Seven organic and inorganic salts were tested for suppression of silver scurf, a postharvest disease of potato tubers caused by Helminthosporium solani. Potassium sorbate, calcium propionate, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, and ammonium bicarbonate were added to V8 agar at concentrations of 0.06–0.2 M. Radial growth of H. solani was significantly reduced (P < 0.05) by all salts at all concentrations. All salts except sodium bicarbonate and potassium bicarbonate were fungicidal at 0.2 M. Effects of postharvest salt treatments on disease severity and sporulation of H. solani on inoculated and naturally infected potato tubers were evaluated in separate experiments. Greenhouse-grown tubers were inoculated with H. solani spore suspensions (2 × 105 spores/ml), incubated for 5 days, dipped into 0.2 M solutions of each of the salts, and incubated in a moist chamber at 22–24°C for 6 weeks. All salt treatments prevented lesion development and sporulation of H. solani and differed significantly (P < 0.05) from the control. Postharvest applications of test compounds (0.2M) also significantly (P < 0.05) reduced disease severity and H. solani sporulation on naturally infected, field-grown tubers after 15 weeks of storage at 10°C. Salt treatments did not differ in disease or pathogen suppression. These relatively nontoxic organic and inorganic salts have potential as postharvest applications for control of silver scurf.

We report three N rate experiments conducted on a gravelly loam soil to assess the N status of potato (Solanum tuberosum L.) using a Minolta SPAD-502 chlorophyll meter. Highly significant linear and quadratic trends were obtained for the regression of N rate on marketable tuber yields and SPAD readings. SPAD readings were taken at four times during the growing season and decreased as plants aged. Based on regression analysis, the early season SPAD readings, associated with N rates giving maximum marketable tuber yields, ranged from 49 to 56 units depending on year, variety, and location. Potato variety significantly affected SPAD values in eight of the 12 situations where readings were obtained. Precision in interpretation was improved when the highest N rates were considered “reference strips” to standardize the SPAD readings across varieties and growing seasons. Our results suggest that field SPAD readings can readily identify severe N deficiency in potatoes, have the potential to identify situations where supplementary sidedressed N would not be necessary, but would be of limited value for identifying situations of marginal N deficiency unless reference strips are used.

Exclusive selection for yield raises, the harvest index of self-pollinated crops with little or no gain in total bipmass. In addition to selection for yield, it is suggested that efficient breeding for higher yield requires simultaneous selection for yield's three major, genetically controlled physiological components. The following are needed: (1) a superior rate of biomass accumulation. (2) a superior rate of actual yield accumulation in order to acquire a high harvest index, and (3) a time to harvest maturity that is neither shorter nor longer than the duration of the growing season. That duration is provided by the environment, which is the fourth major determinant of yield. Simultaneous selection is required because genetically established interconnections among the three major physiological components cause: (a) a correlation between the harvest index and days to maturity that is usually negative; (b) a correlation between the harvest index and total biomass that is often negative, and (c) a correlation between biomass and days to maturity that is usually positive. All three physiological components and the correlations among them can be quantified by yield system analysis (YSA) of yield trials. An additive main effects and multiplicative interaction (AMMI) statistical analysis can separate and quantify the genotype × environment interaction (G × E) effect on yield and on each physiological component that is caused by each genotype and by the different environment of each yield trial. The use of yield trials to select parents which have the highest rates of accumulation of both biomass and yield, in addition to selecting for the G × E that is specifically adapted to the site can accelerate advance toward the highest potential yield at each geographical site. Higher yield for many sites will raise average regional yield. Higher yield for multiple regions and continents will raise average yield on a world-wide basis. Genetic and physiological bases for lack of indirect selection for biomass from exclusive selection for yield are explained.

