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PRESENTED AT 57th ANNUAL MEETING -- Continued The influence of nitrogen and phosphorus fertilization on periderm anatomy in Russet Burbank potatoes. CALLIHAN, R. H., R. E. McDot.~, a~'u P. T. MA>'N, University of Idaho Branch Experiment Station, Aberdeen, Idaho. Russet Burbank potatoes grown on a loam soil with a high rate of nitrogen fertilizer (600 lb N / A ) produced tubers with thinner cork, composed of fewer cork cell layers, but thicker individual ceils as compared with tubers produced without added N. Potatoes grown on a very coarse textured soil with a high rate of nitrogen fertilizer (600 lb N / A ) produced tubers with a thinner cork composed of fewer cell layers than tubers produced without added N. However, these treatments did not result in differences in periderm cell thickness. In contrast, Russet Burbank potatoes grown on a loam soil with added phosphate produced potatoes with thicker cork comprised of more cell layers than tubers without P added. Again, differences in cell thickness were not detected. The southeastern Idaho soils used in this study were low in the added nutrients prior to fertilization, thus unfertilized plots produced deficent plants. Periderm measurements and counts were made on cells and layers which stained with Sudan III. All observations were made near the center of individual net patches, between fissures in the russeted periderm.
Response of Russet Burbank potatoes to slow release nitrogen compounds. KUNKEL, ROBERT, ~N~"HOLSTAD, AND C, ~4~RESGE,Washington State University, Pultman, Washington. Nitrates and sulfates leach readily when soils are wetter than field capacity. This can result in contamination of ground water and added fertilizer costs. When plants are small only small amounts ot fertilizer are needed - - the amounts increasing as plants get bigger. In some situations it would seem desirable to supply the plants with small but uniform amounts of nitrogen thereby maintaining a relatively constant size plant which is producing tubers instead of viues. This would be especially important in the Columbia Basra of Washington wherein potatoes are harvested from 100 to 180 days after planting. In 1971, reducing the amount of readily available nitrogen early in the growing season with urea-formaldehyde or sulfur coated urea ( s c u ) decreased the yield of Russet Burbank potatoes, scu materials of greater solubility were used in 1972 and yields comparable to those of ammonium :utrate, amino, alum sulfate and urea were obtaned but urea-formaldehyde produced lower yields.
Potato yield and quality related to residual potassium fertilizers in coarse textured soils. McDoLE, ROBERT E., University of Idaho Branch Experiment Station, Aberdeen, Idaho. Potassium fertilizer plots were established on Fc!tham loamy sand soils in the Fort Hall area of Southeastern Idaho in 1970. The field on which these plots were established had received no potash fertilizer since being cleared for cultivation in 1968. Potash fertilizer was applied to plots in 1970 at several rates (.0, 150, 300, 600 lb K z O / A ) as muriate oi potash (KC1) and sulfate of potash (KaSO4). Tubers harvested in 1970 and 1972 showed no yield response to the 1970 fertilize~r treatments. The only influence on quality was reflected in specific gravity of tubers. Muriate of potash (KCI) apptied at the highest rate in t970 resulted iu lower specific gravity tubers in 1970 and an apparent residual effect that again reduced specific gravity in the 1972 crop. Soil test K values and petiole levels obtained fronl the plots in 1972 indicated a residual "carry-over" of the potash applied to the plots in 1970. Although the unfertilized plots gave soil test values and petiole levels that would suggest plant deficiencies, no response was observed. Even on these extremely coarse textured soils, under normal irrigation, potash fertilizer residual is sufficient to influence the potato crop at least two years after it was applied. This trial gives some indication of the natural K releasing powers of south Idaho soils.
Pre-plant dinitroanaline herbicides in potato culture. CaLLtHAN, ROBERt H., University of Idaho Experiment Statiol~, Aberdeen, Idaho. Potato weed control with mechanically incorporated toluidine herbicides was better on a silt loam soil with pre-plant application than with post-plant pre-emer-
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gence application where equivalent rates were used. Control of deep germinating susceptible weeds was better, and oat bioassays indicated more advanced degradation, when these herbicides were incorporated pre-plant than post-plant pre-emergence. Pre-plant applications with 67-75% as much herbicide achieved control equivalent to that of post-plant pre-emergence applicat{ons. It is suggested that this performance difference is due to (i) mechanical difficulty in obtaining application uniformity of mechanically incorporated materials in field culture after planting, and (if) the necessarily shallower placement of post-plant applications. The increase in efficacy of pre-plant applications of dinitroanalines was accompanied by a concomitant decrease in potato tolerance, as measured by emergence rate, shoot symptom expression, and total yield, when compared with post-plant preemergence applications. Influence of vine killers on a serious vascular discoloration in R u s s e t Rural tubers.
