Intolerant Cultivars Research Articles

Relationship between Yield Potential and Percentage Yield Suppression Caused by the Southern Root‐Knot Nematode in Cotton

Currently available cotton (Gossypium hirsutum L.) cultivars support significant reproduction of the southern root‐knot nematode [Meloidogyne incognita (Kofoid & White) Chitwood], but they have not been evaluated for differing levels of yield suppression (tolerance) to this nematode. If nematode tolerant (low yield suppression) but susceptible (high nematode reproduction) cotton cultivars can be identified, they could be grown rather than intolerant cultivars to reduce yield loss. The objective of this study was to evaluate a collection of M. incognita–susceptible cotton cultivars for tolerance to parasitism by this nematode. The yield potential and percentage yield loss to M. incognita were measured in 12 genotypes in 2002 and 2003 by comparing yields in 1,3‐dichloropropene–fumigated and nonfumigated plots. The percentage yield suppression caused by M. incognita differed among cotton genotypes in both 2002 and 2003. Yield suppression ranged from 18.0 to 47.3% in 2002 and from 8.5 to 35.7% in 2003. Though significant levels of tolerance were measured in our study, 2 yr of data on percentage yield suppression show that tolerance is not consistently related to specific cultivars in the absence of nematode resistance: susceptible cultivars did not consistently express tolerance, but resistant germplasm did. Thus, it appears unlikely that cotton cultivar selection for tolerance to M. incognita can be utilized to minimize yield suppression. Regression analysis based on the 2 yr of field data revealed a relationship in which percentage yield suppression caused by M. incognita increased linearly as yield potential increased. Because the absolute and percentage losses to nematodes increase as yield potential increases, nematode management becomes increasingly important and beneficial in cotton.

Suppression of Wheat Growth and Yield by Pratylenchus neglectus in the Pacific Northwest.

Many wheat (Triticum aestivum) fields planted annually in the Pacific Northwest are infested by high populations of the lesion nematode, Pratylenchus neglectus. Spring wheat cultivars varying in tolerance and resistance to P. neglectus were treated or not treated with aldicarb to examine relationships between the nematode and growth and yield of annual direct-seeded (no-till) wheat. Increasing initial density of P. neglectus in soil was more strongly associated with declining growth and yield of intolerant (Machete and Spear) than moderately tolerant (Frame and Krichauff) cultivars. Yield suppression by P. neglectus was generally 8 to 36% for intolerant cultivars, but reached 71% in soil also harboring Heterodera avenae, Rhizoctonia solani AG-8, and Gaeumannomyces graminis var. tritici. Intolerant cultivars had lower yields than Krichauff in rainfed but not in irrigated experiments. Density of P. neglectus in mature roots was generally lower for moderately resistant Krichauff than for susceptible Machete and Spear. Aldicarb improved yields in irrigated but not in rainfed experiments, and increased plant height and reduced variability in tiller height, canopy temperature, and density of P. neglectus in roots. This is the first report of damage to wheat by P. neglectus in the Pacific Northwest. Breeding wheat for tolerance and resistance to P. neglectus is suggested.

Changes in growth, photosynthetic capacity and ionic relations in spring wheat (Triticum aestivum L.) due to pre-sowing seed treatment with polyamines

The influence of pre-sowing seed treatment with polyamines (2.5 mM putrescine, 5.0 mM spermidine and 2.5 mM spermine) on growth, photosynthetic capacity, and ion accumulation in two spring wheat (Triticum aestivum L.) cultivars MH-97 (intolerant) and Inqlab-91 (tolerant) was examined. The primed seeds of each treatment and non-primed seeds were sown in a field containing 15 dS m−1 NaCl. Although all three polyamines were effective in improving shoot growth and grain yield in both cultivars under saline conditions, the effect of spermine was very pronounced particularly in improving grain yield. Different priming agents did not affect the net CO2 assimilation rate and transpiration rate of either cultivar. However, pre-treatment with spermidine increased stomatal conductance (gs) in the tolerant cultivar, whereas with spermine stomatal conductance decreased in the intolerant cultivar under salt stress. Priming agents had different effects on the accumulation of different ions in wheat plant tissues. When spermidine and distilled water were used as priming agents, they were effective in reducing shoot [Na+] in the tolerant and intolerant cultivars, respectively under saline conditions. Although all priming agents caused an increase in shoot [K+], distilled water was more effective in improving shoot [K+] in both cultivars under salt stress. Pre-treatment with spermidine was very effective in reducing shoot [Cl−] under saline conditions particularly in the tolerant cultivar. However, the pattern of accumulation of different ions in roots due to different seed priming treatments was not consistent in either cultivar except that root Na+ decreased due to priming with spermine and spermidine in the intolerant and tolerant cultivars under saline conditions. In conclusion, although all three priming agents, spermine, spermidine and putrescine, were effective in alleviating the adverse effect of salt stress on wheat plants, their effects on altering the concentration of different ions and growth were different in the two cultivars differing in salt tolerance.

