Search Results (9)

Pineapples are highly susceptible to “Wilt disease”, caused by the biotrophic insect Dysmicoccus brevipes that also transmits several Wilt-associated viruses (PMWaVs). Conventional farms manage mealybugs and Wilt disease using chemicals. However, many of these chemicals have been banned in Europe due to safety concerns, leading to a critical need for studies on pesticide-free control methods. During their evolution, plants have developed natural defences, such as systemic acquired resistance (SAR), against pathogens and pests. In this study, salicylic acid (10⁻³ M) was applied to MD2 and Queen Victoria pineapple plants as a foliar spray or soil drench, followed by mealybug infestation. This treatment enhanced defences, assessed through mealybug multiplication rates, and biochemical and molecular responses of tissue-cultured plantlets under controlled conditions. Phenylalanine ammonia-lyase activity (PAL) was measured as a potential SAR signalling enzymatic marker. Additionally, the expression levels of four genes were analyzed, which included AcPAL and AcICS2, both linked to salicylic acid synthesis; AcMYB-like, a transcription factor regulating salicylic acid biosynthesis; and AcCAT, which is involved in H₂O₂ level control in plants. SA elicitation reduced the mealybug multiplication rate by 70% on pineapples compared to untreated plants. In this study, the biochemical marker (PAL) and three molecular markers (AcPAL, AcICS2, and AcCAT) showed significant differences between primed and unprimed plants, indicating SAR induction and its role in the pineapple–mealybug interaction. In MD2 and Queen Victoria, PAL increased by 2.3 and 1.5, respectively, while AcPAL increased by 4 and more than 10. The other molecular markers, AcICS2, AcCAT, and AcMYB-like (a transcription factor), increased by 3, except for the last one in Queen Victoria. The reduction in mealybug populations with SAR is less effective than with pesticides, but it provides a valuable alternative on Réunion Island, where the only remaining insecticide will soon be banned. In addition, SAR priming offers a promising, eco-friendly strategy for managing mealybug populations and reducing Wilt disease in pesticide-free pineapple cropping systems. Full article

The cultivation of pineapple (Ananas comosus) is threatened worldwide by mealybug wilt disease of pineapple (MWP), whose etiology is not yet fully elucidated. In this study, we characterized pineapple mealybug wilt-associated ampeloviruses (PMWaVs, family Closteroviridae) from a diseased pineapple plant collected from Reunion Island, using a high-throughput sequencing approach combining Illumina short reads and Nanopore long reads. Reads co-assembly resulted in complete or near-complete genomes for six distinct ampeloviruses, including the first complete genome of pineapple mealybug wilt-associated virus 5 (PMWaV5) and that of a new species tentatively named pineapple mealybug wilt-associated virus 7 (PMWaV7). Short reads data provided high genome coverage and sequencing depths for all six viral genomes, contrary to long reads data. The 5′ and 3′ ends of the genome for most of the six ampeloviruses could be recovered from long reads, providing an alternative to RACE-PCRs. Phylogenetic analyses did not unveil any geographic structuring of the diversity of PMWaV1, PMWaV2 and PMWaV3 isolates, supporting the current hypothesis that PMWaVs were mainly spread by human activity and vegetative propagation. Full article

Pineapple is a globally significant tropical fruit, but its cultivation faces numerous challenges due to abiotic and biotic stresses, affecting its quality and quantity. WRKY transcription factors are known regulators of stress responses, however, their specific functions in pineapple are not fully understood. This study investigates the role of AcWRKY31 by overexpressing it in pineapple and Arabidopsis. Transgenic pineapple lines were obtained using Agrobacterium-mediated transformation methods and abiotic and biotic stress treatments. Transgenic AcWRKY31-OE pineapple plants showed an increased sensitivity to salt and drought stress and an increased resistance to biotic stress from pineapple mealybugs compared to that of WT plants. Similar experiments in AcWRKY31-OE, AtWRKY53-OE, and the Arabidopsis Atwrky53 mutant were performed and consistently confirmed these findings. A comparative transcriptomic analysis revealed 5357 upregulated genes in AcWRKY31-OE pineapple, with 30 genes related to disease and pathogen response. Notably, 18 of these genes contained a W-box sequence in their promoter region. A KEGG analysis of RNA-Seq data showed that upregulated DEG genes are mostly involved in translation, protein kinases, peptidases and inhibitors, membrane trafficking, folding, sorting, and degradation, while the downregulated genes are involved in metabolism, protein families, signaling, and cellular processes. RT-qPCR assays of selected genes confirmed the transcriptomic results. In summary, the AcWRKY31 gene is promising for the improvement of stress responses in pineapple, and it could be a valuable tool for plant breeders to develop stress-tolerant crops in the future. Full article