Understanding what farmers need in potato varieties and assessing available genetic resources at the farmer and district levels is important for the conservation and improvement of potato in Ethiopia. A survey was conducted in six major potato growing districts representing different agroecologies, cropping systems, market outlets, and levels of new variety adoption. Seventy to ninety percent of the farmers surveyed reported growing two or more potato varieties; some farmers reported growing up to five. The greatest diversity at the district level (up to 10 potato varieties) was recorded at Gumer & Geta where there is better access to new varieties while the lowest diversity was reported in districts with low access to new cultivars. The distribution of varieties differed among agro-ecologies as did the traits that farmers were most concerned with, such as drought tolerance, late blight resistance, yield potential, marketability, food value, storage quality, adaptation to low soil fertility, time to maturity and suitability for multiple harvesting. Farmers' decision-making processes and external factors that influence potato variety diversity were also documented. The registration of predominant local varieties and use of these local varieties as a starting point for the development of improved varieties are some of the recommendations for future potato breeding in Ethiopia. Moreover, it is necessary to consider variations in agro-ecologies, cropping systems and market outlets in the process of developing varieties suitable for farmers' and consumers' real needs.Resumen El entendimiento de lo que los agricultores necesitan en variedades de papa y el análisis de las fuentes genéticas disponibles a nivel del productor y del distrito, es importante para la conservación y el mejoramiento de la papa en Etiopía. Se desarrolló una encuesta en seis distritos importantes en la producción de papa, que representaban diferentes agroecologías, sistemas de cultivo, puntos de venta y los niveles de adopción de nuevas variedades. Del 70 al 90 % de los agricultores encuestados reportaron que sembraban dos o más variedades de papa, algunos hasta cinco. La mayor diversidad a nivel de distrito (hasta 10 variedades) se registró en Gumer y Geta, donde hay un mejor acceso a nuevas variedades, mientras que la más baja diversidad se reportó en distritos con poco acceso a variedades nuevas. La distribución de variedades difirió entre las agroecologias, así como los rasgos que más les importaban a los agricultores, tales como la tolerancia a la sequía, resistencia al tizón tardío, potencial de rendimiento, comercialización, valor alimenticio, calidad en almacenamiento, adaptación a baja fertilidad del suelo, tiempo a la madurez, y adaptabilidad a cosecha múltiple. También se documentaron los procesos en la toma de decisiones de los agricultores y los factores externos que influencian la diversidad de variedades de papa. El registro de las variedades predominantes locales, y el uso de estas variedades locales como un punto de partida para e...

A substantial number of farmers in northwest Ethiopia grow potato in the dry season (BBelmehr^, March to August) when rainfall is not dependable for the growth of the crop, resulting in lower yield. Ethiopian Agricultural Research Institutes have tried to change the situation by releasing new late blight tolerant varieties that potentially could allow for production of the crop in the rainy season (BMeher^, May to October). Despite these efforts, the majority of the farmers still grow potato in the Belmehr season using older, local varieties. Cognizant of this fact, this study aimed to characterize the major potato production problems in the two seasons, to identify the traits that farmers consider most important when selecting potato varieties, and to assess the performance of widely grown local as well as newly developed varieties. The study was conducted at sites representing two major agroecological zones in northwest Ethiopia and during both production seasons using 12 varieties (9 local and 3 new) with a 'participatory variety selection' approach. During the Belmehr season, erratic rainfall resulted in low yield and lower average tuber weight. By contrast, in the Meher season, late blight, desiccating wind and severe precipitation, including hail, limited production. These factors were important in both agroecological zones, with varying degrees of importance. Twenty-three traits were found to influence the varieties that farmers selected, with the degree of importance of each trait differing between agroecological zones and gender groups. Some local varieties yielded as well as new varieties in both seasons. Overall, we found participatory variety selection to be an effective approach for identifying factors important for the adoption of potato varieties, including factors that may not be addressed in conventional potato breeding programs.Resumen Un número substancial de agricultores en el noroeste de Etiopía cultivan papa en la época seca (BBelmehr^, marzo a agosto) cuando no se depende de la lluvia para el crecimiento del cultivo, lo que resulta en rendimiento más bajo. Los Institutos de Investigación Agrícola de Etiopía han intentado cambiar la situación mediante la liberación de nuevas variedades tolerantes al tizón tardío que pudieran permitir potencialmente la producción del cultivo en la época de lluvias (BMeher^, mayo a octubre). A pesar de estos esfuerzos, la mayoría de los agricultores aún cultivan papa en la temporada Belmehr usando variedades más viejas, locales. En conocimiento de este hecho, este estudio tuvo como propósito la caracterización de los principales problemas en la producción de papa en las dos épocas, para identificar los rasgos que los productores consideren como los más importantes cuando estén seleccionando variedades de papa, y analizar el comportamiento de variedades locales ampliamente cultivadas, así como las recientemente desarrolladas. Se condujo el estudio en sitios que representaran dos zonas agroecológicas mayores en el noroeste de Etiopía y durante ambas te...