R. W. Goth

Occurrence of the A2 mating type ofPhytophthora infestans in potato fields in the United States and Canada

Ten isolates ofP. infestans collected from blighted potato fields in the U.S. and Canada during the years 1983–1989 were examined for mating type on lima bean, oatmeal, and rye grain media. Two of the ten isolates produced oospores in less than 15 days when cultured in the presence of known A1 mating types from the USA, Mexico, and Europe, indicating they are A2 mating types. When the two A2 isolates (one from Pennsylvania and one from Vancouver, B.C.) were cultured singly or with known A2 isolates, no oospores formed after 6 weeks of culture. Pathogenicity tests showed that both isolates produced typical late blight symptoms on potato foliage and stems, and there appeared to be no difference in virulence between these two A2 and the eight A1 isolates. Inoculations with a mixture of A1 + A2 sporangia also produced oospores in host tissues. This is the first report of the presence of the A2 mating type ofP. infestans in the U.S. and Canada.CompendioDiez aislamientos deP. infestans obtenidos de campos de papa infectados en los EE.UU. y el Canadá durante los años 1983–1989, fueron examinados para determinar el tipo presente en el apareamiento sobre medios de habas, avena y granos de arroz. Dos de los diez aislamientos produjeron oosporas en menos de 15 días cuando se les cultivó en presencia de los ya conocidos tipos A1 de apareamiento de los EE.UU., México y Europa, indicando que ellos son tipos de apareamiento A2. Cuando los dos aislamientos A2 (uno de Pennsylvania y uno de Vancouver, B.C.) fueron cultivados independientemente o con aislamientos A2, no se formaron oosporas después de seis semanas de cultivo. Las pruebas de patogenicidad mostraron que ambos aislamientos producían síntomas típicos de tizón tardío sobre el follaje y tallos y pareció no existir diferencias en virulencia entre estos dos A2 y los ocho aislamientos A1. Inoculaciones con una mezcla de esporangios A1 + A2 produjeron también oosporas en los tejidos del hospedante. Este es el primer informe de la presencia del tipo A2 de apareamiento deP. infestans en los EE.UU y el Canadá.

Generalized plant defense: effects on multiple species

SummaryTwo species of lepidopteran herbivores, Manduca sexta (Sphingidae) and Trichoplusia ni (Noctuidae), were reared on synthetic diet containing either the alkaloid nicotine or the flavonoid rutin. Survival and pupal weight of the specialist M. sexta did not differ when larvae were reared on diet containing nicotine or rutin. In contrast, the generalist T. ni did not survive on diet containing 0.125% nicotine or greater, whereas larvae survived on all concentrations of rutin. These data demonstrate that the alkaloid nicotine is inhibitory toward generalist, but not specialist herbivores, whereas the flavonoid rutin has no effect on specialist herbivores and limited effects on generalist herbivores. Five species of Pseudomonas bacterial pathogens: P. syringae, P. syringae pv. angulata, P. syringae pv. tabaci, P. fluorescens, and P. solanacearum were grown on nutrient agar containing nicotine or rutin at concentrations ranging from 0.0 to 1.0% wet weight in 0.1% intervals. No species of Pseudomonas grew at concentrations greater than 0.5% nicotine when 106 colony forming units (cfu) were used, but growth occurred at all concentrations of rutin when 102 cfu were used. These data indicate that nicotine was inhibitory to growth of both herbivores and pathogens, suggesting that certain plant secondary chemicals with high toxicity are of a generalized nature and affect multiple species. Differences in the sensitivity of organisms to allelochemicals such as generalist or specialist can make it appear that specific allelochemicals affect specific organisms, when in fact it is the tolerance of the organism to the plant chemical that is responsible. In four separate studies, the growth of M. sexta, T. ni and Helicoverpa zea was significantly lower on plants inoculated with P. solanacearum. Alteration in leaf quality by P. solanacearum was due to either reductions in leaf nutrients or increases in allelochemicals. We speculate that localized or systemic induction by both herbivores and pathogens can cause changes in leaf quality, effecting each others subsequent colonization. The generalized nature of plant secondary compounds and potential reciprocal effects on induction by both species suggests that herbivores and pathogens may affect plant quality through induction and diffuse interactions of disparate species can alter the community of organisms colonizing a plant.

