Abstract
Common impromptu observations between 2010 and 2012 of apparent virus-like disease symptoms in watermelons and pumpkins in Uganda prompted this study. However, there was no recorded evidence of virus infection in these crops anywhere in Uganda or eastern Africa as a region. Thus, 374 and 522 watermelon and pumpkin plants, respectively, growing in 13 fields were surveyed to record virus-like disease symptoms in Uganda’s four districts of Mbale and Kamuli (eastern region), Mpigi and Masaka (central region) during August to November 2013, and January to March 2014. Leaf samples were also collected and tested for four viruses known to commonly infect watermelons and pumpkins worldwide. Symptom severity was assessed using a scale of 0 to 5, while virus incidence was determined by serological methods. The four viruses tested were Cucumber mosaic virus (CMV), Watermelon mosaic virus (WMV), Zucchini yellow mosaic virus (ZYMV) and Cucurbit aphid borne-yellows virus (CABYV). In both crops, there was a higher incidence of virus-like diseases in central than in eastern region (P = 0.000). All the four viruses were detected with CMV as the most common, followed by WMV, ZYMV, and CABYV. Differences in virus incidences between the districts were not always significant. Single CMV, dual CMV+WMV and triple CMV+WMV+ZYMV were the most common single, and multiple infections in both crops. Watermelons contained more single virus infections than mixed infections (P < 0.001), but this difference was not significant in pumpkins (P = 0.468). In all, single virus infections were significantly higher in watermelons than pumpkins (P < 0.001). This is the first study to report incidence of viruses and virus-like diseases in watermelons and pumpkins in Uganda, and in eastern Africa as a region. The importance of these results with respect to crop production and next steps in virus disease management are discussed. Key words: Cucurbits, DAS-ELISA, multiple virus infection, TAS-ELISA, virus incidence, Uganda.
Highlights
Plant diseases caused by viruses are major biotic constraints in crop production worldwide (Anderson et al, 2004, Alabi et al, 2011; Navas-Castillo et al, 2011; Tzanetakis et al, 2013)
There was no recorded evidence of virus infection in these crops anywhere in Uganda or eastern Africa as a region
Single virus infections were significantly higher in watermelons than pumpkins (P < 0.001)
Summary
Plant diseases caused by viruses are major biotic constraints in crop production worldwide (Anderson et al, 2004, Alabi et al, 2011; Navas-Castillo et al, 2011; Tzanetakis et al, 2013). The impact of plant virus diseases is exacerbated in the tropics because tropical conditions favour continuous presence of both. Primary and secondary hosts and super-abundance of vectors that efficiently transmit the viruses (Fargette et al, 2006; Morales, 2007; Barult et al, 2010; NavasCastillo et al, 2011; Geering and Randles, 2012; Fereres and Raccah, 2015). Virus diseases in nonpriority crops at local or regional scale when ignored or left to ‘fallow’ may constitute none investigated pathosystems as sources of harmful viruses in surrounding cropping systems (Jones et al, 2010; Lebeda and Burdon, 2013). An example is the watermelon/pumpkin pathosystem in eastern Africa including Uganda that has not been studied, despite pumpkins being common intercrops of other well characterized pathosystems such as cassava (Legg et al, 2011; Ndunguru et al, 2015) and sweetpotato (Valverde, 2007; Clark et al, 2012)
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