Self-incompatibility (SI) is an intraspecific reproductive barrier widely occurring in flowering plants to prevent inbreeding depression by promoting outcrossing. However, this trait severely restricts the production of homozygous lines in hybrid breeding, especially for the forage crops mostly belonging to Fabaceae, Asteraceae and Poaceae with unclear molecular mechanisms of SI. Therefore, SI has become one of the major barriers limiting the development of forage industry in China and even in the world. So far, large progresses have been made in the biochemical and evolutionary mechanisms of five different SI types, providing a good foundation for further exploring the SI mechanisms of Fabaceae, Asteraceae and Poaceae forage crops. Here, we briefly review the mechanisms of the five reported SI types and the research progress of SI and inbreeding depression in Fabaceae, Asteraceae and Poaceae.

The genera of Lolium and Festuca include many cool season forage grasses and turf species, such as Italian ryegrass (L. multiflorum), perennial ryegrass (L. perenne), tall fescue (F. arundinacea) and meadow fescue (F. pratensis). The ryegrass can be used as hay and silage, due to its high yield, broad adaptability, rich nutrition, good palatability, and high digestibility; and it was considered as a high-quality feed. But because its cultivation region in China is limited by geography factors, the current proportion of ryegrass in China’s grass pasture industry is still very small. In order to increase the proportion of ryegrass cultivation, the use of molecular breeding methods to breed excellent varieties maybe one of the key directions. In this review, we summarized recent progress in the Lolium-Festuca complex, especially in Lolium, including classification and evolution study, molecular marker development, linkage map construction, quantitative trait locus (QTL) and genome wide association study (GWAS) for important agronomic traits, genome sequences, transcriptome analysis, gene cloning and variety breeding. We also brought up some biological issues in Lolium species that need to be resolved, and try to provide some reference for further strengthening the basic biological research and molecular breeding of ryegrass.

Oat (Avena sativa) is an annual grass species grown as either a grain or a forage crop. Its valuable nutrition and excellent forage quality make its market demand increase year by year, which brings forth new requirements for innovative oat cultivars. Molecular breeding is the ideal technology for oat improvement with its high precision and efficiency. Genomic study of oat is the very important basis for the analysis of important agronomic traits, the precise utilization of excellent germplasm and molecular design breeding of oats. This article mainly reviews the important achievements of world-wide oat germplasm resources collection and preservation, genome composition and chromosome ploidy level variations in the genus Avena, oat genetic linkage map construction and oat genome sequencing, as well as oat molecular breeding. Furthermore, this article discusses the future directions of oat genomic study and molecular breeding in the post genomic era.

Today, the genomic research of forage grass is still severely insufficient in comparison of food crops, limiting the dissection of its complex traits and the application of molecular-design breeding. In recent years, with increased demand for forage grass, substantially reduced sequencing cost, as well as rapidly developed sequencing and assembly technologies, the genomes of many important forage grasses have been sequenced and analyzed. Here, we review 18 sequenced leguminous-, gramineous- and cyperaceous-forages, and discuss future direction of forage grass genomic research.

In China, the demand for high-quality forage is continuously increasing. Improving the yield and quality of various forages, especially alfalfa (Medicago sativa), has been an important scientific and economic goal for plant breeders. Fixation of carbon dioxide by photosynthesis is the basis for the formation of forage biomass. Nitrogen absorption, fixation, transport and assimilation are important biological processes that affect the crude protein content of forage and determine its quality. Both biological processes are interdependent to each other. Therefore, we propose the new breeding ideas for efficient fixation, transport and assimilation of carbon and nitrogen in alfalfa, and summarize the latest progress in efficient fixation and transport of carbon dioxide, nitrogen fixation and absorption, as well as nitrogen transport and assimilation in recent years, so as to shed some light on molecular design breeding for forage with high biomass and high protein content in the future.

Tall wheatgrass (Elytrigia elongata), belonging to Thinopyrum genus, is a perennial cool season bunchgrass that was originated from southern Europe, Asia Minor and southern Russia. It has been widely cultivated in America, Canada, Australia and other countries for more than a half century. Since tall wheatgrass was induced in China, Zhensheng Li had used it as a wild parent for distant hybridization to breed wheat (Triticum aestivum) varieties from 1956. However, few reports were found for the wide cultivation of tall wheatgrass in China as a forage grass currently. It confers significant tolerance not only to saline and alkaline soil but also to waterlogging, drought and diseases. It can avoid competition of land and water between cereal crops and forage grass and benefit carbon neutrality and food security to cultivate tall wheatgrass on saline-alkali soils in the costal Circum-Bohai sea region. More than 10 cultivars has been released in America, Canada, Australia, Argentina and other European countries. Unfortunately, no tall wheatgrass variety has been certificated in China currently, which restrict the construction of Chinese costal grass belt. The genetic background is complex and the basic research is preliminary in tall wheatgrass, resulting in its breeding technology is lagged far behind the cereal crops like wheat and rice. Here, research progresses on the aspects of molecular breeding of tall wheatgrass including breeding history, speed breeding, tissue culture, genome sequencing and molecular markers were reviewed to promote tall wheatgrass breeding and construction of costal grass belt in China.

