Differences in the tolerance of potato cultivars to potato cyst nematodes (Globodera rostochiensis and G. pallida) in field trials with and without nematicides

In field trials Cara, Brio, Maris Piper and Pentland Javelin were consistently more tolerant of damage by Globodera rostochiensis yielding more than Corsair, Pentland Dell, Maris Anchor and Maris Peer, in untreated, heavily infested soil and giving the smallest increases to nematicide treatment. No yield or growth differences were found between plants in untreated and nematicide treated plots at a nematode-free site. The most tolerant cultivars all had a gene (H₁) for resistance to G. rostochiensis derived from Solanum tuberosum ssp. andigena and in soil infested with G. pallida the tolerance of at least one resistant cultivar (Maris Piper) appeared to be lessened. However, some resistant cultivars were comparatively intolerant, even to G. rostochiensis. Early cultivars were generally less tolerant than late maturing cultivars but there were exceptions. Amongst cultivars with resistance derived from Solanum vernei the early cultivar Guardian was more tolerant than the main crop cultivar Corsair. The effect on the yield of several cultivars of a range of densities of G. rostochiensis, produced either by applying different rates of a nematicide or by cropping in the previous year, was examined at two sites. The results indicated that the slope of the regression for yield in relation to nematode density was less for tolerant than intolerant cultivars. At sites infested with G. rostochiensis Maris Piper was found to be consistently more tolerant than Pentland Crown.     

Effects of potato genotype, oxamyl and the numbers of potato cyst-nematodes, Globodera rostochiensis or G. pallida on tuber yields and nematode increase

A new technique is described for establishing different numbers of the potato cyst-nematode Globodera rostochiensis in field soil, which leaves the soil homogeneous in nutrient status. Field plots established in this way were used to compare yield losses in four potato cultivars (Maris Piper, Pentland Crown, Pentland Dell and Désirée) associated with different numbers of G. rostochiensis. Over the range of 7.4 to 148.4 eggs g^-1 soil at planting, yield losses were 18.7% (Maris Piper), 53.2% (Désirée), 55.7% (Pentland Crown) and 63.5% (Pentland Dell). Similar results were obtained in another experiment on the same field in a different year using only lightly and heavily infested plots. Treating the seedbed soil with oxamyl before planting prevented significant injury to potatoes by G. rostochiensis but increased the yield of Pentland Dell and perhaps Désirée (but not Maris Piper or Pentland Crown) more than expected from nematode control alone. Treating heavily infested soil with such a nematicide cannot therefore be recommended as part of a valid procedure for establishing lightly and heavily infested plots for comparing tolerances of attack by potato cyst-nematodes in a range of potato genotypes. In peaty loam soils moderately or heavily infested with G. pallida, oxamyl at 5.6 kg a.i. ha^-1 incorporated into the seedbed before potatoes were planted generally increased tuber yields, though the effects varied considerably with the cultivar grown. Increase of G. pallida in these soils was controlled better by growing potatoes bred for resistance to it (ZB 35 – 29, Caxton, Santé, Morag, 11233 ab 22, Fingal, A27/23, Cromwell). Increase of G. pallida on susceptible cultivars varied greatly and Romano increased G. pallida no more than the resistant Morag. G. pallida is probably controlled best in peaty loam by growing a resistant cultivar in soil treated with a granular (non-fumigant) nematicide.     

Effects of potato leafroll virus on the crop processes leading to tuber yield in potato cultivars which differ in tolerance of infection

The effects of infection with potato leafroll virus (PLRV) on the four crop processes leading to tuber fresh weight yield were examined in field plots of four cultivars (Montana, Pentland Crown, Maris Piper and King Edward) differing in tolerance to infection. Averaged across cultivars, infection decreased yield by 50%. This decrease was equally due to less light (total solar radiation) being intercepted, a lower efficiency with which intercepted light was converted into dry weight, and a smaller proportion of dry weight being partitioned to tubers. Dry matter content of the tubers was also diminished but to a lesser extent. The main difference between the cultivars in their response to infection was in the partitioning of dry weight. In Montana and Pentland Crown, harvest index was decreased by 15% in infected plants, whereas in the less tolerant cultivars, Maris Piper and King Edward, it was decreased by 25%. The decline in photosynthetic performance of Montana, a cultivar with slightly earlier maturity than the other three, was delayed in PLRV-infected plants. Effects on number of daughter tubers essentially reflected those on yield to the extent that average tuber weight did not change in Maris Piper, was one third less in King Edward, and the change was intermediate in Montana and Pentland Crown.     

