Geddes W. Simpson

Effect of time of inoculation with potato leafroll virus on development of net necrosis and stem-end browning in potato tubers

The Green Mountain cultivar was used in field tests to determine the effects of inoculating potato plants at various times with the potato leafroll virus (PLRV) on development of internal necrosis of tuber tissue. Viruliferous apterae of the green peach aphid,Myzus persicae (Sulz.), were placed on each stem in all hills to be inoculated in each 3.0 m single-row plot. Planting and inoculation dates were varied in all field experiments and, in one, several vine-killing dates were also included. All harvested tubers were stored for approximately four months at 10°C to enhance development of internal necrosis prior to examination. Similar but smaller greenhouse studies involving both apterous and alate green peach aphids were also conducted using Green Mountain, Irish Cobbler, and Russet Burbank cultivars. All results showed that as inoculation was delayed relative to plant development, more net necrosis (NN) occurred. Conversely, when plants were inoculated early, stem-end browning (SEB) rather than NN predominated. A high percentage of naturally occurring SEB tubers (cv. Russet Burbank) were found by ELISA to contain PLRV. Plants produced by these tubers only rarely developed leafroll symptoms. These findings suggest a previously unsuspected causal relationship between SEB and PLRV. Implications of this apparent relationship on the epidemiology of potato leafroll in Maine are discussed.ResumenLa variedad de papa Green Mountain fué usada en los experimentos para demostrar los efectos de la inoculación, en diferentes fechas, del virus enrollador de la hoja de la papa (PLRV) sobre el desarrollo de necrosis interna en tejido del tubérculo. Contaminados áfidos apteros del durazno verde,Myzus persicae (Sulz.), fueron colcocados sobre el tallo que iba a ser inoculado in cada una de las parceles de 3.0 metros. Las fechas de plantación e inoculación fueron cambiadas en todas los experimentos y en uno, las fechas de varias vine-killing fueron también incluidas. Todos los tubérculos cosechados fueron almacenados por aproximadamente cuatro meses a una temperatura de 10°C para acrecentar el desarrollo de la necrosis interna antes de ser examinado. Estudios similares pero en escala más pegueña en invernaderos, fueron hechos involucrando áfidos del durazno verde, con alas y sin alas, en estos experimentos fueron usadas las variedades de papa Green Mountain, Irish Cobbler y Russet Burbank. Todos los resultados demostraron que cuando la inoculación fué retardada en relación al desarrollo de la planta, más necrosis en red apareció (NN). Reciprocamente, cuando las plantas fueron tempranamente inoculadas, “stem-end browning” (SEB) predominó en vez de la necrosis en red (NN). Usando la téchnica ELISA se encontró, que un alto porcentaje de tubérculos que tenían SEB natural (sin inoculación) cv. Russet Burbank, contenían PLRV. Plantas preducidas por estos tubérculos raramente desarrollan sintomas de hojas enrolladas. Estos resultados sugieren una relación entre SEB y PLRV no pospechada anteriormente. Las implicaciones de esta relación aparente, en la epidemiología de la hoja enrollada de la papa, en Maine, son discutidas.