Mealybug wilt of pineapple (MWP) is a destructive disease worldwide caused by a parasitic complex that includes Pineapple Mealybug Wilt-associated Viruses (PMWaVs) and mealybugs (Dysmicoccus brevipes), which concurrently act as vectors for these viruses. Reducing the mealybug population is key to managing MWP, which is achieved in intensive production systems through the use of insecticides. SA (salicylic acid), ASM (acibenzolar-S-methyl), BABA (β-aminobutyric acid), and MeSA (methyl salicylate) are key components of systemic acquired resistance (SAR), the defense mechanism of plants against biotrophic agents such as mealybugs. In this study, these compounds were applied either as pure chemicals and/or as a major constituent of plant extracts. Both the Hawaiian hybrid MD-2 and Queen Victoria tissue culture plants, as well as suckers used for vegetative propagation, were treated with these compounds by direct application on the soil of pineapple pots. Subsequently, five mealybugs were released on each plant or each daughter plant in case of a transgenerational experiment; then, after 45 days, the number of mealybugs was counted. Exogenous SA, ASM, and MeSA reduced the population of mealybugs by a minimum of 50% and up to 80%. These SAR-inducing treatments could be an interesting alternative for controlling mealybugs and are already used in other pathosystems. The SAR mechanisms behind this effect are yet to be confirmed by molecular and enzymatic markers. ASM and MeSA are promising treatments for pineapples using tissue culture plants or traditional shoots. Full article

Pineapple mealybug, Dysmicoccus brevipes (Hemiptera: Pseudococcidae), is a significant pest in pineapple production and a key trade barrier. We explored the potential use of ethyl formate (EF) as a methyl bromide alternative for the postharvest fumigation of D. brevipes in imported pineapples. When treated at 8 °C for 4 h, EF fumigation was effective against D. brevipes with LCt_99, the lethal concentration × time product of EF necessary to achieve 99% mortality of D. brevipes nymphs and adults at 64.2 and 134.8 g h/m³, respectively. Sorption trials conducted with 70 g/m³ EF for 4 h at 8 °C using 7.5, 15 and 30% pineapple loading ratios (w/v) indicated that loading ratio lower than 30% is necessary to achieve the LCt₉₉ values required to control D. brevipes. In a scaled up trial using 1 m³ chamber, EF fumigation with 70 g/m³ for 4 h at 8 °C with 20% pineapple loading ratio (w/v) resulted in a complete control of D. brevipes treated. There were no significant differences in hue values, sugar contents, firmness, and weight loss between EF-treated and untreated pineapples. Our results suggest that EF is a promising alternative to methyl bromide fumigation for the postharvest phytosanitary disinfection of D. brevipes in pineapples. Full article

New and emerging plant diseases are caused by different pathogens including viruses that often cause significant crop losses. Badnaviruses are pararetroviruses that contain a single molecule of ds DNA genome of 7 to 9 kb in size and infect a large number of economically important crops such as banana and plantains, black pepper, cacao, citrus, grapevine, pineapple, sugarcane, sweet potato, taro, and yam, causing significant yield losses. Many of the species in the genus have a restricted host range and several of them are known to infect a single crop. Combined infections of different virus species and strains offer conditions that favor the development of new strains via recombination, especially in vegetatively propagated crops. The primary spread of badnaviruses is through vegetative propagating materials while for the secondary spread, they depend on insects such as mealybugs and aphids. Disease emerges as a consequence of the interactions between host and pathogens under favorable environmental conditions. The viral genome of the pararetroviruses is known to be integrated into the chromosome of the host and a few plants with integrants when subjected to different kinds of abiotic stress will give rise to episomal forms of the virus and cause disease. Attempts have been made to develop management strategies for badnaviruses both conventionally and using precision breeding techniques such as genome editing. Until 2016 only 32 badnavirus species infecting different crops were known, but in a span of six years, this number has gone up to 68. The current review highlights the emerging disease problems and management options for badnaviruses infecting economically important crops. Full article

