Evaluation of genetic diversity in wild orchardgrass (Dactylis glomerata L.) based on AFLP markers

摘要

Orchardgrass (Dactylis glomerata L.) is a highly variable perennial forage grass, widely cultivated in all temperate and subtropical growing regions of the world. It is native to northern Africa, Europe, temperate and tropic Asia (Hultén 1968; Tolmachev et al. 1995), and is widely grown for pasture and hay. It is also an important intercrop in fruit orchards and under shading. Because of its dense network of roots, orchardgrass is recommended as a part of a seed mix for erosion control (Anderson and Brooks 1975; Mclean and Clark 1980). Orchardgrass is indigenous to China where it is primarily distributed in the southwest and northwest areas, mainly growing on forest edges, in shrubs and in sub alpine meadows at elevations ranging from 1000 to 3600 m, where diploid (2n=2x=14) and tetrapoid (2n=4x=28) cytotypes grow in sympatry (Zhang et al. 1994; Zhou et al. 2000). The interest in studying wild orchardgrass germplasm has dramatically increased over the past 20 years since the cultivated varieties selected from the local wild sources offered more advantages including higher yield and adaptability to the environment than those introduced from other countries. Thus, three cultivated varieties from wild material has been developed recently, named cv. Gulin, cv. Baoxing and cv. Chuandong, reflecting their origin regions. The genetic resources of the wild germplasm present indigenously are to be exploited and conserved for breeding purpose. In order to achieve this, it is imperative to assess the genetic variability present among wild accessions.Variations in orchardgrass morphological features, distributional patterns, adaptive and agronomic characters, and allozymes are well documented (Lumaret et al. 1987; Lumaret and Borrientos 1990; Sahuquillo and Lumaret 1995; Volaire and Thomas 1995; Volaire 1995; Bretagnolle and Thompson 1996; Gauthier et al. 1998; Gautier and Lumaret 1999; Lindner et al. 1999; Sugiyama and Nakashima 1999; Tosun et al. 2002). DNA profiling techniques that have been successfully used in assessing genetic diversity and relatedness of orchardgrass germplasm include randomly amplified polymorphic DNA (RAPD) markers (Kolliker et al. 1999; Tuna et al. 2004; Zeng et al. 2006a) and inter-simple sequence repeat (ISSR) (Zeng et al. 2006b). Reeves et al. (1998) used amplified fragment length polymorphism (AFLP) DNA profiles to determine relationship between genome size and altitude of origin in natural populations of orchardgrass. Even though these studies demonstrated the usefullness of DNA profiling in assessing genetic differences in orchardgrass, none has focused on assessing genetic diversity and relationship within the wild Chinese orchardgrass.So far, information on the genetic diversity of wild Chinese orchardgrass at the DNA molecular level is still scarce. AFLP is an efficient, reproducible technique which combines the reliability of RFLP and the power of the PCR technique (Vos et al. 1995). Many forage grasses have been analyzed by this technique, including Lolium perenne (Guthridge et al. 2001), Phalaris aquatica (Rouf et al. 2005) and Eragrostis species (Ayele et al. 1999). Accordingly, we selected AFLP marker: (1) to estimate the levels of genetic diversity among 32 wild orchardgrass originated from various geographic locations in China, together with two wild accessions from USA, (2) to evaluate the genetic relationships between orchardgrass accessions, and (3) to characterize germplasms to select desirable genotypes for breeding and other utilization purposes.