Distribution of potato viruses in Uganda

Viral diseases are among the major factors affecting potato ( Solanum tuberosum L.) production in Uganda. Knowledge of the types of viruses and their distribution levels in the country is vital for targeting sound management strategies. The objective of this study was to assess the prevalence and distribution of potato viruses in different potato growing areas in Uganda. Virus diagnostic surveys were conducted across the main potato producing regions and virus detection was done using DAS-ELISA and RT-PCR techniques. The study showed that the most widely distributed and economically important potato viruses were: PVS (31-90.9%), PLRV (2.6-81.3%), PVY (7.1-54.5%) and PVX (8.3 -53.3%); while the least detected viruses were PVM (18.2%) and PVA (9%). The viruses were prevalent either singly or in mixtures. Up to 42.8% of the samples were infected with one virus, 20.9% with two viruses and 4.2% with three viruses; while no virus was detected in 31.3% of the samples. Of the double infections, the PVY+PVS combination was the most common and widely distributed (2.1-18.2%) in 12 districts; followed by PVY+PLRV (1.8-21.3%) occurring in six districts, PVM+PVS (7.9-16.7%), PLRV+PVX (2.4-14.3%) in 5 districts and PVY+PVX (2.4-4.4%) in 3 districts. Triple infections involving PVY+PLRV+PVS were recorded at prevalence levels of 2.2-18.6% in six district. Altitude, temperature, varieties and seed sources showed relationships with the variation in the prevalence of the viruses. There were high virus prevalence and disease severity levels in low altitude areas (1088-1334 m.a.s.l) of mid-western sub-region (Mbarara and Lwengo), Central (Kibaale, Mubende) and Mid Northern (Pader) sub region compared to high altitude areas (>1600 m.a.s.l). The Virus risk Area Modeling results showed the largest area (48.6%; 1,308,160 ha) at moderate risk of virus infection; while 27.3% (732,305 ha) was at high risk of virus infection. Based on the distribution level of the viruses, potato production could be intensified in areas with less virus pressure mainly, in parts of West Nile and Rwenzori regions.Les maladies virales sont l\u2019un des principaux facteurs affectant la production de pommes de terre ( Solanum tuberosum L.) en Ouganda. La connaissance des types de virus et de leurs niveaux de distribution en Ouganda est essentielle pour cibler des strat\ue9gies de gestion rationnelles. L\u2019objectif de cette \ue9tude \ue9tait d\u2019\ue9valuer la pr\ue9valence et la distribution des virus de la pomme de terre dans diff\ue9rentes zones de culture de la pomme de terre en Ouganda. Des enqu\ueates de diagnostic viral ont \ue9t\ue9 men\ue9es dans les principales r\ue9gions productrices de pommes de terre et la d\ue9tection des virus a \ue9t\ue9 effectu\ue9e \ue0 l\u2019aide des techniques DAS-ELISA et RT-PCR. L\u2019\ue9tude a montr\ue9 que les virus de la pomme de terre les plus largement r\ue9pandus et les plus importants sur le plan \ue9conomique \ue9taient: PVS (31-90,9%), PLRV (2,6-81,3%), PVY (7,1-54,5%) et PVX (8,3% -53,3%); tandis que les virus les moins d\ue9tect\ue9s \ue9taient le PVM (18,2%) et le PVA (9%). Ces virus \ue9taient r\ue9pandus seuls ou en m\ue9langes. Jusqu\u2019\ue0 42,8% des \ue9chantillons \ue9taient infect\ue9s par un virus, 20,9% par deux virus et 4,2% par trois virus; alors qu\u2019aucun virus n\u2019a \ue9t\ue9 d\ue9tect\ue9 dans 31,3% des \ue9chantillons. Parmi les doubles infections, la combinaison PVY + PVS \ue9tait la plus courante et la plus r\ue9pandue (2,1 \ue0 18,2%) dans 12 districts; suivi de PVY + PLRV (1,8-21,3%) survenant dans six districts, PVM + PVS (7,9-16,7%), PLRV + PVX (2,4-14,3%) dans 5 districts et PVY + PVX (2,4-4,4%) dans 3 les quartiers. Des infections triples impliquant PVY + PLRV + PVS ont \ue9t\ue9 enregistr\ue9es \ue0 un niveau de pr\ue9valence de 2,2 \ue0 18,6% dans six districts. L\u2019altitude, la temp\ue9rature, les vari\ue9t\ue9s et les sources de semences ont montr\ue9 une relation avec la variation de la pr\ue9valence des virus. La pr\ue9valence du virus et la gravit\ue9 de la maladie virale \ue9taient \ue9lev\ue9es dans les zones de basse altitude (1088-1334 m d\u2019altitude) de la sous-r\ue9gion du centre-ouest (Mbarara et Lwengo), du centre (Kibaale, Mubende) et du centre-nord (Pader) par rapport aux zones de haute altitude (> 1600 m d\u2019altitude). Les r\ue9sultats de la mod\ue9lisation des zones \ue0 risque viral ont montr\ue9 que la plus grande zone (48,6%; 1 308 160 ha) pr\ue9sente un risque mod\ue9r\ue9 d\u2019infection virale; tandis que 27,3% (732 305 ha) \ue9taient \ue0 haut risque d\u2019infection virale. Sur la base du niveau de distribution des virus, la production de pommes de terre pourrait \ueatre intensifi\ue9e dans les zones o\uf9 la pression virale est moindre, principalement dans certaines parties des r\ue9gions du Nil occidental et de Rwenzori

