THE EFFECT OF AGRO-ECOLOGICAL ZONES ON THE INCIDENCE AND DISTRIBUTION OF APHID VECTORS OF PEPPER VEINAL MOTTLE VIRUS, ON CULTIVATED PEPPER (CAPSICUM ANNUUM L.) IN NIGERIA

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

Genetic diversity of Colletotrichum gloeosporioides in Nigeria using amplified fragment length polymorphismA (AFLP) markers

Colletotrichum gloeosporioides is the causal agent of yam anthracnose disease in Nigeria. Differential cultivars and amplified fragment length polymorphic DNA markers were used to assess the extent of genetic diversity among 39 isolates of the pathogen. Fourteen (14) pathotypes of the pathogen were identified based on inoculation of a differential set of Dioscorea alata genotypes of which pathotype P11 was the most virulent attacking all differential D. alata host genotypes, while pathotype P8 was the least virulent. 52% of the isolates were avirulent, 23% were slightly virulent and 25% were virulent. Amplified fragment length polymorphism (AFLP) analysis confirmed genetic variation among the C. gloeosporioides isolates and was effective in establishing genetic relationships between them. However, the grouping of the isolates based on AFLP analysis was not directly related to virulence groups or geographical origin of the isolates. The genetic variation in C. gloeosporioides is important in choosing strategies to develop durable resistanc