SIECZKA, JOSEPH B., Cornell Uuiversity, Ithaca, New York, JOSEPH D. HARRINGTON, Pennsylvania State University, State College, Pennsylvania, and OTTO E. SCHULTZ, Cornell University, Ithaca, New York. Several commercial lots of Russet Rural tubers were affected with a diffuse brownish discoloration around the vascular ring. The discolored tissue turned dark brown upon chipping. The effects of eight vine killing treatments on this disorder were evaluated in three experiments in upstate New York and Pennsylvania. Internal discoloration data show that stem end browning is not a reliable method of predicting the disorder. To obtain more dependable information, data were collected after tubers were cut longitudinally in half. Ratings were taken on the intensity of the discoloration and the distance the discoloration extended from the stem end. The pattern of discoloration (either "pencil line" or diffuse) was also recorded. The depth of discoloration and the number of tubers havng a "pencil line" discoloration limited to the vascular ring were associated with some vine killing treatments. In Russet Rural tubers, the diffuse discoloration was not associated with vine killing treatments. Laboratory chipping tests confirmed that discolored areas in fresh tubers coincide with those encountered in chips. Kennebec tubers from plots receiving the same treatments did not develop the disorder. Effect of inhibitors on coumarin-induced tuberization of axillary shoots of Solarium tuberosum g r o w n in vitro. STALLKNECHT,G. F., University of Idaho, Aberdeen, Idaho. Studies were conducted on the effects of inhibitors of nucleic acid and protein synthesis, and plant growth retardants on coumarin-induced tuberization of axillary shoots of Russet Burbank potato shoots grown in vitro. Inhibitors of RNA synthesis, Actinomycin D and 5-fluorouracil depressed tuberization by 50% at concentrations above 5:0 ul/ml, whereas the inhibitor of protein synthesis chloramphenol prevented tuberization at a concentration of 25.0 ul/ml. Tuberization was inhibited 80% by a concentration of 100 ul/ml of p-fluorophenylalanine. Coumarin induced tuberization was stimulated by succinic acid-2-2 dimethylhydrazide (ALAR), (2-chloroethyl) trimethylammonium chloride (CCC), (2-ch!oroethyl) phosphonic acid (Ethrel) at concentrations of 0.1 to 100.0 mg/1. When applied in the absence of coumarin, Alar and CCC were not effective in induction of tubers, while Ethrel at concentrations of 10-50 mg/1 was effective in inducing tuberization in 10-30% of the shoots. Coumarin at 25 rag/1 was not effective in induction of tuberization on Skoog medium indicating that the mode of action of coumarin may be quite different from that of Kinetin, in that high nitrogen levels are more inhibitory to the coumarin tuberization mechanism. Effect of s o m e cropping practices on survival of Verticillium.