Control of potato cyst nematode (Globodera rostochiensis) by nematicides and a resistant potato cultivar at four sites in Scotland

The control of potato cyst nematode (Globodera rostochiensis) by the oxime-carbamates aldicarb and oxamyl was tested in four fields in Scotland. Dazomet was tested in three of these fields and carbofuran in one. In untreated plots in the three most heavily infested fields Maris Piper (resistant) yielded better than Pentland Crown (non-resistant). All nematicides increased the yields of both potato cultivars but had a greater effect on the yield of Pentland Crown. Dazomet increased yields of tubers most. Heavy nematode infestation reduced yield of tubers more in a sandy soil than in two sandy loams. In a field with few potato cyst nematodes nematicides did not significantly affect tuber yields. Although the nematicides greatly increased yields, they were not completely effective in controlling potato cyst nematodes. In treated plots in the lightly infested field, there were more nematode eggs following a crop of Pentland Crown than before. In contrast, Maris Piper markedly decreased post-cropping populations and except at one site, where dazomet further decreased nematode numbers, combining nematicides with the resistant cultivar failed to decrease nematode numbers further. Nematicides decreased the numbers of larvae invading potato roots by up to 95%, oxamyl at 5–6 kg/ha being consistently the best treatment.     

A method for assessing the field susceptibility of potato cultivars to blackleg (Erwinia carotovora subsp. atroseptica)

In experiments to develop a method for assessing the field susceptibility of potato cultivars to blackleg (Erwinia carotovora subsp. atroseptica) seed tubers were stab-inoculated near the stolon (attachment end), with a suspension of the bacterium, or with water, before planting. Disease symptoms were recorded in three years (1980–1982) and plant growth and yield in 1982. Estima and Maris Bard were the most susceptible cultivars with many plants failing to emerge and most of those that did showing disease symptoms. Pentland Crown was the most resistant: few plants failed to emerge and few showed blackleg. Nevertheless compared with water-inoculated plants bacterial inoculation of the seed tubers of this cultivar caused loss of yield and differences in tuber size distribution. Cara, Wilja and King Edward showed intermediate reactions.     

The effect of Erwinia carotovora subsp. atroseptica (blackleg) on potato plants. I. Growth and yield of different cultivars

The effect of planting seed tubers inoculated either near the stolon attachment (heel end), among the eyes at the apex (rose end) or mid-way along the tuber with Erwinia carotovora subsp. atroseptica, was assessed in terms of growth of the plant, disease symptoms and yield. Invariably rose-end inoculation had the greatest and heel-end the least effect in decreasing yield when compared with uninoculated plants. Cultivars Majestic and King Edward were the most susceptible, Pentland Crown showed some resistance to invasion of stems (blackleg) although plant vigour, expressed in terms of plant height and stem number was affected and Maris Piper was the most resistant.     

Effect of the nematicide oxamyl on the multiplication of Globodera rostochiensis and G. pallida and on the haulm growth and yield of six potato cultivars with different levels of resistance and tolerance

The effect of a pre-planting application of oxamyl on the yields of six potato cultivars was studied in co-operative field trials in 1981. Two sites were ‘uninfested’ with potato cyst nematodes (PCN), two were lightly infested (<25 eggs/g soil) and six were moderately to heavily infested (three with Globodera rostochiensis and three with G. pallida). At the uninfested and lightly infested sites oxamyl had little effect on mid-season haulm weights or on final tuber yields. At sites moderately to heavily infested with G. rostochiensis the haulm growth of all cultivars tended to be increased by a similar amount on plots treated with oxamyl, Pentland Dell being least responsive. Yield was increased by different amounts, the increases being least for cvs Cara and Maris Piper and most for Corsair and Pentland Dell. At the sites moderately to heavily infested with G. pallida Cara was again tolerant, its yield being increased little by oxamyl compared with the other cultivars. Maris Piper gave the largest yield increase. Final populations of PCN on non-resistant cultivars were reduced by oxamyl at some sites but not at others. Resistant cultivars also decreased the final numbers of PCN at most sites. Two cultivars derived from Solanum vernei with different degrees of resistance, appeared to be almost equally effective in controlling G. rostochiensis and G. pallida.     

