV) for different characters in 48 rice hybrids

Negative heterosis is desirable for days to 50% flowering because this will help the hybrid to mature earlier (Table 3). The nature and magnitude of heterosis revealed that none of the hybrids showed negative and significant heterosis over BP, whereas 14 hybrids showed significant negative heterosis over standard hybrid (Pro Agro 6444) among them top three exhibiting earliness were IR68897A´Krishna Hansa, IR58025A´CR2340-1 and IR68897A´CR2340-1. Heterosis in positive as well as negative direction for days to 50% flowering has also been reported by Lingaraju et al (1999) and Patil et al (2003).


Table 3 Ranking of five desirable hybrids on the basis of per se performance, heterobeltiosis and economic Heterosis for different characters in rice

The short duration varieties are of breeder’s interest to fit them into rainfed cultivation, therefore, heterosis in negative direction is desirable for days to maturity. All the hybrids showed negative and significant heterosis over SH (Pro Agro 6444), among them top three hybrids exhibiting short duration were IR68897A´Krishna Hansa, IR58025A´CR2340-1, and IR 68897A×CR 2340-1. These finding are in agreement with those of Bhave et al (2002) and Sarial et al (2006).
Out of 48 hybrids, 28 exhibited significantly shorter plant stature over SH (Pro Agro 6444), but none over BP. Heterotic effects were observed with highest magnitude over the check (Pro Agro 6444) in crosses Pusa 6A×MTU-7029, IR68897A×MTU-7029 and IR58025A×MTU-7029. Dwarf stature is preferable as it is less prone to lodging (Janardhanam et al., 2001).
Higher number of effective tillers plant-1 generally contributes to higher grain yield. In this study, 6 hybrids possessed positive and significant heterosis over BP and SH (Pro Agro 6444), the hybrids showing highest magnitude of heterosis over Pro Agro 6444 were;Pusa6A×Krishna Hansa, Pusa6A×Badshahbhog, IR68897A×Badshahbhog and Pusa 6 A×Type-3. Such range of heterosis for this trait was also reported Singh (2000) and Patil et al (2003).
Generally, larger panicle is associated with high number of grains panicle-1 resulting into higher productivity, therefore, positive heterosis for panicle length are desirable (Tiwari et al., 2011). Out of 48 hybrids, 16 showed positive heterosis with significant values over better parent and none of the hybrids manifested heterosis over SH (Pro Agro 6444). The similar results were reported by Patil et al (2003), Verma et al (2005) and Eradasappa et al (2007).
Positiveheterosis for number of spikelets panicle-1 is desirable. Sixteen of the hybrids studied expressed high heterotic estimates with positive and significant values over respective better parent. The result of present study indicated that a total of 12 crosses exhibited desirable heterosis over SH (Pro Agro 6444), The heterotic hybrids, IR68897A´Malviya-36, Pusa6A´BPT5204, Pusa6A´Pusa Sugandha-4 and Pusa6A´Malviya-36 are the best hybrids for this trait. These findings are in close conformity with the result of Tiwari et al (2011).
Number of grains panicle-1 is the major yield attributing character, hence significant positive heterobeltiosis and standard heterosis is desirable. Fourteen crosses showed significant positive heterosis over BP and four hybrids over SH (Pro Agro 6444), respectively. The crosses IR68897A×Malviya-36, Pusa6A×Pusa Sugandha-4, IR68897A×BPT-5204 and IR 58025A×Sarju-52 are the top heterotic hybrids for number of grainspanicle-1. These findings are in close conformity with the results of Singh and Haque (2000) and, Saravanan et al (2008).

