Relationship between the concentration of chlorogenic acid in carrot roots and the incidence of carrot fly larval damage

Chlorogenic acid (1·24-3·36 mg/g) was identified as the main phenolic component in the peel of carrots by hplc analysis. The higher the concentration of chlorogenic acid in different cultivars the greater the susceptibility to carrot fly larval damage. Increases in concentration were found both after carrot fly damage and after carrots had overwintered in the field. The presence and location of chlorogenic acid was confirmed in sections of carrot tissues, mounted in 0·05 M ammonia solution by viewing them using a u.v.-epifluorescent microscope. The importance of phenolic compounds and their function in the production of insect cuticle is discussed in relation to the different concentrations of chlorogenic acid and resistance to carrot fly in carrots.     

Using physical barriers to prevent carrot fly (Psila rosae (Fabricius)) damage in domestic production

A field experiment was used to assess the effectiveness of different barriers in protecting garden‐scale carrot production from carrot fly (Psila rosae (Fabricius)) damage. Some of the vertical barriers tested were found to provide a useful method of protecting early season carrots from carrot fly in terms of the percentage of carrots free from damage but, under cumulative pest pressure of several generations of carrot fly, such barriers were found to provide insufficient protection. Gardeners should therefore completely cover their carrot crop to attain an acceptable level of control, and this was found to be especially important for carrots harvested later in the season. There were positive effects of some barrier types on yield which may be due, at least in part, to the protection given by the barriers to carrot seedlings.     

The effects of time of sowing and harvest on carrot biochemistry and the resistance of carrots to carrot fly

Two carrot cultivars which represented contrasting levels of resistance to carrot fly, Psila rosae, were grown in a replicated field experiment at Wellesbourne in 1984–85. Seed was sown on five occasions between April and August 1984 and the crop harvested after a minimum growth in the field of 16 wk on seven occasions between August 1984 and February 1985. A highly significant correlation (r = -0.78; P > 0.001) between the levels of carrot fly damage and the concentration of chlorogenic acid in the roots enabled a model to be formulated to predict the relative predisposition to carrot fly larval damage; high levels of chlorogenic acid early in the season predisposed roots to severe attack when they were older.     

The consistency of the resistance of eight carrot cultivars to carrot fly attack at several centres in Europe

Eight carrot cultivars representing the range of resistance to carrot fly damage as assessed in England were grown at 12 sites in five European countries in 1977 and in 1978. The trials provided evidence of agreement with the findings in England for both years in the ranking of cultivars with respect to their resistance to carrot fly damage. The Nantes cultivar Clause's Sytan Original was the most resistant cultivar tested. Consistent results were obtained from sites where carrots were assessed at harvest and carrot fly attack was severe. A significant interaction between sites and cultivars was largely due to sites where carrots were stored prior to assessment.     

An eco-metabolomic study of host plant resistance to Western flower thrips in cultivated,biofortified and wild carrots

Domestication of plants and selection for agronomic traits may reduce plant secondary defence metabolites relative to their ancestors. Carrot (Daucus carota L.) is an economically important vegetable. Recently, carrot was developed as a functional food with additional health-promoting functions. Biofortified carrots contain increased concentrations of chlorogenic acid as an antioxidant. Chlorogenic acid is involved in host plant resistance to Western Flower Thrips (Frankliniella occidentalis), one of the key agri- and horticultural pests worldwide. The objective of this study was to investigate quantitative host plant resistance to thrips in carrot and to identify candidate compounds for constitutive resistance. As such we explored whether cultivated carrot is more vulnerable to herbivore attack compared to wild carrot. We subjected a set of 14 biofortified, cultivated and wild carrot genotypes to thrips infestation. We compared morphological traits and leaf metabolic profiles of the three most resistant and susceptible carrots using nuclear magnetic resonance spectroscopy (NMR). In contrast to our expectation, wild carrots were not more resistant to thrips than cultivated ones. The most thrips resistant carrot was the cultivar Ingot which is known to be tolerant against carrot root fly (Psila rosae). Biofortified carrots were not resistant to thrips. Plant size, leaf area and number of leaf hairs did not differ between resistant and susceptible carrots. The metabolic profiles of the leaves of resistant carrots were significantly different from those of susceptible carrots. The leaves of resistant carrots contained higher amounts of the flavanoid luteolin, the phenylpropanoid sinapic acid and the amino acid β-alanine. The negative effect of these compounds on thrips was confirmed using in-vitro bioassays. Our results have potential implications for carrot breeders. The natural variation of metabolites present in cultivated carrots can be used for improvement of thrips resistance. This is especially promising in view of the candidate compounds we identified since they do not only confer a negative effect on thrips but as antioxidants also play an important role in the improvement of human health.     

