Rust

Bean rust (Uromyces phaseoli), a common disease with worldwide distribution, is considered one of the most important bean production problems in the tropics. Prolonged periods of moisture and moderate temp. (17-27 degrees C) favor disease development. The infection process begins when a urediospore produces a germ tube, which develops an appressorium after physical contact with the edges of a stomata. The fungus may infect leaves and pods, and rarely stems and branches. For efficient disease control, cultural practices, crop rotation, elimination of harvest debris, biological control, the utilization of chemical products during the initial stages of plant development, and the use of resistant var. are recommended. A table is included on differential var. and infection rates used by different investigators to identify physiological races of this pathogen. Symptoms and damage caused by the disease are illustrated in color. (CIAT)La roya del frijol (Uromyces phaseoli) es una enfermedad a nivel mundial considerada como uno de los problemas mas importantes de la produccion de frijol en el tropico. Periodos prolongados de humedad y temp. moderadas (17-27 grados C) favorecen el desarrollo de la enfermedad. El proceso de infeccion empieza cuando una uredospora produce el tubo germinativo, el cual desarrolla un apresorio despues de establecer el contacto fisico con los bordes de un estoma. El hongo puede infectar hojas y vainas, y algunas veces los tallos y ramas. Para un buen control de la enfermedad se recomiendan practicas culturales (rotacion de cultivos, eliminacion de residuos de cosecha), control biologico, utilizacion de productos quimicos durante las etapas iniciales de desarrollo de la planta y el uso de var. resistentes. En forma de cuadro se incluyen las var. diferenciales y los grados de infeccion utilizados por los diferentes investigadores en la identificacion de las razas fisiologicas del patogeno. Se ilustran a color los sintomas y danos causados por la enfermedad. (CIAT

‘Weihing’ Great Northern Disease-resistant Dry Bean

Nebraska is the leading provider in the United States of Great Northern (GN) dry beans (Phaseolus vulgaris L.). Rust [(Uromyces appendiculatus (Pers.) Unger], common bacterial blight [(Xanthomonas campestris pv. phaseoli (Smith) Dye] (Xcp), and white mold [Sclerotinia sclerotiorum (Lib.) de Bary] diseases cause serious reductions in bean yield and seed quality in Nebraska. Halo blight (Pseudomonas syringae pv. syringae van Hall) has been observed in some years, but is not considered a major problem. Diseaseresistant cultivars should ensure improved seed yields and yield stability, and seed quality, and reduce pesticide application. Upright growth habit, combined with a porous plant canopy, can provide an avoidance mechanism to reduce white mold by improving air circulation, resulting in rapid drying of dew on the foliage (Deshpande et al., 1995). An adapted, highyielding Great Northern cultivar with resistance to strains of the above bacterial and rust pathogens prevailing in Nebraska is needed. An architectural avoidance of white mold is also required because there is no high level of physiological resistance in common beans to that pathogen. Presently, there is no Great Northern variety with this combination of desirable traits. The Great Northern ‘Weihing’ cultivar released in 1998 has the above combination of traits, and should reduce production costs. Origin ‘Weihing’ was derived from intercrosses of advanced lines developed from crosses of adapted and exotic dry bean parents possessing desired traits (Fig. 1). Pedigree selection was used to develop near-homozygous lines for intercrossing cycles. The advanced lines used for intercrossing possessed resistance to rust and levels of resistance to common bacterial blight and halo blight, as well as some avoidance of white mold disease because of upright and more open architecture. Multiple parents were used in the crosses. GN Nebr. #1 sel. 27 was a source of resistance to common blight and halo blight (Coyne and Schuster, 1974). ‘Tacaragua’ (black bean) (source: N.E. Valladares-Sanchez, Universidad de Oriente, Jusepin, Venezuela), ‘Aurora’ (small white), and Pinto 12689 (source: D. Wood, Colorado State Univ., Fort Collins, Colo.) provided resistance to rust. Pinto ‘UI 111’ and GN ‘1140’ contributed genes for earliness. GN ‘Emerson’ and ‘Bulgarian White’ possessed bright white seedcoats (Korban et al., 1981a), and were resistant to seedcoat cracking (Korban et al., 1981b). The upright and porous plant habit of ‘Tacaragua’, ‘Aurora’ (Anderson et al., 1974), and lines A222 and A51-1 [Centro Internacional de Agricultura Tropical (CIAT), Cali, Colombia] provided some architectural avoidance to the white mold pathogen. Fuller et al. (1984), using plastic-covered ground beds in greenhouse tests, also found that ‘Tacaragua’ had partial resistance to white mold