B~'SCH, L. V., University of Guelph, Guelph, Ontario, Canada. The experiment was designed to fit a range of microplots which are 4 ft square and 3 ft dee[~. At the start of the experiment half of the plots were planted to Kennebec potatoes, inoculated with Verticillium albo-atrum and the remainder with V. dahliae. All plants were I00% infected the first year. During the second year three plots in each treatment were again planted to washed Kennebec potatoes, six plots to barley and three plots left fallow. The third year the same three plots in each treatment
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were planted to potatoes, three of the six barley plots and the three fallow plots, and the remaining three plots in each treatment were replanted to barley. The fourth year all plots were again planted to potatoes. In general, the treatment had little effect on the survival of V. dahliae although the(e was some drop in the percentage of infection with dahliae during the second year of the experiment. The following years the percent infection remained almost constant. With Uerticillium albo-atrum, however, only in the plots planted continuously to potatoes was there any significant survival, the percent infection in these plots remained quite constant. In some of the fallow plots there was more V. albo-atrum recovered than expected. The possibility that broad-leaved weeds such as pigweed and lamb's quarters may have acted as hosts cannot be overlooked. Interrelations between nitrogen nutrition and early blight control on yield of potatoes. SOLTANPOUR, P. N., San Luis Valley Research Center, Colorado, and M. D. HARRISON, Colorado State University, Fort Collins, Colorado. Three different rates of soil-applied nitrogen were combined in all possible combinations with different schedules of fungicidal sprays for early blight control in field experiments for three consecutive years. The results indicated that yield response to fungicidal sprays-was more pronounced when potato plants had adequate amounts of nitrogen than when they were deficient. Both spraying and nitrogen applications reduced the percentage of leaflets affected by early blight lesions. However, the effect of the fungicide was more than that of nitrogen. Economic analyses based on the cost and price assumptions showed that $1.00 investment in the optimum number of fungicidal sprays at the adequate rate of fertilizer returned $8.34, $9.17 and $1.89 in 1970, 1971, and 1972, respectively. N e w insecticides for potato tuberworm and green l~each aphid control on potatoes. McCALLEY, N. F., Agricultural Extension, University of California, Salines, California. Nine insecticides were evaluated for control of the potato tu~erworm, Phthorimaea operculella (Zeller), and the green peach aphid, Myzus persicae (Sulzer), in a replicated field experiment at Salines, California in 1972. Six sprays were applied by ground sprayer at 2-week intervals. Tuberworm control was based on larval counts taken i n plant foliage and infested potato tubers at harvest. Green peach aphid populations were assessed by counting aphids on the foliage four times during the experiment. Methomyl (Lannate| monocrotophos (Azodrin| and Monitor| all registered for use on potatoes, controlled both the potato tuberworm and the green peach aphid. Azinphosmethyl (Guthion| applied at twice the registered rate, was effective on tuberworm control,-but increaesd the green peach aphid population, The remaining compounds evaluated are currently not registered for use on potatoes. Orthent~ and phosalone (Zolone| indicated activity against the green peach aphid and potato tuberworm, with Orthene| providing outstanding control of these pests. Phosvel at the rate tested indicated activity against the potato tuberworm, but was not particularly effective in control of the green peach aphid. Oxamyl (Vydate@) and Prirmor| while providing excellent control of the green peach aphid, were the least effective of the compounds evaluated f o r potato tuberworm control, Selection for resistance to potato leafhopper infestation. I. Selection methods. SANFORD, L. L., U S D A - A R S , Beltsville, Maryland, and J. P. SLEESMA~, Ohio Agricultural Research and Development Center, Wooster, Ohio. A randomly mated Solanum tuberosum L. population (three generations) derived from clones from several breeding programs, displayed considerable resistance to potato leafhopper infestation in the field. Infestation levels on the population clones ranged from 2 to 28 nymphs per 45 sec count (mean = 12), whereas a susceptible check averaged 20 nymphs per count. Clones selected for low leafhopper densities in 1971 were compared with the unselected population again in 1972 to evaluate the effectiveness of selecting from small plots (3-hilt) with a minimum of replication. The selected clones averaged 30% lower in leafhopper density than the population did in 1971 and 10% lower in 1972. The average repeatability for one plot per clone per location, two locations, and two 45-see nymph counts per plot equaled 36%.
