Yield Impact and Spread of Pineapple mealybug wilt associated virus-2 and Mealybug Wilt of Pineapple in Hawaii

Mealybug wilt of pineapple (MWP) is a devastating disease found in all the major pineapple growing regions of the world (4– 6,26). The disease is characterized by severe tip dieback, downward curving of the leaf margins, reddening, and wilting of the leaves that can cause total collapse of the plant. The etiology of MWP has long been in question. The disorder is generally associated with the presence of mealybugs (3,6,20), however, not every mealybuginfested plant develops MWP (7,8,16,28, 29,31). Hypotheses have suggested the involvement of a latent transmissible factor such as a virus (8,15), and long flexuousrod shaped particles were isolated from MWP symptomatic plants (14). Subsequently, closterovirus particles were detected in both MWP symptomatic and asymptomatic pineapple worldwide (1,17, 18,27,28,31,32,34). The particles, referred to as Pineapple mealybug wilt associated virus (PMWaV), are actually a complex of at least two different viruses (18,25,31,32). Both viruses are mealybug transmitted (31,33) and are in the Closteroviridae family (22,25). Based on sequence and phylogenetic analyses, PMWaV-1 and PMWaV-2 share approximately 50% homology (M. J. Melzer, A. Karasev, D. M. Sether, and J. S. Hu, unpublished). PMWaV-2 is most closely related to Grapevine leafroll associated virus 3 (GLRaV-3) sharing 69.4, 71.5, 70.1, and 63.9% sequence similarity for the helicase, RNA-dependent RNApolymerase, heat shock protein 70 homolog, and coat protein genes, respectively (25). Two monoclonal antibodies (MAbs), 35-6-5 (PMWaV-1) (18) and 63-2-2 (PMWaV-2) (31) can detect and differentiate the two viruses in tissue blot immunoassays (TBIAs) (17). TBIAs with PMWaV1 and PMWaV-2specific MAbs and reverse transcription polymerase chain reaction (RT-PCR) assays have shown that both viruses are found worldwide in MWP symptomatic and asymptomatic pineapple (17,32). However, PMWaV-2 infection is consistently found in association with MWP (31), whereas PMWaV-1 is not (17). In healthy appearing Hawaiian grown proprietary selections of Ananas comosus cv. Smooth Cayenne, PMWaV-1 occurs at a much higher incidence (26 to 100%) than dual infections of PMWaV-1 and PMWaV2 (0 to 36%) (32). In all but one of the proprietary pineapple selections from Hawaii, single infections of PMWaV-2 occur with the least frequency (0 to 8%) (32). In recent studies, we have shown that both mealybug exposure and PMWaV-2 play a role in MWP etiology (29,31). Mealybug feeding in the absence of PMWaV-2 or PMWaV-2-infection in the absence of mealybug feeding does not result in MWP (31). An experiment using a randomized complete block design consisting of PMWaV-1-free and PMWaV-1-infected pineapple plants either maintained mealybug-free or inoculated with mealybugs at regular intervals was established in a commercial pineapple field on Maui, Hawaii. During the course of this study, we identified and characterized PMWaV-2 (25). This virus was identified in plants that were distributed throughout the treatment plots. RT-PCR assays that could detect and differentiate PMWaV-1 and PMWaV-2 (32) and PMWaV-2-specific TBIAs (31) were used to monitor the spatial patterns of PMWaV-2 infections and MWP over time. Yield impacts of the two PMWaVs, mealybug exposure, and MWP are also presented, and management strategies are discussed.