A theoretical and practical analysis of the optimum breeding system for perennial ryegrass

Authors: CONAGHAN, PATRICK - Teagasc (AGRICULTURE AND FOOD DEVELOPMENT AUTHORITY); Casler, Michael

Submitted to: Irish Journal of Agricultural Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2011
Publication Date: 12/30/2011
Citation: Conaghan, P., Casler, M.D. 2011. A theoretical and practical analysis of the optimum breeding system for perennial ryegrass. Irish Journal of Agricultural Research. 50:47-63.

Interpretive Summary: Recent trends and surveys among forage and livestock producers indicates the need for forage and pasture crops with higher yield. Especially for high-quality species, such as perennial ryegrass, yield of biomass is seen as the factor most limiting livestock production and on-farm profits. This paper delves into the use of biotechnology, specifically DNA markers, to improve the efficiency of breeding for higher biomass yield and to increase the rate of gain in breeding programs. Several breeding methods are presented and their merits are discussed in terms of exactly how breeders could use DNA markers to increase forage or biomass yields. With relatively modest investments of $20 to 40K per year, annual gains in breeding for increased yield could be doubled or tripled, leading to significant increases in on-farm productivity. These results will be of direct value to all forage breeders and indirect value to extension agronomists and forage/livestock producers.

Technical Abstract: The goal of plant breeding is to develop and use methods that effectively and efficiently select for the best phenotypes leading to the development of improved cultivars. The objectives of this review are to describe and critically evaluate breeding methods appropriate to the improvement of perennial ryegrass (Lolium perenne L.) in a dedicated long-term breeding programme. The optimum breeding system is dependent on the traits for improvement, and the resources and skills available. Forage dry matter yield, persistence, disease resistance, nutritional value and seed yield are considered among the most important traits for improvement. Careful consideration should be given to the expression of the trait under the management regime imposed in the breeding programme and under real-world sward conditions in the target region. Recurrent selection programmes for intrapopulation improvement are most appropriate for breeding perennial ryegrass. Three distinct types of recurrent selection may be implemented: (i) phenotypic recurrent selection, (ii) genotypic recurrent selection and (iii) marker-assisted selection. Genotypic recurrent selection will be a necessary part of the breeding system if forage yield is a trait for improvement. Genotypic recurrent selection may be practised using full-sib or half-sib families, each with their own advantages and disadvantages to consider. Phenotypic recurrent selection in tandem (i.e. within family selection) or in succession with genotypic recurrent selection should be used to improve traits that have a high correlation between spaced plants and swards. Genome-wide selection represents the most interesting and exciting potential application of marker-assisted selection, although it remains to be seen how effective and efficient it will be in practise.