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Bacterial wilt (BW) caused by the Ralstonia solanacearum species complex (RSSC) is a serious threat to potato production in Uganda. However, little is known about the extent of the disease and the type of the pathogen strains involved. A nationwide survey was conducted to study BW prevalence and incidence in potato, and potato tuber and stem samples of potential alternative hosts were collected for pathogen isolation. DNA was extracted from pure cultures for genetic diversity studies. The pathogen was phylotyped by multiplex PCR; then, a subset of isolates was typed at sequevar level. Isolates of the same sequevar were then haplotyped using multilocus tandem repeat sequence typing (TRST) schemes. BW prevalence and incidence in potato farms were 81.4 and 1.7%, respectively. Three RSSC phylotypes were identified, with the majority of the strains belonging to Phylotype II (80%) followed by Phylotype I (18.5%) and III (1.5%). Phylotype I strains belonged to Sequevar 31, and Phylotype II strains belonged to Sequevar 1. Potatoassociated Phylotype II Sequevar 1 strains were more diverse (27 TRST haplotypes) than nonpotato Phylotype I (5 TRST haplotypes). Mapping of TRST haplotypes revealed that three TRST haplotypes of Phylotype II Sequevar 1 strains play an important epidemiological role in BW of potato in Uganda being disseminated via latently infected seed. [ABSTRACT FROM AUTHOR]

Sclerotinia sclerotiorumcauses yield losses in a broad range of plant hosts, including carrot, for which a disease risk forecasting model has been previously developed. Detecting and quantifying airborne ascospores as a component of a sclerotinia rot of carrot (SRC) forecast model is currently accomplished using aSclerotiniasemi-selective medium (SSM) in the blue plate test (BPT) which has a threshold of 5 ascospores per plate. To improve the efficacy of applying the SRC forecast model, data from nine years of air sampling were analysed to determine the number of sampling sites needed to accurately estimate the concentration of airborne ascospores in a region (c. 40 km2) of intense carrot production. In six years, ascospore counts were correlated between sites in 20–100% of the possible pairwise comparisons among air sampling sites. The most consistent relationships among the sites were observed during periods of no detection or detection below the BPT threshold. In most years, periods when ascospore counts surpassed the BPT threshold were consistent among sites, but there were some fields and years when these periods were inconsistent. Based on the observations, one air sampling site should be sufficient to detect ascospores when counts are low, increasing to two or more sites during periods when ascospores are detected near or above threshold levels, and cropping and environmental conditions are conducive to disease. [ABSTRACT FROM PUBLISHER]

Limited availability and access to quality seed is a major challenge faced by the Kenyan potato subsector. Smallholder farmers cultivate the bulk of potato mainly planting seed from informal sources without any quality assurance which contributes to low yields. In recent years, private sector businesses have engaged in certified seed potato production with positive impact on the volumes available, relying on minitubers to multiply in the field over three to four generations. Rooted apical cuttings (RACs) provide a productive alternative starter material that can further boost the Kenyan seed systems. Stokman Rozen Kenya Ltd (SRK) is a private sector business that has embraced this technology in 2017. Also, small‐scale nurseries have recently started the commercial production of cuttings. They both sell RACs mainly to seed growers for further bulking, but ware potato farmers can also produce quality seed on‐farm for their own use from RACs when applying good agricultural practices. This paper examines the initial experiences of both SRK and small‐scale nurseries in the production and marketing of RACs as well as their performance during subsequent field multiplications. Producing and selling RACs offers a profitable business opportunity, especially when productivity and sales increase. Compared to other rapid multiplication technologies, RACs also allow to significantly increase the volumes of early generation seed produced. Key recommendations are to create awareness and to develop adequate marketing strategies to promote their uptake, and to ensure RACs are adequately multiplied into commercial seed to improve its availability to smallholder farmers in Kenya. Core Ideas: Rooted apical cuttings are produced from tissue culture plantlets and planted in the field to produce seed tubers.Rooted apical cuttings have the potential to significantly boost the production of quality seed potato in Kenya.Rooted apical cuttings are recognized under Kenya's seed regulations as the same as tissue culture (G0 seed).Key challenges are to create wider awareness of rooted apical cuttings and to develop market demand.Each (seed) potato producer should assess well in advance his/her management capacities of rooted apical cuttings. [ABSTRACT FROM AUTHOR]

In Uganda, potato is primarily grown as a cash crop and smallholder farmers sell majority of their produce immediately after harvest. Only a few farmers store ware potato for later sale using various traditional storage methods. Main reasons are farmers' immediate need for cash, the low volumes of potato harvested, fear of loss during storage due to pests and diseases, and a lack of adequate storage facilities. In order to exploit the seasonal market price fluctuations and increase the economic return of potato farming, improved individual and collective ambient ware potato storage units were introduced. Unlike traditional storage facilities that maintain the marketability of stored potato up to five weeks only, improved ambient stores can maintain their marketability up to nine weeks. This article uses cost-benefit analysis methods to compare the economic performance of improved ambient stores with traditional storage facilities. Results indicate that few of the traditional and improved collective storage units generated profit, an aspect that was attributed to management challenges. The improved individual stores performed overall well, generating higher profit margins than improved collective stores. Improved individual stores had an average payback period of three to four years that could even be reduced to less than one year if used at full capacity. Due to their characteristics, improved individual ambient ware potato stores thus seem to be particularly suitable to substantially increase the income of potato farming households. [ABSTRACT FROM AUTHOR]

