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

Selection of cooking banana genotypes for yield and black Sigatoka resistance in different locations in Uganda

It is imperative to systematically evaluate new banana genotypes in different locations before national release. This enables selection and recommendation of superior genotypes as new varieties for a wider range of environments. The objective of the present study was to select banana genotypes with stable and high performance for bunch yield and leaf black Sigatoka resistance. Eleven cooking banana genotypes developed by the Uganda National Agricultural Research Organization in collaboration with Bioversity International, and two check varieties were evaluated in multi-location preliminary yield trials in Uganda. Data collected were analyzed using Additive Main Effects and Multiplicative Interaction (AMMI) model, AMMI Stability Value, and Genotype Selection Index (GSI). Genotype × location interaction was significant for all the traits assessed. Most of the new genotypes had low interaction effects with locations for bunch yield (69.2%) and black Sigatoka (92.3%). The most stable genotypes for bunch yield were NABIO815, NABIO1117, NABIO216 and NABIO306 whereas for black Sigatoka resistance, were NABIO1011, NABIO815, NABIO1009 and NABIO216. Using the GSI that defines the most desirable genotypes as those that combine high agronomic performance and stability across environments, four genotypes (NABIO306, NABIO1011, NABIO808 and NABIO1009) were selected. These genotypes, in addition to their high performance for agronomic traits and stability, had soft and yellow fruit pulp on cooking, and will be advanced on farm for further evaluatio

Breeding banana (Musa spp.) for drought tolerance: A review

Drought is a major abiotic stress affecting banana production worldwide, leading to yield losses of up to 65%. Consequently, numerous efforts to understand and mitigate drought effects that include developing tolerant crop varieties are ongoing in several banana breeding programmes. The breeding efforts, however, have been greatly slowed down by inherent banana problems (polyploidy and male or female sterility) and complexity of drought tolerance (reportedly controlled by several genes). This review summarizes the pertinent research findings on water requirements of banana for its proper growth and productivity, symptoms of drought‐sensitive varieties and field management strategies to cope with drought stress. The coping strategies deployed by resistant cultivars include high assimilation rates and water retention capacity as well as minor losses in leaf area and gaseous exchange. Reduced bunch weight, leaf chlorosis, wilting and strangled birth are underlined to be directly associated with drought susceptibility. Integration of conventional, molecular breeding and biotechnological tools as well as exploitation of the existing banana genetic diversity presents a huge opportunity for successful banana improvement

Bioengineered potato: Resistance to late blight disease and higher crop yields. Research Brief 01.

Average potato yields in sub-Saharan Africa are four times lower than those in industrialized nations, mostly due to the effects of diseases, particularly late blight. This research demonstrates that the transfer from wild potato relatives of three resistance-conferring genes into a cultivated potato variety provides complete resistance to late blight for several seasons. Initial findings suggest this resistance will be long lasting. Cultivation of this late blight resistant potato would increase family farm incomes by 40% and ensure the supply of fungicide-free potatoes to consumers

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

Determination of hormonal combination for increased multiplication of tissue culture potato plantlets

Use of plant growth hormones either singly or in combination is vital for rapid multiplication of virus-free in-vitro potato (Solanum tuberosum L. ) plantlets for the production of clean seed potato. This study was carried out at Kachwekano Zonal Agricultural Research and Development Institute, Kabale district in south-western Uganda to identify a suitable hormonal combination and optimum concentrations for production of a high number of In-vitro plantlets for three farmer-preferred varieties Kachpot-1, Kinigi, and Victoria. Eight hormonal combinations were formulated and tested using a completely randomized design with three replicates in the tissue culture laboratory. Ten shoot tips from in-vitro raised plantlets were excised and transferred to each of these hormonal combinations. The effect of hormonal combinations was variety dependant. N3 produced the highest mean number of nodes (6.42), buds (4.32) and tallest plantlets (7.38) for Kinigi. N2 produced the highest number of buds in Kachpot 1. N4 produced the tallest plantlets (7.19), highest mean number of buds (5.88) and nodes (7.66) for Victoria. Therefore, N3, N2 and N4 should be used for rapid In-vitro propagation of Kinigi, Kachpot 1 and Victoria respectively.Key words: In-vitro propagation, Solanum tuberosu

Socioeconomic assessment of pest management practices in Lwengo subcounty, Uganda

Proceedings of the workshop on Farmer-participatory testing of IPM options for sustainable banana production in Eastern Africa, Seeta, Uganda, 8-9 December 2003 8-9 December 2003

The performance of East African highland bananas released in farmers' fields and the need for their further improvement

East African highland bananas (AAA, EAHB) form over 80% of the banana cultivars in the Great Lakes region and are a source of food and income for over 40 million in the region. The production of these bananas has been constrained by pests, diseases, soil fertility decline and most recently climate change stresses. Farmers have been managing these problems using cultural practices. These are sometimes effective, such as for Xanthomonas wilt control, but can also be very demanding. For others, no cultural control practices exist, such as for instance for nematodes in established plantations. The banana research program of the National Agricultural Research Organisation (NARO) in Uganda therefore focuses on the improvement of bananas for pest/disease resistance and fruit quality through conventional and molecular breeding to sustain banana production. In collaboration with the International Institute for Tropical Agriculture (IITA), the NARO breeding program has developed and officially released a number of banana hybrids to the farming communities, including 'Kabana 6H' (syn. 'M9') and 'Kabana 7H' (syn. 'M2'). The released and promising hybrids have resistance to black leaf streak and tolerance to nematodes and weevils. Their overall consumer acceptability is not significantly different from that of the landrace local check. The recipient communities value the hybrids since they are being widely distributed through sales and giveaways in addition to recipient farmers expanding their plots. However, these hybrids are susceptible to Xanthomonas wilt, and are very tall and prone to wind damage. There is an opportunity to improve the hybrids for above-mentioned and other traits exploiting Musa's over 36,000 genes in the sequenced genome

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

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