Association of a tospovirus with pineapple red-tip disease

Malaysia, once ranked as one of the top 3 pineapple producers in the world in the 60's and early 70's, has only a relatively modest industry today but shown steady growth over the last several years. Despite this, and the government's recognition as a priority sector of growth, the pineapple industry in Malaysia still faces numerous challenges, one of which is the management of disease and pest. There are several disease that have been reported in Malaysian pineapples, among them is the Mealybug wilt of pineapple (MWP), which is present in all major pineapple growing-areas of the world and red-tip disease, which is a relatively new problem in Malaysian pineapples. It was first recognized in the early 1990's at Simpang Renggam, Johore where it has been found that 10% or more of its leaves starting from the tip had turned red, do not produce fruits or produce small fruits. It was previously associated with MWP which is caused by pineapple mealybug wilt-associated closterovirus based on the symptoms. However, the absence of the mealybug wilt-associated closterovirus virus particle and the lack of mealybug infestation in the affected plants have ruled the possibility of the virus as the causal agent of this disease. Moreover, the leaf would remain healthy and show no sign of wilting. In addition, there were no evidence linking this disease to fungus, bacteria and nutrient deficiency. Nevertheless, the symptoms and the spread of this disease in the field still seemed to point a viral etiology for this disease. Bioassay test on nucleic acid extracted from the red tip affected pineapple plants was done on Nicotiana tabacum cv. coker by rubbing the extracted sap. Localised lesions were observed 3 weeks after inoculation. Negative staining of the fresh diseased sample and inoculated Nicotiana tabacum cv. coker showed the presence of membrane bound spherical particles with average diameters of 94.25nm under transmission electron microscope. The shape and size of the particles were similar to tospovirus. RT-PCR amplification of nucleic acid extracted from the red-tip affected pineapple using tospovirus universal primer,BR60 and BR65 targeting on the N gene of tospovirus showed a band at approximately 400 bp, which is close to the expected band of 453 bp. Nucleic acid sequencing is currently being done to identify the species of the tospovirus, but with the evidence obtained in this study, pineapple red-tip disease could be associated with a tospovirus from the family Bunyaviridae.