T. L. Brandt

Biological control of post-harvest late blight of potatoes

Abstract Introduction of US-8 genotypes of Phytophthora infestans has coincided with an increase in severity of potato late blight in North America. As alternatives to chemical fungicides, 18 bacterial strains patented as biological control agents (BCA) of both sprouting and Fusarium dry rot were cultivated in three liquid media and screened in wounded potato bioassays for their ability to suppress late blight incited by P. infestans (US-8, mating type A2). Washed or unwashed stationary-phase bacteria were mixed with fungal zoospores to inoculate potato wounds with 5µL containing ∼108 bacterial CFU/mL and 2×104 zoospore count/mL. Disease suppressiveness was evaluated after tubers were stored a week at 15°C, 90% relative humidity. One-fifth of the 108 BCA treatments screened, reduced late blight by 25–60%, including among other strains Pseudomonas fluorescens S22:T:04 (showing most consistency), P22:Y:05, S11:P:12 and Enterobacter cloacae S11:T:07. Small-scale pilot testing of these four strains, alone and in combination, was conducted under conditions simulating a commercial application. Suspensions of 4×104 P. infestans sporangia/mL were sprayed at a rate of 1.6 mL followed by 0.8 mL of bacteria treatment at ∼5×109 CFU/mL per each of 90 unwounded potatoes. Three replicate boxes per treatment (30 tubers per box) were randomized in storage and maintained 4 weeks at 7.2°C, 95% relative humidity. All BCA treatments significantly reduced disease; and unwashed bacteria outperformed those washed free of culture broth. Disease suppression ranged from 35% up to 86% the first test year and from 35 to 91% the second year. Highest overall performance rankings significantly above the control were achieved by the following strains in culture broth: four-strain mix > P. fluorescens S22:T:04> P. fluorescens S11:P:12. Combined with previous demonstrations of dry rot and sprout suppression, the consistent late blight control by these strains and strain mixtures suggests the commercial feasibility of a single treatment for broad spectrum suppression of post-harvest potato diseases and sprouting.

CIPC residues on stored russet burbank potatoes : 1. Maximum label application

Residue concentrations of chlorpropham (CIPC) on stored Russet Burbank potatoes were evaluated after thermal aerosol treatment at maximum labeled rates. The aerosol was applied after the potatoes had been placed in the storage structure and the wound healing process was complete. Average residue concentrations four days after the initial application ranged from 6 to 8 mg/kg fresh tuber weight depending on the storage temperature and the application rates. A second aerosol treatment applied 90 days after the first treatment kept the residue concentrations above 5 mg/kg for the duration of the storage period. A direct spray application to the tubers at various times during the study raised the average CIPC concentration an additional 2 to 3 mg/kg. All CIPC residue concentrations measured on tubers in this study were below the EPA established (1996) tolerance of 30 mg/kg. Residue concentrations of CIPC were greater on potatoes near the bottom of the pile than near the top of the pile. These variations in CIPC residue concentrations (3–8 mg/kg between top and bottom of the bulk pile) are appropriate justification for the development of improved application methodology.CompendioConcentraciones residuales de cloroprofam (CIPC) en papas Russet Burbank almacenadas fueron evaluadas luego de recibir un tratamiento termal de aerosol en proporciones consideradas como máximas. El aerosol se aplicó después de que las papas fueron colocadas en la estructura de almacenamiento y el proceso de cicatrización de heridas estuvo completo. Cuatro días después de la aplicación inicial, las concentraciones residuales promedio fluctuaron de 6 a 8 mg/kg del peso del tubérculo fresco, dependiendo de la temperatura de almacenamiento y de las proporciones aplicadas. Un segundo tratamiento de aerosol efectuado 90 días después del primer tratamiento mantuvo las concentraciones residuales encima de los 5 mg/kg para la duratión del período de almacenamiento. Una aspersión directa sobre los tubérculos en diferentes momentos durante el experimento elevó la concentración promedio de CIPC entre 2 y 3 mg/kg más. Todas las concentraciones residuales que se midieron en los tubérculos durante este estudio se encontraron debajo de la tolerancia establecida por la EPA (1996) de 30 mg/kg. Las concentraciones residuales de CIPC fueron mayores en las papas que se encontraban próximas al fondo del montón que cerca de la rima. Estas variaciones en las concentraciones residuales (3–8 mg/kg entre la cima y la base del montón total) justifican el desarrollo de una metodología de aplicación mejorada.

Classic Russet: A Potato Cultivar with Excellent Fresh Market Characteristics and High Yields of U.S. No. 1 Tubers Suitable for Early Harvest or Full-Season Production