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Enzymatic degradation of potato cell waUs by F u s a r i u m r o s e u m ' A v e n a c e u m ' . *~{ULLEN,J. M. AND D. F. BATEMAN, Cornell University, Ithaca, New York. Fusarium roseum 'Avenaceum', causal agent of a potato tuber dry rot, produced exopolygalaeturonase, endopolygalacturonate-trans- eliminase,.galactanase, two arabinosidases and xylanase when cultured in media containing isolated potato cell walls or other appropriate polymeric carbohydrates as carbon sources. Similar enzymes were obtained from F. roseum 'Avenaceum'-infected but not healthy potato tubers. Cell walls isolated from potato tubers contained approximately 30%0 galaetose, 15% galacturonic acid, 8% arabinose, 3% xylose, 3% glucuronic acid, 1% rhamnoes, and 25% cellulose. Wall protein content was not determined. Fungal enzymes produced in culture or in diseased potato tubers degraded up to 50% of isolated potato cell wall preparations within a 5-hour period. Larger quantities of these enzymes were obtained from F. roseum 'Avenaceum'-infected tubers which were virus X-free (highly susceptible to F. roseum 'Avenaceum') than from F. roseum 'Avenaceum'-infected tubers which contained virus X (moderately susceptible to F. roseum 'Avenaceum'). The poor recovery of cell wall degrading enzymes from virus X-infected tubers infected with F. roseum 'Avenaceum' was correlated with high polyphenol oxidase levels. Distribution of aphids in regions of Ontario and their relationship to potato leaf roll. McEwEN, F. L., L. V. B u s c h AN'D G. RITCEY, University of Guelph, Guelph, Ontario, Canada. A summary of potato-infesting aphids in seven regions of Ontario indicated that four species occur in most areas. The relative proportion of the different species varies from region to region and from year to year. The peach aphid was more abundant in southern than in northern parts of Ontario, but did occur in all areas examined in each of the 3 years. High populations of the peach aphid were generally associated with a high percentage infection with potato leaf roll but there were significant exceptions. Resistance to the green peach aphid in some potato species. TARN, T. R. AND J. B. ADAMS, Agriculture Canada Research Station, Fredericton, New Brunswick, Canada. Diploid potato species from Argentina and Peru are being evaluated to identify a source of resistance to aphids to utilize in a breeding program. This paper reports the results of the evaluation of seedlings from Solanum canasense Hawkes, S. multidissectum Hawkes and S. sanctae-rosae Hawkes for resistance to the green peach aphid, M y z u s persicae (Sulzer). Initial screening has been conducted by exposing 50-55 day old seedlings to heavy infestations of M. persicae for 7-11 days and then selecting seedlings .with low aphid populations. From a total of nearly 900 seedlings from 11 accessions, 194 seedlings were retained. Subsequent evaluation of the survivors was conducted with an electronic monitoring system, a Fredericton adaptation of the McLean-Kinsey technique. The aphid and leaf were wired so that the aphid completed an electronic circuit when it salivated or fed, and the changes in conductivity were monitored on a strip chart. The response patterns, which were observed in 8 minutes, measure the acceptance or rejectance of. the host leaf by the aphid. Response patterns will be described and related to the aphid behaviour on the host clone. Effect of fumigation and fertilizers on g e r t i c i U i u m w i l t and nutrient levels in Russet Burbank. Davis, J. R. ANn R. E. McDoLE, University of Idaho, Aberdeen Branch Experiment Station, Aberdeen, Idaho. Main plot treatments consisting of no fumigation and fumigation (Telone C 30 gpa) were compared with several sub-plot fertilizer treatments for control of Verticillium Wilt (Verticillium dahliae) on the Russet 'Burbank variety. All plots received N at 180 lb/A, P2Or, at 160 lb/A, and K.20 at 190 lb/A. Nitrogen fertilizers applied included Ca(NO:I)2 and (NH4)2SO4. Each were applied with and without elemen-i tal S (600 lb S with (NH4)2SO4 and 80(} lb S with C a ( N O 3 ) 2 ) and with and without a micronutrient mix (including B, Cu, Zn, Fe, and Mn). Soil fumigation reduced Verticillium wilt, but no effect was observed on symptom expression with fertilizer treatments. Yield was not affected by treatments. Petiole samples collected
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on two collection dates showed highly significant negative correlations of K, Mn, and NOa with Vcrticillium wilt. In July, before evidence of Vcrticillium symptoms, petioles from fumigated plots showed a significant increase of K, Mn, and NO3 when compared with unfumigated plots. Intoractiou effects between fumigation plots and fertilizer treatments were not significant. No fertilizer treatment showed an increase of K. Treatment with S increased Mn uptake and (NH~).,SO4 showed a significant increase of NO~ uptake when compared with Ca(NOs).,. Results show that treatment with Telone C can significantly increase nutrient uptake and this increase is negatively correlated with disease severity. T h e effect of potato virus X on susceptibility of potato tubers to Fusarium roseum 'Avenaceum'. JONES, E. D. AND J. M. ~{ULLEN, Cornell University, Ithaca, New York. Potato virus X ( P V X ) - f r e e and mild PVX-infected tuber lines originating from the same Katahdin clone were compared for susceptibility to tuber rot incited by Fusarium roseum 'Avenaceum'. The effect of interval between top-kill and harvest on