The effect of seed-and soilborne inoculum ofColletotrichum coccodes on the incidence of black dot on potatoes

Summary Soil in a potato field naturally infested with black dot (Colletotrichum coccodes) was fumigated with methyl bromide at 126 g m⁻² or left unfumigated. Potato seed tubers (cv. BP1) uninfected, lightly infected (1–25% surface affected), severely infected (26–100% surface affected) and severely infected withC. coccodes but dusted with prochloraz manganese chloride as Octave 2.5% DP at 750 g per 100 kg seed were planted in fumigated and unfumigated soil. When harvested, the incidence of black dot on the progeny of infected seed planted in unfumigated soil was twice that of progeny in fumigated soil, with progeny of uninfected seed having a 68.5 times higher disease incidence in unfumigated soil. Black dot on progeny tubers was reduced by pre-treatment of seed with prochloraz in fumigated soil only. With black dot infested fields, planting disease-free seed or treating seed with fungicides would not decrease disease on progeny tubers.     

Improving the field performance of micro-and minitubers

Summary In many seed potato producing areas, micro- and minitubers are too small for direct planting as seed tubers in the field. Such use of these propagules can, however, be feasible if the crop's growth and development can be advanced. Increasing light interception, harvest index and yield of useable progeny tubers has been proved possible with plastic mulch and pre-planting of small tubers in a greenhouse. High amounts of nitrogen (up to 180 kg ha⁻¹) or deep planting (up to 9 cm) were less effective. Using older or pre-sprouted micro- or minitubers may be beneficial, because this might increase the number of sprouts per mother tuber (and thus stems per plant) or advance the growth of sprouts or stems. However, this would require even more careful management, due to the weakness of these sprouts and stems. Micro- and minitubers should be as large as feasible when used for direct planting in the field.     

Prevention of berry formation in potato plants (Solanum tuberosum L.) by single foliar applications of herbicides or growth regulators

Summary Thre seed production in potato plants (Solanum tuberosum L.) may contribute to the persistence of potato cyst nematodes and of viruses, fungi and bacteria. In four experiments MCPA, ethephon, 2,4D-amine, naphtylacetamide, metoxuron and gibberellic acid were tested for their potential to reduce berry formation. MCPA (500 or 750 g a.i. ha⁻¹ and ethephon (144 or 192 g a.i. ha⁻¹) reduced or almost completely prevented berry set and their effect was strongly influenced by the crop growth stage at the time of application. For both chemicals application at early bud stage was the most effective and, whereas MCPA showed no adverse effects on tuber yield, size, dry matter content and fry colour, ethephon substantially reduced the percentage of large tubers over 50 mm.     

Effects of Fungicide and Rate of Application on the Development of Isolates of <Emphasis Type="Italic">Polyscytalum pustulans</Emphasis> Resistant to Thiabendazole and on the Control of Skin Spot

Resistance to thiabendazole, sometimes of varying degrees, has occurred in a number of fungal species causing diseases of potato tubers, including skin spot caused by Polyscytalum pustulans. The effect of applying a range of concentrations of thiabendazole, imazalil or a formulated mixture of thiabendazole and imazalil on the development of isolates of P. pustulans partially or fully resistant to thiabendazole and on the control of skin spot over a number of successive generations of seed potato multiplication was examined in a series of experiments over 3 years. Seed tubers were inoculated with a sensitive, partially resistant or fully resistant isolate in the first year of an experiment and combinations of fungicide and a range of concentrations were applied to the seed tubers annually before planting over two or three successive generations. Immersing seed tubers inoculated with the partially resistant isolate in a relatively high concentration of thiabendazole, 0.7 g a.i. l^-1, did not result in the development of fully resistant isolates. Moreover, the effect of all fungicides in controlling eye contamination and skin spot did not differ between partially and fully resistant isolates. For seed tubers inoculated with the sensitive isolate, applying thiabendazole resulted in the occurrence of resistant isolates on first-generation daughter tubers, but the effect of fungicide concentration on the frequency of resistant isolates, partially or fully resistant, was inconsistent. In one experiment, the highest frequency of resistance was found at the greatest concentration, 0.4 g a.i. l^-1, but, in the second experiment, the frequency was unaffected by the concentration of thiabendazole. On second-generation daughter tubers derived from thiabendazole-treated seed tubers, virtually all isolates were resistant and the frequency of partially and fully resistant isolates was similar to that in the first generation. Applying a mixture of thiabendazole and imazalil to seed tubers inoculated with a sensitive isolate resulted in the development of some resistant isolates in the first year but the frequency did not generally increase with successive applications of the mixture. A mixture of thiabendazole and imazalil, and imazalil alone gave similar control of eye contamination when applied at equivalent concentrations. However, increasing the concentration of imazalil from 0.1 to 0.7 g imazalil l^-1 did result in an increasing impairment of plant growth, but the deposits achieved within that range of concentrations were greater than that recommended by the manufacturer. These results demonstrate that control of P. pustulans by thiabendazole, imazalil and a mixture of thiabendazole and imazalil applied at a range of concentrations was similar for isolates partially or fully resistant to thiabendazole.     