Classic Russet is a medium maturing potato cultivar with rapid tuber bulking making it suitable for early harvest, as well as full-season production. Classic Russet is notable for its attractive tubers with medium russet skin and excellent culinary characteristics. It resulted from a 1995 cross between Blazer Russet and Summit Russet and was released in 2009 by the USDA-ARS and the Agricultural Experiment Stations of Idaho, Oregon and Washington and is a product of the Northwest Potato Variety (Tri-State) Development Program. Classic Russet also shows potential as an early season processing cultivar, with fry color comparable to Russet Burbank and Ranger Russet. Classic Russet total yields were comparable to Russet Norkotah and Ranger Russet in early harvest trials and comparable to Ranger Russet and Russet Burbank in full season trials. When averaged across sites in early harvest or full season trials, U.S. No. 1 yields of Classic Russet were generally greater than those of Russet Norkotah, Ranger Russet, and Russet Burbank. Protein content for Classic Russet is relatively high, averaging 22% higher than Ranger Russet, 32% higher than Russet Burbank and 24% higher than Russet Norkotah. Specific gravity of Classic Russet in early harvest trials was comparable to Russet Norkotah but lower than Ranger Russet and was similar to Russet Burbank in full season trials. The incidence of hollow heart in Classic Russet is low, similar to that of Ranger Russet. It is less susceptible to blackspot bruise than Russet Burbank, Ranger Russet and Russet Norkotah but shatter bruise can be a concern if not matured properly prior to harvest. Classic Russet is moderately resistant to common scab and dry rot and is moderately susceptible to foliar and tuber infections of early blight and symptoms of corky ringspot. It is susceptible to Verticillium wilt, soft rot, foliar and tuber late blight, PLRV and PLRV net necrosis, and the common strain of potato virus Y (PVY°).ResumenClassic Russet es una variedad de papa de madurez media con llenado rápido de tubérculo, haciéndola deseable para cosecha temprana, así como para producción de ciclo completo. Classic Russet es notable por sus tubérculos atractivos con piel corchosa intermedia y de características culinarias excelentes. Fue el resultado de una cruza de 1995 entre Blazer Russet y Summit Russet y se liberó en el 2009 por el USDA-ARS y las estaciones agrícolas experimentales de Idaho, Oregon y Washington y es un producto del Programa de Desarrollo de Variedades de Papa del Noroeste (Tri-State). Classic Russet también presenta potencial de una variedad temprana para proceso, con el color del freído comparable a Russet Burbank y Ranger Russet. Los rendimientos totales de Classic Russet fueron comparables a los de Russet Norkotah y Ranger Russet en ensayos de cosecha temprana y comparable a Ranger Russet y Russet Burbank en ensayos de ciclo completo. Cuando se promedió transversalmente en los sitios de los ensayos de ciclos corto y completo, los rendimientos de U.S. No. 1 de Classic Russet fueron generalmente mayores que los de Russet Norkotah, Ranger Russet, y Russet Burbank. El contenido protéico de Classic Russet es relativamente alto, promediando 22% mayor que Ranger Russet, 32% más alto que Russet Burbank y 24% más que Russet Norkotah. La gravedad específica de Classic Russet en los ensayos de cosecha temprana fue comparable a la de Russet Norkotah pero más baja que Ranger Russet y similar a la de Russet Burbank en ensayos de temporada completa. La incidencia de corazón hueco en Classic Russet es baja, similar a la de Ranger Russet. Es menos susceptible al oscurecimiento por daño mecánico que Russet Burbank, Ranger Russet y Russet Norkotah, pero la desintegración por golpes puede ser de cuidado si no se ha madurado apropiadamente antes de la cosecha. Classic Russet es moderadamente resistente a la roña común y a la pudrición seca y es moderadamente susceptible a las infecciones foliares y de tubérculo de tizón temprano y a los síntomas de la mancha anular corchosa. Es susceptible al marchitamiento por Verticillium, a la pudrición blanda, al tizón tardío en el follaje y en el tubérculo, PLRV y a la necrosis neta por PLRV, y a la variante común de virus Y (PVY°).

Targhee Russet: A High Yielding, Dual Purpose Potato Variety with High Protein and Vitamin C Content and Resistance to Tuber Soft Rot

Targhee Russet is a darker-skinned russet potato variety that has shown higher total and marketable yields than Russet Burbank in most yield trials conducted in the western United States. A major strength of Targhee Russet is resistance to tuber soft rot, and it also has moderate resistance to common scab, Verticillium wilt, and net necrosis associated with Potato leafroll virus. Targhee Russet also has exhibited resistance to hollow heart and blackspot bruise. Analyses have shown Targhee Russet to have significantly higher tuber protein and Vitamin C content than Russet Burbank and Ranger Russet. It produces lighter colored fries out of storage than standard processing varieties, indicating its high potential for the production of premium quality frozen and fresh-cut fries. High merit scores for fresh use are also indicative of it having excellent potential as a dual-purpose russet variety, suitable for both processing and fresh-pack operations.ResumenTarghee Russet es una variedad de papa de piel más oscura y corrugada que ha mostrado más rendimiento total y comercial que Russet Burbank en la mayoría de los ensayos de rendimiento desarrollados en el occidente de los Estados Unidos. Una fortaleza mayor de Targhee Russet es su resistencia a la pudrición blanda del tubérculo, y también tiene resistencia moderada a la roña común, a la marchitez por Verticillium y a la necrosis asociada con el virus del enrollamiento de la hoja de la papa. Targhee Russet también ha mostrado resistencia al corazón hueco y a la mancha oscura por daño mecánico. Los análisis también han mostrado que Targhee Russet tiene significativamente más proteína en el tubérculo y contenido de vitamina C que Russet Burbank y que Ranger Russet. Produce hojuelas más ligeramente pigmentadas al salir del almacén que las variedades estándar para proceso, lo que indica su alto potencial para la producción de papa frita congelada de calidad Premium y para corte en fresco. Las altas calificaciones para uso en fresco también son indicativas de tener excelente potencial como una variedad russet de doble propósito, apropiada tanto para operaciones de proceso como para paquetes en fresco.