Spraying potatoes to prevent leaf roll spread by the green peach aphid

Studies were made at Presque Isle, Maine, 1962–1966, to determine the suppressive effects of several materials against spread of the potato leaf roll cirus,Corium solani Holmes, transmitted by the green peach aphid,Myzus persicae (Sulzer), when applied as foliar sprays to Kennebec, Green Mountain, or Chippewa potatoes in field cages or in field plots. The early cage tests showed that spray mixtures containing 1% of the systemic plant growth regulant chlorocholine chloride (2-chloroethyltri-methylammonium chloride) or 1% of mineral oil were more effective than the insect antifeeding compound AC-24,055® (=ENT-25,651), the aphid-repellent compounds ENT 20,430 or ENT 21,178, or the surfactants Sarkosyl-O® (bis (2-ethylhexyl) sodium sulfosuccinate) or Aerosol-OT® (CH3 (CH2)n CON (CH3) CH2 COOH). Field tests disclosed that chlorocholine chloride at 5.2 lb or 2.6 lb/a/a was more effective when healthy green peach aphids were placed on infector plants in the plots soon after the plants were sprayed, 1 week later, or soon after the 2nd of 2 weekly applications than when the aphids were introduced before spraying. The difference in leaf roll suppression at these two dosages was not significant at the 5% level; as high as 90% control of leaf-roll spread was obtained. When only natural infestations of aphids were involved and field spread of the virus was light, the 86% control of leaf roll spread that was obtained from 4 weekly applications made in late June and in July was not significantly different (P=0.05) from the 79% control obtained from 2 biweekly applications made during the same period of time. The potato plants soon recovered from the slight chlorosis resulting from the spray treatment and there was no reduction in weight of US 1 tubers at harvest. Aphid population trends in treated plots were not affected.

Growth characteristics of potato plants useful in studies of population dynamics and biological control of aphids

During three growing seasons, certain information was recorded weekly that was related to several characteristics of the aerial growth of five varieties of field-growing potatoes, viz. the number of stems and leaves per plant, the length of stems, and leaf area. Conversions of aphid numbers recorded from stratified subsamples of plants in the field to the number of aphids per plant or per unit of leaf area became possible by knowing the number of leaves and the leaf area per plant at the time of each aphid count. The numbers and areas of leaves per plant varied greatly among varieties as well as within and among years. The range in average maximum area of leaves per plant was 533 to 2,523 in.2 for the years 1967 to 1969. The comparable range for number of leaves per plant for the years 1967 and 1969 was 53 to 145. Consideration was given to the probable influence upon the magnitude of errors of estimate of aphid abundance that might result in making conversions of field counts of aphids to the numbers of aphids per plant or per unit of leaf area.

Penobscot: A new variety of potato with leafroll resistance and high solids

SummaryPenobscot is a variety of potato bred primarily for leafroll resistance by the United States Department of Agriculture and tested cooperatively in Maine and other States as part of the National Potato-Breeding Program. The tubers of Penobscot are oblong to ovate in shape with light-cream, buff skin and medium-deep eyes. In the Maine tests, yields of Penobscot compared favorably with those of Kennebec, Katahdin, and Irish Cobbler. The specific gravity values of Penobscot were relatively high and usually exceeded those of three other commercial varieties grown in Maine. Penobscot was similar to Kennebec in chipping qualities determined both after harvest and after storage at 38 F followed by reconditioning, but its French fry color index and texture were slightly less favorable than Kennebec when fried after harvest. Penobscot possesses field immunity from mild mosaic and has considerably more resistance to leafroll in the field than the standard varieties now being grown. Its favorable processing qualities, high specific gravity, and its good yielding ability, along with its disease resistance, are all characteristics that should help to make Penobscot a valuable variety for both grower and processor.

Charles Orville Dirks 1895–1986

Charles Orville Dirks, emeritus professor of entomology at the University of Maine, died on 24 July 1986 in Orono, Maine at the age of 91. He was born in Pawnee Rock, Kans., on 29 March 1895, the son of Peter B. and Lydia (Gates) Dirks.

Report of the Editor-in-Chief July 1981 through June 1982

This report covers parts o f two calendar years; Volume 58, numbers 7 through 12 (1981) and Volume 59, numbers 1 through 6 (1982). During these twelve months, the American Pota to Journal has published 53 articles, slightly fewer than in the same period of time a year earlier. As is usual, most of the space in the Journal is devoted to papers submitted by members of The Pota to Association of America. The section on news and reviews is the next most extensive and includes various aspects o f Association business, and, in one issue, the abstracts of papers presented at the annual meeting. The tabulation below shows the actual contents of the last 12 issues, including unnumbered pages and a few numbered pages that served two purposes.