Rice Genomics and Genetics 2024, Vol.15, No.3, 132-141 http://cropscipublisher.com/index.php/rgg 133 2 Genetic Diversity in Wild Rice 2.1 Taxonomy and distribution of wild rice species Wild rice species, belonging to the genus Oryza, are distributed across various regions globally, with significant diversity observed in Asia and Africa. The genus Oryza includes two cultivated species, Oryza sativa and Oryza glaberrima, and 22 wild species that represent 10 distinct genome types (Ammiraju et al., 2010). Oryza rufipogon, the progenitor of Asian cultivated rice, is widely distributed in Asia, particularly in China, India, and Southeast Asia (Sun et al., 2001; Liu et al., 2015). In Africa, Oryza longistaminata and Oryza barthii are notable wild species, with O. longistaminata found at the edge of its distribution in Ethiopia (Lakew et al., 2021). These wild species are crucial for understanding the evolutionary history and genetic diversity of rice. 2.2 Genetic variability in wild rice Wild rice species exhibit remarkable genetic variability, which is essential for rice breeding and improvement. Studies have shown that Oryza rufipogon possesses higher genetic diversity compared to cultivated rice, with significant polymorphism observed in various populations (Sun et al., 2001). For instance, the genetic diversity of O. rufipogon in China is notably high, with a mean polymorphism information content (PIC) of 0.64, indicating a high level of genetic variation (Liu et al., 2015). Similarly, African wild rice, O. longistaminata, exhibits unique genetic variations at the edge of its distribution, which are valuable for future rice breeding (Lakew et al., 2021). The genetic diversity in wild rice is also reflected in the presence of numerous single nucleotide polymorphisms (SNPs) and structural variations, contributing to the overall genetic variability (Zhang et al., 2020). 2.3 Conservation of wild rice germplasm The conservation of wild rice germplasm is critical for maintaining genetic diversity and ensuring the availability of valuable genetic resources for rice improvement. Efforts have been made to develop core collections of wild rice accessions for ex situ conservation. For example, a core collection of 130 accessions of Oryza rufipogon was developed in China, retaining over 90% of the alleles at 36 marker loci (Liu et al., 2015). Additionally, the Oryza Map Alignment Project (OMAP) aims to leverage the novel genetic diversity from wild relatives for rice improvement by providing comprehensive genus-wide BAC resources (Ammiraju et al., 2010). These conservation efforts are essential for preserving the genetic diversity of wild rice and utilizing it for the development of improved rice varieties with enhanced agronomic traits. The genetic diversity in wild rice species, their taxonomy and distribution, and the conservation of their germplasm are crucial for harnessing natural genetic diversity to improve cultivated rice varieties. The rich genetic variability in wild rice provides a valuable reservoir of alleles that can be utilized for rice breeding and the development of resilient and high-yielding rice varieties. 3 Molecular Basis of Wild Rice Alleles 3.1 Identification and characterization of wild rice alleles The identification and characterization of wild rice alleles have been pivotal in understanding the genetic diversity and potential of wild rice species. Studies have shown that wild rice species, such as Oryza rufipogon and Oryza nivara, harbor a wealth of genetic diversity that has been largely untapped in cultivated varieties. For instance, the resequencing of 50 accessions of both cultivated and wild rice has revealed thousands of genes with significantly lower diversity in cultivated rice, indicating regions selected during domestication that may contain important agronomic traits (Xu et al., 2011). Additionally, the use of molecular markers, such as microsatellites, has been effective in evaluating genetic diversity within rice subspecies, providing a reliable tool for germplasm conservation and cultivar identification (Ni et al., 2002). 3.2 Genomic tools for analyzing wild rice Advancements in genomic tools have significantly enhanced the analysis of wild rice. The development of high-density single-nucleotide polymorphism (SNP) arrays and other genomic resources has facilitated the identification of valuable alleles from wild rice species. Chromosome segment substitution lines (CSSLs) and backcross inbred lines (BILs) are particularly powerful tools for introgressing favorable genes from wild species
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