Abstract

The Exserohilum turcicum fungus causes the Northern leaf blight (NLB) of maize all over the world. In Tanzania, this disease is considered as a major foliar disease with yield losses of 23.9 to 62.8%. To understand the genetic variations of E. turcicum from maize fields in Tanzania, a survey was conducted in four regions, including Morogoro, Iringa, Njombe, and Mbeya. Leaf samples were collected from diseased plants exhibiting NLB symptoms. Using aseptic technique, pure colonies of fungal pathogens were isolated on selective media followed with molecular analysis. The internal transcribed ribosomal DNA (ITS), six microsatellite markers of simple sequence repeat (SSR) nature, and two specific mating type primers (MAT) designed to amplify MAT1 and MAT2 gene sequences were used in this study. With ITS marker, 14 isolates were amplified, Sanger sequenced, and their sequences were deposited to GenBank with accession numbers MT124699-MT124712. The SSR results were scored using base pairs in each genotype and subjected to power marker software to determine genetic variations. A total of four alleles across two loci were detected, with gene diversity (0.26 - 0.58). Polymorphic bands revealed 4 and 5 genotypes using SSR 06 and SSR 024, respectively. The polymorphic information content (PIC) of SSR 06 and SSR 024 loci were 0.25 and 0.52, respectively. The specific MAT markers demonstrated dominance of MAT 2 over MAT 1. The distribution of MAT 1 and MAT 2 in humid highlands of Mbeya, Njombe, and Iringa regions indicated possibility of sexual reproduction and good potential for sexual recombination than in the dry lowland of Morogoro region. This study is the first report on genetic diversity of E. turcicum in Tanzania, further studies using robust molecular and sequencing techniques is imperative in Tanzania.

Key words: Exserohilum turcicum, maize, microsatellite, mating type primers, ITS primers, Tanzania.