How big is the potato (Solanum tuberosum L.) yield gap in Sub-Saharan Africa and why? A participatory approach.

According to potato experts from ten Sub-Saharan Africa (SSA) countries working together in a community of practice (CoP) over a 3-years period, potato farmers across SSA can increase their current annual production of 10.8 million metric tons by 140% if they had access to high quality seed along with improved management practices. This paper describes this innovative new methodology tested on potato for the first time, combining modelling and a comprehensive online survey through a CoP. The intent was to overcome the paucity of experimental information required for crop modelling. Researchers, whose data contributed to estimating model parameters, participated in the study using Solanum, a crop model developed by the International Potato Center (CIP). The first finding was that model parameters estimated through participatory modelling using experts’ knowledge were good approximations of those obtained experimentally. The estimated yield gap was 58 Mg ha-1, of which 35 corresponded to a research gap (potential yield minus research yield) and 24 to farmers’ gap (research yield minus farmer’s yield). Over a 6-month period, SurveyMonkey, a Web-based platform was used to assess yield gap drivers. The survey revealed that poor quality seed and bacterial wilt were the main yield gap drivers as perceived by survey respondents

Challenges and opportunities for quality seed potato availability and production in Uganda

Potato yields in Uganda have remained low at 7.5 t ha-1. This low yield is attributed to low yielding varieties, poor management practices and lack of quality seed potatoes among other factors. This study was conducted to ascertain the challenges and opportunities of quality seed potato availability and production in the southwestern highlands agro-ecological zone (SWHAEZ). A total of 15 farmer groups were randomly selected from a sample size of 200 farmers and individually interviewed. The results of study indicated that high transaction costs (43.5%), lack of clear seed delivery system (40.5%) and limited information on the source of seed (14.0%) were the main constraints limiting farmers’ access to and use of quality seed potato. Up to 93% of the farmers in SWHAEZ use home saved seed from previous harvests and conventional ware potato markets, whose quality is not guaranteed. Although over 70% of the farmers were convinced that quality of seed had a positive effect on yield increase, 72% of them still use poor quality seed often infected by bacterial wilt. In addition, 52% of the farmers lacked specific storage facilities for potato seed; and this further lowered the grade of the seed quality. However, a number of opportunities existed for production and access to quality seed including; various proven technologies for producing quality seed potato and ready demand for potato seed and ware potato. Of the seed potato production technologies, positive selected seed (PSS) seemed to have the highest quantity of seed; while basic seed produced heaviest tubers than the rest of the technologies.Keywords: Quality seed potato, seed system and challenge

Comparative Phenotypic and Agronomic Assessment of Transgenic Potato with 3R-Gene Stack with Complete Resistance to Late Blight Disease

