Species disease composition of sorghum crops in forest steppe of the Middle Volga region

Abstract

The paper presents the results of field and laboratory studies on the disease diversity in sorghum and Sudan grass. It is found that leaf spotting in sorghum in the wooded-steppe of the Middle Volga region is caused by a broader range of pathogens than previously assumed, whilst the symptoms of damage caused by different types of fungi might be similar in occurrence. It is of paramount importance to proceed with phyto-examination of the seeds with further identification of the accumulated infection sources in the seed material under field conditions, at the time of harvest and during subsequent processing of the seed material in seed refiners, etc. For that to happen, the leaves with distinct spotting occurrence are collected and, given the preliminary storage of the material in humidity cabinet, are examined in the laboratory employing microscopic techniques. On the leaves of grain sorghum collected over the vegetation season of 2018 and dried up to be preserved as herbarium, the dark purple coming near to black spots of various sizes and shapes were predominantly observed. When identifying leaf pathogens, the fungi were largely detected and identified, i.e.: Alternaria tenuissima, Botrytis cenerea, Trichothecium roseum. In 2019, the leaves touched by spotting were already picked from different specimen varieties of sorghum and Sudan grass; and their identification was carried out with regard to dissimilar occurrence of symptoms during the period of plant vegetation. In the spotted areas of the infected leaves, there were mycelium and sporulation revealed of the fungi as follows: Cladosporium herbarum genera (82.1% of all specimens studied), Alternaria sp. (71.1%) and Verticillium sp. (71.4%). The midrange frequency of occurrence was estimated for Trichothecium roseum (53.6%), Helminthosporium sp. (42.9%), Cercospora sorghi (39.3%), Fusarium sp. (35.7%). Besides, the bacterial infection was discovered as well in 32.1% of the specimens.