Infectivity of Deinbollia mosaic virus, a novel weed-infecting begomovirus in East Africa

Abstract

Weed-infecting begomoviruses play an important role in the epidemiology of crop diseases because they can potentially infect crops and contribute to the genetic diversity of crop-infecting begomoviruses. Despite the important epidemiological role that weed-infecting begomoviruses play, they remain insufficiently studied in Africa. Recently, we identified Deinbollia mosaic virus (DMV), a distinct begomovirus found naturally infecting the weed host Deinbollia borbonica (Sapindaceae) in Kenya and Tanzania. In this study, we investigated the capacity of DMV to infect a restricted host range of Solanaceae and Euphorbiaceae species. Biolistic inoculation of Nicotiana benthamiana with concatemeric DNAs resulted in systemic infection associated with yellow mosaic symptoms, while DNA partial dimers caused asymptomatic systemic infection. DMV was not infectious to cassava (Manihot esculenta Crantz), suggesting host resistance to the virus. Here, we demonstrate the first experimental infectivity analysis of DMV in N. benthamiana and cassava.

Fig. 1

Amplification of DMV genomic components from naturally infected Deinbollia borbonica. Full-length DNA-A (1), full-length DNA-B, (2), CRA (3), and CRB (4). The DNA rulers used are 1 kb+ ladder (M1), and 100 bp ladder (M2)

Fig. 2

Restriction digestion of DMV DNA partial dimers used for biolistic inoculation. Selected restriction enzymes were used to verify the orientation of PCR fragments of DMV cloned into pUC18: BamHI/EcoRI-pDMVA-1.4 (1), BgIII-pDMVA-1.4 (2), EcoRV-pDMVA-1.4 (3), EcoRV-pDMVB-1.08 (4), BamHI/EcoRI-pDMVB-1.08 (5), and KpnI-pDMVB-1.08 (6). The DNA ruler used is 1 kb+ ladder (M1)

Fig. 3

Symptoms exhibited by D. borbonica and N. benthamiana plants infected with DMV. Field-collected D. borbonica showing yellow mosaic symptoms (A), mock-inoculated N. benthamiana (B), N. benthamiana inoculated with DMV concatemeric DNAs exhibiting yellow mosaic symptoms at 21 dpi (C), N. benthamiana infected with DMV concatemeric DNAs showing stunting at approximately 28 dpi (D)

Fig. 4

Detection of DMV by hybridization and PCR amplification. The presence of DMV was confirmed by the presence of a deep purple signal on the nitrocellulose membrane in dot and tissue blot hybridization assays and by the amplification of a 450-bp PCR product using the B4/F and B4/R primer pair. The detection signals shown are from a D. borbonica infected with wild-type virus (A I, and B 1), healthy D. borbonica (A II), mock-inoculated N. benthamiana (A III, and C a), N. benthamiana inoculated with DNA partial dimers (A IV, B 2, and B 3), and N. benthamiana inoculated with concatemeric DNAs (A V, B 4, B 5, and C b)

Fig. 5

Hypersensitive response (HR) induced by DMV in cassava test plants. Cassava plants inoculated with concatemeric DNAs exhibited a hypersensitive reaction to the virus on leaves developing immediately after the point of inoculation. The photographs represent mock-inoculated test plant controls at approximately 14 dpi (A), and 28 dpi (B). Virus-inoculated plants exhibited spreading of necrosis along the main vein (shown by arrows) and misshaped leaflets 28 dpi (C, and D)