Density Of Glandular Trichomes Research Articles

Micromorphology of trichomes of Thymus malyi (Lamiaceae)

Micromorphological, ultrastructural and morphometric investigations of the trichomes of Thymus malyi were carried out using a light microscope, a scanning electron microscope and a transmission electron microscope. Unbranched non-glandular trichomes, peltate and capitate glandular trichomes were described. The leaves of Thymus malyi bear non-glandular and glandular trichomes on both sides. Estimates of the volume density (i.e. their volume fraction per unit volume) of non-glandular trichomes were higher as compared to volume density of peltate and capitate glandular trichomes. Estimates of the number of these trichomes per area on sections showed that the capitate trichomes were the most abundant. Ultrastructural analyses of cell inner structure have shown numerous mitochondria, big nuclei and plastids with lipid globules and starch grains.

Anatomia foliar de plantas de alfavaca-cravo cultivadas sob malhas coloridas

No presente trabalho, foi avaliado o efeito do controle espectral da luz sobre características anatômicas de folhas em Ocimum gratissimum L. As plantas foram cultivadas por quatro meses sob malhas de 50% de sombreamento nas cores preta, vermelha e azul e a pleno sol. Plantas submetidas a pleno sol apresentaram maior espessura foliar, maior densidade estomática e maior densidade de tricomas tectores e glandulares na face adaxial. As plantas cultivadas sob malhas coloridas não exibiram diferenças quanto à espessura e à área foliar. As plantas mantidas sob malha vermelha tiveram a menor densidade estomática na face adaxial, já as plantas mantidas sob malhas azul e vermelha exibiram maior área foliar total. As plantas mantidas sob malha vermelha apresentaram a menor densidade estomática e as menores densidades de tricomas tectores e glandulares na face adaxial. Tais resultados mostram que tanto a intensidade como a qualidade espectral da luz pode ser modulada durante o cultivo de Ocimum gratissimum L. a fim de serem obtidas características anatômicas desejáveis.

Constituents of glandular trichomes of Tithonia diversifolia: Relationships to herbivory and antifeedant activity

The herbivory activity of the bordered patch larvae ( Chlosyne lacinia, Lepidoptera) on leaves of a Brazilian population of Tithonia diversifolia and the antifeedant potential of its leaf rinse extract were investigated. The caterpillars fed only on the adaxial face, where the density of glandular trichomes is very low, and avoided the abaxial face, which contains high levels of trichomes. Deterrent activity against the larvae was observed in leaf discs treated with leaf rinse extract at concentrations of 1–5% of fresh leaf weight. High-performance liquid chromatography (HPLC) analysis indicated that sesquiterpene lactones are the main constituents of the glandular trichomes. Dichloromethane rinse extracts of the leaves and inflorescences were chemically investigated, and 16 compounds were isolated and identified: 14 sesquiterpene lactones, a flavonoid and a diterpenoid. In this study, five sesquiterpene lactones are described for the first time in the genus, including two lactones, one of which has an unusual seco-guaianolide skeleton. Our findings indicate that the caterpillars avoid the sesquiterpene-lactone-rich glandular trichomes, and provide evidence for the antifeedant activity of the dichloromethane leaf rinse extract. In addition, a study of the seasonal variation of the main constituents from the leaf surface throughout a year demonstrated that a very low qualitative but a very high quantitative variation occurs. The highest level of the main metabolite tagitinin C was observed between September and October and the lowest was from March to June, the later corresponding to the period of highest infestation by the larvae.

Induction of glandular and non-glandular trichomes by damage in leaves of Madia sativa under contrasting water regimes

Plant traits may play multiple functional roles simultaneously. Leaf trichomes have been related to resistance against herbivores as well as to enhanced water economy in the plant. In a greenhouse study, we evaluated the interactive effect of damage (control vs. mechanical damage) and water availability (control vs. low watering) on the expression of glandular and non-glandular leaf trichomes in the annual Chilean tarweed Madia sativa (Asteraceae). We found that the overall trichome density increased both after damage and when plants were grown under water shortage. Interestingly, the type of trichome induced after damage varied with each water environment. While damage induced glandular trichomes only under control watering, non-glandular trichomes were induced by damage only under experimental drought. Results indicate that in M. sativa glandular trichomes are equally induced by drought or damage but there is no additive effect of these factors. In both cases glandular trichome density apparently reached a limit, which may be interpreted in terms of constraint or efficacy. On the other hand, the synergistic effect of damage and drought on non-glandular trichomes might suggest that, compared to glandular ones, these trichomes are less responsive to each stress factor separately. Thus, for plants to induce non-glandular trichomes they must be subjected to a degree of stress above a threshold that was not reached for each individual factor in our experimental setting. We did not detect a significant correlation between trichome types. Thus, the contrasting patterns observed likely reflect independent responses of trichomes to the evaluated factors.