The effect of physiological age and planting date on the response of potatoes to applied nitrogen and on levels of residual nitrogen post-harvest

Summary Experiments were conducted on sandy and deep silty soils to assess the effect of physiological age of seed tubers and planting date on the response of potatoes to nitrogen fertiliser. Nitrogen optima commonly had large standard errors which made interpretation of the data difficult. On the sandy soil with cv. Record, early planting increased yield in two years but had no effect on mean N optimum (303 kg ha⁻¹, NOpt). Mean NOpt was less on the silty soil where the cv. Pentland Squire was grown, and was reduced from 273 kg ha⁻¹ to 241 kg ha⁻¹ when planting was delayed by 4 weeks. Physiological age had no effect on NOpt. On the sandy soil, residual soil mineral nitrogen (RSMN) increased by 0.05 kg ha⁻¹ per kg N fertiliser applied; on the silty soil the increase was four times as large. RSMN was larger following the late planted crop on the silty soil in one year.     

Prevention of berry set and true seed production in six potato (Solanum tuberosum L.) cultivars by single foliar applications of MCPA

Summary True potato seed production may contribute to the spread of several diseases and pests. MCPA (500 or 750 g a.i. ha⁻¹) applied at early or full bud stage reduced berry number and seed number per berry, resulting in reduced true seed production. Effects on berry set differed between cultivars and were dependent on crop growth stage at application and true seed production was reduced most strongly in all cultivars with application at full bud stage. MCPA also slightly reduced yield and tuber size, but did not affect tuber dry matter content or fry colour.     

Beziehungen zwischen Stengel- und Knollenzahl bei der Kartoffel in Abhängigkeit von wichtigen Einflußfaktoren. II. Der Einfluß des Jahres

Zusammenfassung In sieben Versuchsjahren beeinflusste die jahrestypische Stengelzahl die Zahl der Knollenanlagen pro Pflanze positiv (r=+0,77^*) und der Knollenanlagen pro Stengel in der Tendenz negativ (r= −0,39). Die signifikanten Jahresunterschiede in der Zahl erntef?higer Knollen (>3 cm) pro Pflanze und pro Stengel wurden in gewissem Grade durch die Zahl der angelegten Knollen (r= −0,53 bzw. +0,63), in st?rkerem Ausma? jedoch durch die jahrestypische Reduktionsrate der Knollen bestimmt (r= −0,72 bzw. −0,91^*). Diese war hoch, wenn ein Wechsel von guter Wasserversorgung w?hrend der Knollenbildung zu Wassermangelsituationen w?hrend der Knollenwachstumsphase erfolgte.

