Identification of helminthosporium spp on sorghum and their response to some physiologic and nutritional factors

The present work is concerned with the study of the identification of Helminthosporium spp on Sorghum and their response to some physiologic and nutritional factors. The fungi used in this investigation have been isloated from leaves, heads, and roots of sorghum plants collected from Gedarif, Damazine and Gezira. The vegetative mycelium, germination of conidia, conidial size (Length-Width), number of septa and the shape of conidia and conidiophores, for all the isolates were describes by using Camera Lucida drawing and microscopic photos. Then all the isolates were compared with published description of species. Accordingly the isolates were named:- 1. Exserohilum turcicum. 2. Helminthosporium rostratum. 3. Helminthosporium nodulosum. 4. Helminthosporium halodes. 5. Helminthosporium longirostratum. The pathogenicity of these isolates was proved in the glasshouse, and the results from soil inoculation showed that roots infected with Gedarif and Damazine isolates were more severely discoloured than roots infected with isolates from Gezira, root and grain. lso foliar inoculation showed that leaves from plants inoculated with root isolate were more severely infected than leaves from plants inoculated with Gezira, Gadarif, grain and Damazine isolates. Optimum fungal growth was at 27 deg C. Incubation at 20 deg C gave the poorest rate of growth. Interchanged light and darkness was more conducive to better fungal growth than both continuous darkness and continuous daylight inoculation. All tested carbohydrate sources were utilized by the isolates tested. However, Dextrose, Lactose, Dextrin, Starch, Sucrose and Maltose in this order gave the highest fungal dry weight. But Manitol and Galactose were less favourable. Irrespective of the nitogen sources, all the isolates equally utilized nitrogen. Field experiment showed that there was no difference among the isolates in virulence however; with regard to varieties Tabat was obviously more responsive to the disease