Soilborne fungal diseases of small grain cereal crops

Ivo Yanashkov, Giovanna Gilardi, Tzenko Vatchev

Abstract: Small grain cereal crops including wheat, barley, rye, oats, etc. grown in different geographic regions around the world are subject to attack by various soil inhabiting fungi, fungus-like oomycetes as well as primitive zoosporic fungi. All growth stages of the cereal crops are affected, and disease symptoms have been observed ranging from pre-emergence decay of seeds and post-emergence dumping-off of the young plants to root and lower stem rot of the older plants. Some root infections remain latent until favourable conditions or through to harvest. Species of the genus Fusarium rank among the most common soilborne pathogens on cereal crops. Root infections by F. graminearum, F. culmorum and F. avenaceum are associated with significant economical losses in hotter and temperate regions while F. nivale is predominant in cooler regions. Other Fusarium species like F. poae, F. moniliforme, F. equiseti and F. oxysporum are considered widely distributed in all areas where cereal crops are grown. In view of their wide distribution and economic importance fungal species such as Gaeumannomyces graminis, Pseudocercosporella herpotrichoides and Drechslera sorokiniana are frequently reported as causal agents of root rot and stem base necrotic lesions on cereal plants. Similarly, species of genus Rhizoctonia, including R. solani and R. cerealis, are associated with frequent crop failures due to root and stem base infections. Less frequently reported on cereal crops are Colletotrichum graminicola, Aureobasidium bolleyi and representatives of order Agaricales, including parasitic species Naucoria cerealis, Pholiota dura and Marasmius tritici. Large number of fungus-like representatives of the genus Pythium and Lagena (Oomycota) including P. graminicola, P. ultimum, P. irregulare, P. aristosporum, P. volutum, etc. as well as Lagena radicicola are some of the most prevalent pathogens attacking root system of cereal crops in wet, cool conditions. Primitive zoosporic species Olpidium brassicae, Rhizophydium graminis and Ligniera pilorum have been reported to develop most easily on root hairs first, while Polymyxa graminis is known as a vector of several economically important viruses of cereal crops. Various species of the genus Fusarium, along with Gaeumannomyces graminis, P. herpotrichoides, D. sorokiniana and Rhizoctonia spp. have been repeatedly found on roots and lower stems of small grain cereal crops in Bulgaria. Even though, comprehensive data on the prevalence of the different species, their distribution across the country and losses they incure on the cereal crops is currently lacking. All pathogenic species summarized in the present review may infect cereal plants singly and independantly or in various combinations resulting in disease complexes. Pathogens of the genera Fusarium, Drechslera, Pseudocercosporella and Rhizoctonia have been reported to cause mixed infections of two and more fungal species on roots and stem bases of plants. Economic losses caused by soilborne diseases in small grain cereal crops vary widly across the main growing regions depending on the host species, ecological and agronomical conditions of cultivation.

Keywords: small grain cereal crops; soil inhabiting fungi

Date published: 2019-04-11