the development of Fusarium tuber rot was also determined. A series of tubers from both P V X - f r e e and PVX-infected tuber lines was: (i) mechanically bruised and inoculated by immersion in a spore suspension of F. roseum 'Avenaceum', (if) mechanically bruised but not inoculated, (iii) inoculaled only, and (iv) neither bruised nor inoculated. Tubers from all treatments were then stored at temperatures of 65-70 F for a 3-week period prior to being placed in 39 F storage. The amount of rot was determined after a 5-6 month storage period at 39 F. In 'a 3-year study PVX-free tubers were significantly (1%) more susceptible to infection by F. roseum 'Avenaceum' than PVX-infected. Tubers, both P V X - f r e e and PVX-infected, remaining in the ground for a 2-week period following top-kill were significantly (5%) more susceptible to Fusarium tuber rot than those harvesled 3-5 weeks after top-kill. Virus infected plants more resistant to Phytophthora infestans than healthy plants. FERNANDEZ, CARMEN AND H. DAVID,THURST~N, Cornell University, Ithaca, New YOrk. The effect of virus infection on resistance to Phytophthora infestans was studied in the field at Ithaca, New York. Twelve plants each of Katahdin potatoes infected with potato virus X ( P V X ) , potato leaf roll virus ( P L R V ) , potato spindle tuber virus ( P S T V ) , and the potato clone N.Y. 47 infected with potato virus Y ( P V Y ) , were interspersed at regular intervals throughout a field of healthy Katahdin potatoes. Border rows were inoculated August 8, 1972, aud the fungus s u b s e ~ e n t l y spread to all plants in the field. Virus infected plants were more resistailt to the development of late blight than healthy plants when evaluated according to size of lesion, speed of sporulation, amount of sporulation, number of lesions per plant, and percentage defoliation. Differences in size of lesion and percentage defoliation were significant statistically for all four viruses studied; differences in speed and amount of sporulation were significant for P V X , . P V Y , and P S T V ; while differences in number of lesions per plant was significant only for PVY. Similar results were obtained in the greenhouse in 1971-72. Control of early blight in eastern Idaho. DOUGLAS, DEXTER R., ARS, U S D A , Western Region, Aberdeen, Idaho, AND M. D. G~OSKOPP, Sunspiced, Inc., Blackfoot, Idaho. Potato early blight, caused by .4lternaria solani, can be an important disease problem in eastern Idaho, especially on light textured soil where frequent irrigation is used. Different recommendations have been reported regarding numbers of fungicide applications necessary for effective control and the proper time to begin applications. Field trials were conducted for three consecutive )-ears in the Blackfoot area where early blight is a perennial problem. Different fungicide application schedules, ranging from two to seven treatments, were used. A constant rate, 2 lb/A, 9.f fungicide was applied with a tractor-mounted boom sprayer operating at 80-90 p.sa., using 30 gal of water per acre. Disease evaluations were made by estimating the percentage of leaflets infected, size of leaf and stem lesions, overall severity, total yield, and grade-out percentage. Early blight can be adequately controlled with three applications of fungicide with no significant loss in yield, provided the control application is properly timed.
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An application program starting when the plants are small and continuing throughout the season is not necessary. The first application should be timed to coincide with an approximate stage of plant maturity which is directly related to the secondary spread of the fungus. T e s t i n g for latent viruses in potato. WRIGHT, N. S., Canada Department of Agriculture Research Station, Vancouver, British Columbia, Canada. Plants from tubers infected with potato virus S ( P V S ) gave negative tube (local lesious) on Gomphre~m ylobosa at time of emergence and thereafter. Plants inoculated in the field had fully systemic infection of foliage after three weeks. Plants from tubers iufected with potato virus S ( P V S ) agve negative tube precipitin tests at the four and six leaf stages but gave positive tests from all leaves at later stages. Inoculated plants had fully systemic infection after seven weeks. The virus was more concentrated in mid and lower leaves than in upper leaves. The incidence of P V X in seed potato fields was determined on G. globosa by testing samples of 250, 500, or 1000 leaflets per field. Tests were made on composite samples of 50 leaflets and on individual leaflets from composite samples found to contain P V X . Composite samples containing leaf tissue from more than three plants were unreliable in tube precipitin tests for PVS. Effect of intratuber Verticiilium aibo-atrum on current crop of Norgold HOYMAN, ~V. G., ARS, U S D A , Prosser, Washington. Norgold Russet seed infected with Verticillium albo-atr,m and free of tuber-borne inoculum was planted in Verticillium infested and non-infested determine if intratuber infection affected production of this very susceptible It had no effect on emergence, growth rate, size of plants, appearance and of Verticillhon wilt symptoms, total yield, percent U.S. No. 1 tubers nor gravity.
