Robert W. Goth

Relative resistance of the potato cultivar krantz to common scab caused byStreptomyces scabies as determined by cluster analysis

Twenty potato breeding selections and five potato cultivars (25 clones) were evaluated in replicated field plots for their resistance to common scab caused byStreptomyces scabies, at Presque Isle, ME and Cranesville, WV in 1993. At harvest, all tubers in each plot were individually scored for the surface area covered (0=0% to 5>75%) and for lesion type (0=no lesions to 5=pitted lesions). The individual tuber scores for either surface area covered or lesion type for each plot were totaled and divided by five times the number of tubers to create an index of surface area covered (SAI) or lesion type (LI), respectively. Clonal mean SAI ranged from 0.05 to 0.96 in Maine and 0.21 to 0.89 in West Virginia. Clonal mean LI ranged from 0.06 to 1.0 in Maine and 0.48 to 1.0 in West Virginia. There were significant differences among clones for SAI and LI. Clones were clustered on mean SAI and LI in ME and WV. The clones clustered into four groups. The resistance of Krantz and two breeding selections, B0348-2 and B0339-1, was similar to Ontario.CompendioVeinte selecciones de mejoramiento de papa y cinco cultivares (25 clones) fueron evaluados, en 1993, en parcelas de campo con repeticiones, para su resistencia a la sarna común causada por Streptomyces scabies, en Presque Isle, ME y Cranesville, WV. Al momento de la cosecha, todos los tubérculos en cada parcela fueron calificados individualmente por el área de superficie cubierta (0=0 % a 5>75 %) y por el tipo de lesión (0=sin lesiones a 5=lesiones profundas). Las calificaciones individuates por tubérculo, tanto por área de superficie cubierta como por el tipo de lesiones, para cada parcela, fue totalizada y dividida por cinco veces el número de tubérculos, para crear un indice de área de superficie cubierta (SAI) o de tipo de lesión (LI), respectivamente. El promedio clonal del SAI varió de 0.05 a 0.96 en Maine, y de 0.21 a 0.89 en West Virginia. El promedio clonal del LI varió de 0.06 a 1.0 en Maine, y de 0.48 a 1.0 en West Virginia. Hubo diferencias significativas entre los clones, para SAI y LI. Los clones fueron agrupados de acuerdo al promedio de SAI y LI en ME y WV. Los clones se agruparon en cuatro grupos. La resistencia de Krantz y dos selecciones de mejoramiento, B0348-2 y B0339-1, fue similar a la de Ontario.

Evaluation and characterization of advanced potato breeding clones for resistance to scab by cluster analysis

A total of 17 potato breeding lines and 4 cultivars were evaluated in replicated field trials in Presque Isle, Maine, USA, during 1988-91 for their reaction to scab (Streptomyces scabies). All tubers were individually scored for type of lesion (0 = none to 5 = pitted scab) and surface area covered (0 = 0% to 12 = 100%). Computations were made for lesion index (LI), surface area index (SAI) and overall scab index (OSI). Analyses of variance of LI, SAI and OSI revealed significant differences among potato lines during 1989-91. Cluster analyses on the combination of LI and SAI were superior to clustering on OSI alone. Five clusters were defined in 1989-91. It is suggested that cluster analysis provides a means to quantitatively compare the scab reactions of new germ plasm with that of cultivars used as disease standards.

Relative susceptibility of potato varieties toStreptomyces scabiei andS. acidiscabies

In 2000 and 2004, 19 potato varieties were grown in separate plots inoculated with the scab pathogensStreptomyces scabiei andS. acidiscabies. Reaction of the varieties to these two species were highly correlated in both years, with no host variety-pathogen species interaction. These results are consistent with the central role of the bacterial toxin thaxtomin in scab development, and indicate that this and other mechanisms involved in pathogen infection and establishment are not expressed differentially with regard to variety. Likewise, there is no apparent differential response of the pathogens to those host factors determining the degrees of resistance and symptoms expressed in different varieties.

