Abstract
Pastures based on perennial monocotyledonous plants are the principal source of nutrition for ruminant livestock in tropical and subtropical areas across the globe. The Urochloa genus comprises important species used in pastures, and these mainly include Urochloa brizantha, Urochloa decumbens, Urochloa humidicola, and Urochloa ruziziensis. Despite their economic relevance, there is an absence of genomic-level information for these species, and this lack is mainly due to genomic complexity, including polyploidy, high heterozygosity, and genomes with a high repeat content, which hinders advances in molecular approaches to genetic improvement. Next-generation sequencing techniques have enabled the recent release of reference genomes, genetic linkage maps, and transcriptome sequences, and this information helps improve our understanding of the genetic architecture and molecular mechanisms involved in relevant traits, such as the apomictic reproductive mode. However, more concerted research efforts are still needed to characterize germplasm resources and identify molecular markers and genes associated with target traits. In addition, the implementation of genomic selection and gene editing is needed to reduce the breeding time and expenditure. In this review, we highlight the importance and characteristics of the four main species of Urochloa used in pastures and discuss the current findings from genetic and genomic studies and research gaps that should be addressed in future research.
Highlights
We summarize the importance and main characteristics of tropical forage grasses of the Urochloa genus used in pastures, as well the advancement of genomic resources, including molecular markers, transcriptome sequences, genome references, genomic regions of interest, and the status of molecular breeding
One of the largest germplasm banks is located at Embrapa Beef Cattle, Brazil, and is composed of 14 African species of Urochloa imported from the International Center for Tropical Agriculture (CIAT) in Cali, Colombia (Keller-Grein et al, 1996)
There is a strong demand for diagnostic molecular markers for target traits, apomixis and spittlebug resistance
Summary
These species are native to East and Central Africa and were introduced to tropical America in the 1960s Due to their rusticity, adaptability to areas of low fertility, tolerance to cattle trampling, good carrying capacity, and nutritional value, these species have become the main tropical forage grasses cultivated in the world and currently occupy a prominent position in the economic sector related to the seed and beef/milk markets (Jank et al, 2014). Climate change and human population growth are increasing the demand for the global production of foods (Montagu, 2020), including milk and meat Given this scenario, investment in genomic research to develop advanced breeding resources and tools is necessary to support the rapid and continuous development of improved tropical forage grasses to be used in pastures to feed livestock (Pereira et al, 2018; Simeão et al, 2021). The related efforts should include the development of traditional and modern breeding techniques, including genomic and phenomic tools, to achieve the goals in a timely manner
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