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Summary In seven years of field experiments, there were significant differences in the numbers of stems per plant and the number of harvestable tubers (>3 cm) at maturity, per plant and per stem, averaged for two cultivars and three seed treatments (Table 1). There was only a weakly positive correlation between the typical stem number for each year and the number of harvestable tubers per plant (r= +0.2, Table 2), whilst the correlation with the number of tubers initiated was much closer (r= +0.77^*, Table 2). The negative influence of number of stems on number of tubers per stem is shown byr= −0.39 and −0.47 (Table 2). Identical stem populations in the wet, cold spring of 1987, and the warm, dry season of 1983 initiated fewer tubers per stem than in 1989 with its average temperatures and modest precipitation (Table 1). Tuber set per plant and per stem correlated positively with the number of harvested tubers per plant and per stem (r= +0.53 and +0.63) and accounted for some of the yearly variation. A much stronger effect on the number of harvestable tubers came from the annual reduction of tubers (r= −0.72 and −0.91^*, Table 2). This was high if the availability of water deteriorated in the period of growth succeeding tuber formation (Table 1, Fig. 1). The same applied to the seed treatments planted at different stages of development. Tuber development occurred earlier with chitted seed, often at times when there was an adequate water supply. A large number of tubers were initiated and these were in large part reduced in the short dry spells which followed (Figs 2 and 4). Irrigation programmes must take account of this relationship.

     

Improving production and health of seed potato stocks in Italy

Summary When nodal explants from sprouts grown from virus-free tubers of ten cultivars were propagated on half-strength Murashige and Skoog medium, cvs Arsy, Nicola, Kennebec and Spunta grew best. Rooted plantlets, 5–8 cm tall, were transplanted from culture vessels into pots containing soil, vermiculite and sand. They were weaned by growing in a glasshouse for about three weeks. Over 90% of the plantlets survived and these were then planted in the field and protected against aphids by a double screen (a large tunnel covering four adjacent small tunnels) and chemical treatments. Prebasic seed tubers thus obtained were virus-free and production ranged from 49.9 t.ha⁻¹ (‘Monalisa’) to 27.1 t.ha⁻¹ (‘Majestic’). A survey showed that ‘elite’ (near virus-free) seed could be produced from prebasic seed by early planting and early haulm killing regardless of location, but late planting on the plains and normal planting dates on the mountains resulted in 1 to 5% virus infection levels acceptable only for certified seed.     

Serogroups ofErwinia carotovora involved in systemic infection of potato plants and infestation of progeny tubers

Enrichment techniques and serological strain typing methods were used to determine the source of stem and progeny tuber populations ofErwinia carotovora (Ec) in 1980 and 1981. Plots were established in a field that had been planted with potatoes since 1972. Seed tubers of cultivars Russet Burbank and Norgold Russet were assayed forErwinia carotovora pv.carotovora (Ecc) andErwinia carotovora pv.atroseptica (Eca) by tuber peeling and direct plating and plating following enrichment in a pectate-based broth. Levels of seed tuber infestation ranged from undetectable to 2.4 × 10⁴ colony-forming units per g peel tissue. Prior to planting Ecc was detected in soil samples from field plots by enrichment in a pectate-based broth. Ec was isolated from symptomless plants with increasing frequencies from 8 weeks following planting regardless of the level of Ec populations in seed tubers. At harvest progeny tuber recontamination was low and not related to levels of seed tuber Ec populations. In 1980, serological typing of representative Ecc isolates indicated serogroups III, XXIX, and unknown strains isolated from the soil but not the seed tubers prior to planting were isolated from stems and progeny tubers. Serogroup XXIX was isolated from soil, seed, stems and progeny tubers in 1981. Throughout both years, Ecc was isolated more frequently than Eca from seed, soil, stems, and progeny tubers. These data emphasize the potential for reinfestation of seed stocks and infection of plants by populations of Ecc that overwinter in soil under Wisconsin conditions.     

Comparative performance of three small seed tuber sizes and standard size seed tubers planted at similar stem densities

Summary Small seed tubers of 1–5 g, 5–10 g and 10–20 g were planted at the same sprout densities as standard size seed tubers of 40–60 g in order to give similar stem densities. Early ground cover by foliage, total yield, and yield of tubers >45 mm were consistently greater in plots planted with larger seed tubers. The effect of seed tuber size on yield and tuber number per stem varied between years but 1–5 g seed tubers always gave lower yields per stem than larger seed tubers. Reducing the spacing between rows from 90 cm to 60 cm and maintaining the same sprout density was more effective in increasing yields from small seed tubers than increasing sprout density from 20 to 40 sprouts per m² by reducing plant spacing within the row.     

