Quantitative epidemiology of Banana Bunchy Top Virus Disease and its control

Abstract

Models of a banana bunchy top virus disease epidemic were developed to incorporate the two key features of an epidemic in a plantation in the Philippines: an exponential increase in disease incidence over 10 years, and a declining gradient of incidence from the outside edge of the plantation to the centre. A non-spatial model consisted of three difference equations to describe the numbers of latently infected and of infectious plants in the plantation and the size of the inoculum source outside the plantation. In a spatial model the outside portion of the plantation was divided into eight blocks running parallel to the outside edge. The dispersal gradient of the inoculum was assumed to be negative exponential. Analysis of the two models showed that for disease incidence to increase exponentially over time, the rate of disease progress could be dependent either on internal spread and roguing rate (proportion of diseased plants removed and replaced per unit time) or on the rate of increase of external inoculum pressure. The observed incidence gradient from the edge to the centre of the plot could be explained only if external inoculum dominated the parameters in the spatial model. This model was also used to explore a variable roguing rate across blocks. Simulations indicated that this may produce small gains over the adoption of a constant roguing rate over all blocks, but was risky because a shift of roguing emphasis only slightly too far towards the outside blocks can result in a dramatic increase in disease.

Cucumber mosaic virusinfection of kava (Piper methysticum) and implications for cultural control of kava dieback disease

“…(Dale and Harding 1998). An intensive banana plant rogueing regime in the Philippines has been shown to effectively reduce secondary spread of BBTV (Smith et al 1998). Even greater success may be possible with kava dieback because the kava-CMV interaction appears to be similar to that of cassava and African cassava mosaic virus (ACMV).…”

“…Examples include the somewhat similar ACMVcassava pathosystem; when inoculum pressure was high and when much secondary spread occurred, stringent rogueing programmes failed (Thresh et al 1998). Smith et al (1998) concluded that in the presence of numerous external BBTV inoculum sources, rogueing was not effective for banana bunchy top control. In the case of kava and CMV, advantage can be taken of the non-persistent nature of the virus and this can be combined with natural benefits of traditional Pacific Island farming systems to combat these factors.…”

The Impact of Plant Virus Diseases in Developing Countries

“…Similar pest and disease surveys are operated in Malaysia and India, but seldom elsewhere. However, there are routine scouting operations to monitor the incidence and distribution of pests and diseases in large commercial enterprises growing banana and other export crops (Thresh, 1988;Smith et al 1998). The information is required to determine the need for control measures and to influence cropping practices and planting policy, but much of the information obtained is not readily available.…”

Molecular comparative analysis of component 1 (DNA-R) of an Egyptian isolate of banana bunchy top nanovirus isolated from banana aphid (Pentalonia nigronervosa)

“…These streaks consist of a series of ''dots'' and short lines ''dashes'' often known as ''Morse code'' streaking. If fruit is produced, hands may have distorted and twisted forms [41,51,43,12,14,32,42,39].…”

“…It is transmitted by arthropods, insects of the order Hemiptera, family Aphididae; Pentalonia nigronervosa in a persistent manner [26]. The virus spreads in Africa Burundi, Gabon and Egypt [14] and occurs in Australia, Pacific Islands, the Philippines, and Taiwan [12,36,31,42,17].…”