The susceptibility of stems of different potato cultivars to blackleg caused by Erwinia carotovora subsp. atroseptica

The susceptibility of stems of six potato cultivars to Erwinia carotovora subsp. atroseptica was assessed in two years (1981 and 1982) either by direct inoculation in the field or by inoculation of detached stems in the laboratory. These six and a further 22 cultivars were also assessed in three years (1982-84) by inoculating stems of glasshouse-grown plants. Different methods of inoculation and types of inocula were tested. In the field, wooden toothpicks rubbed in bacterial slime were more successful in establishing infection than when dipped in a bacterial suspension, but injection of bacterial suspension with a hypodermic needle was reliable in establishing infection over a range of concentrations. Detached stems were more readily infected and gave more consistent results compared with inoculation in the field. The range of reaction of the six cultivars was similar in both detached stem and glasshouse tests. The early cultivars Pentland Javelin and Ulster Sceptre were most susceptible and of the maincrop cultivars, Maris Piper was intermediate and Desiree and King Edward least susceptible whereas Pentland Crown showed greater resistance in the glasshouse than in the field. Glasshouse tests using hypodermic inoculation indicated a range of susceptibilities; the early cultivars Manna, Maris Bard and Estima were most susceptible and the maincrop Pentland cultivars Crown, Dell, Hawk, Ivory and Squire least susceptible.     

Stem canker (Rhizoctonia solani) on five early and seven maincrop potato cultivars. II Effects on growth and yield

In 1983 and 1984, potato seed tubers of five early and seven maincrop cultivars were inoculated with cultures of Rhizoctonia solani during planting in field experiments to simulate severe seed infection. The size of foliage was assessed during June-August and tuber yields recorded during growth and at harvest in October. Stem canker delayed shoot emergence, decreased the number and length of stems and caused increased variation in stem length; these effects were greatest with Maris Peer and Arran Comet (early cultivars) and King Edward and Pentland Squire (maincrop cultivars). Total weight of foliage was decreased, especially with earlies, dry matter of stems increased and the proportion of foliage on lateral stems increased. With the early cultivars, tuber yield from sprouted Maris Peer seed 11 wk after planting in 1983 was decreased by 24%, and 13 wk after planting in 1984 yields were decreased by 42% (Maris Peer), 40% (Ulster Sceptre), 34% (Estima), 30% (Arran Comet) and 17% (Ulster Prince) with sprouted seed and by 20, 29, 53, 39 and 28% respectively with non-sprouted seed. Decrease in total yield at harvest in October averaged 13% with sprouted seed and 10% with non-sprouted seed. In all cultivars the weight of small tubers was decreased and with Estima the weight of large tubers was increased. Tuber bulking was also delayed with all maincrop cultivars and at harvest yields from sprouted King Edward seed were decreased by 13% in 1983 and by 16% (sprouted seed) and 23% (non-sprouted seed) in 1984; yields of Pentland Squire were decreased by 5, 16 and 21% respectively. Yield losses with other cultivars ranged from 5–13% with sprouted seed and 0–16% with non-sprouted seed. The yields of small tubers were decreased with all cultivars and yields of large tubers were increased with Pentland Squire, Pentland Crown and Cara.     

Restricted distribution of potato leafroll virus antigen in resistant potato genotypes and its effect on transmission of the virus by aphids

