Carl J. Eide

Testing potatoes for field resistance to late blight

SummarySelection of potato clones for field resistance to late blight was made satisfactoly in the field by inoculating 3-hill units with zoospores ofPhytophthora infestans. More precise comparisons were made in replicated 15-hill plots by measuring the spread of the disease from a single inoculated plant in the center of each plot. Certain selections made in the 3-hill plots proved to be more resistant than Sebago when tested in the 15-hill plots. Differences in resistance were found among Sebago, Pontiac and Irish Cobbler. Dazoc, Norland and Redkote were very susceptible. Resistance to stem and tuber infection was generally, but not consistently, associated with resistance to defoliation.ResumenSeleccion de clones de papa por resistencia de campo al anublo (tizón) tardio fue hecha satisfactoriamenta en el campo al inocular zoosporas dePhytophthora infestans en 3 matas individuales. Comparaciones mas precisas fueron hechas en parcelas replicadas de 15 matas en las cuales la dispersión de la enfermedad fue medida desde una planta única inoculada en el centro de cada parcela. Ciertas selecciones hechas en parcelas de 3 matas demostraron mas resistencia que Sebago ensayado en las parcelas de 15 matas. Entre Sebago, Pontiac y Iris Cobbler se halló diferencias de resistencia. Dazoc, Norland y Redkote fueron muy susceptibles. La resistencia a infeccion del tallo y del tubérculo estuvo generalmente, aunque no consistentemente, asociada con resistencia a defoliación.

Prevalence of Verticillium wilt in potatoes in the Red River Valley area of Minnesota.

Verticilium spp. were present in over 60% of potato fields in Clay, Marshall, Norman, and Polk Counties in the Red River Valley in Minnesota.ThreeVerticillium spp. were isolated from 27% of the potato stems collected in commercial fields during 1968–1972.Verticillium alboatrum andV. dahliae were recovered from infected stems in approximately equal amounts (51% to 47%), butV. nigrescens was recovered from less than 2% of all host-infected plants. Of 12 cultivars sampled, Superior, Kennebec, Red Pontiac, Sebago, Irish Cobbler, and Norland were most frequently infected.ResumenVerticillium spp. estuvo presente en mas del 60% de los campos de papa en los condados Clay, Marshall, Norman y Polk del Valle del Rio Rojo de Minnesota. Se aislaron tres especies deVerticillium de 27% de los tallos de papa recolectados en campos comerciales durante 1968–1972. Se aislóV. alboatrum yV. dahliae de tallos infectados en proporciones casi iguales (51a 47%), peroV. nigrescens fue recuperado de menos del 2% de todas las plantas infectadas. Entre 12 cultivares muestreados, los que con mas frecuencia estuvieron infectados fueron Superior, Kennebec, Red Pontiac, Sebago, Irish Cobbler y Norland.

Effect of inoculum concentration ofPhytophthora infestans on potato late blight

Zoospore suspensions ofPhytophthora infestans applied to potato cultivars in the field with an exponential inoculum sprayer resulted in defoliation within a range of severity that was log-normal with respect to inoculum concentration. Regression lines for different cultivars differed in position and, depending upon moisture conditions, slope, indicating that the cultivars differed in resistance to penetration and to invasion of tissue by the pathogen.ResumenSuspensiones de zoosporas del hongoPhytophthora infestans applicadas a campo sobre cultivares de patata mediante un pulverizador exponencial de inócula, dieron como resultado defoliación dentro de un rango de severidad que fue logarítmico con respecto a la concentración de inócula. Las líneas de regresión para diferentes cultivares variaron con respecto a posición y, dependiendo de las condiciones de humedad, con respecto a inclinación o pendiente, lo que indica que dichos cultivares diferián en resistencia a la penetración y invasión de los tejidos por el patógens.

The relation of late blight development on potato foliage to temperature and humidity

SummaryDuring four seasons, late blight on the foliage of potato plants spread to nearby plants during periods described by Wallin and his coworkers as “favorable,”i.e. 10 or more hours of relative humidity above 90 per cent and temperatures between 60° and 77° F.Over 56 per cent of the favorable periods in the 4 years occurred on days with rain. In most instances Hyre’s “moving graph” system of relating weather to blight would have indicated periods of spread accurately.The rate of spread of blight differed in plots on peat and silt loam soil, but the differences were not definitely associated with differences in temperature and humidity recorded by the hygrothermographs.It appears that in regions where primary inoculum occurs sporadically, the prediction of blight development by the use of hygrothermographs should be supplemented by surveys to determine if centers of infection exist in the fields.In a single comparison, race 0 ofPhytophthora infestans spread more rapidly than race 1 in a similar plot.

