Influence of chemical seed and soil treatments onVerticillium-induced yield reduction and tuber defects

Experiments were conducted in 1969 and 1970 to determine the influence of chemical treatments of seed pieces and soil on the development ofVerticillium wilt as measured by tuber yield increases and reduction in severity of tuber defects. The influence of storage onVerticillium-induced tuber defects was evaluated. Seed treatment chemicals tested included zinc ion maneb, maneb, maneb-chloroneb, Polyram, benomyl, and thiabendazole. Soil treatment chemicals included O-Diethyl (O-methyl-sulfinyl) phenyl phosphoro-thioate, disulfoton, phorate, carbofuran, aldicarb, ethyl 4 (methyl- thio)-m-tolyl isopropyl phosphor amidate, benomyl, and thiabendazole. Inoculated seed pieces and artificially infested plot areas were used the first year while the second year natural inoculum from a previous crop was the source of infection. Kennebec and Katahdin cultivars were tested in 1969 and Kennebec alone in 1970. Verticillium-induced yield reductions and tuber defects were more severe in all respects with Kennebec than with Katahdin. With Katahdin the only significant evidence of infection was stem end discoloration. Seed treatments, with the exception of benomyl or thiabendazole, which were erratically phytotoxic, resulted in consistent yield increases and reduction in pink eye severity. In 1969 seed treatment reduced stem end browning in Kennebec. Soil treatment with disulfoton, carbofuran, and aldicarb, both alone and in combination with seed treatments resulted in consistent yield increases with Kennebec. The seed piece and soil treatment combinations tested in 1970 appeared to have an additive effect on yield increase from combination treatments equivalent to the gain from soil treatment alone plus seed treatment alone. The nematicide soil treatment materials did not influence yield. Tuber stem-end browning and pink eye defects in Kennebec did not increase in severity over a five month storage period.     

The effect of barley straw on the survival ofVerticillium albo-atrum in naturally infested field soil

In greenhouse and field experiments amendment ofVerticillium infested field soil with chopped barley straw at rates of 0.4–1.6% by weight reduced theVerticillium population and the amount of infection of potato plants grown in the amended soil. The addition of nitrate or ammonium nitrogen did not alter the effectiveness of the straw amendment.     

Etiology of potato early dying in Delaware

Greenhouse and field plot experiments along with surveys of commercial potato fields were conducted to determine the etiology of potato early dying in Delaware and its impact on yield ofSolanum tuberosum cultivar Superior.Verticillium dahliae was the primary pathogen causing early dying, and no increase in disease severity or yield loss was observed when plants were inoculated with bothV. dahliae andColletotrichum coccodes. The field survey showed thatV. dahliae was the predominant pathogen in symptomatic plants, and nematodes were not essential in association withVerticillium to cause early dying. Disease severity was the same in the presence of a low population or absence of nematodes.     

Non-wound-induced suberization of tuber parenchyma cells: A physiological response to the wilt disease pathogenVerticillium dahliae

Verticillium spp. wilt pathogens enter the root and eventually penetrate xylem vessels of the plant where they can spread into the vascular tissue of the potato tuber. Infected tuber vessel elements often become discolored creating a serious internal tuber quality defect that prevents sale of raw product to its primary market. Despite the costly losses and disease issues created by these infections, the physiological responses to colonization of tuber vessel elements are poorly described, and a model system to study these responses in the laboratory has not been developed. The objectives of this research were to develop such a model system by determining if tuber vessel elements could be infiltrated withVerticillium spp. in a laboratory setting and if a detectable physiological response could be elicited and identified. Results demonstrated that tuber vessel elements in the model system could be infiltrated and that infiltration ofVerticillium dahliae Kleb. conidia into these vessel elements induced a suberization response on the walls of neighboring parenchyma cells. However, the walls of the infiltrated tuber vessel elements did not suberize. A similar suberization response was found in tubers that had been naturally infected byVerticillium dahliae in the field. The suberization response was histochemically determined by assessing the accumulation of suberin poly(aliphatics) and poly(phenolics). This process of internal suberization of tuber parenchyma cells occurred without induction by a wound signal. Consequently, the suberization signal was derived by introduction of the plant-pathogen into the tuber vessel elements. This simple model system provides a versatile tool to investigate the physiological responses of potato tuber to colonization of vessel elements. This is believed to be the first report for such a physiological response toVerticillium spp. in potato tuber.     