Transgenic potato event Vic.172, expressing three naturally occurring resistance genes (R genes) conferring complete protection against late blight disease, was evaluated for resistance to late blight, phenotypic characterization, and agronomic performance in field conditions at three locations during three seasons in Uganda. These trials were conducted by comparison to the variety Victoria from which Vic.172 derives, using identical fungicide treatment, except when evaluating disease resistance. During all seasons, the transgenic event Vic.172 was confirmed to have complete resistance to late blight disease, whereas Victoria plants were completely dead by 60–80 days after planting. Tubers from Vic.172 were completely resistant to LB after artificial inoculation. The phenotypic characterization included observations of the characteristics and development of the stems, leaves, flowers, and tubers. Differences in phenotypic parameters between Vic.172 and Victoria were not statistically significant across locations and seasons. The agronomic performance observations covered sprouting, emergence, vigor, foliage growth, and yield. Differences in agronomic performance were not statistically significant except for marketable yield in one location under high productivity conditions. However, yield variation across locations and seasons was not statistically significant, but was influenced by the environment. Hence, the results of the comparative assessment of the phenotype and agronomic performance revealed that transgenic event Vic.172 did not present biologically significant differences in comparison to the variety Victoria it derives from

Molecular detection of tilapia lake virus (TiLV) genome in Nile tilapia (Oreochromis niloticus) from Lake Victoria

Tilapia lake virus (TiLV) is an emerging pathogen of Tilapiines associated with high mortalities of wild and farmed tilapia posing great threat to the fishery industry worldwide. The virus has been reported in Israel, Ecuador, Colombia, Thailand, Egypt, Taiwan, India and Malaysia. In this study, a reverse transcription polymerase chain reaction (RT-PCR) assay was developed and used to detect TiLV genome in Nile tilapia from Lake Victoria. Nile tilapia samples were collected from the Tanzanian (108 fish) and Ugandan (83 fish) parts of Lake Victoria in 2015 and 2016, respectively. Samples were screened for TiLV by using RT-PCR and the PCR products were sequenced. The findings show that out of the 191 fish examined, 28 had PCR products showing the presence of TiLV genome. The TiLV nucleic acids were detected in the spleen (10.99%, N=191), head kidney (7.69%, N=65), heart (3.45%, N=29) and liver (0.71%, N=140) samples while no PCR amplification was detected in the brain by the developed RT-PCR method. Generally, the findings show that the lymphoid organs, mainly comprising of the head kidney and spleen had the highest number of samples with positive nucleic acids for TiLV followed by heart samples. On the contrary, the liver and brain that have previously been shown to be target organs during acute infection either did not have or had the lowest level of TiLV nucleic acids detected in the present study. All the 28 sequences retrieved had an average length of 768 bp. A blast analysis on NCBI showed that all sequences obtained were homologous to TiLV segment-2 sequences obtained from previous outbreaks in Israel and Thailand. To our knowledge, this is the first detection of TiLV subclinical infections in Nile tilapia in Lake Victoria, a none-outbreak area.Keywords: Lake Victoria, Nile tilapia, PCR, phylogenetic, surveillance, tilapia lake viru

Stacking three late blight resistance genes from wild species directly into African highland potato varieties confers complete field resistance to local blight races

Considered responsible for one million deaths in Ireland and widespread famine in the European continent during the 1840s, late blight, caused by Phytophthora infestans, remains the most devastating disease of potato (Solanum tuberosum L.) with about 15%–30% annual yield loss in sub‐Saharan Africa, affecting mainly smallholder farmers. We show here that the transfer of three resistance (R) genes from wild relatives [RB, Rpi‐blb2 from Solanum bulbocastanum and Rpi‐vnt1.1 from S. venturii] into potato provided complete resistance in the field over several seasons. We observed that the stacking of the three R genes produced a high frequency of transgenic events with resistance to late blight. In the field, 13 resistant transgenic events with the 3R‐gene stack from the potato varieties ‘Desiree’ and ‘Victoria’ grew normally without showing pathogen damage and without any fungicide spray, whereas their non‐transgenic equivalent varieties were rapidly killed. Characteristics of the local pathogen population suggest that the resistance to late blight may be long‐lasting because it has low diversity, and essentially consists of the single lineage, 2_A1, which expresses the cognate avirulence effector genes. Yields of two transgenic events from ‘Desiree’ and ‘Victoria’ grown without fungicide to reflect small‐scale farm holders were estimated to be 29 and 45 t/ha respectively. This represents a three to four‐fold increase over the national average. Thus, these late blight resistant potato varieties, which are the farmers’ preferred varieties, could be rapidly adopted and bring significant income to smallholder farmers in sub‐Saharan Afric