Current epidemiological situation of mealybug wilt of pineapple disease in Ecuador

Mealybug wilt of pineapple (MWP) is the most important virus-associated syndrome affecting pineapple worldwide. The wide range of symptoms including bronze-to-red colouring of leaves, tip dieback, leaf downward-curving and wilting has obscured the aetiology of MWP (Dey et al., 2018). At least five ampeloviruses (family Closteroviridae), Pineapple mealybug wilt-associated virus 1 (PMWaV-1), PMWaV -2, -3, -5 and -6 have been associated with MWP. Recently, additional viruses have been reported in pineapple, including Pineapple secovirus A (PSV-A), PSV-B, -C, and -D, all members of the Sadwavirus genus (family Secoviridae), Pineapple bacilliform CO virus (PBCOV) and Pineapple bacilliform ER virus (PBERV), both members of the Badnavirus genus (family Caulimoviridae) (Larrea-Sarmiento et al., 2022). In Ecuador, PMWaV-1 is the only virus reported from plants showing MWP-like symptoms (Alvarez-Quinto et al., 2015). This study aimed to determine the prevalence of MWP and the viruses potentially associated with the disease in the largest pineapple-producing area of Ecuador. In 2023, a total of 400 pineapple MD-2 hybrid plants were randomly sampled and inspected for disease symptoms to estimate the prevalence of MWP in a planting located in Santo Domingo, Ecuador (Figure. 1). Sampling was done in 36-week-old fields. Only 30 plants (8%) showed the typical tip dieback symptoms characteristic of MWP and these were found on the edge of plantations (Figure. 2). Virus testing was done on all symptomatic plants (n = 30), but also on 30 symptomless plants. Total RNA extraction and RT-PCR for virus testing was done as described by Cornejo-Franco et al. (2023) using primers and PCR conditions detailed by Larrea-Sarmiento et al. (2022) and Alvarez-Quinto et al. (2015). Virus identity was confirmed by Sanger sequencing of cloned amplicons (GenBank Accession Nos. PP479943, PP479944, PP489387-PP489390) Virus indexing showed a strong association between the observed MWP symptoms and co-infections of PMWaV-2 and PMWaV-1 (73%), while single infections of these two viruses were also found (<53%) in symptomless plants. PMWaV-3 and PSV-B were found in both symptomatic and symptomless plants in similar proportions (Table 1) while PSV-A was detected in one third of symptomatic and 13% of symptomless plants. PBCOV was found in 20% of symptomatic plants. All viruses showed high nucleotide identity (>95%) with Hawaiian homologs, except for PSV-A and -B which showed <88% nucleotide identity. No clear association was observed between the occurrence of PMWaV-3, PSV-A, PSV-B, or PBCOV and MWP (Table 1). PMWaV-5 and -6, PSV-C and -D and PBERV were not detected during this study. Pineapple mealybugs (Dysmicoccus spp.) were present in all pineapple plants sampled in this study. Hence, the aetiology of MWP remains to be further studied. These findings are consistent with those previously reported in Hawaii, where PMWaV-2 and mealybugs were present on plants with MWP symptoms (Sether et al., 2002). 22/30 (73%) 30/30 (100%) 14/30 (47%) 0/30 (0%) 0/30 (0%) 10/30 (33%) 26/30 (87%) 0/30 (0%) 0/30 (0%) 6/30 (20%) 0/30 (0%) 16/30 (53%) 11/30 (37%) 12/30 (40%) 0/30 (0%) 0/30 (0%) 4/30 (13%) 24/30 (80%) 0/30 (0%) 0/30 (0%) 0/3 0(0%) 0/30 (0%) This study was funded by Centro de Investigaciones Biotecnológicas del Ecuador, CIBE, through a seed funding call, under project code CIBE-0004-2023. The authors would like to thank Mr. Jhonny España from Cibe for field assistance.