Age-specific bioassays and fecundity of Phthorimaea operculella (Lepidoptera: Gelechiidae) reared on cry1Ac -transgenic potato plants

Variation in the susceptibility of lepidopterous pest larvae of different ages to transgenic crops and the potential for survivors to reproduce could have important consequences for the development of resistance in such pests. Experiments were undertaken in the laboratory to determine if larvae of the potato tuber moth, Phthorimaea operculella, of different ages (0 (< 1 day old), 3, 5, 7 days) varied in their susceptibility to cry1Ac9–transgenic potato (Solanum tuberosum) foliage grown in the glasshouse or field. The survival and fecundity of larvae reared on transgenic tubers was also determined in the laboratory. There were no apparent differences in susceptibility of larvae of different ages to transgenic foliage. Larvae fed glasshouse or field‐grown non‐transgenic foliage had significantly larger relative growth indices and more larvae pupated, than those fed transgenic foliage, regardless of larval age. Eggs from a laboratory colony were placed on transgenic or non‐transgenic tubers to measure survival and fecundity. Between 6% and 15% of eggs placed on transgenic tubers developed into pupae for three of the four transgenic potato lines tested. On one transgenic line, only six adults emerged from 1300 eggs. In contrast, between 71% and 97% of the eggs placed on non‐transgenic tubers developed into pupae. Male and female pupae from transgenic lines weighed less than those from non‐transgenic lines. The fecundity of females from two of four transgenic lines was lower than from the non‐transgenic parent cultivar. Although larvae of different ages did not exhibit any overall age‐dependent pattern of increasing or decreasing susceptibility to transgenic foliage of glasshouse or field‐grown plants, the ability of larvae to survive and reproduce on transgenic tubers suggests this pest has the ability to evolve resistance to the transgenic plants used in the present study.     

Aspects of tuber resistance in hybrid potatoes to potato tuber worm

Tubers produced from crosses between the wild potato, Solanum berthaultii Hawkes (Solanaceae), and the cultivated species Solanum tuberosum L. (Solanaceae) are resistant to potato tuber worm (PTW), Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), infestation compared to those of the popular commercial North American cultivars Allegany, Atlantic, Chieftain, Katahdin, MaineChip, NorDonna, Norwis, Russet Norkotah, Snowden, and Yukon Gold. Given a choice between Atlantic and hybrid tubers, female PTW deposited ca. 50% fewer eggs on hybrid tubers than on those of Atlantic; larval survival and production of prepupae on hybrid tubers were reduced similarly. Time needed for neonates to penetrate eye buds was ca. 100 min greater on hybrid tubers compared to that on cv. Atlantic. Periderm of hybrid tubers is thicker than that of cv. Atlantic and may contribute to the delay in larval penetration of tubers and the success of initial establishment.     

Resistance of potatoes transgenic for a cry1Ac9 gene, to Phthorimaea operculella (Lepidoptera: Gelechiidae) over field seasons and between plant organs

Stable performance of insect‐resistant transgenic plants across field seasons and between plant organs damaged by the insect pest is critical for management of this resistance in the field. To evaluate this, potato (Solanum tuberosum) lines transgenic for a cry1Ac9 gene with resistance to potato tuber moth (Phthorimaea operculella) were established in the field during the southern hemisphere summers of 1997/98, 1998/99 and 1999/00 as small field plots, each of 10 plants. Replicate plots of the non‐transgenic parent cultivars (at least one for every three independently derived transgenic lines) were planted randomly throughout the trials. Field‐grown foliage was challenged with larvae in the laboratory and a growth index (GI) was calculated for recovered larvae from each transgenic and non‐transgenic potato line. Larval growth on young and mature leaves, and on newly harvested or stored tubers was also measured in the laboratory. Foliage from the transgenic lines inhibited larval growth in all seasons tested. For both control and transgenic lines, larvae had slightly lower GIs when reared on mature leaves compared with young leaves, although the correlation between mean GI for young and mature transgenic leaves was high (r = 0.97). The correlation between the mean GIs of larvae on newly harvested tubers and on those stored for 5 months was also high (r = 1.0). However, the GIs of larvae on newly harvested transgenic tubers were larger than on transgenic tubers stored for 5 months. The relative growth indices (RGI = mean GI/number days before final weighing) of larvae reared on newly harvested tubers from transgenic lines were generally higher than those from young transgenic foliage, while the RGIs of larvae reared on non‐transgenic tubers were slightly lower than those fed non‐transgenic foliage. The correlation between mean RGIs of larvae fed tubers or foliage was 0.62. The transgenic potato lines exhibited stable resistance to larvae across field seasons, between affected plant organs, and between plant organs of different ages.     