Metabolic fingerprinting reveals differences between shoots of wild and cultivated carrot (Daucus carota L.) and suggests maternal inheritance or wild trait dominance in hybrids

Differences between the metabolic content of cultivars and their related wild species not only have implications for breeding and food quality, but also for the increasingly studied area of crop to wild introgression. Wild and cultivated western carrots belong to the same outcrossing species and hybridize under natural conditions. The metabolic fingerprinting of Dutch wild carrot and of western orange carrot cultivar shoots using (1)H NMR showed only quantitative differences in chemical content, indicating relatively low divergence after domestication. Main differences reside in the primary metabolite content and in the concentrations of chlorogenic acid and feruloyl quinic acid in the shoots of the different carrot types. Wild×cultivar hybrids cannot be distinguished from wild plants based on the metabolome, suggesting maternal, maternal environment, or dominance effects, and indicating high hybrid fitness in wild conditions. Considering these similarities, introgression is a real possibility in carrots, but understanding its consequences would require further studies using backcrosses in a multiple environments.     

Differences in the relative resistance of two carrot cultivars to carrot fly attack over five seasons

A comparison was made over five seasons of carrot fly (Psila rosae) damage on two carrot cultivars, Sytan and Danvers, which represented the extremes of resistance discovered in screening trials at Wellesbourne. Plants were harvested regularly during the seasons and at each harvest the number and weight of roots was recorded and carrot fly damage was assessed using various techniques; in 1979-80 the numbers of carrot fly larvae and pupae in and around root samples were counted. The experiments confirmed repeatedly the relative resistance of cv. Sytan compared with Danvers. The estimated reduction in carrot fly larvae on Sytan relative to Danvers in early November in four seasons ranged from 40% to 67%. When tested against first generation carrot fly attack the reduction in larvae on Sytan was 54%. There were 45% fewer mines per root on Sytan resulting in less damage at each harvest in all seasons. Larvae took longer to develop on Sytan than Danvers and 18% more plants of Sytan survived carrot fly attack. Differences in seedstock, season, sowing time, generation of carrot fly, plant size and density did not account for observed differences in damage between the two cultivars. The studies indicated satisfactory practical techniques for assessing carrot fly damage in cultivar screening trials.     

Development of carrot inbreds with resistance to carrot fly using a single seed descent programme

Two carrot cultivars, ‘Sytan’ and ‘Long Chantenay’, representing commercially important carrot types and selected for their partial resistance to the carrot fly (Psila rosae) were crossed as the basis for a single seed descent programme. The resulting F₁ progeny were mass pollinated to produce an F₂ generation and approximately 2000 plants were raised from this segregating family in the glasshouse in 1981. By careful choice of sowing date and glasshouse temperatures it was possible to stimulate the plants to flower within 10 months. Individual king umbels were enclosed within bags and pollinated with blowflies. Resulting seed was sown in pots in the following August and the process of seed production repeated in a 12 month cycle. Each inbred line was selfed in this way over three generations until the F₅ stage. Stocks of seed were then multiplied. A total of 753 inbreds were produced by 1987. The vigour of each inbred was evaluated in glasshouse tests and the level of chlorogenic acid was determined by a fluorescence technique. The most vigorous lines with the lowest levels of chlorogenic acid were tested in field experiments against carrot fly at Wellesbourne. Nine inbreds with promising agronomic quality and moderate resistance to carrot fly were selected and seeded. These nine lines were submitted to seed companies with the aim of developing new cultivars of carrot.     