Lesion nematode involvement in potato early dying disease

Ohio field studies in microplots in the past 6 years have demonstrated a synergistic interaction of the lesion nematodePratylenchus penetrans withVerticillium dahliae in potato early dying. Tests with various populations ofP. penetrans andV. dahliae, alone and in combinations, have shown that disease occurs when both pathogens are present at populations which individually have little or no effect. Yield loss is not necessarily associated with foliar symptom development, but occurs with the addition of high temperature stress during tuberization. Comparative studies with two other species ofPratylenchus commonly found in Ohio potato soils have shown thatP. crenatus does not interact withV. dahliae and thatP. scribneri interacts only slightly. Since all three species feed and reproduce well on potato,Verticillium interactions probably are not due to wounding. The involvement ofPratylenchus withV. dahliae in potato early dying is an important factor that must be considered in the development of future crop-loss predictive systems.     

Potato Early Dying and Yield Responses to Compost,Green Manures,Seed Meal and Chemical Treatments

Verticillium dahliae Kleb. is a soilborne fungal pathogen of many crops. In potato, it is the major causal agent of Early Dying. In Manitoba, potato fields planted with cv. Russet Burbank are infested with highly pathogenic V. dahliae isolates, which can produce up to 90 % disease severity. The objective of the study was to evaluate selected compost, green manure, and seed-meal treatments, in comparison with the soil fumigant Vapam, for their ability to reduce propagule density of V. dahliae in soil and decrease disease, and to enhance potato yield. Select green manure crops (oriental and white mustard, Canada milk vetch, sorghum-sudangrass, rye, alfalfa, oat/pea mixture), organic amendments (composted cattle manure and mustard seed-meal), and Vapam, and crop sequences that contribute to the suppression of Verticillium, or the improvement of potato yield were used in a 3-year field study initiated in 2006. Survival in soil of microsclerotia was evaluated as a measure of treatments’ success in potentially reducing Early Dying. Compost and seed-meal treatments, compared to an untreated control, reduced incidence to 30 and 40 %, respectively, but only seed-meal reduced V. dahliae propagule density. Overall, green manures over 1 or 2-years were ineffective in reducing propagule density or improving potato yield. Vapam was partially effective in reducing the propagule density only at the beginning of the potato season, but it did not reduce disease incidence compared to the control. Compost and seed-meal are promising as alternative control of V. dahliae. Only compost reduced disease and increased potato yield, which was associated with improved nutrient availability (phosphorus and sulfate) in soil.     

Potato fungicides interfere with entomopathogenic fungi impacting population dynamics of green peach aphid

Fungicides applied to potato can enhance green peach aphid,Myzus persicae (Sulzer), outbreaks by interference with entomopathogenic fungi. (Order Entomophthorales). Late season aphid numbers were highest in potatoes sprayed with metalaxyl + mancozeb, captafol, or mancozeb, and lowest in potatoes sprayed with benomyl, triphenyltin hydroxide, chlorothalonil, or copper hydroxide. In field-collected aphids,Pandora (= Ernyia) neoaphidis (Remaudière et Hennebert) andEntomophthora planchoniana Cornu (F. Entomophthtoraceae) were the predominant cause of mycoses, 66.7% and 22.3%, respectively.Conidiobolus obscurus (Hall and Dunn) Remaudièe and Keller (F. Ancylistaceae) accounted for 8.5% of mycoses. In the laboratory, fungicides were shown to have direct effects on these entomopathogens. Metalaxyl + mancozeb, mancozeb and captafol were strongly inhibitory of germination of conidia, copper hydroxide was intermediate, and chlorothalonil had little effect. Triphenyltin hydroxide, benomyl, metalaxyl + mancozeb, and mancozeb were strongly inhibitory of growth of mycelia, copper hydroxide was intermediate, and chlorothalonil and copper hydroxide had least effect. Benomyl was highly toxic to green peach aphid, copper hydroxide and chlorothalonil intermediate, and captafol, mancozeb, and metalaxyl + mancozeb least toxic. Possible interference of potato fungicides with aphid pathogens is now an important consideration because of the intensity of spraying required to protect the crop from infection by metalaxyl-resistant strains of the late blight pathogen,Phytophthora infestans (Mont.) de Bary. Minnesota potato growers reported high green peach pressure in both 1995 and 1996, years of intensive fungicide spraying. Concomitantly, there was a marked increased in the incidence of PLRV in seed lots entered for winter testing.     