1000-grainweight is important yield attributing trait. Out of 48 hybrids studied none of the hybrid showed positive and significant heterosis over BP, while 12 hybrids exhibited positive and significant heterosis over the SH (Pro Agro 6444). Top three crosses viz., IR58025A×Pusa Sugandha-4, IR68897A´Narendra-359 and IR 58025A×HUR 3022 exhibited significant positive heterosis over SH. Sarial et al (2006) reported similar observations.
Grain yield is a complex trait. It is the end product of several basic yield components. The standard heterosis is more useful from practical point of view. Virmani et al (1981) suggested that a yield advantage of 20%~30% over best available standard inbreds should be sufficient to encourage farmers to take-up hybrid rice cultivation. In present study among 48 hybrids, 28 showed significant heterosis over better parent. However, only two hybrids viz.; IR58025A×Sarju-52 and IR 58025A×BPT 5204 expressed superiority over SH (Pro Agro 6444) for grain yield plant-1. Several workers have also reported wide range of variation in expression of heterosis for this trait (Verma et al., 2005 and Saravanan et al., 2008).
Less than 70% hulling outturn is not acceptable and may prove uneconomic. In the present investigation out of 48 hybrids evaluated, none of the hybrid exhibited significant heterosis over better parent or SH (Arize-6444) for hulling recovery per cent. However, most of the hybrids showed similar per se performance for this trait when compared with the better parents as well as with SH. The similar type of result has also been reported by Singh (2000). Hence, higher yielding hybrids found in present study with no reduction in hulling % may be considered better.
The present study showed that superior performance for all the characters was not expressed in a single hybrid combination. However, different cross combinations were found to be superior for various characters. These findings are in accordance with those of Bhave et al (2002), Sarial et al (2006) and Savravanan et al (2008).
To develop commercial hybrids it is important to have significantly better heterotic combinations which significantly surpass the yield performance of the best locally adapted inbred variety. It is also important to have economical method of hybrid seed production to ensure hybrid seed availability in larger quantity which has become possible in rice with its CMS parent. Swaminathan et al (1972) and Virmani et al (1981) have suggested that about 20%~30% heterosis over the best available inbreds may be considered sufficient to offset the extra cost of hybrid seed in self pollinated crops. In present investigation several hybrids have exhibited higher yield heterosis over better parent (10.85%~66.35%) and even over standard hybrid; Arize 6444 (11.87%~20.6%). In present findings the promising hybrids shown better performance over BP are; Pusa 6A×Krishna Hansa, Pusa 6A×Tarori Basmati, Pusa 6A×HUR-3022, IR 68897A×BPT5204 and Pusa 6A×Narendra-359 and over SH (Arize 6444) are; IR58025A×Sarju-52 and IR58025A×BPT5204. These promising hybrids may further be tested on larger scale for thier commercial explotation.
Materials and Methods
Experiments of field trials were conducted at Agricultural Research Farm, Institute of Agricultural Sciences, Banaras Hindu University, Varanasi, India during Kharif 2009-2010. The experimental material consisted of 48 crosses (F1s) developed through line×tester mating design involving three CMS lines (IR58025 A, IR68897 A and Pusa 6A) and sixteen restorer lines. The F1s of 48 crosses with parents and one hybrid check; Arize 6444, were planted in Randomized Block Design with three replications. The plot size for each parents, F1`s and check was single row with row length of 3 meters and were spaced at 20 cm×15cm. Five competitive plants were randomly selected from parents, F1`s and check hybrid in each replication. Observations were recorded for days to 50% flowering, days to maturity, plant height (cm), number of effective tillers plant-1, panicle length (cm), number of spikelets panicle-1, number of grains panicle-1, 1000 grains weight (g), grain yield plant-1 (g) and hulling%. In general, reference for data collection was standard evaluation system for rice (Anonymous, 2002; Virmani et al., 1997). Heterosis was estimated as the per cent change in F1 hybrids over the better parent (heterobeltiosis) and standard check (economic heterosis) for above mentioned parameters following standard methods (Fonseca and Patterson, 1968) as below;
Heterobeltiosis (%)=  
 
Economic heterosis (%) = 

Where, F1 is the average performance of crosses, BP is the average performance of better parent, and SV is the average performance of standard variety (standard hybrid in this study, Arize 6444).
To estimate significant differences among hybrids and parents, the mean data of each character were subjected to Analysis of Variance (ANOVA) as suggested by Steel and Torrie (1980). The t test was applied to determine significant difference of F1 hybrid mean from respective better parent and standard check values using formulae as suggested by Wynne et al (1970).
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