Disease management, especially viruses in potato and sweetpotato.

Abstract

Abstract Potato (Solanum tuberosum) and sweetpotato (Ipomoea batatas) are the fourth and seventh most important crop plants. Both are important subsistence crops in East Africa and complement each other since their growth requirements differ. Potato and sweetpotato are vegetatively propagated, making them prone to accumulation of viruses during cultivation, and c.40 and 30 viruses have been reported to infect them, respectively. In East Africa, viruses comprise the only significant disease agents in sweetpotato. The most severe yield losses are caused by dual infection of plants with Sweet potato chlorotic stunt virus (SPCSV, crinivirus) and other, unrelated viruses, because the RNase3 protein produced by SPCSV eliminates antiviral defence. Therefore, control of SPCSV is of utmost importance in the control of virus diseases in sweetpotato. Recent surveys have also highlighted the prevalence of begomoviruses in sweetpotato throughout Africa; significant yield losses have been reported even in symptomless single infection. In potato, Potato leaf roll virus (PLRV, polerovirus) and Potato virus Y (PVY, potyvirus) are the most widely spread and damaging viruses in potato crops. In Eastern Africa, closer knowledge on viruses affecting potato crops is relatively limited, but some recent data are available from Kenya and Tanzania. Healthy seed potatoes and sweetpotato vine cuttings available for planting are a prerequisite for successful production. Knowledge on resistance to the local viruses and virus strains is another important issue when choosing cultivars for production. Antibodies to the most common potato viruses are commercially available and their use for indexing seed potatoes is straightforward with the basic diagnostic capacity. In contrast, antibodies to sweetpotato viruses are commercially unavailable. Analysis of the small interfering RNA (siRNA) molecules resulting from degradation of viral genomes by RNA silencing, the basal antiviral defence mechanism of plants, provides a universal, novel method for detection of plant viruses and does not require advance knowledge of them. It is promising for indexing of the stock plants used for further propagation of planting material. The technology is also applied to the identification of novel viruses and analysis of virus variability throughout Africa, which will inform development of novel control methods and testing regimes to control the most harmful viruses for each region.