2.4.11
EPIDEMIOLOGY OF BANANA VIRUS DISEASES IN SOUTHERN PHILIPPINES

L KENYON1, L HERRADURA2, L MAGNAYE2, T CHANCELLOR1, H WARBURTON1 and SMITH1

1Natural Resources Institute, University of Greenwich, Central Avenue, Chatham Maritime, Kent ME4 4TB, UK; 2 Bureau of Plant Industry, DNCRDC, Bago Oshiro, Davao City, The Philippines

Background and Objectives
The Asia and Pacific region, including The Philippines, is the main centre of origin of the Musacea (bananas and plantains). It is thus likely also to be the centre of origin and diversity of many of the pests and diseases attacking this family. In The Philippines, control measures against Panama wilt (Fusarium oxysporum), Sigatoka leaf spots (Mycosphaerelia spp.) and banana bunchy top virus (BBTV) can account for up to 70% of the banana production costs. Along with BBTV, at least three other viruses have been observed to cause disease in bananas in The Philippines: banana bract mosaic potyvirus (BBrMV), banana streak badnavirus (BSV) and cucumber mosaic cucumovirus (CMV). BBTV is an isometric virus with a multicomponent, single-stranded DNA genome. It is transmitted by the banana aphid, Pentalonia nigronervosa and perpetuated through vegetative propagation of the host [l]. In Australia an epidemic of the disease was controlled through the enforcement of a strict 'search and eradication' scheme [2]. However, this approach does not appear to be working in the commercial plantations of The Philippines. Here, differences in factors such as climate, cultural practices, varieties grown and the close proximity of small-scale growers may be influencing the epidemiology of BBTV and the other diseases.

Materials and methods
This work focused around Davao City, Mindanao, southern Philippines, although the findings are likely to have significance in other countries of the region. BBTV disease records, kindly provided by commercial banana plantations in the area, were collated and analysed to determine if there were spatial and/or temporal trends or patterns. Also, three experimental plots were planted with BBTV-indexed, tissue-culture-derived plants of the local variety 'Lakatan' in different locations in Davao City. These plots were monitored on a regular basis for ingress and spread of BBTV and other virus diseases, and various trapping methods were used to try to monitor the populations of P. ;nigronervosa in each. Participatory rural appraisal (PRA) techniques were used to investigate small-scale and subsistence banana growers' perceptions of the diseases and the measures used or promoted to control them.

Results and conclusions
Analyses of the BBTV incidence records from the plantations and trial plots showed both spatial and temporal patterns in the spread of the disease. They also supported the field observations and growers' perception that the disease is increasing despite the extensive efforts of the commercial growers to control its localized spread within plantations. BBRMV and BSV incidence also appeared to be increasing. However, small-scale and subsistence growers generally could not distinguish between the banana diseases caused by viruses, fungi, bacteria or nematodes, let alone between the different virus diseases. This lack of knowledge of the diseases and the factors affecting their movement and increase means that either no or inappropriate control measures are being used outside the commercial plantations.

References
1. Thomas JE, Dietzgen RG, 1991. Journal of General Virology 72, 217-224. 2. Alien RN, 1987. Australian Journal of Agricultural Research 38, 373-382. This paper is an output from a project (R6579, Crop Protection Programme) funded by the UK Department For International Development (DFID) for the benefit of developing countries. The views expressed are not necessarily those of DFID.