Establishment of Beauveria bassiana as a fungal endophyte in potato plants and its virulence against potato tuber moth,Phthorimaea operculella (Lepidoptera: Gelechiidae)

The potato tuber moth, Phthorimaea operculella, is the most damaging potato pest in the world and is difficult to control as the larvae are internal feeders in the foliage and tubers. Entomopathogenic fungi that colonize plants as endophytes have lethal and sublethal pathological effects on insect pests. We show that Beauveria bassiana colonizes the aerial parts of potato plants endophytically after inoculation through soil drenching. Endophytic B. bassiana persisted in potato foliage for more than 50 days postinoculation. Bioassays indicated that foliage of B. bassiana-inoculated potato plants were pathogenic against larvae of P. operculella. Sublethal experiments indicated that B. bassiana negatively affected the growth, development, and reproduction of P. operculella. Development experiments showed that the weight of P. operculella pupae reared on B. bassiana-colonized potato plants (4.25 mg) was significantly less than that of those reared on uninoculated control plants (8.89 mg). Compared with newly eclosed larvae fed on control plants, those fed on B. bassiana-inoculated plants had significantly lower survivorship, with only 17.8% developing to the adult stage. Oviposition of P. operculella females reared on B. bassiana endophytically colonized plants was significantly lower (35 eggs/female) than of those reared on uninoculated plants (115 eggs/female). This study demonstrates that endophytic B. bassiana can be a potential biological control agent for the control and management of P. operculella. Comparing pupal weights of P. operculella reared on potato plants inoculated with the B. bassiana strain GZGY-1-3 and on untreated control plants, pupae from the control plants were significantly heavier than those from treated plants.     

Determining the number of instars in potato tuber moth Phthorimaea operculella (Zeller) using density‐based DBSCAN clustering

The potato tuber moth (PTM), Phthorimaea operculella (Zeller), is an important pest of Solanaceae crops and especially devastating to potatoes. There is no significant difference in morphological characteristics of PTM from the first to third instar larvae; therefore, it is difficult to directly determine the number of instars of this pest based on morphology. In the present study, head capsule width and length and mandible width of 340 PTM individuals were measured. Density‐based spatial clustering of applications with noise (DBSCAN) clustering was used for instar grouping. The results of DBSCAN clustering were compared with those obtained using Gaussian mixture models and k‐means clustering; the results of the three clustering methods were verified using Brooks–Dyar rule, Crosby rule and linear regression model. The clusters obtained using the three methods were the same and comprised four PTM instars with three morphological characteristics. Moreover, the results of the three methods fit the Brooks–Dyar rule, Crosby rule, frequency analysis and logarithmic regression model well. Head capsule width was the best morphological characteristic for determining the number of instars of PTM, and this characteristic may be used for determining PTM instars in the field. These results show that the DBSCAN clustering method is a promising tool for the identification of insect instars.     

Temporal dynamics of tuber formation and related processes in a crossing population of potato (Solanum tuberosum)

The chronological relationships between stolon formation, stolon tip swelling, tuber initiation, flowering, senescence, growth and resorption of tubers were studied under field conditions in a diploid population of potato with 238 genotypes, the parental clones and seven tetraploid cultivars. Timing of tuber initiation was not closely related to the timing of stolon formation, flowering and duration of the plant cycle. Tuber initiation very often preceded stolon branching. The number and size distribution of tubers were largely influenced by the degree of stolon branching, the length of the stolon swelling period and tuber resorption. The peak production of stolons and swollen stolon tips largely took place within the flowering period, although in most genotypes, some stolon tip swelling took place until the end of the plant cycle. More information on the general temporal relationships between events related to tuber formation and plant development will contribute to a better understanding of the physiological and genetic basis of the processes leading to the production of harvestable tubers.     

