**2. Rice breeding methods**

Rice breeding is an effective mechanism for delivering the benefits of science and technology to millions of resource-poor farmers. Rice is considered one of the crops that has achieved remarkable success through breeding. Notable success includes the contribution to the green revolution with semi-dwarf varieties that averted a looming hunger in Asia in the 1960s [3, 4]. The methods of breeding rice can be categorized into conventional selection, in-vitro, molecular and transgenic. The available conventional selection breeding methods include mass selection, pure line selection, pedigree method, bulk method, backcross method, recurrent selection, and single seed descent [5, 6]. Mass and pure line selections are mostly used for purifying heterogeneous varieties and are rarely used in present day breeding programs. The pedigree method is the most widely used method to develop rice varieties. More than 85% of the released rice varieties were developed through pedigree selection [4]. Backcrossing is commonly used to incorporate one or a few genes into an adapted or elite variety [4–6]. Although hybrid breeding is primarily applicable to outcrossing species such as maize, it has been successfully added to the rice breeding portfolio. The aim of hybrid rice breeding is to raise the yield ceiling of rice beyond what is currently achieved by the semi dwarf varieties [7, 8]. Mutagenesis to some extent has also been employed to develop some valuable rice varieties [4, 9]. The in-vitro methods include tissue culture techniques such as anther culture to develop doubled haploids, somaclonal variation to identify useful variants and embryo rescue to assist in wide hybridization such as the one that led to the development of the NERICAs. In the NERICA development, embryo rescue was used to obtain viable progeny between *Oryza sativa* and *Oryza glaberrima* crosses [10]. Molecular breeding methods mostly involve the use of molecular markers in marker assisted selection to increase the efficiency and precision of conventional breeding [6, 11]. Genetic engineering (transgenic technique) allows addition of alien genes from any living organism to the rice gene pool to impart a useful function. This technique allows breeders to accomplish objectives which cannot be achieved through conventional plant breeding [12]. Quite recently, genome editing technique has been added to the rice breeding methods. By genome editing, specific modification can be made at targeted locations of the rice genome. Unlike genetic engineering, this method does not involve the introduction of foreign genes into the rice genome [13].

**49**

*Hybrid Rice in Africa: Progress, Prospects, and Challenges*

The above breeding methods lead to the development of one of the three main rice varietal types i.e. inbreds (pure lines), hybrids or GM (transgenic) rice [6]. Inbreds are the most commonly used rice varietal type. Since offspring or succeeding generations produced by these varietal types are of the same genetic makeup, seeds harvested from an inbred variety can be used for succeeding planting without losing their varietal identity provided cross pollination with other varieties is avoided. Hybrids are products of crossing two genetically diverse inbred lines. As a result, seeds harvested from the hybrid plants are not recommended for replanting because some vigor is lost resulting in lower yield and genetic segregation [8]. Farmers are recommended to buy new hybrid seeds for each planting season from accredited sources. The increased profits resulting from increased yields of hybrids versus pure line varieties offset the cost of the hybrid seed. Transgenic (GM) rice results from the use of genetic engineering. Though the resulting varieties breed true, they are separated from the conventional (nontransgenic) inbreds due to the involvement of a transgene. Though several transgenic rice lines have been developed, they are yet to find their way into commercial cultivation. Notable transgenic (GM) rice is the Golden rice; a variety engineered to produce beta carotene to help

Hybrid rice is the commercial rice crop grown from F1 seeds of a cross between two genetically dissimilar parents. This could only be possible through the use of a male sterility system due to the strictly self-pollination nature of the rice plant [4, 8]. Hybrid varieties exploit the phenomenon of hybrid vigor (heterosis) to increase the yield potential of rice beyond the level of modern inbred rice varieties. A yield advantage of 15–30% over conventional inbred varieties grown under similar conditions has been reported [14]. The hybrid rice technology concept dates back to 1964 in China. However, it was only after 1976, when a wild abortive pollen plant was identified in Southern China, did the idea begin to materialize [4, 8]. Since the expression of heterosis is confined to the first generation only, farmers have to buy fresh seeds every season to raise commercial crop. Since the hybrids yield 15 to 30% more than pure line varieties, farmers prefer hybrid seeds if the price is economically beneficial and seeds are readily available. Hybrids can offer biological intellectual property protection which attracts and encourages private-sector involvement in seed production research

For a long time, two theories; the dominant and overdominance theories were put forward to explain the phenomenon of heterosis [14]. According to the dominant theory, hybrid vigor is due to the action and interaction of favorable dominant alleles. The overdominance theory on the other hand suggests that heterozygous loci are superior to homozygous loci. Thus, two alleles complement each other and there is overexpression of genes in the heterozygous state [16]. Recently, epistasis or interactions among loci has been recognized as a major contributor to heterosis [17]. Estimates based on mating designs of the relative magnitude of additive, dominance and epistatic components of variance indicate that the magnitude of epistatic variance is small compared to additive and dominance components. This is because statistical designs cannot predict epistasis. Using molecular markers,

*DOI: http://dx.doi.org/10.5772/intechopen.93801*

combat vitamin A deficiency [12].

