E. Alvarez

Emerging pests and diseases of South-east Asian cassava: a comprehensive evaluation of geographic priorities, management options and research needs.

Cassava is a major staple, bio-energy and industrial crop in many parts of the developing world. In Southeast Asia, cassava is grown on >4 million ha by nearly 8 million (small-scale) farming households, under (climatic, biophysical) conditions that often prove unsuitable for many other crops. While SE Asian cassava has been virtually free of phytosanitary constraints for most of its history, a complex of invasive arthropod pests and plant diseases has recently come to affect local crops. We describe results from a region-wide monitoring effort in the 2014 dry season, covering 429 fields across five countries. We present geographic distribution and field-level incidence of the most prominent pest and disease invaders, introduce readily-available management options and research needs. Monitoring work reveals that several exotic mealybug and (red) mite species have effectively colonised SE Asias main cassava-growing areas, occurring in respectively 70% and 54% of fields, at average field-level incidence of 27u2009±u20092% and 16u2009±u20092%. Cassava witches broom (CWB), a systemic phytoplasma disease, was reported from 64% of plots, at incidence levels of 32u2009±u20092%. Although all main pests and diseases are non-natives, we hypothesise that accelerating intensification of cropping systems, increased climate change and variability, and deficient crop husbandry are aggravating both organism activity and crop susceptibility. Future efforts need to consolidate local capacity to tackle current (and future) pest invaders, boost detection capacity, devise locally-appropriate integrated pest management (IPM) tactics, and transfer key concepts and technologies to SE Asias cassava growers. Urgent action is needed to mobilise regional as well as international scientific support, to effectively tackle this phytosanitary emergency and thus safeguard the sustainability and profitability of one of Asias key agricultural commodities.

Diversity and pathogenicity of Colletotrichum species isolated from soursop in Colombia

Anthracnose, caused by Colletotrichum species is a highly limiting disease for the production of the tropical fruit tree crop, soursop (Annona muricata L.). In this study, 83 single-spore isolates of Colletotrichum were obtained from diseased soursoup tissues and subjected to a species complex-specific PCR assay. The isolates were identified as C. gloeosporioides sensu lato (nu2009=u200960), C. boninense s. lat. (nu2009=u200922), or C. acutatum s. lat. (nu2009=u20091). A subset of 21 selected isolates was identified to species level by means of a multi-locus phylogenetic analysis using sequences from the ITS region and partial sequences of the actin, β-tubulin-2, glyceraldehyde-3-phosphate dehydrogenase, and chitin synthase-1 genes. The multi-locus phylogenetic analysis resolved C. theobromicola, C. tropicale, C. siamense, and C. gloeosporioides sensu stricto in the C. gloeosporioides complex; C. karstii and one undetermined species in the C. boninense complex; as well as one undetermined species in the C. acutatum complex. Significant differences in anthracnose severity were observed between Colletotrichum species when tested for pathogenicity on attached twigs of soursop cv. Elita. Colletotrichum theobromicola and C. tropicale were associated with high and intermediate virulence, respectively, whereas the remaining species were associated with low virulence.

Erratum to: Establishment of a loop-mediated isothermal amplification (LAMP) assay for the detection of phytoplasma-associated cassava witches’ broom disease

Cassava (Manihot esculenta Crantz) is one of the most important food crops in the tropics; however, bacterial phytopathogens pose a serious threat to its farming. Cassava Witches’ Broom Disease (CWB) is caused by the infection of phytoplasma and is manifested as reduction in tuber yield and starch content at harvest of 10 and 30xa0%, respectively. Although polymerase-chain reaction provides the gold standard in diagnostics, this method requires significant investments in infrastructure and training. Here, we developed a loop-mediated isothermal amplification (LAMP) assay that allows specific detection of phytoplasma from field-collected samples. Three primer sets were designed, of which two detected phytoplasma DNA sequence encoding 16S rRNA (16S rDNA), the other detected cassava actin. Following a 1xa0h LAMP reaction at 63xa0°C, a positive reaction can be visualized by agarose gel electrophoresis, hydroxynaphthol blue color change, or the presence of a precipitate. In a pilot field study, the assay was able to rapidly distinguish between healthy and CWB-infected cassava. With further development, a LAMP for routine on-site screening of cassava crops can be envisioned.

Phytoplasma Diseases of Industrial Crops

Phytoplasmas are associated with diseases in several hundred plant species, including many economically important industrial crops like sugarcane, sugar beet, cassava, and cotton. A number of phytoplasma diseases are associated with sugarcane. Originally restricted to Asian countries, they are spreading rapidly to newer locations with the help of infected seed material and leafhopper vectors. In cassava, the two phytoplasma diseases causing serious yield losses are cassava frog skin in Latin America and cassava witches’ broom in Asia. Because of unreliable and nonspecific symptoms, the identification and characterization of the phytoplasmas associated with these and other industrial crops at an early stage of plant growth are challenging. Here the progress made in understanding biology, economic importance, symptomatology, diagnosis, epidemiology, and control of phytoplasmas infecting sugarcane, sugar beet, cassava, and cotton crops are summarized.