Efficacy of entomopathogenic nematodes against potato tuber moth,Phthorimaea operculella (Lepidoptera: Gelechiidae) under laboratory conditions

The susceptibility of potato tuber moth, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae) to native and commercial strains of entomopathogenic nematodes (EPNs) was studied under laboratory conditions. Native strains of EPNs were collected from northeastern Iran and characterised as Steinernema feltiae and Heterorhabditis bacteriophora (FUM 7) using classic methods as well as analysis of internal transcribed spacer (ITS) and D2/D3 sequences of 28S genes. Plate assays were performed to evaluate the efficiency of five EPN strains belonging to four species including Steinernema carpocapsae (commercial strain), S. feltiae, Steinernem glaseri and H. bacteriophora (FUM 7 and commercial strains). This initial assessment with 0, 75, 150, 250, 375 and 500 IJs/ml concentrations showed that S. carpocapsae and H. bacteriophora caused the highest mortality in both larval and prepupal stages of P. operculella, PTM. Thereafter, these three strains (i.e. S. carpocapsae, H. bacteriophora FUM 7 and the commercial strains) were selected for complementary assays to determine the effects of soil type (loamy, loamy–sandy and sandy) on the virulence of EPNs against the second (L2) and fourth instar (L4) larvae as well as prepupa. A soil column assay was conducted using 500 and 2000 IJs in 2-ml distilled water. Mortality in the L2 larvae was not affected by the EPN strain or soil type, while there was a significant interactive effect of nematode strains and soil type on larval mortality. The results also showed that EPN strains have higher efficiency in lighter soils and caused higher mortality on early larvae than that in loamy soil. In L4 larvae, mortality of PTM was significantly influenced by nematode strain and applied concentrations of infective juveniles. The larval mortality induced by S. carpocapsae was higher than those caused either by a commercial or the FUM 7 strain of H. bacteriophora. Prepupa were the most susceptible stage.     

An integrated view of the hormonal regulation of tuber formation in potato (Solanum tuberosum)

The hormonal regulation of the consecutive steps in the formation of tubers on the potato plant ( Solanum tuberosum L.) is described and discussed. An integrated view of the complex regulation of the initiation and growth of stolons and tubers is presented, with special emphasis on the commonly observed lack of synchronization of the various steps in tuber formation within a plant.     

The toxicity of some medicinal plant extracts to the potato tuber moth,Phthorimaea operculella (Lepidoptera: Gelechiidae)

The potato tuber moth Phthorimaea operculella is a serious pest of potato both in the field and storage that makes great problem in storage. Farmers routinely rely on chemical insecticides that could be hazardous for human health and environment. Insecticide resistance of P. operculella has been reported all over the world, so botanical origin materials may serve as proper alternative materials for controlling the pest. Natural products are generally preferred because of they are less harmful to non-target organisms, eco-friendly and biodegradable. In the present study, ovicidal activity of essential oils (EOs) of basil, European pennyroyal, lavender, mint, oregano and savoury and oviposition-deterrent activity of methanolic extracts of fumitory, lavender, licorice and oregano were investigated on P. operculella. Probit analysis showed that EOs of Lavandula angustifolia revealed the highest activity (LC₅₀ value 0.4 μL/L air). Fumitory extract elicited the highest reduction in percentage of laying eggs. The results indicated that these medicinal plants could be effective for declining damage of P. operculella in storages.     

Behavior of newly hatched potato tuber moth larvae,Phthorimaea operculella Zell. (Lepidoptera: Gelechiidae), in relation to their host plants

A study was made of neonate larvae of Phthorimaea operculella.Host finding from soil-laid eggs and dispersal from hosts and nonhosts were first examined. Of first-instar larvae hatching from soil-laid eggs, 80% found the potato plant while roughly 50% found each of the other three plants (datura, tobacco, and tomato). Dispersal from potato, datura, and tobacco was very low, while on tomato it was higher and a high mortality was observed in the 24 h period. Dispersal from nonhost plants was high. Behavior on leaves of hosts and non-hosts is described and some host-plant specific behaviors are identified. Effects on behavior of some of the physical and chemical factors are described. Methylene dichloride extracts of potato leaf wax reduced locomotion rates and the number of turns during locomotion. Also methylene dichloride extract and, to a lesser extent, methanol extract caused biting behavior.     