Pineapple (Ananas comosus L. [Merr.]) accessions from the U.S. Tropical Plant Genetic Resources and Disease Research (TPGRDR) in Hilo, Hawaii were subjected to RNA-sequencing to study the occurrence of viral populations associated with this vegetatively propagated crop. Analysis of high-throughput sequencing data obtained from 24 germplasm accessions and public domain transcriptome shotgun assembly (TSA) data identified two novel sadwaviruses, putatively named “pineapple secovirus C” (PSV-C) and “pineapple secovirus D” (PSV-D). They shared low amino acid sequence identity (from 34.8 to 41.3%) compared with their homologs in the Pro-pol region of the previously reported PSV-A and PSV-B. The complete genome (7485 bp) corresponding to a previously reported partial sequence of the badnavirus, pineapple bacilliform ER virus (PBERV), was retrieved from one of the datasets. Overall, we discovered a total of 69 viral sequences representing ten members within the Ampelovirus, Sadwavirus, and Badnavirus genera. Genetic diversity and recombination events were found in members of the pineapple mealybug wilt-associated virus (PMWaV) complex as well as PSVs. PMWaV-1, -3, and -6 presented recombination events across the quintuple gene block, while no recombination events were found for PMWaV-2. High recombination frequency of the RNA1 and RNA2 molecules from PSV-A and PSV-B were congruent with the diversity found by phylogenetic analyses. Here, we also report the development and improvement of RT-PCR diagnostic protocols for the specific identification and detection of viruses infecting pineapple based on the diverse viral populations characterized in this study. Given the high occurrence of recombination events, diversity, and discovery of viruses found in Ananas germplasm, the reported and validated RT-PCR assays represent an important advance for surveillance of viral infections of pineapple. Full article

Mealybug wilt of pineapple (MWP) is a disease of pineapple that has a long history in Hawaii, but is present throughout the world where pineapples are grown in tropical regions. The disease has an interesting etiology that is poorly understood but involves an association with virus particles, mealybug vectors, and ants which spread the mealybug vectors. Several distinct pineapple mealybug wilt-associated virus (PMWaV) species have been identified thus far with potential further member species yet to be characterized. Pineapple mealybug wilt-associated viruses are member species of the Ampelovirus genus of the Closteroviridae family. Ampeloviruses are split into two subgroups, subgroup I and subgroup II. PMWaV-2 is a subgroup II member, and these have a longer and more complex genome with additional genes on the 3’ terminus of the RNA genome compared to subgroup I ampeloviruses. PMWaV-2, along with the presence of mealybug vectors, have been shown to be necessary factors in symptom development in Hawaii. Some of these extra genes in the 3’ of PMWaV-2 have recently been shown to function as silencing suppressors, and may play a role in the virulence of PMWaV-2 and symptom development. In other regions of the world, reports of symptomatic plants without PMWaV-2 infection, but with PMWaV-1, -3 or some combination, contradict the requirement of PMWaV-2 for symptom development in MWP. It is possible that further, uncharacterized PMWaVs may be present in symptomatic pineapple plants that test negative for PMWaV-2, explaining the inconsistency in symptom development. More research is necessary to explore the confusing etiology of the MWP disease, and to perhaps shed light upon the symptom development. Full article

Higher plants use RNA silencing to defend against viral infections. As a counter defense, plant viruses have evolved proteins that suppress RNA silencing. Mealybug wilt of pineapple (MWP), an important disease of pineapple, has been associated with at least three distinct viruses, Pineapple mealybug wilt associated virus -1, -2, and -3 (PMWaV-1, -2, and -3). Selected open reading frames (ORFs) of PMWaV-1 and PMWaV-2 were screened for their local and systemic suppressor activities in Agrobacterium-mediated transient assays using green fluorescent protein (GFP) in Nicotiana benthamiana. Results indicate that PMWaV-2 utilizes a multiple-component RNA silencing suppression mechanism. Two proteins, p20 and CP, target both local and systemic silencing in N. benthamiana, while the p22 and CPd proteins target only systemic silencing. In the related virus PMWaV-1, we found that only one of the encoded proteins, p61, had only systemic suppressor activity. Of all the proteins tested from both viruses, only the PMWaV-2 p20 protein suppressed local silencing induced by double-stranded RNA (dsRNA), but only when low levels of inducing dsRNA were used. None of the proteins analyzed could interfere with the short distance spread of silencing. We examined the mechanism of systemic suppression activity by investigating the effect of PMWaV-2-encoded p20 and CP proteins on secondary siRNAs. Our results suggest that the PMWaV-2 p20 and CP proteins block the systemic silencing signal by repressing production of secondary siRNAs. We also demonstrate that the PMWaV-2 p20 and p22 proteins enhanced the pathogenicity of Potato virus X in N. benthamiana. Full article