Forage grass is the cornerstone of animal husbandry. However, the shortage of forage grass caused by the lack of elite varieties and simple planting structure has been a bottleneck for the forage grass industry. Therefore, the productive yield potential of new forage grass species besides developing traditional forage grass should be mined. New forage grasses developed in recent years have great advantages over the traditional forage grasses in their feeding value, including yield, nutritional quality, adaptability, and stress resistance. In this review, we summarized the research progress, development trend, and core competitive value of several new forage grasses, including bermudagrass (Cynodon dactylon), triticale (×Triticosecale Wittmack), quinoa (Chenopodium quinoa), forage rapeseed (Brassica napus), grain amaranth, sesban (Sesbania cannabina), and wild soybean (Glycine soja). We also discussed the basic biological problems in new forage breeding. Finally, we provided suggestions and strategies for innovation of the new forage grass and sustainable development of forage grass industry, ensuring food security.

Doubled haploid breeding can achieve rapid homogenization of genetic material through the combination of haploid induction and doubling technology, which significantly accelerates the speed of pure line production and the selection process in hybrid breeding, is a common key technology in agricultural breeding. In this paper, we briefly review the methods and progress of plant haploid induction and chromosome doubling, introduce the latest gene editing-mediated in vivo haploid induction technology, and discuss and prospect the application of haploid breeding technology in Medicago sativa and other legumes forage.

Coastal grass belt refers to the development of grass/forage farming systems according to the gradient of salinity along the coastal line, which could help develop grass-based livestock husbandry on saline soil and contribute to food security in China. This review summarizes several successful forage cultivation models in Yellow River Delta, including the forages rotation, rice-triticale/oat rotation, and forest-grass intercropping. We also discussed the biological question that are related to the understanding of the molecular mechanisms of salt tolerance, dissection of molecular modules balancing stress tolerance and biomass production, and development of value-added products of forage grasses. The resolution strategy and realization way of these biological question were summarized.

This paper briefly introduced the status of forage germplasm conservation in China on several aspects, including its development history, work content and current work progress, in order to raise public awareness and attendance about forage germplasm resource protection and seed reproduction and multiplication. Finally, we put forward specific suggestions for the development of forage germplasm conservation in the future on the collection strategy, how to effectively utilize the existing resources and germplasm distributing and sharing policy, so as to provide guidance for the related work in the future.

Sorghum bicolor has the characteristics of salinity tolerance, high biomass and high photosynthetic performance. The stem accumulates high amounts of juice and sugar, making it an important silage crop with development potential. In-depth analysis of the molecular basis underlying the formation of S. bicolor forage traits and stress tolerance traits, as well as improvement and breeding of S. bicolor new varieties for forage are of great significance to the development of pasture-livestock industry in China. This review summarizes the research and breeding progress of S. bicolor, analyzes the existing problems, and puts forward countermeasures for S. bicolor molecular breeding in the future, aiming to promote the development of forage S. bicolor industry and ensure the food security in our country.

Pennisetum, with about 140 species in the world, is a kind of excellent forage. By conventional breeding and modern biology breeding methods, 23 approved varieties have been bred in China for their development and utilization. Here we review the biological and ecological basis of Pennisetum as well as recent research advances in cultivation physiology and silage utilization. Future research should continue to study the biological and genetic basis on high yield and stress resistance of Pennisetum as well as strengthen the multi-resistance breeding, name standardization of Pennisetum varieties, systematically research breeding, cultivation techniques and key technical parameters of silage, to promote the industrial application.

Modern science and technology have just been entering the field of grass-based livestock husbandry, and “less input, low output and poor platform” restrict the development of forage breeding and industry in China. Although the development of grass-based livestock husbandry is ready to take off, the lack of scientific and technological innovation is difficult to ensure China’s food security; furthermore, there are few institutions and teams that focus on forage breeding research in China. Therefore, we organize the special issue ‘Forage Biology’, aiming to promote public awareness of the scientific and technological innovation, industrial development and national forage seed industry safety.

Abstract Forage germplasm resources are national strategic and basic resources, which concern the overall revitalization of the forage seed industry, the basic support for the development of modern agriculture and animal husbandry, and ecological protection and restoration. This paper gives a review on the types, distribution, characteristics, and preservation of global forage germplasm resources. It also analyzes the existing problems, and makes suggestions in order to better protect and utilize forage germplasm resources in China.

Gene editing technology can manipulate the genome of organisms precisely and directionally. It is one of the most eye-catching subversive technologies in the field of life sciences, and has become the key technology in breeding of agriculture and animal husbandry. Recently, the demand for high-yield and high-quality forage grass are increasing in China, therefore, it is urgent to cultivate high-quality forage grass varieties with independent intellectual property rights. Here, we briefly reviewed the development of gene editing technology and its application in agricultural breeding, summarized the research progress in genome editing of gramineous and leguminous forage, and prospected the future direction of molecular module-based technology in forage grass breeding using genome editing.