F. E. Manzer

Effects of differential rates of nitrogen and phosphorus on early blight in potatoes

The Kennebec variety of potato was exposed toAlternana solani inoculum during the 1970 and 1971 seasons to determine the effects of differential rates of nitrogen and phosphorus on the incidence of early blight. Both high nitrogen and low phosphorus treatments significantly reduced the incidence of early blight and the combination of high nitrogen and low phosphorus consistently gave the lowest incidence of the disease during both years. The data suggest that this combination of nutrients may be related to early blight resistance in the plant by extending the period of meristematic activity permitting the plant to wall off infection. Yield data indicated that there was too great a yield difference between fertilization for optimum early blight control and fertilization for optimum yield. Therefore, in Maine, potatoes should be fertilized for optimum yield with a reasonable specific gravity, and early blight should be controlled by the application of fungicides and sanitation measures.

The latex agglutination test as a rapid serological assay forCorynebacterium sepedonicum

The latex agglutination test was evaluated for detection of the potato bacterial ring rot pathogen,Corynebacterium sepedonicum. The bacterium was detected in infected potato stems and tubers tested and in inoculated eggplant stems. Test reliability was confirmed using blind tests. A minimum of 106 bacterial cells/ml was requisite for observable agglutination. Nonspecific reactions were not observed from healthy extracts of plant tissues. Nonspecific reactions with other bacteria maintained in pure culture were eliminated by addition of bovine serum albumin to sensitized latex preparations.ResumenLa aglutinación de látex fue evaluada como prueba para la detección deCorynebacterium sepedonicum, agente etiológico de la podredumbre anular en la papa. Tallos y tubérculos de papas infectadas, así como tallos de berengena previamente inoculados se mostaron positivas a la prueba. Las muestras fueron previamente codificadas, para que el individuo que realizó la prueba desconociera su procedencia (prueba a ciegas). Para observar la aglutinación de látex fue necesario tener una cantidad mínima de 106 bacterias/ml. No se observaron reacciones inespecíficas contra extractos de tejidos vegetales sanos. Las reacciones inespecíficas contra cultivos puros, de otras bacterias fueron eliminadas al agregar albumina bovina a la solución amortiguadora con el látex sensibilizado.

Effects of potato virus S and two strains of potato virus X on yields of Russet Burbank, Kennebec, and Katahdin cultivars in Maine.

Yields of cultivars Russet Burbank, Kennebec, and Katahdin, as affected by potato virus S (PVS) alone and combined with either a mild or a moderate strain of potato virus X (PVX), were compared with yields from virus-free (VF) stocks in each of three years. Over all cultivars, yield weights from PVS-infected seed averaged about 3% lower than those of VF seed. When PVS was combined with mild PVX or moderate PVX, additional reductions of 2 and 5% respectively were obtained. Significant interactions between cultivar and virus were absent but a year by virus interaction was detected. An increase in numbers of large tubers and total tubers was found over all cultivars when mild PVX was present, though not significantly so for VF seed. This trend was evident in all cultivars and especially pronounced in Kennebec. Specific gravity differences, based on data from the 1975 test, were small. Mosaic mottle symptoms were observable only in plants infected with moderate PVX plus PVS. Plants from VF seed often appeared darker green than those carrying virus, and this was most noticeable near season’s end. It was more difficult to maintain seed free of PVS than of PVX. Results of this study and those of others are discussed relative to commercial seed improvement programs.ResumenLos rendimientos de los cultivares Russet Burbank, Kennebec y Katahdin infectados con el virus S (PVS) solamente y combinado tanto con una variante suave como con una moderada del virus X (PVX), fueron comparados con los rendimientos de los nucleos libres de virus (VF) durante 3 anos. Entre todos los cultivares el rendimiento en peso de la semilla infectada con PVS fue en promedio casi 3% más bajo que aquellas de semilla VF. Cuando PVS fue combinado con las variantes suave y moderada de PVX reducción adicional de 2 y 5% respectivamente, fueron obtenidas. No hubo interacción significativa entre cultivares y virus pero una interactión año por virus fue detectada. Un incremento en el número de tubérculos grandes y tubérculos totales rue encontrado para todos los cultivares cuando la variante suave de PVX estuvo presente aunque no significativamente en relación a la semilla VF. Esta tendencia fue evidente en todos los cultivares y especialmente pronunciada en Kennebec. En base a datos de la prueba de 1975 las diferencias en gravedad específica fueron pequeñas.Síntomas de Mosaico o moteado fueron observados solo en plantas infectadas con la variante moderada de PVX mas PVS. Plantas de semilla VF a menudo parecieron mas verde oscuro que aquellas infectadas con virus y esto fue más evidente hacia el final de la estación. Fue más difícil mantener semilla libre de PVS que de PVX. Los resultados de este estudio y los de otros se discuten en relación a los programas de mejoramiento de semilla comercial.

