L. Moreira, and
C. Rivera, Centro de Investigación en Biologia Celular y Molecular, Universidad de Costa Rica, San José, Costa Rica; and
I.-M. Lee, Molecular Plant Pathology Laboratory, USDA-ARS, Beltsville, MD 20705
A new soybean disease outbreak occurred in 2002 in a soybean (Glycine max) plantation in Alajuela Province, Costa Rica. Symptoms on the affected plants included general stunting, small leaves, formation of excessive buds, and aborted seed pods. In the same region, two other diseases, one in sweet pepper (Capsicum annuum) fields and another affecting passion fruit (Passiflora edulis) vines, were also found. Symptoms on sweet pepper plants included unusually dark green leaves, some of which exhibited a rugose symptom with a zigzag pattern to the midvein, and purple vein discoloration. Passion fruit vines exhibited bud proliferation. Collectively, symptoms resembled those commonly attributed to phytoplasmal infections. Total nucleic acid was extracted from veinal tissues of leaves or buds (soybean). A nested PCR assay using primer pair P1/P7 followed by R16F2n/R16R2 (1) was employed for the detection of putative phytoplasmas that might be associated within symptomatic plants. All seven symptomatic plants (three soybean, three sweet pepper, and one passion fruit) tested, but not healthy controls, yielded positive results. Restriction fragment length polymorphism (RFLP) analysis of nested PCR products using restriction enzymes AluI, BfaI, HhaI, MseI, and RsaI indicated that the three diseases were associated with a very similar or identical phytoplasma. RFLP patterns and sequence analysis of cloned 16S rDNAs (GenBank Accession Nos. FJ226068--FJ226073) revealed that the phytoplasma shared less than 97.5% sequence homology with all previously classified phytoplasmas, and, as such, represents a new taxon most closely related to 16SrXII group (1) strains. To our knowledge, this is the first report of a new phytoplasma associated with diseases of soybean, sweet pepper, and passion fruit in Costa Rica.
Reference: (1) I.-M. Lee et al. Int. J. Syst. Bacteriol. 48:1153, 1998.