Impact of Positive Selection on Incidence of Different Viruses During Multiple Generations of Potato Seed Tubers in Uganda

Abstract

Smallholder farmers in Uganda commonly use seed potato tubers from the informal sector, especially by seed recycling over several generations. Therefore, seed tubers are highly degenerated with viruses and other pathogens, resulting in poor yield and quality of the produce. Over one cycle of multiplication, degeneration management by positive seed selection was found to be efficient in reducing virus diseases compared with the farmers' method of selection. The objective of this study was to assess to what extent positive selection over several seasons can reduce six different virus incidences in seed lots of different starting quality in southwestern Uganda. Multi-seasonal trials were carried out in three locations, with five seed lots from four sources and three cultivars. Detection of viruses was based on DAS-ELISA and Luminex xMAP technology. Analysis was carried out with analysis of variance (ANOVA) on angulartransformed percentages of virus incidence. Results showed fluctuations in some viruses over seasons with lower Potato leafroll virus (PLRV) and Potato virus X (PVX) incidences in lots from positive selection compared with lots from farmers' selection. In contrast, some seed lots were initially highly infected with Potato virus S (PVS) and Potato virus M (PVM) and showed no reduction in virus incidence through positive selection. In general, little infection with Potato virus Y (PVY) and Potato virus A (PVA) was found. Based on these results, it is recommended that smallholder farmers are trained in positive selection to opt for less virus-infected plants and tubers, thus increasing potato production.

Epidemiology and control of potato virus Y in Kenya

“…Just like in this study, limited knowledge of plant viruses as opposed to other pathogens has been reported by other authors working on different crops elsewhere (Colvin et al 2012;Adam et al 2015 (Mendez-Lozano et al 2003). Knowledge of virus symptoms can help farmers know when their crop is infected so that they can take appropriate actions like negative selection, positive selection (Priegnitz et al 2019) or replace infected seed tubers with disease free certified seed tubers among other methods.…”

“…All these previous surveys indicated that PVY is one of the most important viruses in Kenya due to the high prevalence reported over the past decades. Virus surveys in the neighboring countries like Tanzania (Chiunga 2013), Uganda (Gildemacher et al 2009;Priegnitz et al 2019) and Ethiopia (Gildemacher et al 2009) similarly report PVY as one of the major viruses in the potato production systems in these countries.…”

“…To lower virus prevalence in farmer's fields, different virus control strategies have been tested by scientists working in Kenya and the East Africa region and were found to have the potential to improve potato tuber yields. Some of these strategies include measures or combinations of measures like spraying insecticides against the virus vectors (Lung'aho et al 2007), use of cultural methods like border crops, mulching and organic plant extracts to control vectors (Muindi et al 2009;Olubayo et al 2010), the use of 'positive seed selection' to obtain tubers from healthy looking plants (without virus symptoms) as planting material for subsequent seasons (Gildemacher et al 2011;Schulte-Geldermann et al 2012;Onduru et al 2018;Priegnitz et al 2019) and selecting cultivars with tolerance to the viruses under field conditions Onduru et al 2019).…”

“…In this study, most farmers did not plant certified seed tubers, a practice that would be contributing to high virus prevalence in farmer's fields. In previous studies, the use of own seed and seed from neighbours or from local markets is a common practice which contributes to low potato yields not only among farmers in Kenya but also among farmers in neighbouring Uganda and Ethiopia (Gildemacher et al 2011;Priegnitz et al 2019). Lack of sufficient quantities of certified seed tubers at affordable prices is one reason that hinders efforts to use certified seed tubers which would reduce potato virus transmission (Kaguongo et al 2008).…”

“…Such practices include: maintaining volunteer potato plants in or around the farm (Wright and Bishop 1981;Jones et al 1996); cutting tubers prior to planting without following proper disinfection procedures; bruising seed tubers after harvest or mechanical injury to haulms during farm operations (Fageria et al 2015); lack of a proper crop rotation/intercropping plan or overlap of potato growing seasons in same or neighbouring farms (Ragsdale et al 2001) and maintaining alternative host plants of potato viruses in the field (Syller and Kaliciak 2009). Some of the potato virus control methods that have been proposed include use of certified seed tubers (Almekinders et al 2019), positive seed selection (Gildemacher et al 2011;Schulte-Geldermann et al 2012;Priegnitz et al 2019), control of aphids (virus vectors) by use of various forms of pesticides (Olubayo et al 2010), use of virus resistant varieties and use of border barriers crops to control aphids (Olubayo et al 2010). Virus control using resistant cultivars which can withstand virus degeneration can be a long-term, cost-effective solution to potato virus problems in this region because over 95% seed tubers planted by farmers are not certified (Gildemacher et al 2011;NPCK 2017) and farmers may be having limited knowledge on virus control.…”