Morfoanatomia e histoquímica de Brosimum gaudichaudii Trécul (Moraceae)

Brosimum gaudichaudii, conhecida como mamacadela, é espécie comum nos cerrados, com grande valor na medicina popular e na indústria de medicamentos. A casca da raiz e do caule é empregada no tratamento do vitiligo, sendo o bergapteno e psoraleno, duas furanocumarinas, responsáveis pela ação farmacológica. Neste trabalho são apresentadas a caracterização morfoanatômica e a histoquímica de órgãos vegetativos de B. gaudichaudii, com informações sobre o embrião e o desenvolvimento pós-seminal. Amostras foram processadas segundo técnicas usuais em anatomia e ultra-estrutura vegetal. O embrião é do tipo total e invaginado, a plântula cripto-hipogéia e o sistema radicular do tirodendro é composto por raiz primária pouco desenvolvida em relação às raízes laterais. Plantas adultas apresentam raízes gemíferas longas, plagiotrópicas originando ramos caulinares aéreos; tais raízes possuem periderme com súber desenvolvido e floema secundário abundante em relação ao xilema, sendo facilmente destacados quando manipulados. O caule jovem e a folha apresentam epiderme unisseriada, grande densidade de tricomas tectores unicelulares e tricomas glandulares. Laticíferos não-articulados ramificados ocorrem em todos os órgãos, podendo invadir os elementos de vaso. Idioblastos fenólicos ocorrem em abundância em todos tecidos e órgãos analisados. O valor das características anatômicas observadas no controle de qualidade da droga é discutido.

Higher glandular trichome density in tomato leaflets and repellence to spider mites

The objective of this work was to evaluate the feasibility of selection for higher glandular trichome densities, as an indirect criterion of selection for increasing repellence to spider mites Tetranychus urticae, in tomato populations derived from an interspecific cross between Lycopersicon esculentum x L. hirsutum var. glabratum PI 134417. Trichome densities were evaluated in 19 genotypes, including 12 from advanced backcross populations, derived from the original cross L. esculentum x L. hirsutum var. glabratum PI 134417. Counts were made both on the adaxial and abaxial leaf surfaces, and trichomes were classified into glandular types IV and VI, other glandular types (types I+VII), and nonglandular types. Mite repellence was measured by distances walked by mites onto the tomato leaf surface after 20, 40 and 60 min. Spider mite repellence biotests indicated that higher densities of glandular trichomes (especially type VI) decreased the distances walked by the mites onto the tomato leaf surface. Selection of plants with higher densities of glandular trichomes can be an efficient criterion to obtain tomato genotypes with higher resistance (repellence) to spider mites.

Effects of arbuscular mycorrhiza and phosphorus application on artemisinin concentration in Artemisia annua L.

Annual wormwood (Artemisia annua L.) produces an array of complex terpenoids including artemisinin, a compound of current interest in the treatment of drug-resistant malaria. However, this promising antimalarial compound remains expensive and is hardly available on the global scale. Synthesis of artemisinin has not been proved to be feasible commercially. Therefore, increase in yield of naturally occurring artemisinin is an important area of investigation. The effects of inoculation by two arbuscular mycorrhizal (AM) fungi, Glomus macrocarpum and Glomus fasciculatum, either alone or supplemented with P-fertilizer, on artemisinin concentration in A. annua were studied. The concentration of artemisinin was determined by reverse-phase high-performance liquid chromatography with UV detection. The two fungi significantly increased concentration of artemisinin in the herb. Although there was significant increase in concentration of artemisinin in nonmycorrhizal P-fertilized plants as compared to control, the extent of the increase was less compared to mycorrhizal plants grown with or without P-fertilization. This suggests that the increase in artemisinin concentration may not be entirely attributed to enhanced P-nutrition and improved growth. A strong positive linear correlation was observed between glandular trichome density on leaves and artemisinin concentration. Mycorrhizal plants possessed higher foliar glandular trichome (site for artemisinin biosynthesis and sequestration) density compared to nonmycorrhizal plants. Glandular trichome density was not influenced by P-fertilizer application. The study suggests a potential role of AM fungi in improving the concentration of artemisinin in A. annua.

