W. J. Hooker

Air pollution injury of potato in Michigan

A disorder of Michigan potatoes tentatively called speckle leaf is associated, in part, with air pollution injury. The disease is characterized by reduced yields following early vine maturity, premature vine death, and yellowing of the lower leaves. Necrotic spots developed on the upper surface of leaves, followed by bronzing, and upward leaf rolling. Severely affected leaves became chlorotic and remained attached to the stem.Potato plants were grown in two plastic houses through which was blown either ambient field air or ambient air filtered through activated charcoal. Plants grown in the plastic house receiving ambient air developed symptoms similar to nearby field plants. Plants grew normally in filtered ambient air and remained free of speckle leaf and air pollution injury symptoms. The potato varieties Haig, Norchip, and Superior were most sensitive, Sebago was intermediate, and Kennebec and Katahdin were most tolerant.Tobacco plants in ambient non-filtered air developed symptoms typical of ozone injury. Bean leaves became bronzed with brown necrotic flecks on both surfaces, and severely affected leaves dropped. Neither tobacco nor bean was affected in the filtered air.

Factors influencing infection of field grown potato by Verticillium albo-atrum

SummaryAspects of Verticillium wilt infection of potato were investigated by determining inoculum survival in vascular discolored potato tubers as evidenced by seed borne disease transmission in the field, isolation attempts, and histological observations. Methods for field inoculation of potato plants were evaluated.Of the different methods used for inoculation, root inoculation and seed surface contamination were the most effective. The leaf inoculation method induced relatively high infection. The other methods used, hypodermic syringe, tooth pick inoculation, root dip, and cut tuber, were intermediate or ineffective in establishing infection.No significant differences between stands, vigor, general appearance, yield, vascular discoloration of tubers, or the presence of viable fungus in the tuber were obtained from healthy as compared to vascular discolored seed lots.Viable fungus in stored vascular-discolored tubers, as demonstrated by isolation from discolored tissue, progressively diminished during 4 and 7 months after harvest.Variability in fungus survival between seed lots necessitates reservation in making generalizations. In the light of the present evidence it does not seem probable that internal seed borne inoculum is an important factor in transmitting Verticillium wilt in potato.Discolored portions of vascular tissue of tubers were examined histologically. Granular material and fungus hyphae within the xylem vessels of tubers are shown.ResumenSe investigó varios aspectos del marchitamiento de la papa causado por Verticillium (Verticillium wilt) determinando la sobreviencia del inóculo en el sistema vascular descolorado de tubérculos, por medio de transmisión de la enfermedad por semilla en el campo, aislamientos, y observaciones histológicas. Se evaluaron métodor de inoculación de plantas de papa en el campo.De los métodos usados, la inoculación de raices y la contaminación de la superficie de los tubérculo semilla fueron los más efectivos. El método de inoculación de hojas produjo relativamente alta infeción. Los otros métodos usados, jeringa hipodérmica inoculación con mondadientes, sumersión de raices, y corte de tubérculo, fueron intermedios o infectivos en la produccion de infección.En comparaciones entre lotes de semilla sana y semilla con descoloracion vascular no se obtuvieron diferencias significativas en el grado de establecimiento de plantas (stand), vigor, apariencia general, rendimiento, o la presencia del hongo viable en tuberculos.El hongo viable en tuberculos, con descoloración vascular, almacenados (demonstrado por aislamientos de tejidos descolorados), disminuyó progresivamente durante 4 y 7 meses después de la cosecha.La variación en la sobrevivencia del hongo entre lotes de semilla necesita cierta réserva para hacer generalizaciones. Con la evidencia que disponemos, no es probable que el inóculo interno de la semilla sea un factor importante en la transmisión del marchitamiento causado por Verticillium en la papa.Se examinaron histologicamente porciones descoloradas de tejidos vasculares. Se muestran material granular e hifa del hongo dentro de las vasos del xilema.