Metabolic changes in rice seedlings with different submergence tolerance after desubmergence

When flash flood intolerant rice cultivars are submerged, they show greater morphological changes such as elongation and chlorosis than tolerant cultivars. These morphological responses are caused by ethylene produced during submergence, however, a visible damage of intolerant cultivars is markedly developing after desubmergence rather than during submergence, which is probably due to oxidative damage. We studied the effect of ethylene produced during submergence on antioxidant content and oxidative damage after desubmergence. When rice ( Oryza sativa) was submerged for 8 days, both tolerant cultivar (BKNFR) and intolerant cultivars (Mashuri and IR42) showed a decrease in ascorbate concentration during submergence. After 3 days of desubmergence, the tolerant cultivar showed a rapid recovery of total ascorbate and ascorbic acid, whereas intolerant cultivars showed a slow recovery of them, an increase in malondialdehyde formation, and low survival rate (about 30%). However, applying 200 mg l −1 of AgNO 3 as an ethylene antagonist to intolerant cultivars suppressed the decrease in ascorbate and the increase in malondialdehyde formation after desubmergence, and improved survival rate to about 60%. Ascorbic acid supply to leaf discs from submerged IR42 suppressed increase in malondialdehyde formation by incubation under the light for 24 h. In addition, strong negative correlations were observed between malondialdehyde formation with ascorbate concentration ( r=−0.93) and with percentage of survival ( r=−0.98). Our results indicate that the accumulated ethylene during submergence adversely affected antioxidant mechanism in intolerant rice cultivars after desubmergence, and ascorbic acid was an important antioxidant in vivo for the recovery of submerged rice seedlings.

The development of potential screens based on shoot calcium and iron concentrations for the evaluation of tolerance in Egyptian genotypes of white lupin (Lupinus albus L.) to limed soils.

European cultivars of white lupin (Lupinus albus L.) grow poorly in limed or calcareous soils. However, Egyptian genotypes are grown successfully in highly calcareous soil and show no stress symptoms. To examine their physiological responses to alkaline soil and develop potential screens for tolerance, three experiments were conducted in limed and non-limed (neutral pH) soil. Measurements included net CO2 uptake, and the partitioning of Fe2+ and Fe3+ and soluble and insoluble Ca in stem and leaf tissue. Intolerant plants showed clear symptoms of stress, whereas stress in the Egyptian genotypes and in L pilosus Murr. (a tolerant species) was less marked. Only the intolerant plants became chlorotic and this contributed to their reduced net CO2 uptake in the limed soil. In contrast, Egyptian genotypes and L pilosus showed no change in net CO2 uptake between the soils. The partitioning of Ca and Fe either resulted from the stress responses, or was itself a stress response. L pilosus and some Egyptian genotypes differed in soluble Ca concentrations compared with the intolerant cultivars, although no significant difference was apparent in the Ca partitioning of the Egyptian genotype Giza 1. In a limed soil, Giza 1 maintained its stem Fe3+ concentration at a level comparable with that of plants grown in non-limed soil, whereas stem [Fe3+] of an intolerant genotype increased. Gizal increased the percentage of plant Fe that was Fe2+ in its leaf tissue under these conditions; that of the intolerant genotype was reduced. The potential tolerance of the Egyptian genotypes through these mechanisms and the possibility of nutritional-based screens are discussed.