Expression and subcellular compartmentation of Aspergillus niger β-glucosidase in transgenic tobacco result in an increased insecticidal activity on whiteflies ( Bemisia tabaci)

Transgenic Nicotiana tabacum plants expressing Aspergillus niger β-glucosidase (EC 3.2.1.21) gene ( BGL1) in different subcellular compartments [cell wall (Tcw), endoplasmic reticulum (Ter), and vacuole (Tvc)] were analyzed to study the effects of BGL1 localization on plant growth and plant–insect interaction. Transgenic and non-transgenic plants were grown and characterized in a greenhouse with 25/16 °C day/night temperatures and natural sunlight. Plant insecticidal activity was analyzed with adult whiteflies ( Bemisia tabaci) in vial and cage experiments. Compared with wild-type controls, Ter and Tvc transgenic plants did not differ significantly in seed germination, plant growth rate, plant height, or flowering time. However, in Tcw seed germination and beginning of flowering were significantly delayed, and leaf area and plant fresh weight were significantly reduced. Transgenic plants had a marked insecticidal effect on whiteflies ( Bemisia tabaci) and on Diptera spp. flies. The density of secretory glandular trichomes was significantly greater in transgenic than in wild-type leaves. This work indicates that hydrolysis of yet to be identified glycosides, may play an important role in plant insect resistance mechanism and plant trichome development.

Karakter Anatomi Daun dari Kultur Tunas Artemisia annua L.

Artemisia annua L. produce artemisinin, an endoperoxide sesquiterpene lactone, which is effective against resistant strains of Plasmodium falciparum , the malarial parasite. Artemisinin in foliar tissue are localized entirely in subcuticular space of capitate glandular trichomes. This research was performed to investigate the anatomical structures especially glandular trichomes which associated with artemisinin production in leaves of five different shoot culture clones (A, B, C, D, and E clones). Observation of anatomical characters of leaves was done by making cross-section, while observation of trichomes was performed using Scanning Electron Microscopy. The leaves of five clones showed bifacial anatomical structure. The leaf thickness of E clone was the highest (96.8 µm), while those of four other clones were relatively the same ranging from 62.8 µm to 66.6 µm. Glandular trichomes were distributed throughout the lamina of leaves with the highest distribution in adaxial parts of the leaves. The size of uppermost secretory cells of glandular trichomes was relatively the same in five clones observed. There were variations in density of glandular trichomes in five clones observed. A and B clones had higher density of glandular trichomes i.e. 56.9 and 60.5/mm 2 , while three other clones had density which range from 43.0 to 49.7/mm 2 . It was suggested that A and B clones were the potential clones in producing artemisinin in vitro due to their larger leaf size and higher density of glandular trichomes. Keywords : Artemisia annua , shoot culture, anatomical structure of leaf

The Nightshade Proteinase Inhibitor IIb Gene is Constitutively Expressed in Glandular Trichomes

The best known property of plant proteinase inhibitor II (PIN2) genes is their wound-inducible expression in leaves and constitutive expression in flowers. Here we show by promoter analysis in transgenic plants and in situ reverse transcription-PCR (RT-PCR) analysis that SaPIN2b, a member of the PIN2 gene family of nightshade (Solanum americanum), is also constitutively expressed in glandular trichomes. SaPIN2b promoter and its deletions were cloned and fused upstream of beta-glucuronidase (GUS) to transform the nightshade and tobacco (Nicotiana tabacum) plants. Histochemical staining assays indicated that SaPIN2b:GUS was expressed constitutively in glandular trichomes, predominantly in the gland cells, of both transgenic nightshade and tobacco plants. Constitutive expression of SaPIN2b in glandular trichomes was further confirmed by liquid phase in situ RT-PCR analysis of nightshade leaves. Deletion analysis from the 5' end of the SaPIN2b promoter revealed that separate regulatory elements control SaPIN2b expression in gland cells and stalk cells of glandular trichomes. Fluorometric GUS assays showed that SaPIN2b:GUS expression was significantly increased in transgenic plant leaves after mechanical wounding or methyl jasmonate treatment. The SaPIN2b promoter sequence contains six MYB-binding motifs and an L1 box that are involved in trichome differentiation and development. Overexpression of SaPIN2b in tobacco resulted in a significant increase in glandular trichome density and promotion of trichome branching. These results suggest that, as well as being an induced defensive protein of the well-known PIN2 family, SaPIN2b could also play roles in trichome-based defense by functioning as a constitutive component of trichome chemical defense and/or by regulating the development of glandular trichomes.