Virus X resistance in potato

Virus X is one of the most important viruses of potato because of its widespread distribution in seed stocks and because of its depressing influence on yield. Resistance to virus X is of considerable interest because of the different types of response within the potato ranging from complete tolerance through hypersensitivity to immunity. The depressing influence of virus X on potato yields is well esablished in the United States, Europe, and Australia. In Maine, yield reductions of approximately 12 to 22 per cent were obtained by Schultz and Bonde (46) over a four-year period with virus X-infected stocks of Chippewa and Katahdin as compared with X-free stocks of the same varieties. Lombard (33), in Maine, obtained small but rather consistent increases in yield with X-free stocks of Chippewa, Sebago, and Teton as compared with X-infected stocks. Yield reduction with Chippewa and Katahdin was 6 per cent with virus X in New York (59) and reduced stands were observed in X-infected Sebago stocks. Stocks of Placid infected with masked virus X (41) tended to yield less than those free from virus X. Smith and Markham (53) have estimated yield losses caused by virus X in the British Isles at 12 per cent. The extent of yield reduction (12) in Majestic and Arran Banner ranged from 5 to 22 per cent depending upon the severity of the X strain present. Clinch and l~{cKay (19) obtained variable yield response to mild strains of virus X in two different clones of Up-to-Date. Lunden (34) observed approximately 11 per cent yield reduction in the variety, Aspotet, over a 3-year period in Norway, and Klinowski (29) reported marked yield reduction in the German varieties Voran and Ackersegen. Gains in yield of 14 to 27 per cent have been obtained using X-free as compared with virus X-infected stocks of Up-to-Date in Australia (7) .

Albinism of potato spindle tuber viroid-infected Rutgers tomato in continuous light

Potato spindle tuber viroid (PSTV) caused albinism in the new growth of Rutgers tomato under continuous light. The albinism response was obtained with 4 isolates causing severe symptoms in tomato and with 1 mild isolate which is normally symptomless.Rutgers tomato inoculated with the 4 severe strains of PSTV developed typical ‘bunchy top’ symptoms in 12 to 16-hr day lengths. Symptoms developed slower and much less distinctly on plants incubated in 6-hr days. New growth in PSTV-infected plants was green in short days (12-hr illumination) and chlorotic to white in continuous light.Infectivities of extracts from white portions of plants were from 3 to 10 times greater than those from green portions of infected plants.Albino symptoms also developed in other tomato varieties when inoculated with PSTV and kept under continuous light. Albinism was most pronounced under continuous light at 30°C, somewhat less intense at 24°, and at 16°, new growth of infected leaves and stems remained green. Albinism did not develop in otherSolanum species which are symptomless hosts of PSTV nor in seedling potato plants grown in continuous light.ResumenEl viroide causante del tubérculo ahusado en la papa (PSTV) produjo albinismo en los nuevos brotes de la variedad de tomate Rutgers cuando se tuvo bajo luz contínua. La reacción de albinismo se obtuvo con cuatro aislamientos que producen smtomas severos en tomate y con un aislamiento benigno que no causa síntomas normalmente.La variedad de tomate Rutgers al ser inoculada con las cuatro razas severas de PSTV desarrolló síntomas típicos de cogollo en ramillete (bunchy top) bajo 12–16 horas de luz por día. Los síntomas se produjeron más lentamente y con mucho menos intensidad en plantas que tuvieron la incubación con días de 6 horas de luz. Los nuevos brotes en las plantas infectadas con PSTV fueron verdes en condiciones de días cortos (12 horas de luz) y fueron cloróticos o blancos si la luz era contínua. La infectividad de los extractos de las porciones blancas de las plantas fue de 3 a 10 veces mayor que la de las porciones verdes en las plantas infectadas.Los síntomas de albinismo también se desarrollaron en otras variedades de tomate cuando se inocularon con PSTV conservándolas bajo luz continua. El albinismo se pronunció al máximo bajo luz contínua a 30°C, fue algo menos intenso a 24°C y a 16°C las hojas y tallos de los nuevos brotes permanecieron verdes. El albinismo no se desarrolló en otras especies deSolanum que son huéspedes sin síntomas del PSTV ni tampoco en plántulas de papa cultivadas bajo luz contínua.

