E. S. Schultz

Kennebec: A new potato variety resistant to late blight, mild mosaic, and net necrosis

SummaryThe Kennebec is a new variety of potato that combines high yield and good cooking quality with a high degree of resistance to late blight in both vines and tubers. In field-exposure tests it has not yet shown the symptoms of mild mosaic or net necrosis. It is late in maturing as grown in Maine, but has been considered medium-late in tests in other States. It is widely adapted. It produces smooth, well-shaped tubers with shallow eyes. Like all other varieties of potatoes, it varies in quality according to the environment in which it is grown and the cultural practices of the growers. As produced in the test plots on Aroostook Farm, Presque Isle, Maine, it has shown excellent market and cooking quality. The keeping qualities in storage appear to be excellent. Kennebec should replace Katahdin in some sections because of its higher yielding ability, its superior cooking quality, and its high degree of resistance to late blight. It should replace Sebago to a large extent because of a higher degree of resistance to late blight and because the tubers of Kennebec are more easily detached from the vines at harvest time than are those of Sebago.

The effect of latent mosaic (virus x) on yield of potatoes in maine

SummaryLatent mosaic caused by virus X is harbored more generally than any other virus disease by most of the old and some of the new potato varieties. This disease is harbored by some varieties without producing symptoms, whereas in other varieties it appears as a typical mosaic.Latent mosaic is caused by several strains of virus X, which are distinguished by the severity of the host reaction. In addition to causing more severe foliage symptoms, the stronger virus X strains depress the yield more than the weak strain.It is shown that latent mosaic reduces the yield by 9 to 22 per cent, that the yield is depressed more in some varieties than in others, and that annual losses amounting to millions of bushels result from this disease.Control measures are indicated involving propagation of seed potatoes on isolated fields, protective inoculation with a weak strain of the virus and the development of varieties immune from latent mosaic.

Potato cull piles as a source of late-blight infection

foliage, and this injury may reduce yields in fields where there is no blight or in those in which the disease is not severe. In Florida, also, new potato varieties, such as the Sebago, even though mildly resistant to late blight, succumb to the disease and can not be grown profitably during blight years unless sprayed or dusted regularly. Late blight can be controlled fairly satisfactorily most seasons, even when the disease is severe, if the potatoes are sprayed or dusted regularly with copper sprays or dusts. Poor control of the disease can be traced to several factors such as ( I ) using seed containing many blighted tubers, (2) ideal conditions for the development of the disease in some seasons, (3) failure of some potato growers to realize the seriousnes~ of the disease and to apply fungicides soon enough and follow a regular dusting or spraying program while the disease is spreading, (4) poor coverage of potato foliage with fungicides due to inefficient operation of sprayers and dusters, or to the use of faulty machines, and (5) prolonged rainy periods during which the organism is disseminated and becomes very destructive in fields which become so boggy that spraying and dusting equipment can not be pulled through them making it necessary to abandon the regular dusting or spraying schedules.

Breeding for resistance to late blight in the potato

Twelve years ago the United States Department of Agriculture, in cooperation with the Maine Agricultural Experiment Station, began a program for breeding potato varieties with high )field, good market qualities, and good cooking qualities, combined with resistance to late blight (Phytophthora infestans (Mont.) DBy.). During this time several reports of progress have been published. In addition, the Sebago variety, which is moderately resistant in both vines and tubers, has been increased and distributed to growers. How well this variety has been received is shown by the fact that in 1944 1,8Ol,596 bushels of certified seed were produced in I I states. About 85 per cent of this amount was produced in Maine, but varying amounts were reported also from Maryland, Michigan, Minnesota, New Jersey, New York, North Dakota, Pennsylvania, Vermont, Washington, and Wisconsin. The present paper is an attempt to bring the results of the blight-resistant phase of potato breeding up-to-date and to discuss some of the newer family lines, selections from which show much higher degrees of resistance than Sebago.

The control of potato late blight tuber rot

PUBLISHED BY THE POTATO ASSOCIATION OF AMERICA N E W BRUNSWICK, N. J. O F F I C E R S AND ~XECUTIV~ C 0 ~ ~ E. B. TUSSING, P r e s i d e n t . . . . . . . . . . . . . . . . Ohio State University, Columbus, Ohio MArx KOEHNKF~ Vice-President..Nebr. Certified Potato Growers, Alliance, Nebr. W. H. MARTIN, Sec.-Treas., Editor..Agr. Exp. Sta., New Brunswick, New Jersey F_, L. NEwmcl~ . . . . . . . . . . . . . . . . . . . . . . . Department of Agriculture, Augusta, Maine W. N. KEENAI~ . . . . . . . . . . . . . . . . . . . . . . Department of Agriculture, Ottawa, Canada F. J. SrEWNSON . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . U. S. D. A., Beltsville, Maryland C. D. GAINES . . . . . . . . . . . . . . . . . . Department of Agriculture, Olympia, Washington A. H. EDDmS . . . . . . . . . Florida Agricultural Experiment Station, Hastings, Florida

Effect of growth regulators on sprouting of stored table stock potatoes and on waste piles for control of diseases.