Field performance of potato minitubers with different fresh weights and conventional seed tubers: Multiplication factors and progeny yield variation

Summary Multiplication factors and progeny yield variation in crops from minitubers of five weight classes (ranging from 0.13–0.25 g to 2.00–3.99 g) and conventional seed tubers were studied in field experiments in three years. Multiplication factors were calculated as the number and weight of progeny tubers produced per planted tuber or per unit planted tuber weight. They were lower for the lighter minitubers when calculated per tuber and higher when calculated per weight. Yield variation was described by coefficients of variation for the number and weight of progeny tubers produced. Variation over individual plants of a crop was higher in stands from the lighter minitubers. Variation over plots within a field was sometimes higher for the lighter minitubers, but variation over years was similar for all minituber classes. Variation over plots in progeny tuber weight was higher for minitubers than for conventional tubers.     

Effect of two plant growth regulators on the yield and quality of russet burbank potatoes

Summary Foliar applications of ethephon (ETH) 300 g a.i. ha⁻¹; chlormequat chloride (CCC) 920 g a.i. ha⁻¹, with a second application of 230 g a.i. ha⁻¹ approximately 2 weeks later; and a mixture of the two (ETH/CCC) 156 g a.i. ethephon and 299 g a.i. chlormequat chloride ha⁻¹ were made to field-grown Russet Burbank potatoes in 1986, 1987 and 1989. All the treatments increased the number of tubers set and reduced the average tuber weight compared to the control resulting in a reduction in premium and marketable tubers, and an increase in small tubers. Differences were greatest for ETH and least for CCC. ETH and ETH/CCC decreased the specific gravity, increased the incidence of deformities, and decreased the incidence of tubers with hollow heart. The growth regulators did not affect fry colour.     

Chemical composition and content of antinutritional factors in Polish cultivars of peas

The seeds of 15 Polish pea varieties contained from 221 to 281 g/kg crude protein with a mean of 240.2±3.5 g/kg dry matter (DM). The weight of 1000 pea seeds, depending on cultivar, ranged from 209.4 to 280.4 g. No interactive effect between the seed mass and the crude protein content was detected. The highest significant negative correlation between weight of seeds and dietary fiber content wasr=−0.815^XX. The content of dietary fiber ranged from 161.5 to 209.9 g/kg with a mean of 187.9±3.8 g/kg. The mean gross energy of seeds was 18.1±0.28 MJ/kg. Amino acid composition of all the cultivars was similar, which was indicated by a similar index of essential amino acids (EAAI) of about 69.7±0.25. Trypsin inhibitor content in seeds was from 2.83 to 7.32 TIU/mg and the content of phytates ranged from 6.32 to 13.36 mg/g DM. The mean content of polyphenols and flavanols in analysed pea cultivars was 0.92 amd 0.46 mg/g, respectively. In the seeds of most cultivars little or no pyrimidine glucosides, i.e. vicine and convicine, were found. The overall mean oligosaccharide content was 64.3±1.8 g/kg, of which α-galactosides were 46.8±2.0 g/kg. The antinutritional factor content was not significantly correlated with protein content. No statistical relationship was found between crude protein and dietary fiber content. It was observed that pea cultivars with higher trypsin inhibitor activity contained significantly less flavanols (r=−0.607^X) and α-galactosides (r=−0.617^X). The varieties with higher seed content of dietary fiber contained the highest amount of α-galactosides (r=0.514^X).     

Influence of stem canker (Rhizoctonia solani Kühn) on tuber yield,tuber size,reducing sugars and crisp colour in cv. Record

Summary In eight experiments in 4 years, inoculating seed tubers withR. solani caused stem canker and in seven experiments decreased the total yield and the yield of tubers 40–70 mm. Yields of larger tubers were usually increased. In most experiments inoculating increased the reducing sugar content of the tubers and darkened the colour of crisps, but did not consistently affect the amounts of sucrose. Treating soil with aldicarb or oxamyl before planting also slightly increased the total reducing sugars.     

