High-Resolution Linkage Map With Allele Dosage Allows the Identification of Regions Governing Complex Traits and Apospory in Guinea Grass (Megathyrsus maximus).

Thamiris G Deo,Anete P De Souza,Antonio A F Garcia,Alessandro Alves-Pereira,Rebecca C U Ferreira,Aline C L Moraes,Letícia A C Lara,Fernanda A De Oliveira,Liana Jank,Mateus F Santos

doi:10.3389/fpls.2020.00015

Abstract

Forage grasses are mainly used in animal feed to fatten cattle and dairy herds, and guinea grass (Megathyrsus maximus) is considered one of the most productive of the tropical forage crops that reproduce by seeds. Due to the recent process of domestication, this species has several genomic complexities, such as autotetraploidy and aposporous apomixis. Consequently, approaches that relate phenotypic and genotypic data are incipient. In this context, we built a linkage map with allele dosage and generated novel information of the genetic architecture of traits that are important for the breeding of M. maximus. From a full-sib progeny, a linkage map containing 858 single nucleotide polymorphism (SNP) markers with allele dosage information expected for an autotetraploid was obtained. The high genetic variability of the progeny allowed us to map 10 quantitative trait loci (QTLs) related to agronomic traits, such as regrowth capacity and total dry matter, and 36 QTLs related to nutritional quality, which were distributed among all homology groups (HGs). Various overlapping regions associated with the quantitative traits suggested QTL hotspots. In addition, we were able to map one locus that controls apospory (apo-locus) in HG II. A total of 55 different gene families involved in cellular metabolism and plant growth were identified from markers adjacent to the QTLs and APOSPORY locus using the Panicum virgatum genome as a reference in comparisons with the genomes of Arabidopsis thaliana and Oryza sativa. Our results provide a better understanding of the genetic basis of reproduction by apomixis and traits important for breeding programs that considerably influence animal productivity as well as the quality of meat and milk.

Highlights

Forage grasses play a fundamental role in the global beef production chain
When the Akaike information criterion (AIC) and Schwarz information criterion (SIC) were not in agreement, we selected the matrices based on the largest difference between the models
Considering the Green matter (GM) trait and the GL matrix, US was selected based on the AIC, and compound symmetry (CS) was selected based on the SIC (US had 567.32 for the AIC and 702.21 for the SIC, and CS had 581.66 for the AIC and 598.53 for the SIC)

Summary

Introduction

Forage grasses play a fundamental role in the global beef production chain. Brazil is the country with the greatest emphasis on this sector, being the main exporter of beef and having the largest commercial herd of beef cattle in the world, with approximately 215 million heads distributed in 162 million hectares of pasture (ABIEC, 2019). The main factor that led to this scenario was the beginning of tropical forage breeding in the 1980s in Brazil, which recent, permitted the country to become the world's largest exporter of tropical forage seeds (ITC, 2018). Panicum maximum Jacq.), known as guinea grass, is one of the most productive forage grasses reproduced by seeds in the Brazilian market and is grown in other Latin American countries (Jank et al, 2011). It has been used mainly in intensive systems with high-fertility soils (Valle et al, 2009). The polyploidy and domestication process of this forage grass ensure high genetic variability to be explored (Jank et al, 2011); a lack of knowledge of the biology and genetics of the species, including its autotetraploidy and facultative apomictic mode of reproduction (Warmke, 1954), may make breeding more difficult and stimulate a need to invest in genetic studies

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