SummaryResults with certain growth regulators or dormancy treatments indicate that sprouting and subsequent development of late blight on potato waste piles can be prevented if the cull potatoes are treated with dormancy treatments before or when the tubers are deposited on the cull piles.

Resistance of solanum species to potato viruses A, X, and Y

SummarySome selections ofS. tuberosum (S. andigenum) were found to possess a high level of resistance to mechanical and graft inoculation with viruses A and X. Nine of the selections proved highly resistant to inoculation with both viruses; graft inoculated plants developed no symptoms nor could either virus be recovered from them. Apparent immunity to graft inoculation with virus X was found in selections ofS. acaule, S. sucrense and 1 species hybrid. Four selections ofS. tuberosum and 1 selection ofS. maglia developed symptoms of virus X infection but were poor hosts for the virus as indicated by low titer upon subinoculating to indicator hosts. One selection ofS. cardiophyllum, 4 ofS. chacoense, 3 ofS. demissum, 2 ofS. hougasii, 1 ofS. phureja, 1 ofS. tuberosum, 8 ofS. stoloniferum and 2 species hybrids were apparently immune from mechanical inoculation with virus Y. Nine of these selections were apparently immune from graft inoculation with virus Y. Apparent immunity to graft inoculation with virus A was found in selections ofS. chacoense, S. demissum, S. hougasii, S. maglia, S. phureja, S. stoloniferum and 8 species hybrids. About half of the selections developed symptoms of virus A infection but the virus could not be recovered from them. No selection was found to be highly resistant to all three viruses.

Merrimack: A new variety of potato resistant to late blight and ring rot and adapted to New Hampshire

SummaryMerrimack is a variety of potato bred by the United States Department of Agriculture and tested in New Hampshire. Maine, and elsewhere as part of the work of the National Potato-Breeding Program. Merrimack competed favorably with standard varieties in New Hampshire. It produced satisfactory yields of potatoes, with a relatively high dry-matter content from which excellent chips and french fries were made.In the Maine tests it did not yield as well as some of the standard varieties but in tests it was found to be highly resistant to, if not immune from, the common race of the late blight fungus in both vines and tubers. It is moderately resistant also to early blight, and was apparently fieldimmune from virus A and highly resistant to net necrosis. Its vines are very susceptible to leaf roll virus. Merrimack is not only highly resistant to ring rot but is the first variety released that is highly resistant to both late blight and ring rot. Its multiple-disease resistance should make it valuable, especially to growers who find it difficult to control late blight and ring rot in standard varieties.

Tests with milk and rice polish to prevent infection of Irish potato with virus Y transmitted by aphids

Different substances have been found to possess properties that inhibit several virus diseases affecting plants. These diseases include some of the aphid-transmitted viruses of potato.. Conflicting results have been reported as to the value of milk for this purpose (1) , (2) , (3) . These results may have been due in part to the viruses or species of test plants involved, the method of treatment, or the environments used in the experiments. In 1958 and 1959 studies were made at Presque Isle, Maine, to determine whether milk or rice polish contain substances that will prevent virus Y infection in potato plants fed upon by infective aphids.

The evaluation of potato seedling varieties for field immunity from potato virus A

SummaryProcedures for the efficient and effective evaluation of potato seedling varieties for field immunity from potato virus A in the greenhouse were developed. Plants of seedling varieties selected from parents possessing field immunity are inarch-grafted with virus-A-infected plants of potato seedling 41956 to eliminate from further tests seedling varieties that show top necrosis and are, thus, field-immune from the virus. Subinoculations to plants ofSolanum demissum P. I. 175404 (local-lesion host) from mottled or symptomless plants about 35 days after grafting will detect, in 4 to 6 days, all seedling varieties susceptible to virus A. These susceptible seedling varieties are replanted, and when the plants are 1 to 2 inches tall they are infested with 25 to 50 virus-A-infective aphids for a 24-hour-period. After an incubation period of 30 to 35 days, diagnosis of infection is made by subinoculation from each plant to the indicator host. Seedling varieties not infected by aphid inoculation are considered field-immune from virus A.