Submergence tolerance of rainfed lowland rice: search for physiological marker traits

The submergence tolerance of four rainfed lowland rice (Oryza sativa L.) cultivars was evaluated after submergence in a natural water pond for different submergence durations (0, 7, 11, and 15 days). Complete submergence of plants induced elongation and accumulation of volatile aldehydes at different rates in the cultivars studied. Total soluble carbohydrates (TSC) and starch content, on the other hand, decreased during submergence. Plant survival recorded after 10 d of desubmergence showed large cultivar differences. Plant elongation during submergence has been found to be negatively correlated with survival (r = -0.77), emphasizing the importance of reduced elongation growth during submergence. Higher amounts of starch and total soluble carbohydrate (TSC), before and at the end of submergence period, greatly improved the survival during submergence and recovery growth after desubmergence. Aldehyde content was measured in the shoots as an indicator of the shift in metabolic activity from aerobic respiration to anaerobic fermentation, which differed in tolerant and intolerant cultivars. Intolerant cultivars invariably produced more aldehydes than tolerant ones. Aldehyde production rate was negatively correlated with plant survival, suggesting that plants utilizing excess energy reserve during submergence stress suffered the most, resulting in poor survival. Our results suggest that greater elongation growth during submergence has pronounced adverse effects on rice plant survival during submergence, and that higher initial carbohydrate (soluble sugar and starch) enable rice plants to sustain submergence stress and regenerate quickly after desubmergence. These findings are discussed in relation to adaptation traits for submergence tolerance in rainfed lowland rice.

Fermentative Metabolism and Organic Acid Concentrations in Fruit of Selected Strawberry Cultivars with Different Tolerances to Carbon Dioxide

Effects of 20 kPa CO2 treatments on concentrations of fermentation products, organic acids, and activities of pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH), were measured in fruit of selected strawberry cultivars (Fragaria ×ananassa Duch. `Annapolis', `Cavendish', `Honeoye', `Kent', `Jewell', `Lateglow', and `NorthEast'). Acetaldehyde, ethanol, and ethyl acetate concentrations accumulated in CO2-treated fruit of `Honeoye' and `Kent', but not in `Cavendish' or `Annapolis'. The former two cultivars were classified as intolerant to high CO2 and the latter two as tolerant to high CO2. Activities of PDC and ADH were higher in CO2-treated than in air-treated fruit of the tolerant cultivars but not in the intolerant cultivars. Succinate accumulated in fruit of all cultivars, but concentrations were higher in the tolerant than in the intolerant cultivars. Results are discussed in relation to tolerance of fruit to CO2.

533 Metabolic Changes Associated with Strawberry Cultivars with Different Tolerances to High Carbon Dioxide during Storage

Several strawberry fruit cultivars were exposed to air or CO2 at 2 °C for up to 9 days. Concentrations of fermentation products and organic acids, and activities of pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH), were measured. Acetaldehyde, ethanol, and ethyl acetate concentrations accumulated in CO2-treated fruit of `Honeoye' and `Kent', but not in `Cavendish' or `Annapolis'. We classified the former group of cultivars as intolerant to high CO2 and the latter group as tolerant to high CO2. Activities of PDC and ADH were higher in CO2-treated than air-treated fruit of the tolerant cultivars but not in the intolerant cultivars. Succinate accumulated in fruit of all cultivars, but concentrations were highest in the tolerant than in the intolerant cultivars. These results will be discussed in relation to mechanisms of CO2 action on fruit metabolism.

Hypoxia Induces Anoxia Tolerance in completely Submerged Rice Seedlings

Summary Survival of four rice (Oryza sativa L.) cultivars was evaluated after submergence in water containing different oxygen concentrations. The presence of O2 in the floodwater was critical for the survival of 14-day-old seedlings: there was no effect of 4 d submergence in air-saturated water (0.24 mol· m-3 · O2), or floodwater containing O2 concentrations down to 0.05 mol · m-3, whereas when seedlings were exposed to an «anoxic shock» (0.00 mol · m-3 · O2), death of all four cultivars occured within 24–42 h. Prior exposure of seedlings to a hypoxic pre-treatment (submergence with 0.05 mol · m-3 · O2 for 24 h) greatly improved the tolerance to 24 h anoxia in all four cultivars. Two submergence tolerant cultivars (IR49830 and FR13A) showed much greater tolerance to anoxia than two intolerant cultivars (IR36 and IR42). Following the hypoxic pre-treatment, only the two tolerant cultivars could tolerate 42 h anoxia, and IR49830 seedlings could withstand up to 3d of submergence in anoxia. The two enzymes of ethanolic fermentation alcohol dehydrogenase (ADH, EC 1.1.1.1) and pyruvate decarboxylase (PDC, EC 4.1.1.1) were induced by the hypoxic pre-treatment. The activity of ADH was correlated to cultivar differences in anoxia tolerance. However, this enzyme is unlikely to limit the rate of ethanol fermentation since its in vitro activity was two orders of magnitude greater than the observed ethanolic fermentation rates. The in vitro activity of PDC was an order of magnitude lower than that of ADH, and showed a clear correlation with ethanol fermentation rates but was not correlated with anoxia tolerance. Our results suggest that the complete absence of oxygen in floodwater will have a major adverse effect on rice plants during submergence, and that the rice plant’s ability to adapt to anoxic conditions is an important component of submergence tolerance. These findings are discussed in relation to metabolic adaptations to alleviate the adverse effects of anoxia during submergence.