A detached-leaf method to evaluate late blight resistance in potato and tomato

We developed a detached leaf method for evaluating potato (Solanum tuberosum L.) and tomato (Lycopersicon esculentum Mill.) germplasm for reactions toPhytophthora infestans, the causal organism of late blight. Primary leaves from the third to the sixth node of potato plants, and the fourth to sixth node of tomato plants were excised at the stem. Their petioles were inserted into 14 mm × 100 mm floral aqua tubes containing 9 ml of sterilized distilled water. The leaves in the aqua tubes were placed with abaxial sides down on galvanized metal hardware cloth (12.5 × 12.5 mm mesh). A 12.5 mm sensi-disc containing 50μl of 2 × 104 zoospores was placed in the centers of the terminal leaflet and the second leaflet pair of the potato leaf. A single disc was placed on the center of the tomato leaf. The supporting hardware cloth was placed 2.5 cm above distilled water (2.5 cm deep) in 31 cm × 17 cm × 8 cm clear plastic boxes with tight fitting lids. Leaves on intact tomato and potato plants were inoculated in a similar manner and placed in a mist chamber. Lesion growth was determined 4, 5, and 6 days following inoculation. There were no significant differences in reactions to isolates ofP. infestans on detached and intact leaves of potato cultivars Green Mountain and Kennebec and the tomato cultivar Bonnie Best.

An efficient technique for prolonged storage ofPhytophthora infestans

A decoction containing ‘Golden Bantam’ sweet corn is a suitable medium fqr prolonged maintance of the late blight organismPhytophthora infestons. Using this procedure, cultures of P.infestons were maintained up to 12 months without transferring. These isolates exhibited no variation in virulence or race.ResumenUn extracto conteniendo maiz dulce “Golden Bantam” es un medio adecuado para mantener en forma prolongadaPhytophthora infestons organismo causante del tizón tardío. Usando este procedimiento, cultivos deP. infestons fueron mantenidos hasta 12 meses sin realizar tranferencias. Estos aislamientos no exhibieron variación en virulencia o raza.

The correlation of yield and specific gravity in the USDA potato breeding program

Every year potato (Solarium tuberosum L.) clones which remain in the USDA potato breeding program after six or more years of selection are entered into yield trials in Maine. Specific gravity and yield data were analyzed for six years (1972, 1975, 1978, 1981, 1984, and 1987) to determine the relationship between specific gravity and yield for populations of white and russet potatoes. In these trials, marketable yields of white-skinned potatoes were significantly greater than those of russet potatoes. Average specific gravity was significantly greater in the white than in the russet potatoes in three of the six years. A slight, but usually not significant, negative correlation of marketable yield with specific gravity was found for russet potatoes. A significant negative correlation of marketable yield with specific gravity was found in three of the six years for white potatoes. Regression analyses of marketable yield on specific gravity showed a great dispersion of values. Since only one or two advanced lines are potential variety releases, the present breeding approach is sufficient to continue to release potato varieties of acceptable yield and specific gravity.CompendioCada año, los clones de papa (Solarium tuberosum L.) que permanecen en el programa de mejoramiento de papa después de seis o más años de selectión son incorporados en ensayos de rendimiento en Maine. Los datos sobre la gravedad específica y rendimiento fueron analizados por seis años (1972, 1975, 1978, 1981, 1984 y 1987) para determinar la relatión existente entre la gravedad específica y el rendimiento para poblaciones de papa de piel blanca y piel roja. En estos ensayos, los rendimientos comerciables de la papa de piel blanca fueron significativamente mayores que aquellos de la papa roja. En tres de los seis afios la gravedad específica promedio fue significativamente mayor en la papa blanca que en la papa roja. Una pequefñia, pero generalmente no significativa correlatión negativa de rendimiento comerciable con la gravedad específica fue encontrada para la papa roja. En tres de los seis años se encontró una correlation negativa significativa del rendimiento comerciable con la gravedad específica para la papa blanca. El análisis de regresión del rendimiento comerciable sobre la gravedad específica mostró una gran dispersión de valores. Desde que solo una o dos líneas avanzadas son variedades potenciales a liberarse, el presente enfoque de mejoramiento es suficiente para continuar liberando variedades de papa de rendimiento y gravedad específica aceptables.