Variety trial of potatoes resistant to Verticillium wilt

Twenty varieties and advanced seedlings, reported tolerant toVerticillium wilt, were compared in field trials during spring and autumn on plots infested withV. dahliae and on comparable non-infested plots. Yield criteria were used to analyze the level of field resistance. Ona-2249 was the only variety tested which gave similar yields in both growing seasons and under both infested and non-infested soil conditions, as compared to those of Up-to-Date, the standard variety.     

Interaction ofErwinia spp. andFusarium roseum ‘Sambucinum’ on the Russet Burbank potato

Laboratory and field studies with the Russet Burbank (RB) potato provide evidence for synergism betweenErwinia carotovora var. atroseptica (Ea) andFusarium roseunt ‘Sambucinum’ (Fs). When these pathogens were inoculated together, the severity of tuber rot was significantly greater than when either pathogen was inoculated separately. Similarly, these pathogens interacted to reduce yield. When both organisms were uniformly applied to puncture wounds on potato seed (inoculum suspension consisted of 10⁸ cells/ml Ea and 10⁵ cells/ml Fs), the total yield was reduced by 46% and U.S. #1 yield by 53%. These reductions occurred even though blackleg symptoms (caused by Ea) were negligible (< 1%). In contrast, inoculations withErwinia carotovora var.carotovora (Ec) and Fs did not interact to reduce potato yield. Potato yields were also not influenced when these pathogens (Ea, Ec, Fs) were separately inoculated.Verticillium wilt (Verticillium dahliae) was significantly less when tubers were inoculated with either Ea, Ec, Fs, Ea + Fs, or Ec + Fs than with uninoculated tubers.     

Detection methods forVerticillium species in naturally infested and inoculated soils

The detection and identification of threeVerticillium species in field soils with a polymerase chain reaction (PCR)-based assay was compared to the traditional plating assay method. The two methods were both able to detect the commonVerticillium species in soils although the PCR method detectedV. tricorpus in three soil samples that the traditional method did not. In addition, the PCR assay was rapid, efficient, and required only 1 to 2 days for positive identification whereas the traditional methods required 4 to 8 weeks. The traditional method provided a quantitative measure of pathogen propagules in the soil with population levels ranging from 0 to 21, 625 colony-forming units per gram of soil. However, it was not able to differentiate between the weakly pathogenicV. albo-atrum strain 2 and the more aggressiveV. albo-atrum strain 1, but these two were distinguished with the PCR assay. Results from this study demonstrate that when symptoms of verticillium wilt are observed in potato plants in the field, the major verticillium wilt pathogens present in field soils can be rapidly and reliably detected by the PCR assay.     

Prevalence of Verticillium wilt in potatoes in the Red River Valley area of Minnesota

Verticilium spp. were present in over 60% of potato fields in Clay, Marshall, Norman, and Polk Counties in the Red River Valley in Minnesota. ThreeVerticillium spp. were isolated from 27% of the potato stems collected in commercial fields during 1968–1972.Verticillium alboatrum andV. dahliae were recovered from infected stems in approximately equal amounts (51% to 47%), butV. nigrescens was recovered from less than 2% of all host-infected plants. Of 12 cultivars sampled, Superior, Kennebec, Red Pontiac, Sebago, Irish Cobbler, and Norland were most frequently infected.     

