QTL Analysis of Morphological, Developmental, and Winter Hardiness-Associated Traits in Perennial Ryegrass

key variables: leaf appearance rate, leaf elongation rate, and leaf lifespan. The expression of each of these traits is Quantitative trait loci (QTLs) for a number of agronomically imunder both genetic and environmental control (Lemaire portant traits of perennial ryegrass (Lolium perenne L.) were identiand Chapman, 1996), and leaf development in Lolium fied by means of a reference molecular marker-based genetic map. Replicated phenotypic data was obtained for a number of field-assessed has been demonstrated to be under genetic control in a morphological and developmental traits as well as the winter hardinumber of studies (Edwards and Cooper, 1963; Rhodes, ness-associated characters of winter survival and electrical conductiv1973; Hazard et al., 1996). Structural characteristics of ity. Marker-trait association analysis was performed by a number of plants such as tiller number, leaf number, and leaf size methods, and a high degree of congruence was observed between the are the result of these morphogenetic traits, and their respective results. QTLs were detected for morphological traits such measurement in breeding programs allows a dissection as plant height, tiller size, leaf length, leaf width, fresh weight at of the complex herbage yield trait as well as predictions harvest, plant type, spikelet number per spike and spike length, as well of the response to grazing. as the developmental traits of heading date and degree of aftermath Different ecoclimatic regions, or pastures under difheading. A number of traits were significantly correlated, and coinciferent grazing regimes, may provide alternative selecdent QTL locations were identified. No significant QTLs for winter survival in the field were identified. However, a QTL for electrical tion goals for these traits. For instance, cool season conductivity corresponding to frost tolerance was located close to a growth is an important breeding objective in climates heading date QTL in a region that may show conserved synteny with mild winters. Mediterranean genotypes of perenwith chromosomal regions associated with both winter hardiness and nial ryegrass have more rapid rates of leaf appearance flowering time variation in cereals. The QTL analysis of multiple and elongation in winter than genotypes from northern phenotypic traits provides the basis for marker assisted selection Europe and hence better cool season herbage yield (MAS) of important agronomic characters, allowing genetic improve(Cooper, 1964). However, this trait may be related to ment of yield, quality and adaptation in perennial ryegrass breeding. the onset of reproductive development (Kemp et al., 1989) and be negatively correlated with survival during harsh winters. In addition, selection for large leaves has P ryegrass is the most widely sown perenbeen shown to increase yield under infrequent grazing nial forage grass in temperate regions of the world. (Rhodes and Mee, 1980; Hazard and Ghesquière, 1997). The popularity of perennial ryegrass in pastoral agriculHowever, interactions between grazing management ture is largely due to high yield of digestible nutrients and optimal leaf size have been detected, with shortcombined with good tolerance to grazing and adequate leaved selections being better adapted to frequent cutseed production (Wilkins, 1991). ting (Hazard and Ghesquière, 1997). The morphogenesis of individual grass plants within Genetic variation in morphogenetic traits associated a grazed sward plays a key role in determining herbage with reproductive development is of practical imporyield, persistence, and recovery from grazing. In vegetatance in perennial ryegrass breeding not only because tive plants, plant morphogenesis is described by three of the potential correlation between these traits and vegetative production, but also because of the association of these traits with seed yield (Elgersma, 1990a). T. Yamada, National Agricultural Research Center for Hokkaido Region, National Agricultural Research Organization, Hitsujigaoka, Traits such as spike numbers, spikelets per spike, and Sapporo, 062-8555, Japan; E.S. Jones, Crop Genetics Research and florets per spikelet have been shown to be heritable Development, Pioneer Hi-Bred International, 7300 NW 62nd Avenue, (Elgersma, 1990b). Johnston, IA 50131-1004; N.O.I. Cogan, A.C. Vecchies, and J.W. The manipulation of these morphological and develForster, Plant Biotechnology Centre, Primary Industries Research Victoria, Department of Primary Industries, La Trobe University, opmental traits in a breeding program can be improved Bundoora, Victoria 3086, Australia and Cooperative Research Centre by knowledge of the underlying genetic control mechafor Molecular Plant Breeding, Australia; T. Nomura, H. Hisano, Y. nisms. The detection of QTLs associated with these Shimamoto, Graduate School of Agriculture, Hokkaido University, traits in perennial ryegrass is consequently likely to proKita 9, Nishi 9, Sapporo, 060-8589, Japan; K.F. Smith, Pastoral and Veterinary Institute, Primary Industries Research Victoria, Departvide breeders with enhanced possibilities for the develment of Primary Industries, Private Bag 105, Hamilton, Victoria 3300, opment of highly adapted germplasm. Australia and Cooperative Research Centre for Molecular Plant Perennial ryegrass is susceptible to winter stresses Breeding, Australia; M.D. Hayward, Rhydgoch Genetics, Rhydhir caused by both snow molds and low temperatures (JaUchaf, Comins Coch, Aberystwyth, Ceredigion SY23 3BJ, Wales, UK. malainen, 1974; Jönsson and Nilsson, 1985; Nakayama Received 11 Apr. 2003. *Corresponding author ([email protected]. gov.au). et al., 2001). In addition to the improvement of growth characteristics, increased winter hardiness of perennial Published in Crop Sci. 44:925–935 (2004). ryegrass is an important breeding objective in northern  Crop Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA cold climate regions. Genetic analysis of the components