High-resolution melt and morphological analyses of mealybugs (Hemiptera: Pseudococcidae) from cacao: tools for the control of Cacao swollen shoot virus spread

Molecular Surveillance, Prevalence, and Distribution of Cacao Infecting Badnavirus Species in Côte d'Ivoire and Ghana

The cacao swollen shoot disease (CSSD) caused by a complex of badnavirus species presents a major challenge for cacao production in West Africa, especially Ghana and Côte d'Ivoire. In this study, CSSD species detection efficiency, diversity, and geographic distribution patterns in cacao plantations in Ghana and Côte d'Ivoire were investigated through field surveillance, PCR detection assays, sequencing of positive amplicons, and phylogeographic clustering. Cumulatively, the detection efficiency of the tested CSSD primer sets that were targeting the movement protein domain of the virus ranged from 0.15% (CSSD-3 primer) to 66.91% (CSSD-1 primer) on all the symptomatic cacao leaf samples assessed. The identified CSSD species differed phylogenetically and overlapped in distribution, with the cacao swollen shoot Togo B virus (CSSTBV) (n = 588 sequences) being the most prevalent and widely distributed compared to the other CSSD species that were encountered in both countries. Geographically, the cacao swollen shoot CE virus (CSSCEV) species (n = 124 sequences) that was identified was largely restricted to the bordering regions of Ghana and Côte d'Ivoire. These results provide updated knowledge of the geographic distribution of the key CSSD species and their diagnostic efficiency and, thus, provide guidance in identifying locations for structured testing of cacao germplasm and optimal diagnostics for the predominant CSSD species in Ghana and Côte d'Ivoire.

Mealybug (Hemiptera: Pseudococcidae) Species Associated with Cacao Mild Mosaic Virus and Evidence of Virus Acquisition

Theobroma cacao is affected by viruses on every continent where the crop is cultivated, with the most well-known ones belonging to the Badnavirus genus. One of these, cacao mild mosaic virus (CaMMV), is present in the Americas, and is transmitted by several species of Pseudococcidae (mealybugs). To determine which species are associated with virus-affected cacao plants in North America, and to assess their potential as vectors, mealybugs (n = 166) were collected from infected trees in Florida, and identified using COI, ITS2, and 28S markers. The species present were Pseudococcus jackbeardsleyi (38%; n = 63), Maconellicoccus hirsutus (34.3%; n = 57), Pseudococcus comstocki (15.7%; n = 26), and Ferrisia virgata (12%; n = 20). Virus acquisition was assessed by testing mealybug DNA (0.8 ng) using a nested PCR that amplified a 500 bp fragment of the movement protein-coat protein region of CaMMV. Virus sequences were obtained from 34.6 to 43.1% of the insects tested; however, acquisition did not differ among species, X² (3, N = 166) = 0.56, p < 0.91. This study identified two new mealybug species, P. jackbeardsleyi and M. hirsutus, as potential vectors of CaMMV. This information is essential for understanding the infection cycle of CaMMV and developing effective management strategies.

Cacao biotechnology: current status and future prospects

Theobroma cacao-The Food of the Gods, provides the raw material for the multibillion dollar chocolate industry and is also the main source of income for about 6 million smallholders around the world. Additionally, cocoa beans have a number of other nonfood uses in the pharmaceutical and cosmetic industries. Specifically, the potential health benefits of cocoa have received increasing attention as it is rich in polyphenols, particularly flavonoids. At present, the demand for cocoa and cocoa-based products in Asia is growing particularly rapidly and chocolate manufacturers are increasing investment in this region. However, in many Asian countries, cocoa production is hampered due to many reasons including technological, political and socio-economic issues. This review provides an overview of the present status of global cocoa production and recent advances in biotechnological applications for cacao improvement, with special emphasis on genetics/genomics, in vitro embryogenesis and genetic transformation. In addition, in order to obtain an insight into the latest innovations in the commercial sector, a survey was conducted on granted patents relating to T. cacao biotechnology.

Rapid identification of bacteria associated with Acute Oak Decline by high-resolution melt analysis

Two Gram-negative Enterobacteriaceae, Gibbsiella quercinecans and Brenneria goodwinii, are frequently isolated from oak suffering from Acute Oak Decline. These two species are difficult to identify based on colony morphology, carbohydrate utilization or 16S rRNA gene sequence, and identification using gyrB gene sequencing is time-consuming and laborious. A rapid identification technique, based on high-resolution melt analysis of the atpD gene, was designed to efficiently process numerous isolates from an increasing number of affected woodlands and parks. Principal component analysis of the resulting melt curves from strains of G. quercinecans, B. goodwinii and their close phylogenetic relatives allowed differentiation into distinct clusters based on species or subspecies identity.

SIGNIFICANCE AND IMPACT OF THE STUDY

Acute Oak Decline is an increasing threat to Britain's native oak population. Two novel bacterial species both belonging to the family Enterobacteriaceae, Gibbsiella quercinecans and Brenneria goodwinii, are thought to play an important role in symptom development. Here, we describe a rapid identification technique using high-resolution melt analysis of the atpD gene able to assign isolates to either G. quercinecans or B. goodwinii in a single assay, greatly reducing the time taken to identify if either or both of these species are present in symptomatic oak.