PCR assay for detection of the phytoplasma associated with maize bushy stunt disease

DNA amplification by polymerase chain reaction (PCR) was used to detect the phytoplasma associated with maize bushy stunt (MBS) disease. A pair of oligonucleotide primers was synthesized according to partial sequences of a cloned l-kb fragment of genomic DNA of the MBS phytoplasma (Texas isolate) maintained in sweet corn. PCR performed for 30 cycles with primer annealing at 61 degrees C amplified a DNA product of about 740-bp in reaction mixtures containing template DNA derived from symptomatic corn singly infected with MBS phytoplasma isolates from either Texas, Florida, Costa Rica, or Mexico. No comparable product was amplified from DNAs of healthy corn, plants affected by various other phytoplasmal diseases, or from Spiroplasma kunkelii. Forty cycles of PCR enabled detection of a Florida isolate of the MBS phytoplasma in all leaf and stalk samples tested from presymptomatic plants 12 days after plants were fed upon by inoculative vector Dalbulus maidis leafhoppers and in the majority of nonvector Peregrinus maidis planthoppers after 1 to 5 days of exposure to symptomatic plants.