Reunion Island: general survey of pineapple parasites with a focus on wilt disease and associated viruses

Victoria pineapple is the main fruit exported from Reunion Island to the European Union and accounts for 80% of the volume of tropical fruit grown in Reunion. A survey conducted in 2017-2018 of 45 fields representative of the pineapple cropping area to assess the pressure of parasites (nematodes, symphylans, and the mealybugs Dysmicoccus neobrevipes and D. brevipes) on the crop. Populations were assessed using a sieving-centrifugation method for nematodes (R. reniformis, P. brachyurus, Meloidogynae spp.), a bait and trap technique for symphylans, and visual indexes for the level of mealybugs and wilt disease. PCR analysis was used to detect PBCoV and multiplex RT-PCR to detect PMWaV1, -V2, -V3. The survey showed all pineapple cropping areas were subject to limited infestations of nematodes and symphylans. High population levels of mealybugs and incidence of wilt disease were observed in most production areas with a negative impact on pineapple production. In 21 of the 40 fields, PMWaVs viruses associated with wilt disease were observed in 210 samples. Pineapple viruses were present in all the field samples, always included PMWaV1 and PBCoV (100%), and often PMWaV2 (41%) and PMWaV3 (46%). Analysis of cultural practices suggests that fewer viruses were present in fields located at or above 500 m above sea level and when the cropping system was based on crop rotations. Wilting of pineapple leaves appeared to be associated with the presence of the viruses in general but in this general survey, could not be specifically attributed to one of the four viruses. Viruses were also detected on asymptomatic pineapples. Mealybugs were only found on 19% of the selected plots but the infection rate reached as high as 79%. Only one field, planted with tissue culture plants three years before the survey, was virus free. Preliminary results of a second survey in progress eliminating the symptoms other than those of wilt (red spiders, nematodes and symphylans) are presented. Wilt disease is the main biotic stress in pineapple in Reunion Island today. Alternative approaches for the control of wilt disease are currently under development, including the production of virus-free planting material from nurseries planted with clean tissue culture plants, biocontrol to reduce the multiplication of mealybugs, and agroecological and prophylactic measures to limit the spread of wilt disease and other parasites. The next step will be to employ Next Generation Sequencing methods to better understand the etiology of the wilt disease and virus involvement in the wilt symptoms.