Immunity to virus X in potato: Selection of immune plants in the breeding program

Virus X is one of the most important viruses of potato because it is universally present in all seed stocks of certain susceptible varieties and widely distributed in the seed stocks of many others. At present, no large stocks of X free potato seed are available for commercial use in this country and only one imnmne variety of suitable commercial type, Saco, has as yet, been released (1) . Resistance to virus X in potato has recently been reviewed (3) and a brief report of the work reported herein has been made (8). This paper describes procedures for mass inoculation of small seedling potatoes in selecting virus X immune plants in the breeding program. Relatively few advances in techniques of breeding for virus X immunity have been made following identification of immunity in seedling S 41956 (7) and identification of the abnormal graft reaction of X immune stocks (5) . Selection of imnmne segregates in a breeding program is dependent upon a means of rapidly and efficiently eliminating susceptible individuals from large populations. Factors influencing symptom expression of the virus in X free susceptible potatoes propagated as clonal lines (9) and in populations of young seedling plants (10) were investigated. The mechanical inoculation test was at least as reliable as the graft test of Raleigh and had the advantage of greater ease of testing and economy of space. Furthermore, the mechanical inoculation test could be applied to small potato plants grown from true seed whereas the graft test could not. Reliability of symptom expression in susceptible potatoes mechanically inoculated with virus X was dependent upon the virulence of the isolate selected for inoculation. When suitable ring spot strains of virus X were used, symptoms in susceptible plants consisted of local necrotic spotting of inoculated leaves and a systemic top necrosis, whereas immune plants showed no reaction. The most effective isolate incited visible local and systemic symptoms on all susceptible plants tested making it relatively simple to eliminate susceptible plants from large populations of small seedlings in greenhouse flats prior to transplanting. Results reported by Timian, Hooker and Peterson (10) were based upon seedling plants individually inoculated by rubbing the leaves with

Unusual aspects of lightning injury in potato

Additional aspects of lightning injury of potato are described. A cross hatched or ladder like breakdown of stem pith is characteristic of injury and is useful in diagnosis.The usually accepted pattern of incidence within the field is a well defined circular or elliptical area containing injured or killed plants. In contrast, injured plants may be scattered as individuals or in small groups intermingled with those less severely affected or unaffected. When injury is dispersed a clearly defined center is frequently lacking. Individual plant symptoms were similar with either type of distribution.Injured tubers showed extensive collapse of the central pith with less severe damage in the outer cortical tissue. Lightning injury frequently extended as a hole completely through the tuber.

Sublethal chilling injury of potato leaves

ResumenSe describen los síntomas de daño subletal causado por heladas en hojas de papas. El daño resultó tanto a consecuencia de bajas temperaturas sufridas naturalmente en el campo como por bajas temperaturas inducidas experimentalmente. Se cree que el tejido meristémático es él principalmente afectado produciendo hojas deformadas con varios grados de jaspeado, manchas amarillas y deformación de hojas. Se describe la deformación de hojas. Se describe la deformación de hojas resultante del elargamiento incompleto de venas. Bajo las condiciones experimentales usadas se obtuvo evidencia de un desarrollo unilateral.Las hojas que se desarrollan después de pasada la helada, como también las desarrolladas antes de la helada, mantienen un aspecto normal saludable.Se han demostrado diferencias varietales en la reacción al daño por heladas.

Tawa: A new early potato variety resistant to late blight, scab, and immune to latent mosaic

On June 11, 1956, the United States Department of Agriculture, in cooperation with the Iowa and Michigan Agricultural Experiment Stations, announced the release of a new potato variety named Tawa 4. This is the first variety combining resistance to late blight and scab with a high degree of resistance approximating immunity to virus X. Tawa matures early and produces smooth attractive tubers with good cooking and chipping quality.