Resistance of Annual Ryegrass Germplasm to a Highly Aggressive New Strain of Blast (Gray Leaf Spot)

摘要

Annual ryegrass (Lolium multitlorum Lam.) is a mgniy nutritive, fast-growing, C3 cool-season annual forage. Blast or gray leaf spot is a fungal disease of ryegrass caused by Magnaporthe orygae (anamporph Pyricularia oryzae). The disease kills seedlings as well as adult plants. Blast-resistant annual ryegrass cultivars are not available at present. Therefore, identifying sources of resistance and developing blast-resistant germplasm are priorities to circumvent the devastating disease. Incorporation of germplasm screening in a breeding program requires an efficient, low-cost, and high-throughput evaluation system. Screening methods reported in literature lack both efficiency and throughput capabilities suitable for breeding. The aims in this work were to develop a low-cost, high-throughput phenotyping system, and to screen the annual ryegrass National Plant Germplasm System (NPGS) collection with a highly aggressive, newly isolated M. oryzae strain from naturally infected annual ryegrass plants, which was named MoGAI. Host specificity was tested on four species in addition to annual ryegrass. Extensive damage was caused to perennial ryegrass (Lolium perenne L.) and tall fescue {Lolium arundinaceum (Schreb.) Darbysh), whereas rice {Oryza sativa L.)and orchard grass (Dactylis glomerata L.) exhibited a hypersensitivity response and resisted the infection, suggesting that pathogenicity of the strain was limited to the Lolium genus. A portable low-cost, high-throughput screening system capable of screening 1,536 plants per unit was developed and used to screen 138 ryegrass accessions with MoGAI. Two accessions showed resistance to the pathogen and produced seed. These two entries can be used to incorporate blast resistance in annual ryegrass germplasm.