Serological detection of viruses infecting tomato and pepper in Southwest Nigeria and their distribution

Tomato and pepper are important vegetable crops grown in Nigeria, accounting for 50% of the African production. Pathogen diversity is a prerequisite for breeding resistant cultivars, as a means of improving the production. A survey for virus disease incidence on field grown pepper and tomato was carried out in three state of southwestern part of Nigeria, and a total of 135 leaf samples comprising 58 tomato and 77 pepper leaf samples were collected from farmers’ fields. Infecting viruses were detected using specific polyclonal antibodies were used in enzyme-linked immunosorbent assay (ELISA). Four viruses, Potato virus Y (PVY), Tomato mosaic virus (ToMV), Cucumber mosaic virus (CMV), and Pepper veinal mottle virus (PVMV) were detected. In tomato the distribution of viruses was 5.2% (CMV), 5.2% (PVY) and 39.7% for PVMV, respectively. Leaf samples of pepper had incidence rate of 19.5%, 3.9% and 67.5% for CMV, ToMV and PVMV respectively. TSWV and TYLCV were not detected in any of the samples tested. The most prevalent virus on tomato and pepper was PVMV which was also the most prevalent virus in Osun, Ogun and Oyo States in Southwest Nigeria; similarly, CMV was detected in pepper crops in all the states surveyed and the most prevalent after PVMV in the three states. Mixed viral infections were few, PVY + PVMV occurring only in one tomato leaf sample while PVMV + CMV occurred on three pepper leaf samples. The control of aphid vectors that transmit these viruses and good sanitary practices against soil borne ToMV would minimize disease incidences and subsequent yield loss.

Introduction disease resistance. An understanding of the viruses and Potato virus Y (PVY) genus Potyvirus. involved is needed in order to develop methods of virus and disease control to increase both productivity DAS-ELISA Protocol used and quality of these crops. This research will provide Microtitre wells of ELISA plates were coated the much needed key information for the national with 100 µl of appropriately diluted immunoglobulin G breeding programs that is aimed at the development (IgG) to each of the respective viruses under test in of disease tolerant and/or resistant varieties for coating buffer containing 1.59 g Sodium carbonate optimum production of the crops.
(Na CO ) and 2.93 g Sodium bicarbonate (NaHCO ) per 2 3 3 The ability to detect and identify viruses litre, pH 9.6. Plates were incubated at 37°C for 2 h after allows selection of pathogen-free plant material for which the contents were decanted and wells washed propagation, resulting in higher productivity and three times with single strength phosphate buffer with quality. Of importance also is validation of 0.05 % tween 20 (v/v) (PBS-T) composed with 8.0 g economically important virus pathogens of fruit Sodium chloride (NaCl), 0.

Results
The virus PVY was detected in 2 samples Varied symptoms were observed on pepper (2.6%) while TYLCV and TSWV were not detected in any and tomato plants which included mottling, leaf of the leaf samples of pepper crops surveyed. curling, veinal chlorosis, severe mosaic and veinbanding. Out of 135 tomato and pepper leaf samples collected and indexed using 7 polyclonal antibodies, 74.8 % (101 of 135) were positive. The most prevalent virus on both tomato and pepper leaves sampled was PVMV ( Figure 2). It had the incidence of 55.6 % (75 of 135) followed by CMV which had 13.3 % (18 of 135). Three viruses, CMV, PVY and PVMV were detected in all the sampled leaf samples with incidence values of 13.3, 3.7 and 55.6 % respectively. Of all the viruses tested, TYLCV and TSWV were not detected in any of the samples tested.  In 58 leaf samples of tomato crops indexed, PVMV was detected in 17 (29.3 %), CMV was singly detected in 3 (5.2%) and PVY (5.2%) respectively ( Figure 3).
Mixed viral infections were few, PVY and PVMV occurred together only in one tomato leaf sample (0.7 %) while mixture of PVMV and CMV occurred on three pepper leaf samples (2.2%).

Figure 3: Virus incidence in Tomato leaf samples from three states in southwest Nigeria in 2011
Discussion From the survey, it was evident that three Seventy-seven (77) leaf samples of pepper major viruses infected tomato and pepper plants in the were collected and tested but only 72 (93.5%) area surveyed during the period. tested positive for one or two viruses. The most Major virus symptoms observed on tomato prevalent virus detected in pepper leaves was PVMV included mosaic, leaf curl and mottling, and the and it was detected in 52 (67.5%) leaf samples of associated viruses were PVMV, PVY and CMV while on pepper followed by CMV which was detected in 15 pepper the symptoms were vein banding, leaf curl and samples (19.5%) and ToMV in 3 samples (3.9%) mottling, and key viruses included were PVMV, CMV and ( Figure 4). ToMV.