Rhizoctonia seedling disease of hemp and its control

Rhizoctonia solani Kuhn was isolated from hemp (Hibiscus cannabinus) seedlings affected by damping-off disease. The fungus was highly pathogenic on artificial inoculation. There is no earlier record of this disease in Iraq. Of nine fungicides tested as seed treatment, Bavistin (carbendazim), Homai (thiram), Vitavax (carboxin), Topsin (thiophanate), Fundazol and Benlate (benomyl) gave effective control of the disease.     

Ute Russet: An oblong Russet potato cultivar with resistance to leafroll net necrosis andSclerotium rolfsii

Ute Russet is an oblong, smooth, fresh market potato with a dark net. It emerges slowly, produces an erect, medium sized vine, and is late maturing. Ute Russet is resistant toSclerotium rolfsii Sacc, and leafroll net necrosis, and moderately resistant toVerticillium wilt and scab. Its total and U.S. No. 1 yield potential is comparable to Centennial Russet in the San Luis Valley of Colorado and greater than Centennial Russet in Kern County, California.     

Hampton: A main season golden nematode resistant variety

Hampton is a golden nematode resistant variety suited for main season tablestock production. It is resistant toVerticillium wilt, but susceptible to scab and late blight. Hampton yields as well as Katahdin and produces essentially the same distribution of tuber sizes. Its shape is distinctively spherical with shallow eyes. Its specific gravity is like Katahdin and it will not produce acceptably light colored potato chips.     

Pectic enzyme production by two strains of pseudomonas fluorescens associated with the pinkeye disease of potato tubers

A bacterium identified asPseudomonas fluorescens was isolated from pinkeye lesions of infected Kennebec potato tubers. Two isolates which rapidly macerated tuber slices were selected for further study. Supernatants from macerated potato tuber slices inoculated previously with either isolate 13 or 31 ofP. fluorescens contained pectic enzyme activity. Trace amounts of pectin methylesterase activity were observed in the supernatants. Optimum viscosity reduction of sodium polypectate (NaPP) or pectin substrates by the enzyme complexes occurred at pH 8.6 and 7.2 respectively. Paper chromatography of hydrolysis products indicated that substrates were hydrolyzed terminally as well as randomly when the reaction mixtures were buffered from pH 7.1 to 7.5 NaPP was degraded more rapidly than pectin by both enzyme complexes. Reducing group data indicated the greatest hydrolysis of both substrates occurred near pH 8.6 and that both enzyme complexes hydrolyzed NaPP preferentially. Trans-eliminase activity was found in both enzyme complexes. Optimum activity occurred between pH 8.0 and 9.0 using a NaPP substrate and between pH 7.0 and 8.0 using pectin. The addition of calcium to the reaction mixture increased hydrolysis suggesting the importance of calcium as a co-factor for trans-eliminase activity. Both enzyme complexes macerated potato tuber slices rapidly. Data suggested a relationship between viscosity reduction of NaPP, transelimination of NaPP, and loss of coherence of tuber tissue slices by enzyme complexes of both isolates.     

Detection and identification of fluorescent compounds in potato tuber tissue with corky patch syndrome

A corky patch syndrome that effects potato tuber tissue may be a later manifestation of pink eye disease of potato although an actual cause and effect relationship between the two diseases has not been firmly established. The causal agent for pink eye of potato is unknown but the disease has been associated with the fungiVerticillium andRhizoctonia and the bacteriumPseudomonas fluorescens. Pink eye and corky patch symptoms on the periderm of affected tubers are accompanied by a band of tissue beneath that is intensely auto-fluorescent when viewed under ultraviolet illumination. Studies to determine the cause of the fluorescent reaction were performed using HPLC and a fluorescence monitor. Three phenylpropanoid compounds, chlorogenic acid, esculin and scopoletin, were found to be involved. It appears that these compounds are produced by tuber tissues in response to pathogen invasion and also as part of the wound healing process. Tissues with corky patch syndrome, silver scurf and root-knot nematode contained high concentrations of chlorogenic acid and esculin and low concentrations of scopoletin. Tissues infected with dry rot were visibly less fluorescent, and contained less chlorogenic acid and esculin, and no detectable level of scopoletin.     