Characteristics and Distribution of Potato Latent Carlavirus (Red LaSoda Virus) in North America

A carlavirus (code name RLSV and subsequently named potato latent carlavirus, PotLV) with serological and biological characteristics different from those of potato M carlavirus (PVM) and potato S carlavirus (PVS) was detected in the potato (Solanum tuberosum) cultivar Red LaSoda by the Scottish Agricultural Science Agency in 1992. During a routine electron microscope testing of accessions in the Vancouver Collection of Virus-Free Potatoes growing in the California winter test in 1993, a filamentous rod-shaped virus similar to PVS and PVM was found in a Red LaSoda clone from Nebraska. The virus was isolated and purified. The monoclonal antibody, MAb 4E12, which is highly specific to the PotLV virus, was developed. From 1994 to 1998, the accessions in the Vancouver Collection of Virus-Free Potatoes were assayed by triple antibody sandwich enzyme-linked immunosorbent assay (TAS-ELISA) using the 4E12 MAb. Seven accessions tested from 1994 to 1996 were infected with PotLV. None of the 270 and 267 accessions in this collection tested positive for this virus in 1997 and 1998, respectively. In 1997 and 1998, the 137 accessions in the U.S. National Varietal Collection maintained at Presque Isle, Maine, were also assayed using the 4E12 MAb. The cultivars High Plains, Platte, and Red LaSoda were the only accessions that tested positive for PotLV. Nicotiana benthamiana, N. megalosiphon, and N. occidentalis are new systemic hosts for PotLV. TAS-ELISA with the 4E12 MAb is now part of the standardized test for PotLV in Canada.

Evaluation of the reliability of determining soft rot resistance in potatoes by the tuber slice method

Soft rot resistance in potato (Solanum tuberosum L.) tubers can be determined by inoculating tuber slices with soft rotErwinia species. Questions have been raised in the literature concerning the reliability of the tuber slice method. The objectives of this study were to 1) examine the statistical assumptions underlying the analysis of variance for different response variables as measures of soft rot resistance using the tuber slice method of evaluation; 2) estimate the sample sizes necessary to detect specified differences with power 0.83; and, 3) choose the “best” variable for measuring resistance to soft rot based on valid statistical analysis and minimal sample size. Slices from fifteen tubers from each of three cultivars (Atlantic, Norchip, Superior) were inoculated withErwinia carotovora subsp.atroseptica, E. carotovora subsp.carotovora orE. chrysanthemi and incubated at two different temperatures (20 C and 30 C) for 48 hrs. The test was conducted on two dates. Tuber samples were sliced and weighed prior to inoculation and after the macerated tissue was removed following a 48 hr incubation period. The maximum diameter of macerated tissue, actual weight loss, four measures of proportional weight loss, and various transformations of these variables were analyzed. The “best” response variables for measuring resistance to soft rot by the tuber slice method were the diameter of the macerated tissue and the square root transformation of one of the measures of proportional weight loss. No differences were found among the cultivars nor theErwinia subsp. for either of these response variables, and the cultivar ×Erwinia subsp., cultivar × temperature and cultivar ×Erwinia subsp. × temperature interactions were not significant. However, there were significant differences between the incubation temperatures, and theErwinia subsp. × temperature interaction was significant for both response variables. Estimates of sample sizes necessary to find a 20% difference in main effect and interaction effect means were calculated.ResumenSe puede determinar la resistencia a la pudrición blanda en tubérculos de papa (Solanum tuberosum L.) mediante la inoculación de rodajas de tubérculo con especies deErwinia causantes de esta enfermedad. Han surgido interrogantes en la literatura en cuanto a la confíabilidad de este método. Los objetivos de este estudio fueron: 1) examinar los supuestos estadísticos que subyacen el análisis de la variancia para las diferentes variables como medidas de la resistencia a la pudrición blanda empleando el método de evaluación en las rodajas del tubérculo de papa; 2) estimar los tamaños de muestras necesarios para detectar diferencias específicas con poder 0.83; y 3) escoger la variable “mejor” para medir la resistencia a la pudrición blanda basándose en los análisis estadísticos válidos y en el tamaño mínimo de la muestra. Las rodajas de quince tubérculos de cada uno de los tres cultivares analizados (Atlantic, Norchip, Superior) fueron inoculadas conErwinia carotovora subsp.atroseptica,E. carotovora subsp.carotovora o E. chrysanthemi e incubados a dos temperatures (20 C y 30 C) durante 48 horas en dos fechas diferentes. Los tubérculos fueron rebanados y pesados antes de la inoculación y luego de que el tejido macerado fuera extraído después de un período de incubación de 48 horas. Se analizaron el máximo diámetro del tejido macerado, la pérdida real de peso, las cuatro medidos de la pérdida proporcional de peso y diversas transformaciones de estas variables. Las “mejores” variables para la medición de la resistencia a la pudrición blanda mediante el método de rodajas de tubérculo fueron el diámetro del tejido macerado y la transformación de la raíz cuadrada de una de las medidas de la pérdida proporcional de peso. No se encontraron diferencias entre los cultivares o subespecies deErwinia para ninguna de estas variables y las interacciones de cultivar ×Erwinia subsp., cultivar × temperatura y cultivar ×Erwinia subsp. × temperatura no fueron significativas. Sin embargo, hubo diferencias significativas entre las temperaturas de incubación, y la interacciónErwinia subsp. × temperatura fue significativa para ambas variables. Se calcularon estimados de los tamaños de muestras necesarios para hallar un 20% de diferencia en el efecto principal y el medio del efecto de interacción.