Russette: A Russet-skin potato variety, combining high quality, high yields, and adaptation to the Northeastern states and Florida

Russette is a new, late maturing, russet potato variety adapted primarily for the northeastern United States and northern Florida. Tubers are oval to oblong, smooth with a medium-russet skin, and shallow eyes. Its specific gravity is similar to those of BelRus and Russet Burbank in areas of adaptation. Glycoalkaloid content is about 11 mg/100 g fresh weight. Baking quality is excellent, flesh is white, and best color of french fries is obtained from tubers stored at or above 13°C (55°F). Its long rest period makes it amenable to storage at a relatively high temperature before a chemical sprout inhibitor is needed. Russette is immune to virus A and leaf roll-induced tuber net necrosis; highly resistant to Verticillium wilt, tuber pinkeye, and tuber heat necrosis; and has good tolerance to scab, early blight, and Rhizoctonia infection of sprouts, stolon, and roots. Losses to rots and shrinkage in storage have been minimal. Russette is not resistant to viruses X, S, Y, and leaf roll and bacterial ring rot. Russette emerges to a stand about 10 days later than most varieties, however, subsequent vine growth is rapid until tuberization begins. Large-sized tubers may develop hollow heart under a late-season regime of high nitrogen and high moisture. A 22–30 cm (9″- to -12″) seed-piece spacing and 220 kg/ha (180 pounds/a) of nitrogen are recommended for production on mineral soils.ResumenRussette es una nueva variedad de papa de maduración tardia y de superficie escamada que ha sido adaptada sobre todo para la parte nordeste de los EE.UU. y el norte de Florida. Los tubérculos son entre ovalados y oblongos, lisos, con una cáscara semi-escamada y ojos no profundos. Su gravedad específica es similar a las de BelRus y Russet Burbank en las áreas de adaptación. El contenido de glicoalcaloides es aproximadamente 11 mg/ 100 g de peso fresco. Tiene una calidad excelente para ser horneada, su pulpa es blanca. El mejor color de papa frita a la francesa se obtiene de los tubérculos almacenados en 13°C (55°F) o más. Su largo período de descanso la hace tolerante al almacenamiento en una temperatura relativamente alta antes que se necesite un inhibidor quimico de brotes. Russette es inmune al virus A de la papa y a la necrosis reticulada en el tubérculo inducida por el virus del enrollamiento de las hojas de la papa; es altamente resistente a la marchitez por Verticillium, al ojo rosado del tubérculo y a la necrosis interna por efecto de alta temperatura. Tiene una buena tolerancia a la sarna, al tizón tardio y a la infección en los brotes, estolones y raíces por Rhizoctoniasis. Las pérdidas debidas a pudriciones y encogimiento durante el almacenamiento han sido minimas. Russette no es resistente a los virus X, S, Y y del enrollamiento de las hojas de la papa, ni a la pudrición anular bacteriana. La emergencia completa de Russette ocurre aproximadamente 10 días más tarde que la de la mayoría de las variedades; sin embargo, el crecimiento foliar subsiquiente es rápido hasta que se inicie la tuberización. Los tubérculos de tamaño grande pueden desarrollar corazón vacío bajo un régimen de temporada tardía de alto nitrógeno y mucha humedad. Se recomienda un espaciado de los tubérculos-semillas de 22–30 cm (9″ a 12″) y 220 kg de nitrógeno/ha (180 libras/acre) para la producción en suelos de alto contenido mineral.

