First Report of East African Cassava Mosaic Begomovirus in Ghana

Phenotypic and molecular screenings for determination of cassava mosaic disease (CMD) status in farmers' fields in Ebonyi State, Nigeria

African cassava mosaic virus (ACMV) and East African cassava mosaic virus (EACMV) are among the major constraints to cassava productivity within tropical and sub-tropical regions, including Ebonyi State, Nigeria. Thus, virus indexing has become imperative to determine the status of cassava mosaic disease (CMD) in Ebonyi State, to implement appropriate preventive and control strategies. Seventy-eight cassava accessions obtained from different locations of Ebonyi State were phenotypically scored, using scales 1-5 depending on CMD symptomatic expressions, followed by multiplex-PCR and sequencing for validation. 11% of cassava accessions cultivated in Afikpo were resistant (RE) to ACMV compared to 8% of moderately-resistant (MR) accessions in Izzi and 55% of tolerant (TO) ACMV accessions in Ebonyi. 100% of cassava accessions in Onicha and 66% in Afikpo South were susceptible (SU) and highly susceptible (HS) to ACMV, respectively. With multiplex-PCR, 97.4% (ACMV) and 2.6% (EACMV) were positive. Dunn's multiple comparison tests of CMD mean incidence demonstrated differences (P < 0.05), except between RE and MR, and TO and MR. More transitions (A/G, C/T) compared to transversions (A/T, G/T), were detected, with nonsynonymous mutations (Leucine/Isoleucine; Valine/Isoleucine; Arginine/Lysine; Methionine/Isoleucine), and good bit-scores (91.13-99.07% identites; e-values of 7.00e-148-0.00e+00). Phylogeny resolved the sequences into five major groups. DNA sequencing validated the detected ACMV and EACMV species. This study revealed variants of ACMV and low adoption of RE and MR cassava accessions in the farmers' fields. The findings will guide in getting disease-free and resistant varieties as planting materials to significantly mitigate the CMD spread in Ebonyi State, Nigeria.

Cassava mosaic geminiviruses in Africa

Cassava mosaic disease (CMD) caused by cassava mosaic geminiviruses (CMGs) (Geminiviridae:Begomovirus) is undoubtedly the most important constraint to the production of cassava in Africa at the outset of the 21st century. Although the disease was recorded for the first time in the latter part of the 19th century, for much of the intervening period it has been relatively benign in most of the areas where it occurs and has generally been considered to be of minor economic significance. Towards the end of the 20th century, however, the inherent dynamism of the causal viruses was demonstrated, as a recombinant hybrid of the two principal species was identified, initially from Uganda, and shown to be associated with an unusually severe and rapidly spreading epidemic of CMD. Subsequent spread throughout East and Central Africa, the consequent devastation of production of the cassava crop, a key staple in much of this region, and the observation of similar recombination events elsewhere, has once again demonstrated the inherent danger posed to man by the capacity of these viruses to adapt to their environment and optimally exploit their relationships with the whitefly vector, plant host and human cultivator. In this review of cassava mosaic geminiviruses in Africa, we examine each of these relationships, and highlight the ways in which the CMGs have exploited them to their own advantage.

Variants of East African cassava mosaic virus and Its Distribution in Double Infections with African cassava mosaic virus in Nigeria

In a survey for cassava mosaic begomoviruses conducted in 1997 and 1998 in Nigeria, East African cassava mosaic virus (EACMV) was detected by the polymerase chain reaction together with African cassava mosaic virus (ACMV) in 27 out of 290 cassava leaf samples of infected plants from 254 farmers' fields in five agroecological zones. One plant was infected with EACMV only. Five variant isolates of EACMV were observed based on their reactions to primers that could detect Cameroonian and East African strains of EACMV. Isolates of variants 1 and 3 occurred mostly in the derived or coastal and southern Guinea savannahs, while variants 4 and 5 predominated in the humid forest region. Isolates of variant 2 were widely distributed across the three agroecologies. EACMV was not detected in the northern Guinea savannah and arid and semiarid zones. Most doubly infected plants showed more severe symptoms than plants with single infection. Occurrence of EACMV variants together with ACMV detection and information about their distribution in Nigeria could be used for the selection of cassava clones in cassava mosaic disease resistance programs.