Summary: This review of the literature on varietal change in sub‐Saharan Africa looks in detail at adoption of new varieties of bananas in Uganda, cassava in Nigeria, potato in Kenya, sweetpotato in Uganda and yams in Côte d'Ivoire. The review explored three hypotheses about drivers of varietal change. There was a strong confirmation for the hypothesis that insufficient priority given to consumer‐preferred traits by breeding programmes contributes to the limited uptake of modern varieties (MVs) and low varietal turnover. Lack of evidence meant the second hypothesis of insufficient attention to understanding and responding to gender differences in consumer preferences for quality and post‐harvest traits was unresolved. The evidence on the third hypothesis about the informal seed system contributing to slow uptake of MVs was mixed. In some cases, the informal system has contributed to rapid uptake of MVs, but often it appears to be a barrier with inconsistent varietal naming a major challenge. [ABSTRACT FROM AUTHOR]

Integrating crop species with different photosynthetic pathways has great potential to increase efficiency in the use of scarce resources. In order to tap the resource complementarity emanating from this mix, this study intercropped potato (Solanum tuberosum L.) with lima bean (Phaseolus lunatas L.) and dolichos (Lablab purpureous L.), and related soil temperature with radiation use efficiency and crop water productivity of rainfed potato in the upper midland (1552 m above sea level (masl), lower-highland (1854 masl) and upper-highland (2553 masl)) agro-ecological zones of Kenya. Leaf area index (LAI), light interception, soil temperature and soil water contents (SWC) were quantified at different stages of potato growth and related with the radiation use efficiency (RUE) and crop water productivity (CWP) of potato. Intercropping increased crop LAI by 26–57% relative to sole potato stands and significantly lowered the soil temperatures in the 0–30 cm depth by up to 7.3 °C. This caused an increase in SWC by up to 38%, thus increasing RUE by 56–78% and CWP by 45–67%. Intercropping potato with legumes is coupled with optimum root-zone soil temperature and soil water content, thus potentially exerting additive relations in radiation interception and subsequent conversion into crop biomass. [ABSTRACT FROM AUTHOR]

Continuous cultivation of potato (Solanum tuberosum L.) in monoculture systems represents the greatest factor deteriorating soil organic matter (SOM) in smallholder farms. With an aim to breaking this norm, a 2-year field trial intercropping potato with two legumes: lima bean (Phaseolus lunatus) and dolichos (Lablab purpureus), was conducted in the upper-midland (1552 meters above sea level (masl.)), lower-highland (1854 masl.) and upper-highland (2552 masl.) agro-ecologies of Kenya. Residues from each cropping system were quantified at the end of each season and incorporated back into the soil at start of the subsequent season. A combined physical and density fractionation was used to separate the soil in macro-aggregates (>250 μm), micro-aggregates (250–50 μm) and silt plus clay fractions (<50 μm), while SOM was partitioned into labile (density of 1.65 to 1.85 g cm−3) and stable (2.60 g cm−3) fractions. Microbial biomass contents were determined by chloroform fumigation while enzymatic activities were assessed by hydrolyses of fluorescein diacetate and dehydrogenase. Compared to sole potato, intercropping increased the contents of light fraction organic matter by 12–28%, dissolved organic matter by 7–21% and microbial biomass by 15–38%, thus stimulating enzyme activities. Trends in soil microbial respiration followed those of enzyme activity and were 20–34% higher in intercropping than in sole potato. Intercropping ensured high residue returns which got short-term residence within the macro-aggregates, thus ensuring steady supply of substrates to the soil microbes. These results affirm legume intercropping as a possible entry point to restoring the impoverished soil quality in smallholder potato farming systems. • Intercropping increased content of light fraction organic matter by 12–28%. • Intercropping ensured high residue returns which resided within the macroaggregates. • Intercropping potato with legumes increased microbial biomass content by 15–38%. • Intercropping potato with legumes increased microbial respiration and enzyme activity. [ABSTRACT FROM AUTHOR]

An accurate estimation of crop evapotranspiration and soil water balance under potato-legume intercropping is important for improving the crop water productivity of rainfed potato. This study quantified the evapotranspiration, yield, and soil water balance of potato (Solanum tuberosum L.) intercropped with lima bean (Phaseolus lunatus L.) or dolichos (Lablab purpureus L.) in comparison to the same crops under monocropping. The experiment was set up in three agroecological zones of Kenya: upper midland (with an altitude range of 1500–1653 m above sea level (masl)), lower highland (1892–1923 masl) and upper highland (2502–2594 masl). The dual crop coefficient approach was adopted with the SIMDualKc model to estimate crop evapotranspiration and compute the soil water balance. The dual crop coefficient partitions crop evapotranspiration into crop transpiration and soil evaporation by applying both soil evaporation and basal crop coefficient. The model was calibrated and validated using field data observed along four crop growth seasons. The basal crop coefficients, the ratios of soil evaporation to evapotranspiration, and that of transpiration to evapotranspiration were determined. The yields of different intercrops were converted into equivalent yield of potato based on price of the produce. Good agreement between the observed and simulated data for available soil water and crop evapotranspiration was found with modeling efficiency > 0.8. The residual mean square error was low and ranged from 0.01−0.08 m3 m-3 for available soil water and 0.03−0.09 mm d-1 for crop evapotranspiration. The transpiration to actual evapotranspiration ratio of potato-legume intercropping was 6−28% greater than that of the sole potato because legume intercrops fully covered the ground by mid-season, thus limiting the energy available for soil evaporation. Crop yields were significantly greater under intercropping as transpiration occurred near its potential rate, thus not limiting yields. These results support the dual crop coefficient method as an appropriate tool to estimate and accurately partition crop evapotranspiration under potato-legume intercropping. • The SIMDualKc simulated crop evapotranspiration and soil water balance with high accuracy. • Evapotranspiration was the main component of soil water balance across the treatments. • Soil water depletion was greater under sole potato relative to legume intercropping. • Transpiration occurred near its potential in intercrops, thus not limiting yields. [ABSTRACT FROM AUTHOR]