Cultivar response to bacterial ring rot infection in Maine

An account of several years of testing cultivars for response to bacterial ring rot (BRR) infection is reported. Inoculum was prepared by grinding infected tuber tissue and adding distilled water to make a slurry. Seedpieces of cultivars to be tested were dipped in the slurry, planted and covered immediately in the field. Five hill plots were arranged in a RCB design with four replications and cultivars of known reaction to BRR were included as checks. Assessment of symptom expressions was begun when symptoms were first observed in any entry and repeated weekly for the remainder of the growing season. Results of tests on named cultivars and a few advanced, numbered selections are presented for the years 1983 through 1986.CompendioSe presenta un informe de varios años de pruebas con cultivares para observar su respuesta a la infección bacteriana de la pudrición en anillo (Corynebacterium sepedonicum). El inóculo fue preparado triturando tejidos de tubérculos infectados y agregando agua destilada para formar una suspensión. Pedazos de tubérculos-semillas de los cultivares tivares a probarse se sumergieron en la suspensión, se sembraron y se taparon inmediatamente en el campo. Parcelas de cinco hoyos fueron dispuestas en bloques completos al azar con cuatro repeticiones, incluyendo como testigos a los cultivares de reacción conocida a la pudrición en anillo. La determinación de los síntomas se inició cuando éstos fueron observados por primera vez en cualquiera de las entradas y se repitió semanalmente en todo el resto de la temporada. Se dan los resultados de las pruebas sobre los cultivares nominados, y unas cuantas selecciones avanzadas numeradas, para los años 1983 a 1986.

FACTORS AFFECTING INFECTION, DISEASE DEVELOPMENT, AND SYMPTOM EXPRESSION OF BACTERIAL RING ROT

ConclusionsIt is clear from the foregoing that, although much is known about BRR, much more work needs to be done. While laboratory detection methods have improved significantly in recent years, it still remains for the seed inspector to find the infected plants in the field. This situation is not likely to change in the near future, and therefore, all of the factors affecting symptom expression must be known. Any procedure that could appreciably enhance the development of BRR symptoms would be of immeasurable value.

Effect of physiological maturity and storage temperature on emergence and yield of potatoes

SummaryA three-year study was conducted at Presque Isle, Maine to determine the effects of maturity and storage temperature on the yield and emergence of Katahdin seed potatoes. Virus X, place-effect, and variations in cultural practices were not confounding factors in these studies.Variations in maturity of the seed stocks compared did not show any significant differences in plant emergence or yielding ability of progeny produced. When the variables of virus X, place-effect, storage temperature, and growing practices were eliminated as confounding factors, there was no effect on productiveness of progeny produced from seed stocks varying in maturity.Storage temperatures affected emergence rate of seed potatoes and their yielding ability. From the results of this study, seed stored at 38F was more productive than seed stored at 32F or 45F.ResumenEn Presque Isle, Maine, se llevó a cabo un estudio de tres años para determinar los efectos causados por temperaturas de almacenaje y madurez en el rendimiento y emergencia de semillas de papa Katahdin. Virus x, efecto de colocación, y diferencias en practicas de cultivo fueron factores que no interfirieron con el estudio.Con variaciones en la madurez de las semillas comparadas, no se observó ninguna diferencia significativa en la emergencia de las plantas o en la capacidad de rendimiento de la progenie producida. Cuando las variantes de virus x, efecto de colocación, temperatura de almacenaje, y prácticas de cultivo fueron eliminadas como factores interfirientes, la madurez de la semilla tampoco afectó la productividad de la progenia producida.La habilidad de rendimiento y la emergencia inicial de las semillas de papa fueron afectadas por las temperaturas de almacenaje. De los resultados obtenidos en este estudio, las semillas almacenadas a 38F fueron más productivas que las almacenadas a 32F o a 45F.

