Rice Genomics and Genetics 2024, Vol.15, No.4, 190-202 http://cropscipublisher.com/index.php/rgg 191 pests, and improved stress tolerance in crops. The concept of heterosis has been exploited in various crops, including maize, sorghum, and rice, to achieve substantial yield improvements. The genetic basis of heterosis involves the interaction of alleles from the parent lines, which can result in increased vigor, growth rate, and productivity in the hybrid offspring. This genetic interplay often leads to the expression of desirable traits that are not present or are less pronounced in the parent lines. Understanding the genetic mechanisms underlying heterosis is crucial for developing effective breeding strategies aimed at maximizing crop yields. Heterosis is particularly significant for rice breeding programs as it offers a viable solution to the limitations of traditional breeding methods. Hybrid rice varieties have been shown to yield 15%~30% more than conventional varieties under optimal conditions (Virmani, 1996). This yield advantage is critical for addressing food security challenges and improving the economic viability of rice farming. The objective of this study is to explore the genetic basis of heterosis in rice and to identify effective breeding strategies to maximize rice yields. The study aims to provide a comprehensive understanding of the genetic and molecular mechanisms underlying hybrid vigor in rice. By synthesizing current research findings, it offers insights into how heterosis can be harnessed to improve rice productivity. This study promotes the understanding and application of heterosis in rice breeding. By exploring the genetic basis of hybrid vigor and identifying effective breeding strategies, the study supports efforts to maximize rice yields and enhance global food security. The findings are intended to provide important insights for researchers, breeders, and policymakers involved in rice production and agricultural development. 2 Understanding Heterosis in Rice 2.1 Historical perspectives on heterosis Heterosis, commonly known as hybrid vigor, was first observed by Charles Darwin and later formally described by George Shull and Edward East in the early 20th century. The concept revolutionized plant breeding, particularly in maize, where hybrids showed remarkable improvements in yield and resilience. In rice (Oryza sativa L.), the application of heterosis has been more complex due to the crop's predominantly self-pollinating nature. However, the potential benefits of hybrid rice-such as higher yields, better stress tolerance, and improved resistance to pests and diseases-have driven extensive research and breeding efforts since the 1970s. The success of hybrid rice in China, initiated by the pioneering work of Yuan Longping, marked a significant milestone. Yuan’s development of the first commercial hybrid rice variety in the 1970s demonstrated the feasibility of exploiting heterosis in rice, leading to widespread adoption and significant yield gains. Today, hybrid rice accounts for over 50% of the total rice cultivation area in China and has contributed to food security and agricultural sustainability. 2.2 Theories and mechanisms of heterosis Understanding the underlying mechanisms of heterosis is crucial for effective hybrid breeding. Several theories have been proposed to explain heterosis, each highlighting different genetic and molecular aspects. The dominance theory posits that heterosis arises when dominant alleles mask the deleterious effects of recessive alleles. In hybrid plants, the combination of alleles from two genetically diverse parents can result in the suppression of harmful recessive alleles, leading to improved performance. This theory suggests that the greater the genetic divergence between the parents, the higher the potential for heterosis. Dominance theory has been supported by numerous studies in various crops, including rice. Research has shown that hybrid rice varieties often exhibit higher levels of heterozygosity, which correlates with increased vigor and yield (Li et al., 2020). However, dominance theory alone cannot fully explain all aspects of heterosis, prompting the exploration of additional theories. Overdominance theory, also known as the single-gene heterosis theory, suggests that heterosis results from the superior performance of heterozygous genotypes at certain loci. According to this theory, the heterozygote is more vigorous than either homozygote, leading to enhanced traits in the hybrid. This phenomenon can occur due to
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