Krantz: A Russet cultivar for the irrigated sands

Krantz is an oblong to slightly blocky, russet-skinned potato cultivar with medium-late maturity and a vigorous vine. It is resistant to hollow heart, has high resistance to common scab and possesses high field resistance to late blight. It is moderately resistant toVerticillium wilt, susceptible to early blight, viruses S and X, and exhibits symptoms of bacterial ring rot. Krantz is adapted to the irrigated sands, but will growth crack in heavier soils.     

Effects of soil fumigation with Telone C on soil and plant nitrogen,verticillium wilt and yield of Norland and Norgold potatoes

Two fields in Weld County, Colorado were fumigated in the fall or spring with Telone C in an attempt to restore their productivity. The soils were Julesburg sandy loams and had been cropped to either corn or potatoes for many years. Observations were made over three years on the following: soil ammonium and nitrate nitrogen carry over, seasonal changes in these two forms of nitrogen, petiole nitrate concentration,Verticillium population, verticillium wilt expression,Verticillium stem infection and potato yields of two varieties. No significant differences occurred between control and fumigated blocks in the carry over of soil ammonium or nitrate nitrogen. During the growing season of the first year, no significant differences in soil nitrate concentrations occurred, while during the second and third year at certain times, all fumigated blocks contained significantly less nitrate nitrogen than the control block. Significant seasonal differences measured between blocks in soil ammonium concentration were not related to fumigation. Petiole nitrate concentrations while similar during the first year, were significantly higher in most fumigated treatments the second year and generally lower than the controls in the third year. Verticillium populations were not consistently affected by fumigation. Fluctuations not associated with fumigation prevented drawing definite conclusions. Both spring and fall fumigation reduced wilt severity in the two varieties. Effects of spring fumigation carried through two seasons while fall fumigation did not. Plant infection, determined by culturing stem sections, corresponded with the wilt severity ratings. Fall fumigation increased market yields of Norland potatoes but the increase was not statistically significant. Usually, both fall and spring fumigation significantly increased market yield of Norgold potatoes and over three years, spring fumigation was significantly better. Yield increases resulting from fumigation were considered greater than could be explained from alteration in the soil ammonium to nitrate ratios and/or verticillium wilt control as measured in this study.     

Verticillium wilt of potato in central Peru

Studies in the 1950’s indicated thatVerticillium alboatrum was present in potato fields in the irrigated coastal valleys of central Peru. No further studies were carried out in Peru until those in the late 1970’s initiated at The International Potato Center. So far, Verticillium wilt of potatoes has been observed in several valleys of the coast as well as in highland valleys at elevations up to 3400 m. Although the frequency of isolation ofVerticillium sp. has been much greater in the highlands, the disease is of less consequence there because of low temperatures during the growing season. The most common symptom observed in the field is early senescence, including yellowing and stunting of the foliage. Typical “wilt” symptoms are rarely found. Both in the coastal valleys and in the highlands, onlyVerticillium dahliae has been identified. Although no studies on losses and the economic importance of Verticillium wilt of potatoes have been done, it is clear that the two most important crops used in rotation in coastal valleys of central Peru, potato and cotton, are severely affected.     

Potato early dying—A serious threat to the potato industry

Potato early dying (PED) is characterized by a loss of plant vigor during mid to late summer followed by senescence and death of the crop a few weeks prior to normal maturity. This disease is of serious importance in areas of long-term or intensive potato production and is largely uncontrolled. Symptoms of PED, which are difficult to distinguish from normal senescence, especially in early-maturing cultivars, are uneven chlorosis and necrosis of vines and tan discoloration of vascular tissues. The basic cause of PED is the soil fungusVerticillium. Two species are involved—V. alboatrum predominating in cooler areas andV. dahliae in warmer areas. Both fungi commonly occur in cultivated soils and persist as melanized hyphae or microsclerotia, respectively. Infection occurs through roots followed by colonization of the vascular system. Contamination of uninfested fields can occur by wind or mechanical movement of soil-borne propagules or introduction of infested seed stock. AlthoughVerticillium is the primary pathogen in potato early dying, other soil organisms are involved, resulting in a “disease complex.” Research is under way in many areas to further our understanding of these pathogenic interactions and to exploit this knowledge for use in new systems of prediction and control.