Search

The whitefy Bemisia tabaci, a species complex consisting of many morphologically indistinguishable species divided into distinct clades, is one of the most globally important agricultural pests and plant virus vectors. Cassava-colonizing B. tabaci transmits viruses that cause cassava mosaic disease (CMD) and cassava brown streak disease (CBSD). Half of all cassava plants in Africa are affected by these viral diseases, resulting in annual production losses of more than US$ 1 billion. Here we report the draft genome of the cassava whitefly B. tabaci Sub-Saharan Africa - East and Central Africa (SSA-ECA), the super-abundant population that has been associated with the rapid spread of viruses causing the pandemics of CMD and CBSD. The SSA-ECA genome assembled from Illumina short reads has a total size of 513.7 Mb and a scaffold N50 length of 497 kb, and contains 15,084 predicted protein-coding genes. Phylogenetic analysis suggests that SSA-ECA diverged from MEAM1 around 5.26 million years ago. A comprehensive genetic analysis of cassava-colonizing B. tabaci in Africa was also conducted, in which a total of 243 whitefly specimens were collected from 18 countries representing all major cassava-growing regions in the continent and genotyped using NextRAD sequencing. Population genomic analyses confirmed the existence of six major populations linked by gene flow and inferred the distribution patterns of these populations across the African continent. The genome of SSA-ECA and the genetic findings provide valuable resources and guidance to facilitate whitefly research and the development of strategies to control cassava viral diseases spread by whiteflies.

Introduction: Banana bunchy top disease (BBTD) caused by banana bunchy top virus (BBTV) poses a significant threat to Uganda's food and income security. Methods: To map BBTD spread and inform its management, a delimiting survey was undertaken covering the high-risk zones bordering the Democratic Republic of Congo (DR Congo) in the west, Rwanda and Tanzania in the south, and South Sudan in the north. BBTD is endemic in the DR Congo and present in Tanzania and Rwanda. The survey and environmental data were then used to map the vulnerability of Uganda's banana landscapes. Results and discussion: BBTD was only confirmed on 9% of sampled farms in north- and midwestern Uganda, with yield losses of 75% to 100%. Farmers observed BBTD over a 0.5-4.4-year period, suggesting a delayed detection. Suckers were the predominate planting materials used, increasing the risk of disease spread. Landscape suitability for BBTD was influenced by precipitation of the driest month, banana presence in 2016, land surface temperature difference (LSTD), the interaction between wind speed and LSTD, isothermality, wind speed, and the normalized difference vegetation index. These variables affect either or both the virus and aphid vector populations. Altitude did not influence the model, possibly due to disease introduction at mid to high altitudes through infected planting materials. The low-lying zones (around River Nile and Lakes Albert, Edward, and Victoria) are highly vulnerable. BBTD risk was low in northeastern Uganda with low banana production. The prediction map shows some suitable landscapes in the southwest that can expose this major banana production zone to BBTD, necessitating proactive measures. [ABSTRACT FROM AUTHOR]

Anthracnose is a very limiting disease affecting production, as well as postharvest quality of numerous fruit crops in Colombia. The current management practices for this disease are partially effective due to limited information about the etiology, the inoculum sources, population structure and variation of the pathogen. A total of 293 Colletotrichum isolates were obtained from symptomatic tissues collected from Tahiti lime, tamarillo and mango orchards. To determine the Colletotrichum species causing the symptoms, amplification, and PCR product analysis for intergenic regions of the ribosomal DNA were conducted. Genetic diversity of the fungal population was assessed with Random Amplified Microsatellites (RAMS). Results of this study indicated that anthracnose in Tahiti lime and tamarillo are caused by Colletotrichun acutatum whereas symptoms on mango were induced by the species Colletotrichum gloeosporioides, which was also fund in fewcitrus samples. RAMS data analysis indicated the existence of two distinct species groups, with a low similarity index (35%). RAM profiles also showed a clear host differentiation of isolates. The C. acutatum population originated from tamarillo exhibited a narrow and homogeneous genetic base, while the C. acutatum population from Tahiti lime was more heterogeneous and genetically complex, as determined by the analysis of molecular variance (AMOVA) and of Ni-Li coefficient. The C. gloeosporioides population originated from mango and Tahiti lime was heterogeneous and highly diverse, with clear host differentiation according to RAM profiles. Collectively, the results from this study provide new insight into the general characteristics of Colletotrichum populations on various hosts; this type of knowledge will prove useful in designing more effective management practices.

Angular leaf spot (ALS), caused by the fungus Phaeoisariopsis griseola (Sacc.) Ferr., is one of the most important diseases of common bean (Phaseolus vulgaris L.) in tropical and subtropical bean producing areas. The common bean accession G 10474 has been widely resistant to P. griseola, including pathotype 63-63, one of the most virulent P. griseola pathotypes characterized. The objectives of this study were to determine the inheritance of angular leaf spot resistance and to identify molecular markers linked to the resistance gene in G 10474. Resistance to P. griseola pathotypes 63-63 in G 10474 was investigated in [F.sub.2] populations derived from a cross between G 10474 and Sprite (universally susceptible). Inoculation of parents, [F.sub.1], [F.sub.2], and backcross-derived plants with race 63-63 revealed that a single dominant gene conditioned ALS resistance in G 10474. A combination of the amplified fragment length polymorphism (AFLP) technique and bulked segregant analysis (BSA) was applied to the [F.sub.2] population to identify molecular markers linked to the ALS resistance gene in G 10474. Three AFLP markers (E-ACA/M-CT[T.sub.330], E-AAC/M-CA[G.sub.310], and E-AAC/M-CA[T.sub.285]) segregated in coupling phase with the resistance gene in G 10474. The E-ACA/M-CT[T.sub.330] marker was successfully converted to a codominant sequence characterized amplified region (SCAR) marker at 5 cM from the resistance gene. Validation of the SCAR marker outside the mapping population showed that the utility of this marker for marker-assisted selection (MAS) was limited to the Andean gene pool of P. vulgaris. Therefore, the SCAR marker we report can only be used to introgress the ALS resistance of G 10474 into Andean backgrounds., COMMON BEAN is one of the most food important legumes in the world because of its commercial value, extensive production, consumer use, and nutrient value (being a source of carbohydrate, [...]