Soil-borne virus diseases in wheat: a threat that struggles to be fully recognized

In cereal crops some soil-borne diseases of viral etiology were described a few decades ago and the causal agents were identified as elongated bipartite RNA viruses, transmitted by the endoparasitic plasmodiophorid Polymyxa graminis. As found in all continents, these virus diseases are also present in Europe where two virus species appear predominant, Soil-borne cereal mosaic virus (SBCMV, belonging to the genus Furovirus) and Wheat spindle streak mosaic virus (WSSMV, belonging to the genus Bymovirus). These viruses tend to induce similar symptoms on winter cereals, including a general yellowing and size reduction of the plant, appreciable mainly in early spring, usually accompanied by mosaic on leaves. The extent of yield reduction has been estimated between 30 and 70%. The prevalence of these viruses is difficult to establish only by observing symptomatology, mainly because symptoms can be confused with nutrient deficiencies and/or water stress. Extended surveys have only rarely been performed. In Italy SBCMV and WSSMV were reported on both common (Triticum aestivum L.) and durum [Triticum turgidum L. subsp. durum (Desf.) Husn.] wheat in several regions, but a nation-wide investigation has not yet been carried out. This kind of survey would require technologies and protocols capable of collecting representative materials from the cereal growing areas at the right time of the year (March and April) and analysing a high number of plant samples for both viruses. Another type of analysis would be sampling soils for the presence of the P. graminis vector. As a step towards these goals, we have re-examined the analytical protocols currently available in the literature and developed a multiplex assay capable of detecting SBCMV and WSSMV simultaneously in wheat tissues, as well as an assay for detecting the presence of P. graminis in the soil. This work is supported by Regione Lombardia, d.d.s. n. 4403 28/03/2018, grant n° 42 - SURF.