Relationship of Verticillium wilt with pink-eye of potato in Maine

In 1988 and 1989, the effect of Verticillium wilt on the incidence and severity of pink-eye of potato was studied. Six cultivars and 12 advanced breeding lines (clones) of Solanum tuberosum with varying degrees of resistance to Verticillium wilt were selected. Entries were inoculated with either Verticillium albo-atrum, V. dahliae, or a combination of both species; the control was noninoculated. Significant differences in the severity of Verticillium wilt symptoms were found for different clones and pathogens, and there was a significant year-by-clone interaction. Veriticillium wilt symptoms were more severe in 1989 than in 1988. Pink-eye-infected tubers were found in all treatments, and the clones differed significantly in both incidence and severity of the disease. Significant positive correlations were found between the severity of Verticillium wilt with V. albo-atrum or the combination of species, and the incidence or severity of pink-eye. The incidence of pink-eye was enhanced by the presence of Verticillium, but the presence of Verticillium was not necessary for pink-eye to develop.

Verticillium wilt resistant germplasm: release of Russet clone B0169-56

Potato breeding selection B0169-56 is being released by the United States Department of Agriculture, Agricultural Research Service as germplasm that is highly resistant toVerticillium albo-atrum Reinke & Berthier andV. dahliae Kleb. In five years of field testing in the Verticillium wilt plot in Presque Isle, Maine, the level of resistance as measured by symptom severity is equal to that of Russette. In 1993, in plots inoculated with both species ofVerticillium, there was a 15,27 and 62% yield reduction for B0169-56, Russette, and Superior, respectively. After four years of evaluation in yield and processing trials in Presque Isle, Maine, B0169-56 has yielded and fried as well as Russet Burbank. Tubers are russet-skinned, oblong to long and cylindrical. Tubers of B0169-56 size early, a necessary quality for an eastern russet. It is both female and male fertile. This selection is currently undergoing further evaluation at multiple state locations for possible commercialization. Seed is available from the USDA/ARS, Beltsville, Maryland.

Evaluation of potato clones for severity of verticillium wilt, yield and specific gravity in Maine

In 1994 and 1995, the effect of Verticillium wilt, caused byVerticillium dahliae andV. albo-atrum, on tuber yields, number and weight of U.S. No. 1 and B size tubers, and specific gravity was studied in northern Maine, an area with a short growing season. Seven clones (four resistant and three susceptible) were evaluated in a split-plot design with three replications. Clones were the whole-plot factor, and seed pieces in sub-plots were either uninoculated or inoculated with 50 ml of 4 × 104 cfu/mlVerticillium spp. at planting. Individual plants were scored for Verticillium wilt symptoms before harvest on a 1= <3% wilt to 10= >97% wilt. Differences among clones for wilting and specific gravity were significant. The inoculation treatment had no effect on any of the tuber traits measured. However, there were significant clone x inoculation interactions for most tuber traits. Reductions in yield, weight and number of U.S. No. 1 potatoes, and specific gravity were greater in the Verticillium wilt susceptible clones than in the resistant clones. These results suggest that breeding clones with resistance toVerticillium spp. will reduce yield losses, while maintaining tuber size and specific gravity under disease pressure.

Maintenance and growth ofHelminthosporium solani

We have found that by using water agar as an isolation medium, V-8 juice agar as a growth substrate, and sterilized rye grains as a storage medium we can: 1) produce copious amounts ofHelminthosporium solani conidia that were successfully used as inoculum and: 2) the sterilized rye grains could be used to maintain viable cultures of the five isolates ofH. solani used in this study for 16 months. All of the isolates were pathogenic on tubers of the potato cultivars Katahdin and Superior.ResumenAislamientos deHelminthosporium solani, el organismo causal de la costra plateada de la papa, fueron mantenidos sin ser transferidos, en granos de centeno esterilizado. Cuando se colocaron granos de centeno infestados por el hongo en medios agar V-8 y en agar agua, se desarrollaron conidioforos grandes con conidia en la superficie de los granos y en la superficie del medio de cultivo adyacente al grano. El inóculo consistente de conidia producidas sobre los granos o sobre la superficie del medio se ha usado con éxito para inducir costra plateada de la papa en estudios de invernadero y de campo.