Enzyme-linked immunosorbent assay was used to measure the concentration of potato leafroll virus (PLRV) antigen in different parts of field-grown secondarily infected plants of three potato genotypes known to differ in resistance to infection. The antigen concentration in leaves of cv. Maris Piper (susceptible) was 10–30 times greater than that in cv. Pentland Crown or G 7445(1), a breeder's line (both resistant). Differences between genotypes in antigen concentration were smaller in petioles and tubers (5–10-fold) and in above-ground stems (about 4-fold), and were least in below-ground stems, stolons and roots (about 2-fold). PLRV antigen, detected by fluorescent antibody staining of tissue sections, was confined to phloem companion cells. In Pentland Crown, the decrease in PLRV antigen concentration in leaf mid-veins and petioles, relative to that in Maris Piper, was proportional to the decrease in number of PLRV-containing companion cells; this decrease was greater in the external phloem than in the internal phloem. The spread of PLRV infection within the phloem system seems to be impaired in the resistant genotypes. Green peach aphids (Myzuspersicae) acquired < 2800 pg PLRV/aphid when fed for 4 days on infected field-grown Maris Piper plants and < 58% of such aphids transmitted the virus to Physalis floridana test plants. In contrast, aphids fed on infected Pentland Crown plants acquired <120 pg PLRV/aphid and <3% transmitted the virus to P. floridana. The ease with which M. persicae acquired and transmitted PLRV from field-grown Maris Piper plants decreased greatly after the end of June without a proportionate drop in PLRV concentration. Spread of PLRV in potato crops should be substantially decreased by growing cultivars in which the virus multiplies to only a limited extent.     

Stem canker (Rhizoctonia solani) on five early and seven maincrop potato cultivars I. Infection of shoots, stolons and tubers

In 1983 and 1984, potato seed tubers of five early and seven maincrop cultivars were inoculated with cultures of Rhizoctonia soluni during planting to simulate severe seed infection. Shoot and stolon infection was assessed in June-August and black scurf on tubers recorded after harvest in October. Almost all shoots of all cultivars had stem canker in both years and disease on shoots, stolons and tubers was more severe in 1984 than in 1983. In 1983 similar amounts of disease developed on all early cultivars and between 11% (Ulster Sceptre) and 32% (Maris Peer) shoots were pruned off. Maris Peer had a stem canker score lower than other cultivars in 1984 but more than half the shoots were pruned off. Shoot pruning on Estima, Ulster Prince and Ulster Sceptre was more common on plants from sprouted than non-sprouted seed. Between 30 and 50% of stolons were pruned off. After harvest in 1985, black scurf was least prevalent on Arran Comet and Maris Peer tubers and in 1984 on Arran Comet and Estima tubers from non-sprouted seed. Of the maincrop cultivars, King Edward plants from sprouted seed had many shoots pruned off in both years. Shoot pruning was also prevalent on Maris Piper and Pentland Squire plants from non-sprouted seed. Record had fewest pruned shoots and stolons and the lowest stem canker score. The disease was more severe on Pentland Crown and Maris Piper plants from non-sprouted than sprouted seed. Black scurf was most common on Cara and King Edward tubers in 1983 and on King Edward and Record tubers in 1984. In both years few shoots but many tubers were infected on plants from non-inoculated seed and the significance of this is discussed.     

A comparison of inoculation methods for determining potato cultivar reaction to black leg

Two methods of inoculating tubers, one by dipping them in an aqueous suspension of Erwinia carotovora subsp. atroseptica, the other by inserting the end of a wooden toothpick charged with undiluted bacteria into the rose-end near a sprout, were compared over two years for their ability to produce black leg and for their effect on plant growth and yield on a number of cultivars chosen because of expected differences in susceptibility. Although both methods produced a similar rank order for cultivar reaction, the more consistent results were obtained using the toothpick method, clear differences in black leg incidence and yield being evident between the susceptible cultivars Ulster Sceptre and Maris Bard and the more resistant Pentland cultivars. As some cultivars appear more tolerant to black leg than others, yield may be as important a criterion as disease incidence when assessing overall cultivar performance. The inoculation of the base and middle of stems and the infiltration of the bacterium into tubers were also investigated as alternative methods for assessing cultivar susceptibility.     

Transmission of Fusarium solani var. coeruleum and F. sulphureum from seed potatoes to progeny tubers in the field

In experiments in three years, seed tubers were inoculated before planting with either Fusarium solani var. coeruleum or F. sulphureum to initiate a rot, or were contaminated by dipping in soil slurries containing spore suspensions of one or other of the pathogens. Transmission to progeny tubers was tested by uniformly wounding and incubating tubers and by dilution plating of soil samples. In two years, transmission of F. sulphureum was greater from highly contaminated than from rotting seed and was greater on cv. Pentland Crown than on cvs Desiree and Maris Piper. F. solani var. coeruleum appeared to be transmitted most readily from rotting seed and Maris Piper was the cultivar most extensively contaminated. In experiments with different harvest dates, transmission of both fungi from highly contaminated seed could be detected by late June or mid-July. More progeny tuber wounds rotted in F. sulphureum than in F. solani var. coeruleum plots and in one year, F. sulphureum caused more rots on cv. Record than on cv. Maris Piper. These differences between the pathogens may be related to their differing abilities to sporulate underground on the surface of seed tubers and on stem bases.     