Relative resistance of potato cultivars to bacterial wilt

Fifty-one potato cultivars were evaluated for reaction to infection byPseudomonas solanacearum Sm. under high disease pressure in a field plot near Tifton, Georgia during the spring of 1978 and 1979. Plots were infested by clipping beds of thickly seeded tomato plants with a rotary mower contaminated with the wilt baterium in 1975, 1976, 1977 and 1978. The plants were incorporated into the soil following disease development. In addition to the use of infested soil, one stem on each potato plant was inoculated in late May by cutting with a knife blade dipped in a bacterial suspension. Most of the cultivars evaluated were highly susceptible to bacterial wilt. Ontario was the only cultivar highly resistant to the disease, with only 1% and 8% dead or dying plants in 1978 and 1979, respectively. Based on tuber infection, Ontario and Snowchip were the most resistant, with 9% and 14% infection, respectively, in 1978 and both 4% in 1979. Saco, Green Mountain and Sebago also showed some resistance.ResumenSe evaluaron para su reacción a infección porPseudomonas solanacearum Sm. 51 cultivares de papa bajo presión alta de la enfermedad en una parcela de campo cerca de Tifton, Georgia durante la primavera de 1978 y 1979. La infestación de la parcela fué realizada cegando camas de tomate densamente sembrado con una cegadora de césped rotativa contaminada con la bacteria en 1975, 1976, 1977 y 1978. Después del desarrollo de la enfermedad se incorporaron las plantas al suelo. Además de usar suelo infestado, se inoculó un tallo de cada planta de papa a fines de Mayo con una cuchilla sumergida en una suspensión de la bacteria. La mayoría de los cultivares fureon altamente susceptibles a la marchitez bacteriana. El único cultivar altamente resistente fué Ontario, con sólo 1% y 8% plantas muertas o moribundas en 1978 y 1979, respectivamente. En base a infección de tubérculos, Ontario y Snowchip fueron las mas resistentes con 9% y 14% de infección, respectivamente en 1978 y ambos con 4% en 1979. Los cultivares Saco, Green Mountain y Sebago también mostraron cierta resistencia.

Production of fumonisins B1, B2 and B3 byFusarium proliferatum Isolated from rye grains

Using the seed- plate technique, we have isolated a strain ofF. proliferatum from rye grains that produces 3 fumonisins, fumonisin B1 (FB1), FB2 and FB3 on inoculated rice and corn. Inoculated corn and rice were extracted with an aqueous methanol solution and fumonisin concentrations estimated using high performance liquid chromatography. Production of all 3 fumonisins (FB1, FB2 and FB3) was much higher on rice than corn; ranging from 3816, 1068 and 985 ppm to 1643, 350 and 162 ppm respectively. We conclude that all natural substrates whereF. proliferatum is present as a component of the mycoflora should be monitored for the presence of fumonisins.

NEMARUS: A GOLDEN NEMATODE RESISTANT, RUSSET-SKIN POTATO VARIETY

NemaRus, a russet-skinned potato variety resistant to race A of the golden nematode (Globodera rostochiensis), is medium-late in maturity (110 days) and adapted primarily to the Northeastern United States and Northern Florida. Tubers are oblong to long with moderately shallow eyes, and medium-to-heavy russeted skin. The specific gravity of NemaRus is similar to the popular Western U.S.A. fresh market russet variety Centennial Russet. Flesh is creamy white. Glycoalkaloid content of NemaRus averages about 12.0 mg/100 g fresh tissue. NemaRus is field-immune to the common strains of potato virus X and to tuber net necrosis caused by late current-season infection by the potato leaf roll virus. It is resistant to race O ofPhytophthora infestans to tuber rot caused byFusarium sambucinum & F. coeruleum; tolerant to scab, Verticillium wilt, and the pinkeye bacterial disease complex. It is also highly resistant to internal tuber net necrosis associated with high temperatures during tuber initiation and enlargement. NemaRus yielded 24% more U.S. No. 1 tubers than BelRus in Maine and 22% more than Centennial Russet in Northern Florida.CompendioNemaRus, una variedad de papa de piel rojiza resistente a la raza A del nematodo dorado (Globodera rostochiensis), es semi-tardía en maduración (110 días) y principalmente adaptada al noreste de los Estados Unidos y al norte de Florida. Los tubérculos son oblongos a alargados con ojos moderadamente superficiales y con una piel mediana a fuertemente rojiza. La gravedad específica de NemaRus es similar a la de la popular variedad rojiza para consumo fresco del oeste norteamericano, Centennial Russet. La pulpa es blanco-cremosa. El contenido de glico-alcaloides de NemaRus promedia aproximadamente 12,0 mg/100 g de tejido fresco. NemaRus posee inmunidad de campo a las razas comunes del virus X de la papa y a la necrosis en red del tubérculo causada por la infección con el virus del enrollamiento de la hoja al final de la temporada. Es resistente a la raza O dePhytophthora infestans y a la pudricíon del tubérculo causada porFusarium sambucinum + F. coerculeum; tolerante a la sarna común, a la marchitez porVerticillium y al complejo de la enfermedad bacteriana ojo rosado. Es también muy resistente a la necrosis en red del interior de los tubérculos asociada con las altas temperaturas durante el inicio de la tuberización y crecimiento de los tubérculos. NemaRus rindió 24% más de tubérculos U.S. No. 1 que BelRus en Maine y 22% más que Centennial Russet en el norte de Florida.

