Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 17, 1996
Publication Date: N/A
Interpretive Summary: Corn (Zea mays L.) is a widely grown, economically important crop in both Brazil and the United States. In both countries, corn crops are affected by disease that is typified by symptoms of stunting and reddening of leaves. In the United Staes, this symptom syndrome appears not to be a major limiting factor in corn production over a wide area, but in Brazil this syndrome (called "red stunt") is the hallmark of a spreading epidemic disease situtation that has emerged as a major limiting factor in corn production over a wide area of that country. In some corn fields in Brazil, complete loss has been experienced. Yet, the cause of the epidemic corn disease problem in Brazil is still not known. Furthermore, it has not been known whether or not the pathogen(s) responsible for the disease problem in Brazil are related to pathogens that already exist in, or could invade, U.S. corn crops. In this work, we have uncovered the first concrete evidence indicating that maize bushy stunt phytoplasma, previously known to occur in corn in southwestern United States and Central America, is present in Brazil as an infection in corn plants with symptoms of stunting and red leaves. Although the epidemic spread of corn red stunt in Brazil cannot be ascribed to MBS phytoplasma based on the new evidence, this work provides a definitive target pathogen for further investigation of the epidemic in Brazil and for assessing potential for development of a similar situation in U.S. corn. The information in this report will benefit interests of APHIS and state agencies, farmers, diagnosticians, and corn seed companies.
Technical Abstract: Plants of corn (Zea mays L.) exhibiting symptoms of stunting and leaf reddening were assayed for the presence of phytoplasma gene sequences by use of phytoplasma rRNA, ribosomal protein gene, and maize bushy stunt (MBS) phytoplasma-specific oligonucleotide primers in polymerase chain reactions (PCR). Polymorphisms in 16S rDNA amplified from diseased plants were those characteristic of phytoplasmas classified in 16S rRNA gene grou 16SrI, subgroup I-B, of which MBS phytoplasma is a member. Amplification of ribosomal protein (rp) gene sequences in PCR primed by phytoplasma- specific primers confirmed presence of a phytoplasma in the diseased plants. Restriction fragment length polymorphism (RFLP) patterns of the amplified phytoplasma rp gene sequences were similar or identical to those observed for a known strain of MBS phytoplasma. In separate PCR, an MBS-specific oligonucleotide pair primed amplification of a MBS-characteristic DNA from templates derived from the diseased corn. The data provide the first firm evidence for presence of maize bushy stunt phytoplasma in corn in Brazil.