Effects of soil treatments and cultivars on 'early dying' disease of potatoes caused by Globodera rostochiensis and Verticilliurn dahliae

Plots in a field infested with Globodera rostochiensis and Verticillium dahliae were treated in 1971 with methyl bromide, dazomet, aldicarb, benomyl or aldicarb + benomyl and potatoes (cv. Pentland Dell) were grown in four consecutive years. In 1971, all treatments delayed the development of haulm symptoms, decreased soil populations of G. rostochiensis and increased yields. In the second year yields were increased by all treatments except dazomet whereas in the third and fourth years only benomyl or aldicarb + benomyl increased yields. Soil populations of V. dahliae were decreased by methyl bromide in 1971 but not by other treatments or in later years. In 1976, Pentland Dell and Pentland Crown were grown on an infested field in plots fumigated with methyl bromide. Fumigation slightly delayed shoot emergence but increased plant height, ground cover and the size and persistence of the leaves; development of haulm symptoms was delayed and yield increased. Fumigating with methyl bromide at five times the normal rate was more beneficial to Pentland Dell than to Pentland Crown. In a comparison of 10 cultivars in 1975, symptoms developed sooner and yields were smaller on a field infested with G. rostochiensis and V. dahliae than on a non-infested field and on both sites Maris Peer plants died soonest and yielded least. Pentland Crown yielded most on the non-infested field and Maris Piper on the infested field.     

Stem canker (Rhizoctoniu solani) on three early and three maincrop potato cultivars: effects of seed tuber size on growth and yield

Large seed tubers (mean 134 g) and small seed tubers (50 g) of three early and three maincrop potato cultivars, spaced respectively 48 and 30 cm apart within rows, were inoculated with Rhizoctonia solani at planting in 1985 and 1986. All seed of early cultivars was sprouted and maincrop seed was either sprouted or not sprouted. In all cultivars, plant emergence was slower from small than large seed and with both was delayed by inoculation. From 11 wk after planting numbers of stems and tubers and weights of foliage and tubers/m² were usually similar from small and large seed when not inoculated, but inoculating delayed plant growth and decreased tuber numbers and yield more from small than large seed. Inoculating decreased mean yields from large and small seed of early cultivars at 11 wk by respectively 24% and 31% (Arran Comet), 12% and 18% (Estima) and by 10% and 28% (Wilja) and losses were greatest with saleable sized tubers (3–4 cm). When grown to maturity inoculating decreased yields by 7% (Arran Comet), 5% (Estima) and 14% (Wilja). With maincrop cultivars, yields in October from large and small seed were decreased by respectively 4% and 10% (DCsirke), 9% and 12% (Maris Piper) and by 14% and 22% (Pentland Squire). In all cultivars yields of tubers < 44 mm and 44–70 mm were decreased and, with Pentland Squire, tubers > 82 mm were increased. The incidence of stem canker and of black scurf on progeny tubers was not affected by seed size but in all cultivars the percentage of greened tubers was slightly increased by inoculation.     

Varietal susceptibility of potatoes to wireworm herbivory

1 Wireworms, the soil dwelling larvae of click beetles, Agriotes spp., have recently become a more prevalent pest of potatoes. The present study investigated whether potato varieties showed variable susceptibility to wireworm herbivory, and also tested whether increased susceptibility was associated with lower concentrations of glycoalkaloids. Twelve varieties were originally screened across a range of experimental scales, including laboratory and tunnel experiments and a large‐scale field trial involving over 2000 tubers. 2 In laboratory no‐choice tests, Maris Peer, Marfona and Rooster varieties were significantly more susceptible to wireworm attack, with 63% of tubers showing damage, compared with just 15% of the less susceptible varieties of King Edward, Nadine and Maris Piper. There was also greater tissue consumption and weight gain when wireworms were reared on the most susceptible varieties. 3 In choice tests, wireworms showed a significant preference for those varieties previously identified as being the most susceptible to wireworm herbivory (4.2 holes per tuber) compared with the least susceptible (1.2 holes per tuber). Similar patterns of susceptibility were seen in the field trial, although there was generally more variation in susceptibility. 4 In a tunnel experiment, Marfona and Maris Peer were significantly more susceptibile to wireworm attack (47% of tubers showing damage) compared with Nadine, King Edward and Maris Piper (27% of tubers showing damage). Although Nadine, in particular, had the highest glycoalkaloid concentrations (309.33 mg/kg) and lowest amounts of wireworm herbivory, the relationship between susceptibility and glycoalkaloid concentrations was weak, suggesting that this is unlikely to be the sole mechanism underpinning varietal susceptibility.     