Chemical control of potato seed piece decay

SummaryLaboratory and field tests in 1957 and 1958 indicate that some chemical protectants are toxic to decay-producing organisms and that some improved stands and yields from potato seed pieces which were stored before planting. Some of the commonly used chemical protectants such as certain antibiotics and acid mercury were not effective against seed piece decay under the conditions of the tests. Decay-producing organisms apparently are present on most potato tubers making artificial inoculation superfluous.

The waseca, chisago and satapa potatoes

The Minnesota Agricultural Experiment Station has been engaged in potato breeding work with the objective of developing for the potato growing areas of Minnesota varieties producing high yields and tubers of satisfactory market and table quality. While breeding work is also in progress on disease resistance, particularly common scab, late blight and latent mosaic, the three varieties herein described are not superior to the common varieties in this respect. They represent improvements in market and culinary quality and in adaption to the principal potato growing regions of Minnesota.

Resistance to common scab of potatoes in parental clones and in their hybrid progenies

Summary1.Selection of individual plants in seedling families in the scab test plot was relatively ineffective in isolating scab resistant seedlings.2.Consistent ratings for mean scab index were obtained by growing four hills of a clone in a heavily infected scab test plot.3.Crosses between parents of the same clonal resistance resulted in progenies which differed widely in the percentage of resistant seedlings.4.Crosses between parents derived from the same resistant ancestor seemed to produce progeny of slightly lower resistance than where the two parents had different resistant ancestry.5.A test of 399 selections from 30 crosses showed that when both parents had a scab index of 3 or less, from 11 to 37 per cent of the selections had an index of 2 or less, and from 43 to 63 per cent an index of 3 or less.

Forecasting potato late blight in Minnesota

SummaryPeriods of 10 hours or more concurrent temperature ≤75° F. and relative humidity ≥90 per cent followed by temperature maxima < 95° F. were used to predict potato late blight development. One favorable period a week was considered sufficient for limited reproduction and subsistence of the fungus in the foliage.During 1950. 1951. 1952. and 1953. blight developed as forecast in those areas near the weather-blight observation posts.The results thus far warrant continued efforts to forecast late blight on the basis of the same temperature and relative humidity relationships, with more consideration devoted to the influence of high temperature maxima immediately succeeding a period favoring secondary infection processes.Because the early part of the record on each hygrothermograph chart is at least a week old when it reaches the forecaster any further delay in the receipt of these records decreases the practical value of the forecasts.

Abstracts of papers presented at Annual Meeting

HEILIGMAN, F., AND I. R. W A G N E R EFFECTS OF CHLORO-IPC ON SPROUTING AND LOSSES IN WHITE POTATOES DURING STORAGE The use of 3-Chloro-lsopropyl-N-Phenyl Carbamate (Chloro-IPC) reduced losses in white potatoes stored at 55, 72, and 85 ° F. when compared to untreated controls. The material was effective when used as a dip, as a spray, or when incorporated in water emulsion potato wax. The treatment controlled sprouting and reduced weight losses during storage. There is some evidence that the material may have some indirect effect in controlling losses caused by microbial decay. H O Y M A N , WM. G. COMPARATIVE REACTIONS OF ATTACHED AND DETACHED LEAVES TO P H Y T O P H T H O R A I N F E S T A N S Thirty potted potato selections 6 to 12 inches in height and detached leaves from them were simultaneously inoculated with zoospores from a culture of race 0. The inoculations were made in a plastic-covered chamber at 70 ° F. and 100 per cent relative humidity. The reaction of each of the 30 selections was recorded as soon as symptoms appeared and the final reading was made the eighth day following inoculation. Sporulation occurred on attached and detached leaves of 8 selections. Sporulation also occurred on the attached leaves of one selection, whereas the reaction of the detached leaf consisted of large lesions. The symptoms on both types of leaves of the 3 selections consisted of necrotic spotting. The attached leaves of 4 selections showed no symptoms, whereas the detached leaves showed definite necrotic spotting. No reaction was evident on leaves of 14 selections.