Resistance to accumulation of Soil-borne cereal mosaic virus in eight cultivars of Triticum durum Desf.

The concentration of Soil-borne cereal mosaic virus (SBCMV) and Wheat spindle streak mosaic virus (WSSMV) was monitored during two seasons in the roots and shoots of eight cultivars of durum wheat (Triticum durum Desf.) grown in a field near Rome (Italy) with natural inoculum sources of these viruses. SBCMV and WSSMV titers were determined using an amplified immunosorbent electron microscopy (ISEM) procedure and – in one season – also with A sandwich enzyme-linked immunosorbent assay (PAS-ELISA). Particles of SBCMV were detected in the roots and shoots of all cultivars, in both seasons and on most collection dates. The cultivars manifested wide differences in SBCMV particle oncentration maxima in both roots and shoots. Results showed that the defense mechanism mainly responsible for such differences was directed at SBCMV accumulation. Three of the cultivars classified as susceptible to SBCMV accumulation showed dubious signs of ther partial resistance to early root infection or – in one season - to upward SBCMV movement, but neither of the latter defense mechanisms, if indeed present, had appreciable effects on the ltimate virion concentration in roots and shoots of these cultivars. The amount of SBCMV particles in roots was closely correlated to that detected in shoots throughout the greater part of both seasons, suggesting the presence of a generalized resistance mechanism controlling virion accumulation in the plants as a whole. Reappraisal of previously published data suggests that at least some of the cases of resistance to upward movement and to early root infection reported in the literature for SBCMV and for the losely related Soil-borne wheat mosaic virus (SBWMV) could also be explained in terms of generalized resistance to virus accumulation. Resistance to WSSMV could not be investigated due to the exiguous amount of this virus detected in most of the root and shoot samples examined. PAS-ELISA data proved markedly less informative than those obtained using ISEM for both SBCMV and WSSMV.