Importance, Biology, Epidemiology, and Management of Loose Smut (Ustilago nuda) of Barley (Hordeum vulgare): A Review

Abstract

Barley (Hordeum vulgare) is an economically, nutritionally and industrially important cereal crop worldwide. Ethiopia is believed to be the center of origin and diversity of the cultivated barley crop. The crop has been cultivated in the country since time immemorial. The midlands and highlands of Ethiopia are suitable for barley cultivation. However, there are many biotic and abiotic factors that reduce production and productivity of the crop in Ethiopia and elsewhere. Of the various fungal plant diseases limiting barley productivity, loose smut (Ustilago nuda) is one of the major cosmopolitan and destructive seedborne pathogen in many barley-producing countries in the world. This piece of work was undertaken to: 1) review the economic importance and ecological requirements of barley and extent of grain loss due to barley loose smut; 2) review the biology and ecological requirements of the pathogen leading to epidemics; and 3) compile the management options for sustainable barley production and productivity. To achieve these objectives, data and information were gleaned from scientific journal publications, PhD dissertations, Master’s theses, research reports, books and book chapters, proceedings and symposia papers, relevant compendia, internet resources, personal communications, and similar other resources. From the reviews made, it could be deduced that barley loose smut on average causes estimated grain yield losses that range from 25 to 30% in the world. The systemic pathogen is embedded in the scutellum part of the embryo and easily transmitted to the next cropping season. The pathogen sori commonly replace the spike during anthesis and healthy ears are infected at flowering through the teliospores blown by wind. Warm soil when seedlings emerge is more conducive to loose smut than cold soil; however, moderate temperature (15 to 22 oC) and damp cloudy weather or heavy rainfall at flowering time are the preconditions required by the pathogen for heavy infection because of elongated or extended period of open flowers. Barley loose smut can be better managed through the use of proper cultural practices in integration with hot water and solar heat seed treatment, use of resistant varieties, and effective systemic fungicides, like Azoxystrobin, Carboxin, Difenoconazole, Mancozeb, Propiconazole, Tebuconazole, Triadimenol, and Triticonazole. It could, thus, be concluded that barley loose smut is a very important disease that seriously affects barley production and productivity worldwide, but can be reasonably managed through the use of smut-free seed, certified seed, host resistance, and hot water/solar heat or systemic fungicidal seed treatment or their integration.