**3. Hybrid rice technology**

and development [15].

**3.1 Genetic basis of heterosis**

**2.1 Rice varietal types**

#### **2.1 Rice varietal types**

*Recent Advances in Rice Research*

**2. Rice breeding methods**

climate change, and natural resource degradation, national, regional, and international institutions have increased investment toward boosting rice production on the continent. Consequently, many countries have national strategic plans and favorable policies for increasing rice production in place. The current situation is encouraging and requires strengthening existing partnerships to address the challenges across the whole rice value chain to enhance sustainable food security across the continent [2]. Promoting the adoption of productivity enhancing technologies including hybrid rice technology is key to the continent's rice self-sufficiency agenda. Hybrid rice has the penitential of increasing rice productivity and encouraging private sector involvement in seed production research and development in Africa. Since there is currently no proper plant variety protection (PVP) system in place in most of Sub-Saharan countries; the hybrid system could serve as a form of biological intellectual property through the control of the hybrid parents. This chapter examines the procedures of hybrid rice development, current state of development

and commercialization in Africa as well as its prospects and challenges.

Rice breeding is an effective mechanism for delivering the benefits of science

and technology to millions of resource-poor farmers. Rice is considered one of the crops that has achieved remarkable success through breeding. Notable success includes the contribution to the green revolution with semi-dwarf varieties that averted a looming hunger in Asia in the 1960s [3, 4]. The methods of breeding rice can be categorized into conventional selection, in-vitro, molecular and transgenic. The available conventional selection breeding methods include mass selection, pure line selection, pedigree method, bulk method, backcross method, recurrent selection, and single seed descent [5, 6]. Mass and pure line selections are mostly used for purifying heterogeneous varieties and are rarely used in present day breeding programs. The pedigree method is the most widely used method to develop rice varieties. More than 85% of the released rice varieties were developed through pedigree selection [4]. Backcrossing is commonly used to incorporate one or a few genes into an adapted or elite variety [4–6]. Although hybrid breeding is primarily applicable to outcrossing species such as maize, it has been successfully added to the rice breeding portfolio. The aim of hybrid rice breeding is to raise the yield ceiling of rice beyond what is currently achieved by the semi dwarf varieties [7, 8]. Mutagenesis to some extent has also been employed to develop some valuable rice varieties [4, 9]. The in-vitro methods include tissue culture techniques such as anther culture to develop doubled haploids, somaclonal variation to identify useful variants and embryo rescue to assist in wide hybridization such as the one that led to the development of the NERICAs. In the NERICA development, embryo rescue was used to obtain viable progeny between *Oryza sativa* and *Oryza glaberrima* crosses [10]. Molecular breeding methods mostly involve the use of molecular markers in marker assisted selection to increase the efficiency and precision of conventional breeding [6, 11]. Genetic engineering (transgenic technique) allows addition of alien genes from any living organism to the rice gene pool to impart a useful function. This technique allows breeders to accomplish objectives which cannot be achieved through conventional plant breeding [12]. Quite recently, genome editing technique has been added to the rice breeding methods. By genome editing, specific modification can be made at targeted locations of the rice genome. Unlike genetic engineering, this method does not involve the introduction of

**48**

foreign genes into the rice genome [13].

The above breeding methods lead to the development of one of the three main rice varietal types i.e. inbreds (pure lines), hybrids or GM (transgenic) rice [6]. Inbreds are the most commonly used rice varietal type. Since offspring or succeeding generations produced by these varietal types are of the same genetic makeup, seeds harvested from an inbred variety can be used for succeeding planting without losing their varietal identity provided cross pollination with other varieties is avoided. Hybrids are products of crossing two genetically diverse inbred lines. As a result, seeds harvested from the hybrid plants are not recommended for replanting because some vigor is lost resulting in lower yield and genetic segregation [8]. Farmers are recommended to buy new hybrid seeds for each planting season from accredited sources. The increased profits resulting from increased yields of hybrids versus pure line varieties offset the cost of the hybrid seed. Transgenic (GM) rice results from the use of genetic engineering. Though the resulting varieties breed true, they are separated from the conventional (nontransgenic) inbreds due to the involvement of a transgene. Though several transgenic rice lines have been developed, they are yet to find their way into commercial cultivation. Notable transgenic (GM) rice is the Golden rice; a variety engineered to produce beta carotene to help combat vitamin A deficiency [12].
