Nematology, 2001, Vol. 3(6), 581-592 Variation in reproductive capacity and virulence on different genotypes and resistance genes of Triticeae, in the cereal cyst nematode species complex Roger RIVOAL 1;¤ , Sadia BEKAL 1 , Sylvie V ALETTE 1 , Jean-Pierre GAUTHIER 1 , Makram BEL HADJ FRADJ 1 , Aïssa MOKABLI 2 , Joseph JAHIER 3 , Julie NICOL 4 and Amor Y AHYAOUI 5 1 UMR INRA/ENSAR, Biologie des Organismes et des Populations appliquée à la Protection des Plantes (BiO3P), B.P. 35327, 35653 Le Rheu, France 2 Institut National Agronomique, Département de Zoologie Agricole et Forestière, El Harrach, Algérie 3 INRA, UMR INRA/ENSAR, Amélioration des Plantes et Biotechnologies végétales, B.P. 35327, 35653 Le Rheu, France 4 CIMMYT International, Wheat Program, P. K., Emek, 06511 Ankara, Turkey 5 ICARDA, Cereal Pathology, P.O. Box 5466, Aleppo, Syria Received: 27 April 2001; revised: 25 June 2001 Accepted for publication: 5 July 2001 Summary – Two sets of experiments in 1998 and 1999 studied the (a)virulence status of 14 populations of Heterodera avenae, and two populations each of H. lipjevi and H. latipons towards the resistance genes and genotypes of Triticeae, presently known to be resistant to H. avenae, the main species of the cereal cyst nematode (CCN) species complex. Susceptible controls were Triticum aestivum cv. Arminda and Triticum turgidum cv. Cham1. Even in controlled experimental conditions, host responses differed between replicates in the same test and between consecutive tests for unexplained reasons. In spite of that, it has been conrmed that several of these CCN populations differ in their intrinsic capacity to reproduce, and this has to be taken into account in resistance screening. Consequently, the (a)virulence status of a CCN population is better established by a qualitative demarcation between resistant and susceptible plant genotypes based on an average of one cyst limit per plant. The matrix inferred from such a classication of host responses of pooled 1998 and 1999 data showed a complex distribution of avirulent and virulent phenotypes in these CCN populations which seems to arise from a mosaic-like evolution. The more or less wide virulence spectrum shown by this complex of populations and species is discussed in relation to their phylogenetic relationships. Correspondence factor analysis of the pooled data demonstrated a geographical demarcation between several populations of H. avenae and the representatives of H. lipjevi and H. latipons for their (a)virulence to either Cre1 or Cre3 genes and T. aestivum AUS4930 genotype. This could reveal local or regional selection of new pathotypes, more particularly in H. avenae. Genetic introgression to improve resistance to these nematodes in both bread and durum wheats is discussed for regional and global applications. Keywords – Heterodera avenae, H. lipjevi, H. latipons, host reaction, pathotype, Triticum. Small grain cereals can suffer considerable economic damage from different species of the cereal cyst nema- todes (CCN, Heterodera spp.) which are widely distrib- uted throughout the world (Rivoal & Cook, 1993; Evans & Rowe, 1998; Nicol, 2001). For economic and envi- ronmental reasons, the control of these nematodes has to be based on integrated cropping systems, of which resistant varieties will constitute an important compo- nent. Cultivars resistant to H. avenae, the most important ¤ Corresponding author, e-mail: rivoal@rennes.inra.fr species of the CCN complex, have been intensively bred and cultivated for barley and oat in Northern Europe and wheat in Australia and France (Andersen, 1982; Ander- sson, 1982; Brown, 1984; Rivoal et al., 1990). They are needed in other regions such as East and West Asia and North Africa, where monocultures of cereals have devel- oped economically damaging densities of these pathogens (Sikora, 1987; Ibrahim et al., 1999). c ° Koninklijke Brill NV, Leiden, 2001 581