RESUMEN
Successive plantings of sweet corn in Orange Walk District, Belize (<200 m ASL) were observed to be performing poorly. Plants were stunted with shortened upper internodes, over-production (proliferation) of ears, and chlorosis of ears and leaf bases. Plants of hybrid white corn in Cayo District (<200 m ASL) had leaf-base chlorosis, mid-vein reddening, chlorotic bands on the leaves, and die-back of leaf tips: symptoms attributed to infection by the corn stunt complex (CSC) pathogens. Spiroplasma kunkelii was detected in symptom-bearing leaf-base samples of white corn but not sweet corn, using a specific F(ab')2 protein-A enzyme-linked immunosorbent assay (ELISA; D. Gordon, Ohio). Polymerase chain reactions with maize bushy stunt (MBS) phytoplasma-specific primers (1) resulted in amplification products of the expected size (740 bp) when DNA extracts from either sample type were used as template. DNAs from apparently healthy sweet or white corn from the field, or from glasshouse-grown sweet corn, did not yield this product. MBS and S. kunkelii are transmitted by leafhoppers of the genus Dalbulus, often simultaneously with maize rayado fino virus, the other CSC component (not tested for in this study). All the sweet corn varieties examined had a high incidence of the symptoms, suggesting that they are highly susceptible to one or both of the CSC mollicutes. With the increase in area dedicated to maize production and successive year-round plantings, the potential for spread and increased incidence of MBS or CSC in Belize is considerable. Reference: (1) N. A. Harrison et al. Plant Dis. 80:263, 1996.
RESUMEN
Gliricidia sepium is a multipurpose, legume tree species native to Central America and Mexico with wide social and economic importance. Gliricidia little leaf disease (GLLD) is associated with infection by a phytoplasma and is manifested by one or more symptoms, including leaflet yellowing, leaflet size reduction, shortened internodes, and shoot proliferation, often leading to branch die-back or death of young trees. Trees with symptoms were seen in fences and natural stands in the Nicoya Peninsular and on road sides west of San Jose, Costa Rica. Shoot samples were collected from eight symptom-bearing trees in different locations and from two healthy-looking trees in the southeast where no GLLD symptoms were observed. DNA from each sample was used as template in polymerase chain reaction (PCR) with universal phytoplasma rRNA gene primers P1 and P7 (1). DNA from a GLLD-infected tree from Honduras, and a pigeon pea witches'-broom infected Cajanus cajan from Florida, served as positive controls, while DNA from healthy G. sepium and C. cajan seedlings were used as negative controls. A 1.8-kb PCR product, indicative of presence of phytoplasma DNA, was amplified from all symptom-bearing tree samples and positive control DNAs, but not from DNA from the apparently healthy trees or seedlings. Restriction fragment length pattern analysis of PCR products with a range of endonucleases showed no difference between the Honduran and Costa Rican phytoplasma isolates. The distribution and symptom types observed in Costa Rica suggest that GLLD has recently arrived from Nicaragua and is spreading southeast. Reference: (1) L. Kenyon et al. Plant Pathol. 47:671, 1998.