Effect of time of inoculation with potato leafroll virus on development of net necrosis and stem-end browning in potato tubers

The Green Mountain cultivar was used in field tests to determine the effects of inoculating potato plants at various times with the potato leafroll virus (PLRV) on development of internal necrosis of tuber tissue. Viruliferous apterae of the green peach aphid,Myzus persicae (Sulz.), were placed on each stem in all hills to be inoculated in each 3.0 m single-row plot. Planting and inoculation dates were varied in all field experiments and, in one, several vine-killing dates were also included. All harvested tubers were stored for approximately four months at 10°C to enhance development of internal necrosis prior to examination. Similar but smaller greenhouse studies involving both apterous and alate green peach aphids were also conducted using Green Mountain, Irish Cobbler, and Russet Burbank cultivars. All results showed that as inoculation was delayed relative to plant development, more net necrosis (NN) occurred. Conversely, when plants were inoculated early, stem-end browning (SEB) rather than NN predominated. A high percentage of naturally occurring SEB tubers (cv. Russet Burbank) were found by ELISA to contain PLRV. Plants produced by these tubers only rarely developed leafroll symptoms. These findings suggest a previously unsuspected causal relationship between SEB and PLRV. Implications of this apparent relationship on the epidemiology of potato leafroll in Maine are discussed.ResumenLa variedad de papa Green Mountain fué usada en los experimentos para demostrar los efectos de la inoculación, en diferentes fechas, del virus enrollador de la hoja de la papa (PLRV) sobre el desarrollo de necrosis interna en tejido del tubérculo. Contaminados áfidos apteros del durazno verde,Myzus persicae (Sulz.), fueron colcocados sobre el tallo que iba a ser inoculado in cada una de las parceles de 3.0 metros. Las fechas de plantación e inoculación fueron cambiadas en todas los experimentos y en uno, las fechas de varias vine-killing fueron también incluidas. Todos los tubérculos cosechados fueron almacenados por aproximadamente cuatro meses a una temperatura de 10°C para acrecentar el desarrollo de la necrosis interna antes de ser examinado. Estudios similares pero en escala más pegueña en invernaderos, fueron hechos involucrando áfidos del durazno verde, con alas y sin alas, en estos experimentos fueron usadas las variedades de papa Green Mountain, Irish Cobbler y Russet Burbank. Todos los resultados demostraron que cuando la inoculación fué retardada en relación al desarrollo de la planta, más necrosis en red apareció (NN). Reciprocamente, cuando las plantas fueron tempranamente inoculadas, “stem-end browning” (SEB) predominó en vez de la necrosis en red (NN). Usando la téchnica ELISA se encontró, que un alto porcentaje de tubérculos que tenían SEB natural (sin inoculación) cv. Russet Burbank, contenían PLRV. Plantas preducidas por estos tubérculos raramente desarrollan sintomas de hojas enrolladas. Estos resultados sugieren una relación entre SEB y PLRV no pospechada anteriormente. Las implicaciones de esta relación aparente, en la epidemiología de la hoja enrollada de la papa, en Maine, son discutidas.

