Exotic RNA Virus Identified in Cotton in the Southeastern United States
A single-stranded RNA virus has been detected and is infecting cotton in at least six southeastern U.S. states. A range of symptoms have been observed in cotton testing positive for this new virus. Some infected plants exhibit extensive leaf reddening, while in others, few or no reddish leaves are observed. There are plants that exhibit extensive leaf crinkling in the mid-canopy. Other plants have shortened internodes and dwarfed, dark green leaves in the upper canopy. The most severely affected cotton fields in south Alabama have only about 20% boll set or no bolls at all. These barren plants have released vegetative growth and appear elongated, with leaders of new growth extending above the canopy.
The new pathogen is a polerovirus. While resembling two other cotton leaf roll dwarf virus (CLRDV) variants, it has less than 95% overall sequence identity with those identified in Argentina and Brazil. Poleroviruses are transmitted by aphids. In the Southeastern United States, symptoms of the disease appear in late August, whereas cotton aphids are infrequently seen colonizing cotton after mid-July. The commercial cotton cultivars tested in 2018 were all susceptible to the virus. We have yet to determine if the cotton genotypes that are resistant to blue disease or atypical blue disease in Brazil are resistant to the virus currently in the U.S.