Cassava mosaic disease and its management in Southeast Asia

Abstract

Key message Status of the current outbreak of cassava mosaic disease (CMD) in Southeast Asia was reviewed. Healthy cassava seed production and dissemination systems have been established in Vietnam and Cambodia, along with integrated disease and pest management systems, to combat the outbreak. Abstract Cassava (Manihot esculenta Crantz) is one of the most important edible crops in tropical and subtropical regions. Recently, invasive insect pests and diseases have resulted in serious losses to cassava in Southeast Asia. In this review we discuss the current outbreak of cassava mosaic disease (CMD) caused by the Sri Lankan cassava mosaic virus (SLCMV) in Southeast Asia, and summarize similarities between SLCMV and other cassava mosaic begomoviruses. A SATREPS (Science and Technology Research Partnership for Sustainable Development) project “Development and dissemination of sustainable production systems based on invasive pest management of cassava in Vietnam, Cambodia and Thailand”, was launched in 2016, which has been funded by The Japan International Cooperation Agency (JICA) and The Japan Science and Technology Agency (JST), Japan. The objectives of SATREPS were to establish healthy seed production and dissemination systems for cassava in south Vietnam and Cambodia, and to develop management systems for plant diseases and insect pests of cassava. To achieve these goals, model systems of healthy seed production in Vietnam and Cambodia have been developed incorporating CMD-resistant planting materials through international networks with The International Center for Tropical Agriculture (CIAT) and The International Institute of Tropical Agriculture (IITA).

Expansion and impact of cassava brown streak and cassava mosaic diseases in Africa: A review

“…To control the potentially devastating disease, Government representatives, development partners, and cassava research scientists from Cambodia, Thailand, and Vietnam gathered to devise a regional plan. Science and Technology Research Partnership for Sustainable Development (SATREPS) project was launched whose objectives were to develop pest management technologies and a system for the production and cultivation of healthy seedlings (Uke et al, 2022). Prior to first report of CMD outbreak in Cambodia, a study conducted in 2016-2017 on the movement and exchange of cassava planting materials in Cambodia and Vietnam within communes found 82 and 78% of seed provided to others being exchanged between family and acquaintances, respectively (Delaquis et al, 2018).…”

Mutations in DNA polymerase δ subunit 1 mediate CMD2-type resistance to Cassava Mosaic Geminiviruses

“…Resistance segregated at 1:1 ratio (Fig. 1b, across all populations, x 2 p-value = 0.59), indicating that the dominant wildtype allele of CMD2 is sufficient to restore resistance, and that the CMD2 and LCR phenotypes are caused by a single genetic locus. If LCR results from a somaclonal epiallele, then passage of CMD resistant F 1 progeny through morphogenesis would result in the LCR phenotype.…”

“…Cassava yields are suppressed by infections with cassava mosaic geminiviruses (CMG, Family Geminiviridae : Genus Begomovirus ) which collectively cause cassava mosaic disease (CMD). Eleven species of CMG are known to infect cassava across sub-Saharan Africa, the Indian subcontinent, and recently in several countries of South-East Asia 2 . CMGs possess two circular single-stranded DNA genomes that are transmitted by the whitefly Bemisia tabaci and spread by farmers who plant infected stem cuttings to establish the next cropping cycle 3,4 .…”

“…The disease rating distribution across all populations segregates at 1:1. ! 2 = 0.59 (C) In each population, ∼15% of lines with consistent phenotypes over the two years were selected for bulk segregant analysis (BSA) mapping (solid circles).…”

Validation of KASP markers associated with cassava mosaic disease resistance, storage root dry matter and provitamin A carotenoid contents in Ugandan cassava germplasm

“…Application of MAS in cassava breeding programs would help in several ways, including: (i) elimination of genotypes with unfavorable alleles at the early stage of the selection scheme, thus allowing for field testing of a reduced number of genotypes, (ii) rapid introgression of resistant genes into existing cassava clones, in places where the disease has recently spread to, for example in Southeast Asian countries ( Uke et al., 2022 ), (iii) early selection of traits that are best measured at the late crop developmental stages, (iv) selection for resistance under environments where the disease pressure is low; and (v) discrimination of genotypes homozygosity and/or heterozygosity. Despite the promise from MAS, its use in cassava breeding is limited and lags considerably behind progress in other major crops such as maize, rice and wheat.…”