Rice Seed Vigor and Seedling Establishment in Anaerobic Soil

The rice (Oryza sativa L.) crop is established under hypoxia when sown into flooded or water‐saturated soft. This study was conducted to clarify the interrelationship between seed vigor and seedling growth in anaerobic soil and to identify seedling characteristics that predict establishment in the field. Different levels of seed vigor were obtained with different cultivars, times of harvest, and accelerated aging treatments. Seeds of cultivars tolerant of anaerobic soil (ASDI, JC178, Taothabi, and Kuhei 2) and of intolerant cultivars (IR36 and IR50) were produced by harvesting 25, 30, 35, and 40 d after heading. Another set of seeds was aged at 43°C and 100% relative humidity for 0, 3, 6, and 9 d. The characteristics measured were germination and germination rate in petri dishes, coleoptile and mesocotyl lengths in N2 gas in llasks, and seedling establishment, vigor index (which indicates the speed of emergence), height, leaf development, mesocotyl length, and shoot weight in flooded soil in trays and in water‐saturated soil in the field. The harvest time did not affect seedling establishment in the field. Aging reduced seedling establishment significantly in the cultivars tested except ASD1, which was tolerant to aging. Seedling establishment in the field was closely correlated with the vigor index in the field (simple linear correlation coefficient r = 0.8 to 1.0), establishment and vigor index in the tray (r = 0.5 to 0.9), and coleoptile length in N2 gas (r = 0.4 to 0.9), suggesting that these characteristics would be useful in the prediction of seedling establishment in anaerobic soil.

Inheritance of Tolerance to Manganese Deficiency in Soybean

Manganese deficiency is a recurring problem in soybean [Glycine max (L.) Merr.] grown on high pH soils. Presently, the application of chemical fertilizers is used to alleviate yield losses associated with this deficiency. Because chemical control is often ineffective, genetic tolerance could be used in areas where Mn deficiency is a problem. The development of soybean genotypes tolerant to Mn deficiency is facilitated if the mode of inheritance is understood. The F2 and F2:3 progeny of the tolerant germplasm line A14 and the intolerant cultivar Pride B216 were evaluated in the field for tolerance to Mn deficiency. The observed wide range in progeny response to Mn deficiency suggested digenic inheritance. This model was supported by the results of a cluster analysis applied to the F2:3 family mean ratings and variances. Low estimates of narrow sense heritability (h2 = 0.19) in the F2 generation indicated that F2 phenotypic differences were largely due to environmental variation, thereby making yield selection for tolerance to Mn deficiency in the F2 generation difficult. Estimates of narrow sense heritability based on F2:3 family means were greater (h2 = 0.70), indicating that selection based on F2:3 family means should be effective.

COMPARISON OF RAPD MARKERS BETWEEN HEAT-TOLERANT AND INTOLERANT CULTIVARS OF LIMA BEANS

Lima beans are an important vegetable crop to the processing industry in Delaware, but yields in Delaware are below other areas due to heat. The objective was to correlate RAPD markers from heat-tolerant and intolerant cultivars with phenotypic data. Twenty-five primers were used, 10 of which generated 25 polymorphic bands among 11 cultivars. MDS analysis of genetic distance among the cultivars shows segregation into two major clusters, with Kingston as a distant outlier. Kingston's position can be correlated to published data reporting its consistently good yields even when temperatures are high. The results of this study indicate RAPD markers may be used to screen for cultivars that have high yield potentials despite high temperatures. Further studies to screen F, and inbreeds will determine the usefulness of these markers in breeding programs.

Differential Transcript Levels of Genes Associated with Glycolysis and Alcohol Fermentation in Rice Plants (Oryza sativa L.) under Submergence Stress.

