Bacterial wilt caused by Xanthomonas translucens pv. graminis (Xtg) is a major disease of economically important forage crops such as ryegrasses and fescues. Targeted breeding based on seedling inoculation has resulted in cultivars with considerable levels of resistance. However, the mechanisms of inheritance of resistance are poorly understood and further breeding progress is difficult to obtain. This study aimed to assess the relevance of the seedling screening in the glasshouse for adult plant resistance in the field and to investigate genetic control of resistance to bacterial wilt in Italian ryegrass (Lolium multiflorum Lam.). A mapping population consisting of 306 F1 individuals was established and resistance to bacterial wilt was assessed in glasshouse and field experiments. Highly correlated data (r = 0.67-0.77, P < 0.01) between trial locations demonstrated the suitability of glasshouse screens for phenotypic selection. Analysis of quantitative trait loci (QTL) based on a high density genetic linkage map consisting of 368 amplified fragment length polymorphism (AFLP) and simple sequence repeat (SSR) markers revealed a single major QTL on linkage group (LG) 4 explaining 67% of the total phenotypic variance (Vp). In addition, a minor QTL was observed on LG 5. Field experiments confirmed the major QTL on LG 4 to explain 43% (in 2004) to 84% (in 2005) of Vp and also revealed additional minor QTLs on LG 1, LG 4 and LG 6. The identified QTLs and the closely linked markers represent important targets for marker-assisted selection of Italian ryegrass.

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Crown rust, caused by Puccinia coronata f. sp. lolii, is one of the most important diseases of temperate forage grasses, such as ryegrasses (Lolium spp.), affecting yield and nutritional quality. Therefore, resistance to crown rust is a major goal in ryegrass breeding programmes. In a two-way pseudo-testcross population consisting of 306 Lolium multiflorum individuals, multisite field evaluations as well as alternative methods based on artificial inoculation with natural inoculate in controlled environments were used to identify QTLs controlling resistance to crown rust. Disease scores obtained from glasshouse and leaf segment test (LST) evaluations were highly correlated with scores from a multisite field assessment (r = 0.66 and 0.79, P < 0.01, respectively) and thus confirmed suitability of these methods for crown rust investigations. Moreover, QTL mapping based on a linkage map consisting of 368 amplified fragment length polymorphism (AFLP) and simple sequence repeat (SSR) markers revealed similar results across different phenotyping methods. Two major QTLs were consistently detected on linkage group (LG) 1 and LG 2, explaining up to 56% of total phenotypic variance (V (p)). Nevertheless, differences between position and magnitude of QTLs were observed among individual field locations and suggested the existence of specific local pathogen populations. The present study not only compared QTL results among crown rust evaluation methods and environments, but also identified molecular markers closely linked to previously undescribed QTLs for crown rust resistance in Italian ryegrass with the potential to be applied in marker-assisted forage crop breeding.

Perennial ryegrass (Lolium perenne L.) is the most important grass species used in temperate grassland agriculture. Our objective was to obtain an overview of the genetic relationships between 20 individual genotypes of perennial ryegrass of diverse origins, using amplified fragment length polymorphism (AFLP), inter-simple sequence repeat (ISSR), random amplified polymorphic DNA (RAPD) and two sets of simple sequence repeat (SSR) markers. All 20 individuals were uniquely fingerprinted by all four marker systems and comparisons were made on the basis of 85 markers each. Mean genetic similarities were estimated at 0.31, 0.43, 0.23 and 0.15 for AFLPs, ISSRs, RAPDs and SSRs, respectively. Cophenetic values resulted in good (AFLP and SSR-B = 0.88) to moderately good fits (ISSR = 0.76, RAPD = 0.70, and SSR-A = 0.79). Comparing the four marker systems to each other, AFLP and SSR-A were correlated best (r = 0.57). All other comparisons revealed rather low correlation coefficients in the Mantel Z test. With twice as many markers cophenetic values increased to a very good fit for AFLPs (0.90) and SSRs (0.92).

A 3 hr treatment period with a 0 .2% aqueous solution of colchicine was given to one week old seedlings of inbred lines of perennial ryegrass (Lolium perenne L .) . The surviving plants developed as mixoploids and were subsequently split down into single tillers and then classified as either diploid or tetraploid . The undoubted diploids of the treated material (C2x) were then self-pollinated and the seeds grown in the following generation (CT1) without any further treatment . In the CT1 generation comparisons were made between the C2x and the control 2x treatments within the same inbred lines, and heritable differences were found for leaf mesophyll cell plan areas and chloroplast numbers . The cell areas were significantly less in the C2x compared with the 2x treatment in four out of the five lines studied, and the chloroplasts numbers were likewise lower in two out of the five lines . In one line there was a significantly higher mean number of chloroplasts per cell in the C2x material compared with that of the 2x .

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A short period of colchicine treatment at the seedling stage induces changes in the capacity for tillering, vegetative growth and flowering time in inbred lines of Lolium multiflorum. The changes are heritable and are observable in the selfed-seed generation following that in which the treatment was given. Information is also given to confirm such changes in an additional ten inbred lines of Lolium perenne. INTRO D U CTI ONIn previous studies in which we have used colchicine as a chromosome doubling agent to produce tetraploids from diploid inbred lines of perennial ryegrass (Lolium perenne) we have observed that the colchichine treatment itself induces heritable changes in the undoubled diploids that were used as controls (Hague and Jones, 1987;Francis and Jones, 1989). The changes involved characters of agronomic significance such as tiller number and fresh and dry weight of leaf material. In the lines investigated so far we have found that these chages varied in their magnitude between lines, and that they were directional in that vegetative production was either increased or else the differences between the treated and untreated controls were nonsignificant. The changes were not random. We have further demonstrated that in perennial ryegrass these coichicine-induced changes are heritable, and that they are transmitted undiminished through a selfed-seed generation (Francis and Jones, 1989). In this publication we present new results for coichicine-induced heritable variations in Italian reygrass (L. multiflorum), and we also confirm the results for L. perenne using ten additional inbred lines that have not been previously studied. MATERIALS AND METHODSThe Italian ryegrass lines originate from experimental material produced by Professor G. Kobabe, University of Göttingen and the perennial ryegrass lines are from the inbred material which was originally produced at Hohenheim by Utz and Oettler (1978). The L. perenne lines have their origin in the German ryegrass varieties Odengrün and Odenwãlder. In both cases it can be assumed that we are dealing with pure breeding homozygous lines.Seeds from ten lines of Italian ryegrass and ten lines of perennial ryegrass were "sown" on moist filter paper in petri dishes in October 1986. The petri dishes were placed in a refrigerator at 4°C for one week to aid germination. When the seedlings had grown to 2-3 cm some of them were treated by total immersion in O2 per cent aqueous colchicine for 3 hrs at room temperature, and others were immersed in water as the untreated controls. After washing and recovery from treatment the two groups of seedlings were planted in John Innes Compost and grown on in plastic multitrays in a heated greenhouse for two weeks. The survival rate of the coichicine-treated material was of the order of 65 per cent.At 7 weeks of age the plants were transferred to 5-inch pots in John Innes Compost and grown on to flowering in an unheated glasshouse. Flowering occurred in May-June 1987 and all of the plants were then bagged for self-pollination. The co...