Abstracts 60th annual PAA meeting (Part II)

S 60th ANNUAL PAA MEETING (Part Il) The Inheritance o/Resistance to Heterodera pallida in Clones o[ Solanum tuberosum ssp. andigena. LANDEO, J., P.R. Rowe, and M. Mayer de Scurrah, International Potato Center; Lima, Peru. Eight clones of Solanum tuberosum ssp. andigena with resistance to Heterodera pallida populations collected from Otuzco (Northern Peru) and Cuzco (Southern Peru) were selected. Three clones were resistant to the Otuzco population; three to Cuzco; and two had apparent partial resistance to both populations. Five families representing various combinations of resistances were obtained. Progenies were tested against both nematode populations in 10 cm clay pots with nematode-infested soil. Three families segregated in a 1:1 ratio against the Otuzco population, while no family had any resistance to the .Cuzco population. The results suggest that a single dominant gene gave resistance to the Otuzco population. The Enigma o/ Triploid Potatoes: A Reappraisal. Jackson, M.T., ~P.R. ROWE, International Potato Center; Lima, Peru; and J.G. Hawkes, University of Birmingham; Birmingham, England. Solanum x chaucha Juz. et Buk. is a triploid, cultivated potato species found throughout the Andean region of Peru and Boliva. Its apparent abundance alongside tetraploid and diploid varieties in native cultivations has been taken as an indication of fairly free hybridization between the putative parents, yet in experimental 4x 2x crosses, the frequency of triploid formation was low. Although this species may represent up to 10% of the varieties collected in the Andes variability studies using morphological and chemotaxonomical data have shown that there are probably no more than 25 genotypes. Triploid formation is inhibited by the low frequency at which the cross occurs between the tetraploid and diploid gene pools, and the triploid block. The effectiveness of the triploid block varies among tetraploids, although it is never entirely absent. It is hardly surprising that there are so few triploid varieties when it is realized that from the millions of tetraploid seeds produced each year, relatively few seedlings survive to maturity. However, once triploids entered the population, man retained and increased a number of the superior clones using quality factors such as high dry-matter content and flavour among his selection criteria. The Reaction of Some Clones of Diploid Cultivated Potatoes to Infection by the Root-Knot Nematode, Meloidogyne incognita acrita. Jatala, P., H.A. MENDOZA, International Potato Center; Lima, Peru, and F.L. Haynes, North Carolina State University; Raleigh, North Carolina. Over 800 clones selected in Peru from S. phureja S. stenotomum populations developed in North Carolina were grown in a screenhouse in 396 AMERICAN POTATO JOURNAL (Vol. 53 La Molina. Three to five tubers each were planted in 10 cm clay pots containing sterilized soil and grown in a screenhouse with an average minimum maximum 19 28°C air temperature. One week later approximately 2 gm of comminuted Meloidogyne incognita acrita infected potato roots were added to the soil in each pot. Two months later root systems were carefully removed from the soil, washed and observed for galling and nematode reproduction. Relative severity of root infection as expressed by root galling and/or nematode reproduction was rated on a scale of zero to four. A score of one was used for no root galling and/or nematode reproduction and a score of four for very severe root-galling and /or a very high nematode reproduction. Roots of the clones with a rating of one (trace of galling and /o r nematode reproduction) and zero were considered as resistant. Most of the clones had a score of three indicating severe root galling and/or a high nematode reproduction. Seventeen clones had an average root galling score of 1.5 while 10 clones rated one. Only one clone had a rating of zero. Those clones with a rating of O, 1, and 1.5 will be evaluated further and used in the breeding program. Analysis oJ Tetraploid-Diploid Hybrids in Potatoes. Tai, G.C.C. and H. DEJONG, Agriculture Canada, Research Station; Fredericton, New Brunswick, Canada Several Group Tuberosum cultivars and breeding stocks were crossed as female parents with two Group Phureja-haploid Group Tuberosum hybrids. Progeny families of 4x-2x matings were evaluated under simulated commercial agricultural practices in 1974 and 1975. The range of the observed values for the 4x-2x hybrids exceeded the range of the 4x parents for nearly all measured traits. The mean for total yield of the 4x-2x hybrids was equal to (1974 experiment) or significantly higher (1975 experiment) than the mean of the 4x parents. In the 1975 experiment 17.8% of the 4x-2x hybrid plots produced a higher total yield than the highest yielding 4x parents. The 4x-2x hybrids exhibited a significantly lower mean than the 4x parents for marketable yield, tuber weight and specific gravity but