Four fertilizer treatments were applied to two PVMV susceptible pepper (Capsicun annuum) varieties (NHV1-D96 and NHV1-E96) and one PVMV tolerant variety (NHV1-G96) to determine their effects in reducing the incidence and severity of pepper veinal mottle virus disease and on yield and agronomic parameters. The treatments were: (1) no manure application, (2) poultry litter organic manure at the rate of 10 tons/ha, (3) poultry litter organic manure at the rate of 20 tons/ha, and (4) NPK (20:10:10) at the rate of 0.26 tons/ha inorganic fertilizer. Broadcasting method was used for all the fertilizer applications. The experiment was carried out both in the field using a randomized complete block design and in 5 kg sterilized soil-potted experiment in the greenhouse in complete randomized design. The treatments showed a significant effect (P < 0.01) on PVMV disease incidence and severity, plant height, leaf number, internodes distance, number of fruit per plant, and fruit yield both in the field and greenhouse plants. The interactions between the treatments were also significant (P < 0.05) for PVMV disease incidence and severity, plant height, leaf number, internodes distance, number of fruit per plant and fruit yield. Mean PVMV disease incidence and severity, plant height, leaf number, internodes distance, number of fruit per plant and fruit yield, varied significantly (P < 0.05) in all the treatments applied. The application of 10 tons/ha and 20 tons/ha poultry manure showed a significant (P < 0.01) effect in reducing the incidence and severity of PVMV disease on the three pepper varieties. The poultry manure treatments were also observed to have positively and significantly contributed (P < 0.05) to the plant height, leaf number and fruit yield of PVMV infected pepper plants in all the three pepper varieties used both in the field and in the greenhouse. The yield of pepper decreased with increasing PVMV disease incidence and severity in all the treatments.
The distribution of aphid vectors of Pepper veinal mottle virus (PVmV) was studied on cultivated pepper between 2003 and 2005 in the major pepper producing areas of the six agro-ecological zones in Nigeria. The aphids were isolated, identified and their transmission ability determined. Population of aphid vectors increased progressively in all the agro-ecological zones from march at the onset of raining season reaching a peak in August and then declining from September at the on set of the dry season. The Humid forest and derived Savanna agro-ecological zones recorded highest mean population of aphids / leaf and types of aphid's species compared with other agro-ecological zones. Six species of aphid, Myzus persicae (Sulzer), Aphis gossipii (Glover), Aphis craccivora (Koch), Aphis spiraecola (Patch), Aphis fabae (blanchard), and Rhopalosiphum maidis (Fitch), were identified on the pepper fields surveyed in all the agro-ecological zones. There was no significant difference in the occurrence of M. persicae, A. gossipii, A. craccivora, and R. maidis while A. spiraecola and A. fabae that varied in occurrence in all the zones. Ability to transmit PVmV to a healthy pepper plants varied in all the identified aphid species but R. maidis was not able to transmit PVmV from infected to a healthy pepper plant. A more sustainable approach to controlling pepper viruses is by targeting the aphid vectors and preventing the vectors from reaching the crops because the aphid vectors which are virus specific are the major means of transmitting virus to healthy plant.
Several programmes have been initiated for the development of maize varieties with resistance traits of Maize streak virus (MSV) by International Institute of Tropical Agriculture (IITA), Ibadan, and have been released to farmers and research scientists. Therefore, a survey was conducted in five states in the south west of Nigeria (Oyo, Ogun, Ondo, Ekiti and Osun) during the raining planting season to determine the incidence of MSV disease by visual examination and serodiagnostic screening of symptomatic plants. The determination of infection rate of MSV disease by Cicadulina triangular on maize plant and its distribution from the lowest diseased leaf was also studied. The mean MSV disease incidence observed in these states was 35.95% which confirms the presence of MSV in the south west of Nigeria. Sero-diagnostic screening of virus-induced symptomatic leaf samples indicated that out of the 250 leaves sampled per state, 24.4% tested positive for MSV in Oyo, 25.6% in Ondo, 34% in Ogun, 19.6% in Ekiti and 38.8% in Osun. In two-week-old plants, symptoms developed on the leaves that were emerging at the time of inoculation, while in six-week-old plants, symptoms developed on the leaves directly below the emerging leaves irrespective of the number of C. triangular used. These suggest that the lowermost leaf with symptoms of the disease indicates the growth stage at which a plant was infected. There was a relationship between symptom expression and plant age which could be very effective when carrying out surveys to gather information for epidemiological studies. In addition, the 10 varieties of maize inoculated with MSV through C. triangular transmission showed no significant difference in disease severity over time irrespective of the number of C. triangular used.
There have been various reports about the devastating effect of Pepper veinal mottle virus (PVMV), a Potyvirus disease of pepper in Nigeria contributing to its low yield and reduced fruit quality leading to great economic loss. Different strains of the virus have been identified and characterised over the years and the disease incidence, severity and aphid vector distribution across agro-ecological zones studied. Different cultural management techniques have been tried and found to be effective with varying degree of success, and these included the use of organic manures, intercropping with tall companion crops, time and date of planting and the use of tolerant/resistant varieties. Integrated pest management techniques for PVMV disease have been found to be very effective.
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