Russet. external soils to variety. severity specific
Influence of m a n g a n e s e on local lesion expression of potato spindle tuber 'Metavirus' in $co~olla sinensis. SINGIt, R. P. AND C. R. LE~:, Agriculture Canada Research Station, Fredericton, New Brunswick, Canada. Influence of Mn on the local lesion expression of potato spindle tuber 'metavirus' was studied in Scopolia sincnsis plants grown iu sand cultures containit~g from 0 to 18 mg/ml of Mn. Optimum numbers of local lesions were observed on plant leaves containing Mn conteuts of 1900 m g / g and M u / F e concentration ratios of 27. Uppermost mature leaves exhibited more local lesions than lower leaves at this tissue Mn content in short term tests. These results further support the contention that sufficient soluble Mn must be available in the potting medium to provide above normal tissue Mn contents and M n / F e ratios in host plants for cousistent and accurate potato spindle tuber metavirus tests. Influence of potato viruses X and S on yield of Russet Burbank potatoes. KUNKEL, ROBERT, N. HOLSFAD,H. BL'TALA,AND R. E. THORNTON, Washington State University, Pulhnan, Washington. Potato seed free of P V X and P V S from four seed sources was compared with comparable virus containing check tubers for yielding potential and no differences were found among them. The specific gravity of the tubers from the virus free plants was significantly higher and the blackspot iudex significantly lower than for the tubers from the virus infected plants. Comparison of P V X - f r e e Russet Burbank Canadian source seedstock w i t h regular P V X - i n f e c t e d Idaho seedstock, OHMS, RICHAP-:D E., Twin Falls, Idaho; A. J. '~VALz. Parma, Idaho; GENE RINEBOLD, Twin Falls, Idaho; JAY GARNER, Blackfoot, Idaho; GLENN \:OGT, Idaho Falls, Idaho; H. McKAY, University of Idaho Branch Experiment Station, St. Anthony, Idaho; AND J. PAVEK) University of Idaho Branch Experiment Station, Aberdeen, Idaho. From one potato virus X ( P V X ) free, but P V S infected, Russet Burbank tuber, obtained from the Canada Research Staton, Vancouver, Canada in 1967, a PVX-free seed supply was established. At the University of Idaho Tetonia Experiment Station in
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1971, this P V X - f r e e seedstock and the regular ldaho Foundation PVX-infected seed-stock were increased and stored under nearly identical conditions. Single-drop seed of these two seed stocks was used to make comparative field tests in 1972. The trials were conducted at nine locations representing a range of Idaho's environmental and soil conditions from the southwestern to the southeastern parts of the State. There was a total of 42 replications. At all these locations, the P V X - f r e e seedstock produced higher yields and, in eight of the nine trials, higher specific gravity than the regular Idaho PVX-infected foundation seedstock. T~he P V X - f r e e stock excelled in U.S. # 1 over 10 oz by 11.1 c w t / A ; total U.S. # I , 48.9 c w t / A ; total yield, 43.8 c w t / A ; and specific gravity, 0.001. In 1973, all of the Uuiversity of Idaho Foundation Russet Burbank seed i.s from the PVX-free stock.
Solanum demissum, P I 230579, a true seed local lesion host for potato virus Y.
~VEBB, R. E., A R S , U S D A , Agricultural Research Center, Beltsville, Maryland, and DAVID R. WILSON, Aroostook State Farm, Presque Isle, Maine. Intact seedlings or individual leaves of 5". demissum P I 230579 developed dark, slightly elongated local lesions in 3-4 days following inoculation with three strains of potato virus Y ( P V Y ) at temperatures of 70-74 F. Local lesions did not develop following similar inoculations with two or more strains each of potato viruses A, M, S, X, and spindle tuber. Inoculations with P V Y in mixtures with these viruses did not change the time of appearance, color, or size of the local lesions induced by P V Y alone. 5". demissum P I 230579, used in the form of young plants or individual leaves, is a valuable aid in indexing aphid or mechanically inoculated potato clones for resistance to PVY. It is a superior diagnostic host for differentiating P V Y from other viruses commonly found in potatoes in the United States. The current status of the cooperative S t a t e / F e d e r a l golden nematode program in the United States. SAND, P. F., A P H I S , U S D A , Washington, D. C. Golden nematode was first discovered in North America in July 1941 when it was found to be responsible for damage in a potato field in Nassau County, Long Island, New York. A total of 19,488.52 acres of land has been found infested on Long Island since the beginning of the program. Of this amount, approximately 11,500 acres have been permanently removed from agriculture for real estate development; 6,491.31 acres have been fumigated and released for potato production and approximately 1,200 acres have been plantel to nonhost crops or are pending development and have not been treated. In 1972-73, 367 acres were found infested and all but 68 acres, which is being planted to a nonhost crop, will