transgressive segregants were found for these traits in both experiments. The heterosis and variability of the hybrids indicates that this breeding method is a potentially powerful tool in potato improvement. Effects oJ Potato Virus X and Potato Virus S on Netted Gem Potato. WRIGHT, N.S., Vancouver Research Station, Vancouver, British Columbia. Potato Virus X (PVX) and Potato Virus S (PVS) were transmitted singly and in combination to virus-free Netted Gem potato. Test materials were increased for two years before being planted in randomized blocks for comparisons. One strain of PVX was latent and another caused a mild mottle. The PVS was latent and so was the combination of latent PVX plus PVS. The viruses did not affect the number or specific gravity of the tubers. Neither latent virus reduced tuber size or yield when inocu1976) NEWS AND REVIEWS 397 lated singly but latent PVX plus PVS reduced the number of tubers with a minimum diameter of 5 cm and also reduced yield. The mottle PVX had similar effects. The reductions, which were significant at the 5% level, were 11-12% in total yield and 17-26% in marketable yield. Helminthosporium solani, Growth, Sporulation and Pathogenicity. GOTH, R.W., USDA, ARS, PGGI, Vegetable Laboratory, BARC-WEST, Beltsville, Maryland; S.A. Ostazeski, USDA, ARS, PGGI, Field Crops Laboratory, BARC-West; Beltsville, Maryland; and R.E. Webb, USDA, ARS, PGGI, Vegetable Laboratory, BARC-West; Beltsville, Maryland. We reported elsewhere on the use of dessicated rye grain cultures for H. solani inoculum production and stock culture maintenance. The medium was prepared by soaking overnight a volume of grain with an equal volume of water, followed by sterilization on two successive days. We have found that a similar medium using a fortified vermiculite substrate would permit culture maintenance and abundant sporulation; but, in addition, could also be used to evaluate potato tuber reactions to this organism. This medium was prepared by placing a volume of fine vermiculite in an equal volume of 1.8% V-8 juice followed by sterilization. H. solani grew well and sporulated abundantly on this medium. When used as inoculum, it has the advantage of readily adhering to the tuber surface, but can be easily washed off; it does not injure nor require injury of epidermal cells; it provided continuing sporulation; and, most important, it caused the development of typical silver scurf symptoms. Tubers from Leaf-Cuttings: A Tool for Potato Seed Certification and Breeding program. LAUER, FLORIAN I., University of Minnesota; St. Paul, Minnesota. The use of leaf-cuttings as a tool for rapid clonal increase was studied in 6 cultivars. Small tubers can be obtained directly from leaf-cuttings maintained for 7 weeks in sand-filled pots or benches. The tubers ranged in size up to la,4 inches (3 cm) in diameter. The number of leaf-cuttings ranged from 37 to 288, depending on size of mother plant. They averaged 115 cuttings. Almost all of the leaf-cuttings produce tubers. The procedure is fast and simple, and would provide for the rapid increase of selected stocks. Presence o[ Colletotrichum atramentarium in Idaho and Relation to Verticillium Wilt (Verticillium dahliae). DAVIS, J.R. and M.N. Howard, University of Idaho Research and Extension Center; Aberdeen, Idaho. Colletotrichum atramentarium (Berk. & Br.) Taub., causal organism of black dot, was first observed in Idaho during the summer of 1971. Since then, this fungus has been found throughout southern Idaho and recovery from green stems of potato (Solanum tuberosum L. Russet Burbank) has consistently been accompanied with Verticillium dahliae Kleb. recovery. Inoculation of potato with several Idaho isolates (C. atramentarium) pro398 AMERICAN POTATO JOURNAL (Vol. 53 duced symptoms of root rot, tuber necrosis, cortical sloughing, and yellowing of leaves. When inoculated in the presence of V. dahliae, results show that C. atramentarium has the potential to significantly contribute to Verticillium wilt severity. Inoculations with a mixture of V. dahliae (107 propagules/ml) and C. atramentarium (105 propagules/ml) significantly increased death of potato plants beyond that observed when either V. dahliae or C. atramen.tarium were inoculated separately at the same respective inoculum levels. Under natural field conditions, however, the significance of C. atramentarium to potato wilt is still open to question. In a field where both V. dahliae and C. atramentarium were present, several fumigation treatments reduced V. dahliae recovery from either stems or roots and decreased wilt severity. In contrast, these same treatments showed no significant effect on C. atramentarium recovery from either stems or roots. Although inoculum levels of C. atramentarium from stem tissue were high for all treatments (6-9 x 104 propogules/gm), wilt symptoms were consistently suppressed when V. dahliae was suppressed by soil fumigation. Respiration of Gomphrena globosa Leaves an, d Multiplication of