Biological effects of some natural and chemical compounds on the potato tuber moth,Phthorimaea operculella Zell. (Lepidoptera:Gelechiidae)

The olfactory reaction of larvae and moths was investigated towards 18 oils (6 natural oils and 12 commercial chemical oils). Some of these oils such as peppermint and camphor (natural oils) and eugenol and camphene (commercial oils) were repellent to both larvae and moths. Other oils such as strawberry and d-limonene were attractive to both larvae and moths.Some of the repellent oils were, therefore, tested for their effect on certain biological aspects of the insects.Eugenol and peppermint oils, each at the 0.01% conc., caused a significant depression in the fecundity of moth and decreased the percentage of egg hatchability. Eugenol oil was much more effective than peppermint oil at 1%. Dried (leaves, fruits or seeds) powder of 14 different plants species were tested in different concentrations with talcum powder (carrier material) against egg deposition. The results indicated that dried powders of Allium cepa, Curcuma longa, Colocasia antiqurum, Ocimum basilicum. Dodonaea viscose and Thuja orientalis played a highly significant role in reducing egg deposition. The most impressive effect was displayed by powders of D. viscose and A. cepa, which caused the highest depression in egg deposition as well as in the emerging offsprings. Ethanolic extracts of 11 plants indicated that extracts of Pithuranthos tortosus and Iphiona scabra caused the maximum inhibition of egg hatchability, followed by C. longa, Citrullus colocynthia and T. orientalis. Ethanolic extracts of Schinus terebenthiflius (leaves) and I. scabra caused the highest depression in the deposited eggs, as they played a remarkable role as ovipositor deterrents.The majority of the plant extracts at 1% conc. could protect potato tubers at different intervals according to the calculated tuber damage index as follows: Iphiopna > Pithuranthos > Curcuma > Schinus (fruits) Thuja > Schinus (leaves) > Dodonaea > Citrullus.     

Tuber on a chip: differential gene expression during potato tuber development

Potato tuber development has proven to be a valuable model system for studying underground sink organ formation. Research on this topic has led to the identification of many genes involved in this complex process and has aided in the unravelling of the mechanisms underlying starch synthesis. However, less attention has been paid to the biochemical pathways of other important metabolites or to the changing metabolic fluxes occurring during potato tuber development. In this paper, we describe the construction of a potato complementary DNA (cDNA) microarray specifically designed for genes involved in processes related to tuber development and tuber quality traits. We present expression profiles of 1315 cDNAs during tuber development where the predominant profiles were strong up- and down-regulation. Gene expression profiles showing transient increases or decreases were less abundantly represented and followed more moderate changes, mainly during tuber initiation. In addition to the confirmation of gene expression patterns during tuber development, many novel differentially expressed genes were identified and are considered as candidate genes for direct involvement in potato tuber development. A detailed analysis of starch metabolism genes provided a unique overview of expression changes during tuber development. Characteristic expression profiles were often clearly different between gene family members. A link between differential gene expression during tuber development and potato tissue specificity is described. This dataset provides a firm basis for the identification of key regulatory genes in a number of metabolic pathways that may provide researchers with new tools to achieve breeding goals for use in industrial applications.     

Estimating temperature‐dependent developmental rates of potato tuberworm,Phthorimaea operculella (Lepidoptera: Gelechiidae)

Abstract The potato tuberworm, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), is the most destructive pest of potato, Solanum tuberosum L. (Solanaceae), in tropical and subtropical regions in both field and storeroom situations. The modeling of temperature‐dependent development can be useful in forecasting occurrence and population dynamics of the pests. Published developmental parameters for this pest vary greatly for many reasons. We determined temperature‐dependent development of P. operculella at seven constant temperatures (16, 20, 24, 28, 32, 34 and 36 °C). Developmental period of whole immature stage (egg to the end of the pupal stage) varied from 75.5 days at 16 °C to 17 days at 32 °C. The population failed to survive at 36 °C. The observed data was modeled to determine mathematical functions for simulating P. operculella development in each stage of development and overall. Two linear models, ordinary linear regression and the Ikemoto linear model were used to describe the relationship between temperature and development rate of the different stages of P. operculella and estimating the thermal constant and lower temperature threshold. The lower temperature threshold (t) and thermal constant (k) of whole immature stage were estimated to be 11.6 °C and 338.5 DD by Ikemoto linear model, and the estimated parameters were not substantially different with those estimated by ordinary linear models. Different models provided a better fit to the various developmental stages. Of the eleven nonlinear models fitted, the Beriere‐1, Logan‐6 and Lactin‐1 model was found to be the best for modeling development rate of egg, larva and pupa of P. operculella, respectively. Phenological models based on these findings can be part of a decision‐support tool to improve the efficiency of pest management programs.     