Reevaluation ofSolanum species accessions showing resistance to bacterial ring rot

One hundred and fifty-six plant accessions, including susceptible checks, from the IR-1 collection were evaluated for resistance/immunity to bacterial ring rot (BRR). Each accession selected had been previously rated as highly resistant to BRR based on symptom expression but, in our tests, 57 of them yielded no plants which failed to produce symptoms. However, the remaining 99, represented by a total of 2589 inoculated plants, yielded 1000 plants which failed to produce BRR symptoms after eight weeks. Immunofluorescent antibody stain testing showed that 679 of the symptomless plants supported detectable numbers ofCorynebacterium sepedonicum cells. Comparison of root-inoculated and tuber-inoculated accessions showed that root-inoculations yielded significantly fewer symptomless and bacterial cell-free plants. No significant differences were found in BRR reactions of fiveSolanum spp. when inoculated with two different strains ofC. sepedonicum. Appreciable numbers of symptomless plants were obtained from inoculated progeny of crosses with resistant cultivars but none of those retested proved to be immune.CompendioCiento cincuenta y seis entradas de plantas, incluyendo controles susceptibles, de la colección IR-1 fueron evaluadas para resistencia/inmunidad a la pudrición anular bacteriana (BRR). Cada una de las entradas seleccionadas habían sido previamente calificadas como altamente resistentes a la BRR basándose en la expresión de síntomas, pero en las pruebas, 57 de ellas no dieron plantas que no mostraran síntomas. Sin embargo, las 99 restantes, representadas por un total de 2 589 plantas inoculadas, produjeron 1 000 plantas que no mostraron síntomas de la BRR después de ocho semanas. La prueba de tinción inmunofluorescente de los anticuerpos mostró que 679 de las plantas sin síntomas portaban numéros detectables de células deCorynebacterium sepedonicum. La comparación de entradas inoculadas en la raíz con aquellas inoculadas en los tubérculos mostro que las primeras presentaban un número significativamente menor de plantas sin síntomas y libres de células bacterianas. No se encontraron diferencias significativas en las reacciones a la BRR de cincoSolanum spp. cuando se les inoculó con dos variantes deC. sepedonicum. Se obtuvo un apreciable número de plantas sin síntomas en una progenie de cruzamientos con cultivares resistentes, pero ninguno de los que fueron nuevamente probados fueron encontrados inmunes.

Effect of time and date of inoculation, plant age, and temperature on translocation of potato leafroll virus into potato tubers

Movement of potato leafroll virus (PLRV) to tubers following placement of viruliferous aphids on foliage was studied on the medium-maturing cultivar, Katahdin and the late-maturing cultivar, Russet Burbank. Inoculation was begun on August 20 and continued at three-day intervals until mid-September. There was no trend of increasing or decreasing numbers of leafroll-infected tubers from early to late inoculation. Several variables were examined to determine their effects on the incidence of PLRV-infected tubers. Multiple regression analyses showed that inoculation date, maximum daily temperature, minimum daily temperature, plant age, and length of time from inoculation to harvest explained 38% of PLR incidence in tubers of cv. Katahdin. Length of time from inoculation to harvest and minimum daily temperature explained 40% of PLR incidence in tubers of the cv. Russet Burbank.

Bacterial ring rot disease development in resistant and susceptible cultivars

In two greenhouse tests, we compared cell populations ofCorynebacterium sepedonicum in inoculated cultivars which had failed to show symptoms in field inoculation tests against cultivars that produce well-defined symptoms. Both population studies showed that cell numbers as high as 1 × 109 colony-forming units per gm of fresh weight (cfu gm-1) were reached in some cultivars prior to symptom development. In one of these tests, conducted when day length averaged 14 1/2 hrs, some cultivars failed to show symptoms 11 wks after inoculation but were found to have cell populations as high as 3.2 × 108 cfu gm-1 7 wks after inoculation. In another study, root and seed piece inoculations were compared in susceptible and resistant cultivars and only minor differences in symptom expression due to mode of entry of the pathogen were found.