The complementary effects of plant resistance and the choice of sowing and harvest times in reducing carrot fly (Psila rosae) damage to carrots

The benefits of combining a partially-resistant carrot cultivar with different sowing and lifting dates to reduce carrot fly, Psila rosae, damage were investigated at Wellesbourne in 1983 and 1984-85. The partially-resistant cv. Sytan was less damaged and supported fewer insects than the susceptible cv. Danvers on all lifting dates. The estimated reduction of carrot fly larvae on Sytan compared with Danvers ranged from 33 to 95%. Nine combinations of sowing and lifting dates provided more than 75% marketable roots of Sytan compared with only three combinations of dates for Danvers. An early June sowing of both cultivars provided roots of a marketable size with the least attack. More than 90% of Sytan roots were still marketable in December and fewer insects were produced by the end of the season on these roots than on those sown earlier. In addition, sowing in June decreased the number of pupae produced on cv. Danvers by 10 times compared with earlier sowings. Combining partial resistance with specific sowing and lifting times enabled satisfactory yields of marketable carrots to be obtained in a field infested by high populations of carrot fly.     

Bionomics of the carrot fly Psila rosae F.; the infestation and sampling of carrot crops

The headlands of a carrot field are generally more heavily attacked by carrot fly larvae than the remainder of the field.
The methods of sampling a carrot crop are outlined: it has been found that, for fields up to 10 acres, samples of carrots taken in alternate twos and threes in the midfield, and in twos on the headlands, give a reliable measure of the infestation. For larger fields the number of carrots is doubled. Transects of headlands and whole fields have been made, and are useful in showing the actual amount of damage in a crop. Thus it is possible to represent each field as a three-dimensional body showing the amount and distribution of the attack.
The deterioration of attacked carrot crops during autumn and winter has been followed. Deterioration is measured by (1) percentage carrots attacked, (2) number of mines per 100 carrots and (3) the percentage of carrots unsaleable or unfit for market. The relations between (1) mines per 100 carrots and time, (2) percentage attack and time, (3) mines per 100 carrots and percentage attack, and (4) mines per 100'carrots and percentage unsaleability are stated. Based on the above relationships, methods of prediction of deterioration have been worked out.
The importance of shelter in determining the degree and position of attack is discussed and the relative effects of different types of shelter on infestation are compared.     

Intensity of radicle fluorescence as related to the resistance of seedlings of lettuce to the lettuce root aphid and carrot to the carrot fly

A technique is described which indicates by u.v. fluorescence the concentration of caffeoylquinic, chlorogenic and isochlorogenic acids in roots of germinating lettuce and carrot. The surface fluorescence of radicles from lettuce root aphid (Pemphigus bursarius) resistant seedlings was more intense than for susceptible seedlings, attributable to the higher concentration of isochlorogenic acid. In contrast, radicles of carrot seedlings resistant to carrot fly (Psila rosae) were less fluorescent than susceptible seedlings, corresponding to the lower concentration of chlorogenic acid in resistant seedlings. The technique is non-destructive and has been developed to distinguish between cultivars or breeding lines potentially resistant to these insect pests.     

Hybrids between cultivated and wild carrots in natural populations in Denmark

Many cultivated plant species are able to hybridize with related wild plants. However, it is not clear whether their hybrids are able to survive and reproduce outside managed fields, and if cultivar genes introgress into wild populations. In areas where wild carrots co-occur with carrot root-crops, pollen and seeds may flow from two different sources in the fields to the surrounding wild populations: from pure cultivar plants that occasionally flower, and from flowering 'bolters' that originate from hybridizations between wild (male) and cultivated carrots (female) in seed production fields in warmer regions of the world. To test whether hybrids are formed and survive in wild Danish populations, and whether prolonged hybridization has led to introgression of cultivar genes, we collected leaf material from adult individuals growing close to carrot fields and analysed their genotypic composition by AFLP. Four hybrids were identified among the 71 plants analysed, and these were most likely F(2) or backcross individuals, sired by pollen from hybrid bolters. Wild populations close to fields were genetically somewhat more similar to cultivars than wild populations far from fields, suggesting that neutral or beneficial cultivar alleles can introgress into the wild gene pool. Despite generations of improvement and adaptation of cultivar carrots to highly managed field conditions, hybrids can thus sometimes survive in wild populations close to carrot fields, and their genes transfer to wild populations by introgression.     