Expression of genes encoding enzymes involved in specialized metabolic pathways is assumed to be regulated coordinately to maintain homeostasis in plant cells. We analyzed transcript levels of rice (Oryza sativa L.) genes associated with glycolysis and alcohol fermentation under submergence stress. When each transcript was quantified at several times, two types (I and II) of mRNA accumulation were observed in response to submergence stress. Transcripts of type I genes reached a maximum after 24 h of submergence and were reduced by transfer to aerobic conditions or by partial exposure of shoot tips to air. In a submergence-tolerant rice cultivar, transcript amounts of several type I genes, such as glucose phosphate isomerase, phosphofructokinase, glyceraldehyde phosphate dehydrogenase, and enolase, increased significantly compared to an intolerant cultivar after 24 h of submergence. This suggests that the mRNA accumulation of type I genes increases in response to anaerobic stress. mRNA accumulation of type II genes, such as aldolase and pyruvate kinase, reached a maximum after 10 h of submergence. Following transfer to aerobic conditions, their transcript levels were not so rapidly decreased as were type I genes. These results suggest that the mRNA levels of genes engaged in glycolysis and alcohol fermentation may be regulated differentially under submergence stress.

Relationship between Coleoptile Elongation and Alcoholic Fermentation in Rice Exposed to Anoxia. II. Cultivar Differences

The relationship between coleoptile elongation and survival vs. alcoholic fermentation of rice under anoxia is examined using eight cultivars differing in submergence tolerance. Anoxia was imposed on either 1 or 4 d aerated seeds either by N2 flushing submerged tissues or by incubating tissues in stagnant deoxygenated agar at 0·1% w/v; the latter simulated the stagnant conditions of waterlogged soil. Two cultivars that were most tolerant to submergence also had the greatest tolerance to anoxia, while a submergence intolerant cultivar was also intolerant to anoxia.Coleoptile growth under anoxia was related to rates of ethanol synthesis (RE), however differences between growth during anoxia and survival after anoxia indicated that post-anoxic injury may also be important in rice seeds exposed to anoxia. The correlation between coleoptile growth and RE measured on a tissue basis using intact seeds was r2 = 0·67 among six varieties over 0-3 d anoxia. This correlation improved to about r2 = 0·85 using RE of (embryos plus coleoptiles) over 0-3 d, or coleoptiles at 3 d after anoxia. Coleoptile growth of individual seeds was usually poorly correlated to RE in these cultivars at 2-3 d after anoxia. When coleoptiles of similar lengths were obtained from different cultivars using 4 d aerated seeds, there were differences in RE and coleoptile growth which were related to coleoptile growth during 3 or 5 d anoxia, either on a tissue (r2 = 0·85) or a fresh weight basis (r2 = 0·70-0·97 respectively). Results are discussed in relation to factors which may limit ethanol synthesis in rice exposed to anoxia and the importance of growth to the survival of seeds and mature plants during submergence in the natural environment.

Nematode Tolerance Increases Drought Stress in Young Oat Plants

The role of drought avoidance mechanisms in tolerance to Heterodera avenae was examined in two oat cultivars differing in tolerance to this nematode. Withholding water for 8 days in 22-day-old nematode-infested plants increased the rate of leaf dehydration in the nematode tolerant, compared to the intolerant cultivar. This was attributed to greater root growth inhibition in the intolerant cultivar, resulting in a slower rate of dehydration despite higher stomatal conductance in the infested intolerant cultivar. The results suggest that mechanisms that alleviate water deficit stress could play a role in determining tolerance of cereals to H. avenae but only under well-defined conditions.

Cyst Nematode vs. Tolerant and Intolerant Soybean Cultivars

AbstractThe soybean cyst nematode (SCN), Heterodera glycines Ichinohe, is a major pathogen in soybean [Glycine max (L.) Merr.], and although resistant cultivars have been developed, new races of H. glycines build up that are capable of damaging the resistant cultivars. The use of tolerant and susceptible genotypes of soybean, which support SCN development and reproduction without serious plant growth reduction, is a promising method for limiting SCN yield suppression without creating selection pressure for new races of this nematodeA field study was conducted for 2 yr to determine the effect of SCN initial population (Pi) densities on soybean root and shoot development in the intolerant and susceptible cultivar, Bragg, and the moderately tolerant cultivar, Wright. Shoot and root growth was stimulated at the low Pi but reduced at high Pi in both years. Harvest seed weight showed a similar response in 1986, but declined steadily with increasing Pi in 1987 when there was less rainfall. The moderately tolerant cultivar, Wright appeared to be a smaller, more efficient plant than the intolerant cultivar, Bragg. Wright had a smaller root system than Bragg, but the roots in the top 0.15 m exhibited compensatory growth in response to early infection by SCN whereas Bragg root growth was suppressed. Wright also had a proportionately deeper root system, compared to Bragg, and this may be part of the mechanism of tolerance.

