PATHOTYPE CHARACTERIZATION OF THE CEREAL CYST NEMATODE, HETERODERA AVENAE, IN SAUDI ARABIA

The cereal cyst nematode (CCN), Heterodera avenae woll, has been reported on wheat and other cereals in many countries with different climate types throughout the world (Holdeman & Watson, 1977; Meagher, 1977; Sturhan & Rumpenhorst, 1966). In 1987, the nematode was also reported from irrigated wheat fields in Saudi Arabia (Youssif, 1987). Since then, II. avenae has been increasingly detected in Saudi Arabia year after year and has become recognized as a danmaing pathogen of wheat and barley, especially in Al-Kharj, Hail and Al-Gassim, the three major wheat producing regions. (Al-Hazmi, 1992; Al-Hazmi et al., 1994). Growth and physiology of infected wheat and barley are adversely affected (Al-Yahya et al., 1988), and yield loss is as much as 92% in heavily infested sites of some wheat fields (Ibrahim et al., 1999). Some records of cereal cyst nematode may refer to other species other than H. avenae. For example, comparative biochemical and morphological studies made by Sturhan and Rumpenhorst (1996) on numerous H. avenae and H. avenae-resembling populations from several geographic origins in eastern Europe and west Asia proved that these populations are in fact. H. filipievi Madzhidos. However, the protein pattern of the Saudi population from Al-Kharj region closely agreed with that of typical H. avenae (Sturhan & Ruympenhorst, 1996). Cotten (1967) reported that more than three phatotypes of CCN were present in England and Wales and, since then, variations in virulence of CCN populations on different cereal genotypes have been described from Asia (Mathur et al., 1974; Shimizu et al., 1987; Dhawan, 1988; Zheng Jing et al., 1997) and many other countries Swarup & Sosa Moss, 1990; Rivoal & Cook, 1993). Characterization of the cereal cyst nematode species and pathotypes is essential for resistance breeding and nematode management programmes. The objective of this study was to characterize the pathtype of three populations of H. avenae collected from the three major wheat-producing regions of Saudi Arabia