The degree of starch phosphorylation as influenced by phosphate deprivation of potato (Solanum tuberosum L.) plants

Summary The levels of starch phosphorylation in potato tubers were investigated in relation to fertilization with phosphorus (P) of field-grown and greenhouse-grown plants. The field-grown plants received 0, 15 or 30 kg P ha⁻¹. Starch from plants grown without P-fertilizer contained 15.6 nmol P (mg starch)⁻¹ whereas starch from plants grown with 30 kg P ha⁻¹ contained 20.6 nmol P (mg starch)⁻¹. The greenhouse-grown plants were cultured in inert media and received nutrient solutions containing 0, 3, 12 or 24 mg P l⁻¹, respectively. Plants grown with no P-fertilizer produced tuber starch with phosphorylation levels reduced to approximately 30% of the level found in plants grown with an ample supply of P. Thus, the level of starch phosphorylation can be modified by limiting the P-supply through the root system. Application of foliar P-fertilizer to the greenhouse-grown plants had no significant effect on the phosphorylation of the tuber starch.     

Fungi Causing Dry Tuber Rots of Seed Potatoes in Storage in Scotland

The occurrence, pathogenicity (1997 isolates only) and fungicide sensitivity of pathogens causing dry tuber rots in Scottish seed potatoes was investigated over three storage seasons between 1997 and 2000 in relation to region of production, cultivar, class and generation of seed potatoes, type of temperature control in store and earthiness of tubers. A total of 156 samples, each comprising up to ten rotted tubers, was received over the three seasons. The relative importance of each pathogen in causing rots was summarised by calculating a mean rot index that combined the prevalence of a pathogen in the samples with the incidence of tubers affected by the pathogen within those samples. Phoma foveata (gangrene) had the highest rot index, which was five times greater than for P. exigua and ten times greater than for P. eupyrena. This relationship was mirrored by the relative pathogenicities of P. foveata and P. eupyrena, as measured by size of rots developing at inoculated wounds in test tubers. Fusarium avenaceum appeared to be the greatest cause of Fusarium dry rots, having a rot index at least twice as great as that for F. solani var. coeruleum. Infection by F. sulphureum was relatively uncommon. In the pathogenicity test, F. avenaceum, F. solani var. coeruleum and F. sulphureum produced rots of similar depths and widths and larger than those of F. culmorum. The mean rot index for Cylindrocarpon spp. was slightly more than that for F. avenaceum, whereas C. destructans produced smaller rots in the tuber pathogenicity test. Region of production affected the prevalence of P. foveata and F. avenaceum, but only the occurrence of P. foveata was affected by class and generation of seed potatoes. Isolate sensitivity to thiabendazole and imazalil was examined in vitro over 2 years. Six out of seven isolates of F. sulphureum were resistant to thiabendazole, with the remaining isolate being partially resistant. The growth of two out of 34 isolates of F. avenaceum was inhibited by more than 50% only at 100 mg thiabendazole l⁻¹. All isolates, except those of F. avenaceum,, were inhibited in their growth by more than 50% at either 1 or 10 mg imazalil l⁻¹. However, the growth of 40% of isolates of F. avenaceum was inhibited only at 100 mg l⁻¹. The various changes in pathogen prevalence and isolate sensitivity to fungicides recorded in this study highlight the need for regular monitoring programmes to be conducted in order that disease-control strategies can remain effective.     

Performance of Dimethomorph + Mancozeb Applied to Seed Potatoes in Early Management of Late Blight (<Emphasis Type="Italic">Phytophthora infestans</Emphasis>)

