Donald Folsom

Pseudomonas fluorescens in relation to certain diseases of potato tubers in Maine

SummaryFluorescent bacteria were isolated frequently from discolored xylem and parenchyma of Maine-grown potato tubers that had the red-xylem disease, pink eye, or infected bruise cracks. Isolates were identified as strains ofPseudomonas fluorescens. Some strains produced softening of potato slices and a progressive black rot inside tubers, whereas other strains produced neither; the former did not lose their pathogenicity in the course of several years’ maintenance in broth. In the field, pink eye, associated with Verticillium wilt, was correlated positively with soil moisture. Black rot was more active at 35° F. than at 50° or 70°. Infection in bruise cracks was less frequent in tubers dipped in solutions of Agri-mycin, sodium hypochlorite or Phygon previous to bruising than in comparable untreated, noninoculated tubers. Stolon and tuber stem-end inoculation induced red-xylem symptoms. Tuber eye-end inoculation induced pink-eye.

Permanence of greening of potato tubers

ConclusionsPotato tubers greened faster at ordinary room temperature than in a cool place. Greening, as seen through the skin, faded faster in the dark at 75° F. than at 35° F., faded somewhat in a month of dark storage after 2 to 4 days’ exposure to light, faded in 5 months only in the warm storage after 7 to 31 days’ exposure to light, and was obscured or replaced by red or brown when fading in dark storage. Cortical greening developed faster and faded less in Katahdins than in Chippewas and Green Mountains, faded faster in warm than in cool storage, and faded less after longer exposure to light. Culinary tubers if exposed to light for 2 days may require over a month in warm dark storage for fading of the green, and if exposed to light for longer periods may require several months of warm dark storage for fading of the green.

Resistance of potato seedling varieties to the natural spread of leaf roll

SummaryPotato seedlings were exposed to field spread of leaf roll from adjacent rows in an area where leaf roll spreads consistently year after year. Parents used at first included commercial American and European varieties reputed to be resistant to leaf roll, and a few of the crosses contained some seedlings resistant to the natural spread of leaf roll. When these resistant seedlings were used as parents, the resulting crosses generally were more resistant to field spread than crosses of other kinds. Greater resistance in one of the parents did not always mean greater resistance in the cross. Greater resistance in a cross (on the basis of percentage of seedlings showing any leaf roll) was not necessarily correlated with the percentage of total plants showing leaf roll in the infected seedlings. Field resistance in given seedlings and varieties varied from one season to another on the same farm. Although green peach or spinach aphids (Myzus persicae) probably are an important factor in the field spread of leaf roll, aphid resistance in seedlings is not necessary for field resistance to leaf roll. It is possible to combine field resistance to leaf roll with many characteristics considered commercially desirable in this country.

Testing potato seedling varieties in Maine for field resistance to leafroll and for desirable horticultural characteristics

From 1938 to 1948, inclusive, 16,006 potato seedling varieties were introduced to a test for resistance to the natural spread of leafroll at Highmoor Fa rm in southwestern Maine. Progress reports were published in 1943 (31) and 1946 (11). Potato leafroll is still an important problem in Maine and other potato-growing areas. The data presented here may help to indicate what nmst be done if leafroll is to be controlled through varietal resistance. They also throw some light on methods that are important in testing potato seedling varieties that have resistance to other virus diseases. The chief topics to be considered are field exposure methods, insect counts, inheritance of resistance, desirable horticultural characteristics, yield tests, tuber size, tuber type, cooking tests, and a comparison of field tests with aphid-inoculation tests.

Growing seed potatoes under an aster cloth cage

Infestations of the wheat wireworm (A.mancus Say) start in fields which afford abundant protection to beetles from ,desiccatiom Under the farm rotation system most common in western New York this protection is afforded by, and eggs are deposited in, hay or sod fields. The elimination of cover in fields to be planted to potatoes, f rom the middle of May to the middle of June, has reduced wireworm populations and eliminated injuries to potato tubers. Since some beetles will emerge every spring potato land must be kept free from cover every year to avoid reinfestation. Th, e best method of attaining this end is an individual problem. The exact cropping system to be employed is a matter of far reaching importance which can best be determined through consultation of individual growers with authoritative sources of information.

Potato tuber bruise rots in relation to crop rotation in Maine 1945–1956

Potato tuber bruises, so far as this paper is concerned, are cracks and groups of cracks resulting in the tuber flesh from impacts received during harvesting and other handling of the crop. Bruises, even the worst, may renIain free from infection by fungi or bacteria. Other bruises beconie infected restdting in bruise rot which may vary from a thin zone of discolored flesh adjoining the cracks, to larger lesions in which there is no longer evidence of the original cracks (6) . Bruises and bruise rots cause losses through their effect on shrinkage and sales appeal. It has been claimed, as will be detailed below, that bruise rot is caused by organisnis present on or in the tuber skin at the time of bruising and that the abundance of certain of these organisms is affected by the type of crop rotation that has been practiced in the field in which the crop was grown. Several dozen Maine fields, which were used for potato growing in one or more years of the period 1945 to 1956 inclusive, furnished soil samples which were tested as to pathogenicity in freshly bruised tubers.

Verticillium wilt of potato in relation to fungicides added to the fertilizer

SummaryAlthough two to four years in other crops can eliminate danger to potatoes from field-infestation by microsclerotia-freeVerticillium alboatrum in Maine, such a rotation is too long for many potato growers and they would prefer a quick chemical method of control if it were practical. Certain fungicides were tested, as fertilizer admixtures, with respect to plant growth and Verticillium wilt. In the greenhouse the results with potatoes were much different from those with tomatoes. With potatoes the results in the field were very different from those in the greenhouse. The field results were not promising for the several chemicals that were tested.

Inheritance of predisposition of potato varieties to internal mahogany browning of the tubers

ConclusionPredisposition to mahogany browning varies from one commercial or seedling variety to another, the relative amount of injury as between varieties may change with the temperature of storage, and predisposition is inherited.

Tuber-line seed plots

SummaryTuber-lines were helpful but not sufficient in the development of mosaic-free and leaf roll-free seed stocks in Maine. When such seed stocks were planted in seed plots, there was about a 50-50 chance that disease would enter the plot. Mosaic control was favored by location outside the northeastern part of the State, by earliness, by larger size, and by better isolation of seed plots. Leaf roll control was favored by location in the northeastern part of the State, by earliness, and by larger size, of seed plots. The effects of these factors were often greater than the effects of tuber-unit planting.

Sample size and reliability

Pota to tubers are planted by some agencies in the greenhouse and in the South in order to determine as early as possible how much virus disease is present in the seed stocks, represented by the tubers. The larger the number of tubers representing a given seed stock, the more reliably will they forecast the amount of disease to be found later in the field. However , the cost of planting a number of samples will be greater. Eve ry agency must decide for itself what size sample will offer the best compromise with respect to reliability and expense. The decision may be made easier by the availability of a table showing the min imum sample size that may be expected to give reliability of a certain degree.