The cereal cyst nematode (Heterodera avenae) on oats. I. Identification of attributes useful in early screening for tolerance to H. avenae

Variation in morphology, development, and water relations of four oat cultivars inoculated with a range of densities of Heterodera avenae larvae was assessed during early growth to identify distinguishing traits for tolerance. Experiments were performed under glasshouse conditions on cultivars previously rated for tolerance. Cultivar differences were found in the effects of H. avenae on final leaf length, and on root and shoot mass within 20 to 30 days of planting. These differences corresponded to cultivar differences in tolerance to H, avenae at maturity. Differences between cultivars in their sensitivity to root stunting by H, avenae were also related to their final tolerance ratings. Tiller removal generally enhanced tolerance but had little effect on the overall tolerance ranking of the four cultivars examined. H. avenae infection had the least effect on the water use efficiency (WUE) of the most tolerant cultivar and the greatest effect on the least tolerant cultivar. In the absence of nematodes, intolerant cultivars used water more efficiently than did tolerant cultivars. Results suggest that oats can be screened for tolerance to H. avenae during early plant development.

Genetic variation for aluminum tolerance in Kenyan wheat cultivars

Abstract A study was conducted to examine the genetic variability for tolerance to aluminum toxicity in several Kenyan cultivars. The F2 seedlings from eleven crosses between tolerant and intolerant cultivars exhibited a wide range of segregation ratios and indicated that aluminum tolerance in this group of parents was conditioned by two or more genes in each cross. Four of the individual crosses fitted a two‐gene model, and none fitted a single gene model. Expression of the tolerance genes in the F2 progeny was dependent on the genetic background. In three out of four crosses between tolerant parents, a high frequency of susceptible segregates was obtained. The segregation ratio tests performed on the F2 seedling populations suggested that the tolerant parents Romany, PF7748, K. Kongoni and K. Tembo had different tolerance genes. The results from crosses involving K. Fahari, K. Swara and Siete Cerros (all susceptible) indicated that aluminum susceptibility was controlled by recessive genes. The F2 progen...

Effects of rates of a nematicide and of fertiliser on the growth and yield of cultivars of potato which differ in their tolerance of damage by potato cyst nematodes (Globodera rostochiensis andG. pallida)

Potato plants growing in soil heavily infested with potato cyst nematode (PCN) contained less N, P and K in their leaf dry matter than plants growing in the same soil treated with a nematicide. These differences were less in tolerant than intolerant cultivars. Applying additonal fertiliser increased the growth of untreated plants more than that of nematicide-treated plants and nematicides increased growth most in plots receiving the lowest rate of fertiliser. Overall, the results are consistent with the hypothesis that damage by invading juveniles of PCN decreases the effectiveness of the potato root system leading to a chronic deficiency of one or more nutrients and a consequential reduction in the rate of top growth.

Tolerance of potato to potato cyst nematodes (Globodera rostochiensis and G. pallida) in relation to the growth and efficiency of the root system

SUMMARYPotato cyst‐nematode (Globodera rostochiensis) was shown to damage potato plants in several ways. A major cause of damage, affecting all cultivars to a similar extent, was a reduction in the top to root weight ratio. Intolerant cultivars also suffered a reduction in the weight and length of their root systems when grown in heavily infested soil, the combined damage resulting in a marked decrease in nutrient uptake and top growth. In addition intolerant cultivars tended to senesce prematurely when heavily infested, further decreasing their leaf area duration and yield.Cultivars tolerant of potato cyst‐nematode (PCN) differed from intolerant cultivars in that their root systems tended to grow larger in heavily infested soil than in lightly infested or nematicide‐treated soil, so partly compensating for the reduction in the top/root ratio. In a growth cabinet experiment Maris Anchor was more severely damaged at a soil temperature of 10 than at 15 °C. In a glasshouse, without temperature control, differences were obtained between cultivars in small pots (10 cm) in the effect of PCN on root growth which correlated well with differences in tolerance obtained in field trials.