Use of a stress inducible promoter to drive ectopic AtCBF expression improves potato freezing tolerance while minimizing negative effects on tuber yield

Solanum tuberosum is a frost-sensitive species incapable of cold acclimation. A brief exposure to frost can significantly reduce its yields, while hard frosts can completely destroy entire crops. Thus, gains in freezing tolerance of even a few degrees would be of considerable benefit relative to frost damage. The S . tuberosum cv. Umatilla was transformed with three Arabidopsis CBF genes ( AtCBF1-3 ) driven by either a constitutive CaMV35S or a stress-inducible Arabidopsis rd29A promoter. AtCBF1 and AtCBF3 over-expression via the 35S promoter increased freezing tolerance about 2 °C, whereas AtCBF2 over-expression failed to increase freezing tolerance. Transgenic plants of AtCBF1 and AtCBF3 driven by the rd29A promoter reached the same level of freezing tolerance as the 35S versions within a few hours of exposure to low but non-freezing temperatures. Constitutive expression of AtCBF genes was associated with negative phenotypes, including smaller leaves, stunted plants, delayed flowering, and reduction or lack of tuber production. While imparting the same degree of freezing tolerance, control of AtCBF expression via the stress-inducible promoter ameliorated these negative phenotypic effects and restored tuber production to levels similar to wild-type plants. These results suggest that use of a stress-inducible promoter to direct CBF transgene expression can yield significant gains in freezing tolerance without negatively impacting agronomically important traits in potato.     

Oviposition deterrence of shoots and essential oils of Minthostachys spp. (Lamiaceae) against the potato tuber moth

Abstract:  The potato tuber moth is a noxious pest of potato in stores, where the use of repellent plants is an environmentally sound alternative to the application of chemical pesticides. We evaluated the protective effect of native Minthostachys species (Lamiaceae) against tuber infestation by the potato tuber moth in a rustic store in Cusco, Perú. We covered potato tubers with dried shoots of Minthostachys spicata and Minthostachys glabrescens and compared tuber damage with a control treatment of maize straw. We also conducted a no-choice oviposition bioassay in the laboratory, testing the oviposition deterrence of essential oils of M. spicata , M. glabrescens and Minthostachys mollis at natural concentrations. We recorded the number of eggs laid by mated moths on filter paper treated with essential oils of each of the three species and on two control treatments: hexane and untreated blank. Finally, we tested for differences in oviposition deterrence among five full-sib families of potato tuber moth raised under identical conditions. We found that dried, chopped leaves and flowers of Minthostachys species reduced the percentage of tuber damage in stores in comparison with the control (5% vs. 12%), but no difference in protection was found between species. Essential oils at natural concentrations deterred moth oviposition, reducing the number of eggs laid by about 80% compared with the control treatments; again, there were no significant differences between Minthostachys species. Finally, whereas we detected among-family variation in oviposition on filter papers treated with essential oils, no difference was found in the number of eggs laid on control substrates. Therefore, there was genetic variation for oviposition deterrence in the potato tuber moth and resistance to repellent plants might evolve thereafter.     

The potential of the fungus, Muscodor albus, as a microbial control agent of potato tuber moth (Lepidoptera: Gelechiidae) in stored potatoes

Potato tuber moth (PTM), Phthorimaea operculella, is a serious pest of stored potato in most countries where potatoes are grown. Entomopathogens offer promise as alternatives to broad spectrum insecticides for management of this pest. The fungus Muscodor albus, which produces a mixture of antimicrobial volatile organic chemicals, was tested for its insecticidal activity against PTM. Adults and neonate larvae were exposed to volatiles generated by 15 or 30 g of M. albus rye grain culture plus water for 72 h in hermetically sealed 28.3 L chambers at 24 degrees C. Mean percent mortalities in adult moths exposed to 0, 15, and 30 g of fungal formulation were 0.9, 84.6, and 90.6%, respectively. Development to the pupal stage of PTM that were exposed as neonate larvae to 15 or 30 of M. albus culture was reduced by 61.8 and 72.8%, respectively, relative to controls.     