Problems in field selection for resistance to carrot fly (Psila rosae) in carrot cv. Long Chantenay

In field trials between 1973 and 1982 families of carrots of cv. Long Chantenay were assessed for their resistance to carrot fly (Psila rosae). In some but not all years, families selected for their observed resistance in earlier trials seemed more resistant than the parent line. In more than half the trials there was an association between carrot fly damage and root density, there being less damage on those families from which more roots were harvested. Thus, family selection within cv. Long Chantenay did not lead to a consistent improvement in resistance to carrot fly. Alternative strategies for achieving plant resistance to this pest are discussed.     

Dry Matter Distribution Between the Shoot and Storage Root of Carrot (Daucus carota L.): II. Effect of Foliar Application of Gibberellic Acid

The effects of foliar sprays of gibberellic acid (GA) on drymatter distribution in carrots were investigated in three fieldexperiments between 1977 and 1979. The results were interpretedby using a simple quantitative model of assimilate partitioningbetween storage root and shoot. Although the response to GAvaried depending on the year in which the experiment was done,the model successfully described the effects of spraying time,GA concentration, planting density, plant age and cultivar.The maximum effects on repartitioning were achieved with concentrationsof 100–500 mg 1_–1 GA and, except for very earlyor late sprays, the effect was constant with time over a roughly4-week period. The multiplicative nature of the model was usefulin that despite the occurrence of various interactions, a similarassimilate partitioning response to GA in all four cultivarswas demonstrated. The model did not suggest an explanation forthe seasonal effects. Daucus carota L., carrot, assimilate distribution, dry matter distribution, storage root, gibberellic acid, partitioning model     

Low temperature differentially affects tillering in spring and winter wheat in association with changes in plant carbon status

The higher tillering potential of winter wheat cultivars as compared to spring ones has been attributed to an earlier tillering onset in the former. Tillering in grasses is known to depend on temperature and light environment, and may be mediated by plant C status. The aim of this work was to elucidate whether differences in carbohydrate accumulation between wheat types at low temperature may contribute to differences in tillering potential. A set of experiments with contrasting temperatures was conducted in both field enclosures (high irradiance, three experiments) and growth chambers (low irradiance, two experiments). The relative tiller production rate (RTR) was the highest in winter cultivars grown in cool field enclosures, and the lowest in spring cultivars in growth chambers, either cool or warm. Plant C status was inversely related to temperature the response being more pronounced in winter cultivars. Components of RTR, site filling and phyllochron, responded differently to environment and plant C status. Phyllochron increased with temperature, and was inversely correlated to sugar concentration irrespective of cultivar type. Site filling increased with irradiance in both cultivar types while sugar concentration contributed additively to its promotion solely in winter cultivars. Nevertheless, variation in site filling was larger in percentage than variation in phyllochron (200% and 41%, respectively, between most contrasting treatments). Thus, differences in tillering potential between winter and spring wheats may be attributed not only to the earlier tillering onset in the former but also to their differential response to environment and C status.     

The influence of plant density and position in field trials designed to evaluate the resistance of carrots to carrot fly (Psila rosae) attack

The results of field trials designed to evaluate the resistance of carrots to carrot fly (Psila rosae) attack were influenced by plant density and position within trials. Five trials are described, their results analysed and implications for future work discussed. Density effects were of major importance when the range of densities within a trial was greater than about three-fold. Density and damage were associated, carrot cultivars and families with the most roots having the least damage; plant densities achieved should therefore be as close as possible to the targets set. Positional effects were often very important, so trials should ideally have no more than about 10 plots in a block, possibly by using an incomplete block design. Conventional analyses of variance removing block effects may be sufficient but it is desirable, especially with large blocks, to use some form of nearest neighbour analysis for which the various possible techniques gave similar results.     