Treating seed potatoes with contact fungicides prevents infection of Phytophthora infestans from tuber to tuber during handling but does not prevent field infections in the young plant. Dimethomorph (DMM) 9% + mancozeb 60% (Acrobat MZ, BASF) can cover both aspects due to the contact and systemic action of mancozeb and DMM, respectively. Experiments were performed under greenhouse and field conditions (three seasons and two locations) with cvs Kennebec, Shepody, Spunta, Russet Burbank, and Ranger Russet. Immediately after cutting, seed pieces were treated with Acrobat MZ at doses equivalent to 2, 3, and 4 kg ha⁻¹. At any dose, Acrobat MZ protected healthy seed tubers against P. infestans infections. Acrobat MZ (4 kg ha⁻¹) also protected the foliage of all cultivars against artificial inoculation of P. infestans, assessed by the detached-leaf method. These effects were observed up to 30 days after emergence in greenhouse experiments and up to 28 days after crop emergence under field conditions in two growing seasons. In cv Spunta, significant foliage protection was observed up to 35 days after field emergence whereas in seed tubers of cv Kennebec planted in sandy soils, significant foliage protection persisted longer. Additional evidence for acropetal translocation of Acrobat MZ in field crops was also found. With this strategy, there is no need to apply contact or systemic fungicides early in the season, and spraying costs and environmental risks are also reduced.     

Influence of storage temperature on rate of potato tuber tissue infection caused byPhytophthora infestans (mont.) de bary estimated by digital image analysis

Summary Potato tubers were inoculated with two biotypes ofPhytophthora infestans then stored at 3,7, 10 and 15°C. Image analysis quantified average reflective intensity (ARI) of diseased tissue from cut surfaces of sample tubers. Tuber tissue infection and infection rate were measured by calculating Mean ARI of samples. Average tuber tissue infection and infection rate was minimal at 3°C (P.i.-US8 orP.i.-US1). Tuber tissue infection increased at temperatures >3°C, from 220 Mean ARI seven days after inoculation (dai) to 190–150 Mean ARI 50 dai (depending on cultivar and biotype ofP. infestans). Rate of tuber tissue infection caused byP.i.-US1 at 7°C was about zero in cv. Snowden but greater than −0.2 ARI day⁻¹ (cvs Russet Burbank and Superior). Rate of late blight infection in tuber tissue generally increased with temperature from −0.2 ARI day⁻¹ (at 7°C) in all cultivars to a maximum of −0.8 ARI day⁻¹ (10°C).     

Impact of earthen waste storage on nitrate concentration of surface water

In 1992 and 2002, investigations on the water quality and hydrology were carried out in a small agricultural catchment where swine waste was stored in earthen waste storage. The in-stream nitrogen loads and the nitrogen inputs on a sub-catchment scale were estimated and compared between 1992 and 2002. For the entire catchment, the estimated nitrogen inputs increased from 22.5 to 32.9 ton year⁻¹ (from 406 to 594 kg ha⁻¹ year⁻¹), whereas the nitrate nitrogen concentration at the outlet was constant—27 mg l⁻¹. In a sub-catchment (area C) with earthen waste storages, the nitrate nitrogen concentrations at the outlet were high, 42–51 mg l⁻¹. In a sub-catchment (area A) with an earthen waste storage, which was not in service since 1990, although the nitrogen inputs were maintained at 390 kg year⁻¹ (53 kg ha⁻¹ year⁻¹), the nitrate nitrogen concentrations at the outlet decreased from 26 to 4.9 mg l⁻¹. With assuming that the nitrogen transport rates for sources except swine waste are equal to the rates estimated for a sub-catchment without earthen waste storage, the in-stream nitrogen loads for area A were estimated to decrease from 1,334 to 94 kg year⁻¹ and the transport rates for area A were estimated to decrease from 3.95 to 0.73. These results suggest that the effluent from earthen waste storage has affected surface water quality two years after the storage was out of service and its effect largely decreased after a decade.     

The effects of (S)-(+)-carvone treatments on seed potato tuber dormancy and sprouting

Summary Potato seed tubers may suffer from premature sprouting during storage, thus limiting their suitability for cultivation. Commonly used sprout suppressant treatments negatively affect but viability and therefore a reliable method to inhibit bud development must still be found for seed tubers. The monoterpene carvone ((S)-(+)-carvone) was tested in small scale experiments. The vapour of this compound fully inhibited bud growth of tubers cv. Monalisa stored at 23°C without affecting bud viability throughout 6 months of treatment. The most effective range of carvone vapour concentrations was between 0.34 and 1.06 μmol mol⁻¹. With these qualities we can expect carvone to become a suitable sprout suppressant for seed tubers.