USE OF PCR FOR DETECTION OF MYCOSPHAERELLA-FIJIENSIS AND M-MUSICOLA, THE CAUSAL AGENTS OF SIGATOKA LEAF SPOTS IN BANANA AND PLANTAIN

There are two Sigatoka leaf spot diseases of banana and plantain, yellow Sigatoka and black Sigatoka, yellow Sigatoka is caused by Mycosphaerella musicola, and black Sigatoka by M. fijiensis. Because unambiguous diagnosis of these leaf spots is often not possible by symptoms alone, we have used the polymerase chain reaction (PCR) to distinguish between the two species, and to detect the pathogens in DNA from infected leaf tissue. Two 21-base oligonucleotide primers were synthesised from a variable region identified in the nucleotide sequence of the internally transcribed spacer (ITS) 1 region of ribosomal DNA (rDNA) of Mycosphaerella fijiensis and M. musicola. These primers (MF137 and MM137 respectively) were used in association with primer R635 (from a conserved sequence of the rDNA). Primers MF137 and R635 produced an amplification product of approximately 1000 bp in size with DNA from M. fijiensis. This product was not formed when DNA of M musicola, M. minima, or a number of other fungi which are commonly found on banana leaves, was amplified. Primer combination MM117 and R635 produced an amplification product of approximately 1000 bp with DNA from M. musicola. The primers amplified similar sized fragments from the DNA extracted from banana leaf tissue infected with M. fijiensis and M. musicola. Southern hybridization analysis confirmed the fungal origin of these fragments.