Degeneration in sweetpotato due to viruses, virus‐cleaned planting material and reversion: a review

Abstract

This review examines viral degeneration in sweetpotato in different regions of the World, particularly that caused by Sweet potato chlorotic stunt virus (SPCSV) and Sweet potato feathery mottle virus (SPFMV), comparing impacts on yield in single and complex infections of all the major viruses affecting the crop. How cultivars are generated and virus resistance are also covered, especially for Africa. The synergistic (SPCSV + SPFMV) sweet potato virus disease (SPVD) is amongst the most dramatic diseases of sweetpotato but its overall yield impacts may not be as high as is generally assumed. It is constrained by resistance, roguing and selection of symptomless planting material. Instead, the cumulative impact of individual and combinations of symptomless viruses may be globally greater. These include sweepoviruses and various potyviruses, of which the commonest is SPFMV. A number of aspects of virus‐cleaned planting stocks are identified, including reinfection rates, that need investigating before their use is considered as sustainable in developing countries. Popular East African cultivars appear to sustain their long‐term survival by reverting from symptomless infection. The likely biochemistry of this is discussed, and parallels are drawn with other crops. It is concluded that breeding for this attribute will be the best strategy for achieving long‐term control of most sweetpotato viruses.

Invertebrate pests and diseases of sweetpotato (Ipomoea batatas): a review and identification of research priorities for smallholder production

“…Symptoms are also influenced by cultivar, crop stage, nutrient availability and climate . In some areas sweetpotato viruses are a major constraint, often reducing yield by more 50% and up to 90% (Carey et al, 1999;Gutiérrez et al, 2003;Gibson et al, 2004;Valverde et al, 2007;Davis & Ruabete, 2010;Wang et al, 2010;Okpul et al, 2011;Clark et al, 2012;Cuellar et al, 2015;Gibson & Kreuze, 2015). The most common form of spread of viruses is through propagation material, in which a taxonomically diverse range of viruses can be present (Clark & Moyer, 1988;Moyer & Larsen, 1991;Gibson et al, 1997;Mbanzibwa et al, 2014).…”

“…Accordingly, distribution of a resistant variety offers the protection from a given disease for an indefinite period, even if farmers propagate from crops that have been exposed to disease, with 'resistance breakdown' from overuse being the only risk requiring management, something that is generally easy given the diversity of varieties that tends to be used in developing countries. Accordingly, developing and distributing disease resistant varieties has a greater durability than providing fresh PT material every two to three years (Gibson & Kreuze, 2015). Set against this, however, is the major issue that many pathogens threaten sweetpotato and each is likely to require different genes for resistance (Tugume et al, 2010;Ngailo et al, 2013).…”

“…There is a large literature on sweetpotato viruses including reviews by Clark et al (2012) and Gibson & Kreuze (2015). In recent years the introduction of molecular detection methods has expanded understanding of sweetpotato viruses and virus complexes .…”

“…More commonly, however, losses are lower because of the high yield potential of sweetpotato and its capacity for compensatory growth (Chalfant et al, 1990;Chalfant & Seal, 1991;Gibson & Kreuze, 2015;. The most problematic arthropods in tropical smallholder production are listed in Table 1.…”

Delivering New Technologies to the Tanzanian Sweetpotato Crop Through Its Informal Seed System

“…We would in particular recommend supporting formal plant breeders, ideally working in a participatory manner, breeding additional top-quality varieties. The informal system is relatively inefficient at this (Gibson et al 2000), especially at breeding ones with resistance to virus infection, on which informal systems rely (Gibson and Kreuze 2014).…”