Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/15/2002
Publication Date: 7/1/2002
Citation: Brown, J.K., Idris, A.M., Alteri, C., Stenger, D.C. 2002. A new cucurbit-infecting begomovirus species capable of forming viable reassortants with related viruses in the squash leaf curl virus cluster. Phytopathology 92:734-742. Interpretive Summary: A new whitefly transmitted geminivirus was isolated from cucurbits grown in the American Southwest and Northern Mexico. Cucurbit leaf curl virus (CuLCV) represents the latest episode of geminivirus emergence in the greater Sonoran Desert agroecosystem. Natural hosts of the virus included squash, pumpkin, watermelon, cucumber, and honeydew melon. Experimental hosts included these cucurbits as well as bean and tobacco. The complete nucleotide sequences of CuLCV DNAs A and B were determined and compared to other geminiviruses. CuLCV was most closely related to squash leaf curl virus-E (SLCV-E) and SLCV-R, two geminiviruses infecting cucurbits in the same geographic region. Cloned DNA of CuLCV was infectious and progeny virus was transmissible by the whitefly vector, thereby demonstrating that CuLCV causes the distinct leaf curl and mosaic symptoms associated with field-infected plants. Genomic component reassortant experiments indicated dthat CuLCV may form viable pseudorecombinants with genome components of SLCV-E and SLCV-R,demonstrating that these viruses have the potential to produce novel genomes with distinct symptoms.
Technical Abstract: Cucurbit leaf curl virus (CuLCV), a whitefly-transmitted geminivirus from the southwestern US and northern Mexico, was identified as a distinct bipartite begomovirus species. Experimental and natural host range studies indicated that CuLCV has a relatively broad host range within the Cucurbitaceae and also infects bean and tobacco. An Arizonan isolate, designated CuLCV-AZ, was cloned and completely sequenced. Cloned CuLCV-AZ DNA A and B components were infectious by biolistic inoculation to pumpkin and progeny virus was transmissible by the whitefly vector, Bemisia tabaci, thereby completing Koch's Postulates. CuLCV-AZ DNA A shared highest nucleotide (nt) sequence identity with Squash leaf curl virus-R (SLCV-R), SLCV-E, and Bean calico mosaic virus (BCMoV) at 84.1%, 82.6%, and 80.2, respectively. The CuLCV DNA B component shared highest nt sequence identity with BCMoV, SLCV-R, and SLCV-E at 70.6%, 69.7%, and 67.7%, respectively. The cis-acting replication specificity element (GGTGTCCTGGTG of the CuLCV-AZ origin of replication is identical to that of SLCV-R, SLCV- E, and BCMoV, suggesting that reassortants among components of CuLCV-AZ and these begomoviruses may be possible. Reassortment experiments in pumpkin demonstrated that both reassortants of CuLCV-AZ and SLCV-E A and B components were viable. However, for CuLCV-AZ and SLCV-R, only one reassortant (SLCV-R DNA A/CuLCV-AZ DNA B) was viable on pumpkin, even though the cognate component pairs of both viruses infect pumpkin. These results indicate that reassortment among sympatric begomovirus species has the potential to generate begomoviruses bearing distinct biological properties.