Occurrence of a whitefly transmitted Carlavirus in soybean in Puerto Rico

Soybean is cultivated in Puerto Rico in summer nurseries to advance breeding programs by several seed companies. In Puerto Rico symptoms of leaf vein and stem necrosis and plant stunting were observed in soybean experimental field plots in municipalities of Juana Diaz, Santa Isabel and Isabela. Observations in a winter nursery in Santa Isabel showed 100 percent incidence in some soybean lines, indicating the potential of damage of this disease in soybeans. Samples were collected and transmission assays were conducted at Rio Piedras Experimental Station. Mechanical inoculation, stem grafting and whitefly (Bemisia tabaci) transmission resulted in development of the same symptoms as those observed in the field. All assays were conducted using the soybean line 2053A. Leaf tissues were pre-fixed in Karnovsky's fixative and processed for transmission electron microscopy. Ultrathin sections of diseased tissues showed in the cytoplasm the occurrence of brush-like inclusions, which have been reported before in association with Carlavirus infections. RNA was extracted from symptomatic and healthy plants. RT-PCR using specific primers available for Carlavirus amplified a fragment of the expected size only from symptomatic plants. Full characterization of the virus, host range and soybean resistance are needed.