Temperature‐dependent phenology and growth potential of the Andean potato tuber moth,Symmetrischema tangolias (Gyen) (Lep., Gelechiidae)

The Andean potato tuber moth, Symmetrischema tangolias (Gyen) [Lepidoptera, Gelechiidae], is an economically important pest of potato (Solanum tuberosum L.) in the mid‐elevated Andean region and an invasive pest of partially global importance. Determination of the pest's population life table parameters is essential for understanding population development and growth under a variety of climates and as part of a pest risk analysis. The development, mortality and reproduction were studied in two pest populations (from Peru and Ecuador) in which cohorts of each life stage were exposed to different constant temperatures ranging from 10°C to 28°C. Using the Insect Life Cycle Modeling software, nonlinear equations were fitted to the data and an overall phenology model established to simulate life table parameters based on temperature. The temperature‐dependent development curve was statistically well described for eggs by Ratkowsky's model and for larvae and pupae by Taylor's model. Variability in development time among individuals independent of temperature was significantly described by a log‐logistic model. Temperature effects on immature mortality were described using different nonlinear models. Optimal temperature for survival was between 14° and 17°C. Temperature effects on adult senescence and oviposition time were described by simple exponential models; within‐group variability was described by a Weibull distribution function. Fecundity per female due to temperature followed a nonlinear model indicating maximum reproduction at ~17°C. The established model revealed good convergence with historical life tables established at fluctuating temperatures. The results confirm that S. tangolias is more adapted to cooler temperature than the common potato tuber moth, Phthorimaea operculella (Zeller). S. tangolias develops at temperatures within the range of 8–28.8°C with a maximum finite rate of population increase (=1.053) at 21°C. The established process‐based physiological model can be used globally to simulate life table parameters for S. tangolias based on temperature and should prove helpful for evaluating the potential establishment risk and in adjusting pest management programmes.     

Protection of potato crop against Phthorimaea operculella (Zeller) infestation using frass extract of two noctuid insect pests under laboratory and storage simulation conditions

The oviposition deterrent effect of water extract of Spodoptera littoralis and Agrotis ipsilon larval frass on Phthorimaea operculella adult females was studied using two types of larval food “Natural host and Semi-artificial diet” under laboratory and storage simulation (semi-field) conditions. Extracted frass of fed larvae on semi-artificial diet showed complete oviposition deterrent effect at treatments with 4th, 5th and 6th instars of S. littoralis, also at treatments with 1st–3rd and 6th instars of A. ipsilon, while the same effect was observed when the larvae fed on castor oil leaves as a natural host only at treatment with frass extract of A. ipsilon 6th instar larvae. Presence of low amounts of phenols and flavonoids in water extract of A. ipsilon larval frass resulted in relatively more effect as oviposition deterrent to fertile adult females on treated oviposition sites, while the opposite effect was obtained in S. littoralis larval frass experiments. At semi-field experiments, the percentage reduction of laid eggs reached 100% after two?days at treatments with frass extracts of 4th and 5th S. littoralis larval instars and A. ipsilon 6th instar larvae fed on semi-artificial diet and/or castor oil leaves. Percentage reduction of laid eggs for untreated sacks reached 93.24 and 48.95% after 2 and 30?days, respectively, when placed between treated sacks, in comparison with the mean number of laid eggs for isolated control.     

Immunolocalization of extensin and potato tuber lectin in carrot, tomato and potato

Tissue-specific expression of two members of the cell wall hydroxyproline-rich glycoprotein (HRGP) family, extensin and potato tuber lectin, was examined by immunolocalization at the light microscope level in various organs (leaves, stems, roots, fruit, tuber) of carrot ( Daucus carota cv. Thumbelina), tomato ( Lycopersicon esclentum cv. Pixie Hybrid II), and potato ( Solanum tuberosum cv. Kennebec). Extensin was prominently expressed in vascular tissue, particularly xylem and also phloem, although virtually all cells displayed some degree of staining which varied as a function of the tissue, organ, and plant under study. Antibodies against potato tuber lectin (PTL) displayed a localization pattern similar to that observed for extensin; notably PTL did not stain cambium but did stain epithelial cells lining secretory cavities. These distribution patterns are consistent with a role for extensin, and possibly PTL, in providing mechanical support in tissues subjected to compression or torsional stress imparted by vascular growth, or by similar stress brought about by transport of vascular fluids.