Coastal Chip: A chipping potato variety resistant to heat stress

Coastal Chip is a medium-late maturing potato chipping variety suitable for production in locations along the east coast of the United States where heat stress reduces internal quality of tubers. It yields as well as the variety Atlantic but is not as susceptible to heat necrosis. The specific gravity of Coastal Chip averages approximately 0.010 less than Atlantic at locations subject to heat stress. In the seed producing areas of Maine it’s specific gravity averages approximately 0.005 less than that of Atlantic. Tubers are round, netted-skinned, and have moderately deep stem and bud ends. Chips from Coastal Chip are slightly lighter in color than those produced by Atlantic. In mid-Atlantic states where heat stress adversely affects chip color Coastal Chip processes into chips for a slightly longer period of time after harvest than does Atlantic. Glycoalkaloid content of Coastal Chip averaged 7.9 mg/100 g fresh tissue. Sunburned (green) tubers of Coastal Chip develop purple streaks that remain following processing. Hills must be properly covered to reduce losses. Coastal Chip is resistant to race A of the golden nematode (Globodera rostochiensis) and potato virus A. It is tolerant to Verticillium wilt, more susceptible to common scab and Rhizoctonia than Atlantic and susceptible to potato virus X.CompendioCoastal Chip es una variedad de papa de maduracion semitardía, de buena calidad para fritura a la inglesa, apropiada para ser producida en lugares de la costa oriental de los Estados Unidos donde el estrés por calor reduce la calidad interna de los tubérculos. Rinde tanto como la variedad Atlantic, pero no es susceptible a la necrosis por calor. La gravedad específica de Coastal Chip promedia aproximadamente 0,010 menos que la de Atlantic en los lugares expuestos al estrés por calor. En las zonas productoras de semilla en Maine su gravedad específica promedia aproximadamente 0,005 menos que la de Atlantic. Sus tubérculos son redondos, con piel reticulada y tienen extremos basales y apicales moderadamente deprimidos. Las papas fritas de Coastal Chip son de color ligeramente más claro que aquellas producidas con Atlantic. En los estados centrales del Atlántico donde el estrés por calor afecta severamente el color de las papas fritas a la inglesa, el procesamiento de Coastal Chip, después de la cosecha, toma un tiempo ligeramente mayor de aquel registrado para Atlantic. El contenido de glicoalcaloides de Coastal Chip promedia 7,9 mg/100 g de tejido fresco. El verdeo de los tubérculos de Coastal Chip expuestos al sol desarrolla estrías de color purpura que permanecen aún después del procesamiento. Los montículos de papa deben ser cubiertos adecuadamente para reducir las pérdidas. Coastal Chip es resistente a la raza A del nematodo dorado (Gbbodera rostochiensis) y al virus A de la papa. Es tolerante a la marchitez porVerticillium, más susceptible a la sarna común y aRhizoctonia que Atlantic y susceptible al virus X de la papa.