Maize Head Smut: Pathogenesis, Epidemiology, and Management Options

Abstract

Maize (Zea mays) head smut caused by Sphacelotheca reiliana, a basidiomycete with worldwide distribution, can cause devastating crop losses that pose a food security threat. While Kenya has experienced high incidences of the disease in the recent years, the seed certification regulation has a zero tolerance on S. reiliana. The spores of S. reiliana remain viable in soil for many years and serve as the main inoculum source as they germinate when the conditions are favourable and infect the host in the early stages of growth after germination. After penetration, the fungus grows systemically as the plant matures eventually transforming part or all of the inflorescence (ears and tassels) tissues into smut galls. The symptoms develop because the inflorescences have increased levels of reactive oxygen species, auxin, and misregulation of floral regulatory transcription factors. The most practical control strategy for maize head smut encompasses the use of resistant/tolerant cultivars, fungicide treatment (of seed or drenching of rows immediately after seeding), and field hygiene/ sanitation. Crop rotation may help when host crops are not planted for between 2-3 years or even more. Resistance genes, including ZmWAK, found in the major quantitative trait locus qHSR1/qHS2.09 regulate resistance of maize to head smut. The objective of this review paper is to provide an understanding of the head smut disease pathogenesis, epidemiology, and effective management options.