The susceptibility of tubers of potato cultivars to black dot (Colletotrichum coccodes (Walk.) Hughes)

In experiments with commercial seed of different cultivars at Rothamsted and Woburn, Bedfordshire in 1985 – 88 the severity of black dot on daughter tubers at harvest differed between cultivars. The disease was most severe on Desiree tubers. Amounts of disease were similar at both sites in 1986 – 88 but in 1985 it was more severe at Woburn than at Rothamsted. Disease-free seed of 12 (1987) or 15 (1988) cultivars were planted in experiments at Rothamsted (inoculated with Colletotrichum coccodes or not) and at Mepal, Cambridgeshire (not inoculated) and black dot assessed at harvest in October 1987 and in September and October 1988. There were significant differences in the amount of disease on different cultivars and the order of severity was similar at the two sites, on the two harvest dates in 1988 and in both years. Desiree, Maris Piper, Maris Peer and Record were amongst those cultivars severely affected whereas Cara, Pentland Crown and Romano were least affected. Skin discoloration caused by black dot was more noticeable on white-skinned than red-skinned cultivars and was severe on the Dutch cultivars Estima, Marfona, Santé and Wilja.     

LABORATORY STUDIES ON DAMAGE TO POTATO TUBERS BY SLUGS

The ability of eight species of slugs to damage intact potatotubers c .v. Maris Piper was investigated. Four species, previouslyimplicated as pests of field crops, caused primary damage totubers. Interactions between three of the species Milax budapestensis(Hazay), Arion hortensis (Fèrussac) and Deroceras reticulatum(Müller) were studied using potato tubers of five cultivars.Single species groups caused most damage to tubers and interactionbetween species reduced damage irrespective of cultivar. Theresults are discussed in relation to past work. ^*Present address: 59 Valley Park Drive, Clanfield, Hants. PO80PL. (Received 19 August 1986;     

Antibiotic resistance in potato cultivars to the aphid Myzus persicae

Commercially-grown potato cultivars were assessed for antibiotic resistance to Myzus persicae in a culture room at 19°C with a 2°C range and a 16 h photoperiod. The resistant rankings obtained were consistent for the following aphid metrics: maturation time, teneral adult weight, embryo complement and the production of nymphs. Intrinsic rates of increase (r_m) correlated with the above parameters of aphid growth and reproduction but this was not always the case for nymphal survival rate. The cultivars Ulster Tarn, Record and Maris Piper were relatively resistant to M. persicae and cultivars Desirée and King Edward were the most susceptible. When the aphid clone or the culture plants were changed there was no significant effect on the relative resistance of the potato cultivars under test. The relationship between the number of embryos in teneral adults and the production of nymphs by aphids was examined by grouping aphids in weight batches. There was a strong relationship between these two variables.     

Use of resistant and susceptible potato cultivars in the trap cropping of potato cyst nematodes, Globodera pallida and G. rostochiensis

The effects of planting date and growing period of potato cultivars on their efficiency as trap crops for potato cyst nematodes (PCN) were studied. Plots were planted with susceptible or resistant cultivars in April, June and August and these were grown for 5, 6 or 7 wk before removal of the plants by hand lifting. Crops planted in June provided the best overall reductions in PCN population density of up to 95%, with cv. Santé significantly more effective than the other cultivars. Population reductions from the August planting were only slightly less than from planting in June but the tuber yields obtained were much greater: Maris Piper and Maris Bard produced 16.4 and 21.4 t ha^-1 respectively, with 37% and 43% respectively, of a size useful for canning (i.e. between 20 and 40 mm diameter).