Effects of carrot psyllid (Trioza apicalis) feeding on carrot yield and content of sugars and phenolic compounds

Carrot psyllid, Trioza apicalis, is a serious pest of carrot in Northern Europe, as it can significantly damage young carrot seedlings in a period as short as 3 days. This study was conducted to investigate effects of carrot psyllid feeding at different plant growth stages on carrot yield and to assess changes in content of sugars, phenolics and related compounds in carrot roots resulting from the psyllid feeding. In addition, reflectance of carrot leaves was measured to assess the intensity of discolouration in damaged leaves. Results showed that carrot yield was significantly reduced by a 3‐day carrot psyllid feeding period when the seedlings were exposed to psyllids at 1‐ or 2‐leaf stage. However, at 4‐leaf stage feeding by one carrot psyllid did not reduce yield. Sucrose concentration in the damaged roots was significantly decreased, whereas concentrations of some phenolic compounds were significantly increased. The reflectance of leaves of damaged carrots differed significantly from those of undamaged control leaves. These observations indicate that carrot psyllid damage has potential to lower not only the carrot yield, but also the carrot crop quality. No phytoplasma was detected in the carrots exposed to psyllids, but recently, T. apicalis has been associated with ‘Candidatus Liberibacter solanacearum’. The role of carrot psyllid feeding and the psyllid‐associated bacterium in the damage formation are discussed.     

Phenolic metabolism in root slices of selected carrot cultivars

Carrot root slices, stored for 4 days at 20 °C reacted with a strong accumulation of total phenols, especially chlorogenic acid. A significant accumulation of isocoumarin content within the peel was observed in stored slices. Synthesis of phenols was accompanied by an increase in phenylalanine ammonia lyase activity, wound induced respiration and ethylene production. The great variability among the studied four cultivars was found concerning isocoumarin synthesis, PAL activity, respiration rate and ethylene evolution, but less distinct in the case of chlorogenic acid accumulation. The carrot slices obtained from freshly harvested roots were more sensitive to mechanical damage and short-term storage than those prepared from roots previously stored.     

Guilty by association: an evaluation of millipedes as pests of carrot and sweet potato

An evaluation of the pest potential of millipede species occurring in Ontario sweet potato and carrot fields was conducted in response to recent grower concerns about the presence of millipedes in close proximity to damaged vegetables. This study is the first North American survey of millipedes on arable soils and the first evaluation of North American millipede damage to sweet potatoes and carrots. Through field surveys, Cylindroiulus caeruleocinctus was found to be the dominant millipede species in Ontario sweet potatoes and carrots. Fields were surveyed over the growing season, and the factors important to each species’ abundance were evaluated using Minimum AIC Estimation (MAICE). Post‐harvest damage assessments were performed, and MAICE analysis was used to determine which arthropod and environmental parameters were most important in explaining damage to sweet potatoes and carrots. Wireworm (Elateridae) abundance was consistently found to explain root damage better than C. caeruleocinctus abundance, and it is concluded that the majority of field‐observed damage was caused by wireworms. C. caeruleocinctus was negatively correlated with both wireworms and damage in carrot fields and is not likely to be a pest of that vegetable. However, abundance of C. caeruleocinctus in sweet potatoes was positively correlated with both wireworms and damage. This species may cause some damage to sweet potato tubers under field conditions, but management tactics should focus on wireworms as the primary source of damage.     

The protection of carrots against carrot fly (Psila rosae) with granular and emulsifiable concentrate formulations of chlorfenvinphos incorporated in gels used for drilling pre germinated seed in a sandy loam

Field experiments were done in a sandy loam in 1979 and 1980 to investigate the performance against carrot fly on carrots of e. c. and granular formulations of chlorfenvinphos incorporated in gels used for drilling pre-germinated seed. With 9·4–66·7 mg a. i./m row, the two formulations performed similarly in a natural hydrocolloid and a mineral colloid gel. Thus the emergence of carrot seedlings 6–7 wk after drilling was similar on plots with untreated gel and those with insecticide-treated gel and, about 6 months after drilling when > 90% of carrots grown without insecticide were damaged by carrot fly larvae, an approximately six-fold increase in dose of both formulations increased the estimated larval mortality from about 70 to 95%. Mean concentrations of residues of total (Z + E) isomers of chlorfenvinphos in harvested carrots treated with 9·4–56·5 mg a. i./m row were50% of the insecticide had been released into both gels.