be treated. An infestation was discovered in a 55-acre potato field in Prattsburgh, Steuben County, Ne~v York, in December 1967. Additional survey resulted in the discovery of infestations on seven additional properties with an overall total of 340 acres infested. One of these fields (55 acres) was sold to Cornell University .for golden nematode research. A cooperative State/Federal research program on golden nematode was established in 1969. Fumigation of the other seven fields was completed in 1969 and 1970, and no additional viable cysts have been found on them or in the regulated a rea. On February 7, 1969, golden nematode cysts were recovered from soil collected the previous fall from a 350-acre potato field in New Castle County, Delaware. The soil was fumigated and released from quarantine March 18, 1970, after an intensive specially designed soil survey recovered no additional cysts. Beginning with 1972, all infested fields that are fumigated will either be planted to a resistant variety of potatoes or to a nonhost crop for an indefinite period. The first crop season for these fields will be 1973. Two resistant varieties, Wauseon and Peconic, are available to growers, and a new variety, Hudson, will be available in 1975. In 1971, a nationwide golden nematode biometric survey was initiated in all important potato-producing areas in the United States. Over a 5-year period, 10,000 sites will be examined.
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Overwintering of potato spindle tuber virus in Solanum duleamara L. YANG, T. C. AND W. J. HOOKER, Michigan State University, East Lansing, Michigan. In the early summer of 1972, S. dulcamara seedling plants were mechanically inoculated with crude sap form potato spindle tuber virus infected Rutgers tomato plants. After inoculation, plants were grown outside of the greenhouse throughout the balance of the summer, fall, winter and spring. Virus recovery tests were made at intervals by mechanical and/or grafting methods to young Rutgers tomato seedlings. Isolations were attempted in late October, January, February, April and June. P S T V was consistently recovered from inoculated plants and control plants were virus free. This suggests that diseased S. dulcamara plants are capable of carrying P S T V overwinter under Michigan conditions and that perennial plants such as S. dulcamara could serve in nature as primary inoculum.
Why there is need for virus-free seed potato certification programs in North America. MUNRO, JAMES, Canada Department of Agriculture, Ottawa, Ontario, Canada. Of the many countries that produce high acreages of certified seed potatoes, only a few do not have "virus-testing" procedures as part of a complete official national seed potato certification program. There are probably two main reasons for inclusion of procedures required for such a program: (i) the claimed economic increase in returns obtained from such crops; and (if) less doubt in the fields as to whether slight departures from the normal in growing plants are caused by virus infections. Development of virus X free crops under certifying agencies began in countries where, perhaps because of whole seed planting, virus X free clones could be selected from all varieties. IThe importance of virus X lies in its variability, and growing crops in the field are infected with a mixture of strains. Unlike potato virus Y, it is difficult to obtain a single strain of virus X and maintain it as such. By constant roguing and perhaps by choice of area for uniformity of growth, growing crops of certain stocks of a variety may vary little irom year to year. But those same stocks may show obvious or even severe symptoms of mosaic every year when grown elsewhere. In this mixture of strains, the dominant strain determines the severity of the disease; and when dominance changes, apparent health in a plant-may become obvious disease. Rugose mosaic usually attributed to infection by virus Y, may sfiU occur as a symptom of virus X infection in the field, and the strains of virus Y that may be carried without symptoms of infection in some varieties may cause obvious symptoms in others. Some varieties select from within mosaic virus strains those to which they are apparently more susceptible; this specificity to strain infection also occurs with the test plants, tobacco and Datura strarnonium. m
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I h e r e w i t h r e m i t $ 1 0 . 0 0 ( $ 1 2 . 0 0 in f o r e i g n c o u n t r i e s e x c e p t t h e A m e r i c a s ) i n p a y m e n t of o n e y e a r ' s m e m b e r s h i p in T h e P o t a t o A s s o c i a t i o n of A m e r i c a w h i c h i n c l u d e s a y e a r ' s s u b s c r i p t i o n to t h e American Potato Journal m o n t h l y . M a k e c h e c k s p a y a b l e to T h e P o t a t o A s s o c i a t i o n of A m e r i c a . Name Address
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C i t y & S t a t e ............................................................................
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