However, Koch's postulates have only been demonstrated for CSSTBV ( Hagen et al., 1994). In 1944, CSSD was reported in Nigeria ( Murray, 1945), where native plant species have been implicated as primary virus reservoirs ( Abrokwah et al., 2016).Ī complex of at least seven badnaviruses (genus Badnavirus, family Caulimoviridae) have been associated with swollen shoot disease, cacao swollen shoot Togo A virus (CSSTAV), cacao swollen shoot Togo B virus (CSSTBV), cacao swollen shoot CD virus (CSSCDV), cacao swollen shoot CE virus (CSSCEV), cacao swollen shoot Ghana M virus (CSSGMV), cacao swollen shoot Ghana N virus (CSSGNV), and Cacao swollen shoot Ghana Q virus (CSSGQV) ( Muller and Sackey, 2005 Oro et al., 2012 Chingandu et al., 2017a, b, 2019 Muller et al., 2018 Ramos-Sobrinho et al., 2020). The cacao genotype “Amelonado,” known to be susceptible to CSSD badnaviruses ( Thresh et al., 1988), was considered an important factor contributing to the emergence and rapid spread of CSSD badnaviruses in cacao plantations in West Africa ( Abrokwah et al., 2016 Muller, 2016 Muller et al., 2018). cacao “Amelonado” was introduced to West Africa due to its production characteristics and suitability to the climate ( Muller, 2016). Together, the CSSD virus complex is responsible for significant losses due to reduced quality and yield, affecting millions of smallholder farmers ( Wessel and Quist-Wessel, 2015).Īlthough the first outbreak of swollen shoot disease occurred in Ghana in 1936 ( Steven, 1936), disease symptoms were observed in small cacao plantings as early as 1922 ( Paine, 1945). Several badnaviruses appear to have re-emerged following an era of reduced CSSD disease incidence and spread, while other species had not been characterized until recently. To date, at least seven badnavirus species, presumably endemic to West Africa, have been associated with cacao swollen shoot disease (CSSD) in the region ( Muller et al., 2018 Ramos-Sobrinho et al., 2020, 2021). The West African countries, Cote d'Ivoire, Ghana, Nigeria, and Togo have historically produced ~70–75% of the world's cocoa beans ( Ameyaw et al., 2014 FAOSTAT, 2017). ![]() The cacao tree ( Theobroma cacao L.) is native to the Amazon River Basin in South America and was introduced to West Africa during the 1920s, where it rapidly became a socioeconomically important crop. Based on the development of characteristic CSSD symptoms and recovery of partial and complete genome sequences of CSSGMV-Nig9 from systemically infected cacao plants, Koch's postulates have been fulfilled. The complete CSSGMV genome sequence was determined, by Illumina sequencing, from representative AI and BI plants and shared >99.5% pairwise nucleotide identity with CSSGMV-Nig9 (GenBank Accession No. The PCR results indicated that 14 of 18 and 15 of 15 BI and AI plants, respectively, were systemically infected. Viral infection was verified by PCR-amplification and sequencing of a 1068 bp fragment of the CSSGMV ORF3 from newly expanding leaves 60 dpi. By 120 dpi, three of 15 AI plants exhibited characteristic stem-swelling. Newly expanded leaves of BI (10/18) and AI (12/15) plants developed foliar mosaic and curling symptoms 30-days post inoculation (dpi), with chlorotic mottling and necrotic crinkling being evident by 90 dpi. To establish causality and characterize the symptomatology associated with infection by the badnavirus cacao swollen shoot Ghana M virus (CSSGMV), an infectious clone (1.3-mer) was constructed and used to inoculated cacao “Amelonado” seedlings by biolistic inoculation (BI n = 18) and agroinoculation (AI n = 15). ![]() associated with infection by a group of poorly characterized badnaviral species.
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