Developmental Regulation of Phenylpropanoid Biosynthesis in Leaves and Glandular Trichomes of Basil (Ocimum basilicum L.)

Basil (Ocimum basilicum L.) essential oil phenylpropenes have ecological and economic importance. These compounds are specifically synthesized and accumulate in basil peltate glandular trichomes, and their content and composition depend on plant developmental stage. Studies on gene expression and enzymatic activity indicate that the phenylpropene biosynthetic genes are developmentally regulated. These previous studies, however, did not systematically investigate the levels of gene expression, enzyme activity, and phenylpropene accumulation through plant development. In this study, we systematically investigated methylchavicol accumulation in basil leaves and the enzyme activities and gene expression of both chavicol O‐methyltransferase (CVOMT) and eugenol O‐methyltransferase (EOMT) in all leaves at four plant developmental stages. Methylchavicol accumulation decreased over time as the leaves matured. There was a significant correlation between methylchavicol accumulation and CVOMT and EOMT enzyme activities, suggesting that the levels of biosynthetic enzymes control the essential oil content. CVOMT and EOMT transcript expression levels, which decreased with leaf age, followed the same pattern in both whole leaves and isolated glandular trichomes, providing evidence for the first time that CVOMT transcript levels are developmentally regulated in basil glandular trichomes themselves and that differences in CVOMT expression observed in whole leaves are not solely the result of differences in glandular trichome density.

Time Allocation of Activities of Two Heteropteran Predators on the Leaves of Three Tomato Cultivars with Variable Glandular Trichome Density

Abstract Plant glandular trichomes can confer protection from herbivores, but may also affect natural enemies. We studied time allocation of activities (inactive, moving, probing, feeding, and grooming) of nymphs of the predatory bugs Macrolophus pygmaeus and Orius niger on the upper surface of tomato leaflets from the cultivars Dombito, Elxis, and H30. In H30, which had the highest density of type VI glandular trichomes on the upper surface, both insects spent more time in grooming their tarsi and rostrum than the other two cultivars. In Dombito and Elxis, which have trichome densities that didn’t differ much, no significant differences were observed in time allocation of activities for both insects. When averaged across cultivars, younger instars of M. pygmaeus spent less time on probing and more time on grooming, whereas for O. niger, the nymphs of first stage spent more time on grooming and less on movement than the nymphs of older stages. Between species, O. niger first instars groomed more and walke...

Relação entre zingibereno, tricomas foliares e repelência de tomateiros a Tetranychus evansi

O objetivo deste trabalho foi quantificar os teores de zingibereno em populações segregantes (F2) do segundo retrocruzamento para Lycopersicon esculentum a partir da espécie selvagem L. hirsutum var. hirsutum, e verificar a relação entre estes teores e a densidade de tricomas glandulares e a repelência a Tetranychus evansi. Na quantificação do zingibereno, utilizou-se um método espectrofotométrico; os tricomas foram contados a partir de cortes paradérmicos e a resistência a ácaros foi avaliada por um bioteste de repelência. A seleção indireta quanto ao teor de zingibereno promoveu aumentos correlacionados no número de tricomas glandulares e na repelência ao ácaro, e o zingibereno nos tricomas glandulares participou efetivamente na resistência aos ácaros. A densidade de tricomas glandulares influencia de maneira determinante os teores de zingibereno, sendo que o tricoma tipo VI destacou-se por apresentar alta correlação com este aleloquímico. Os teores de zingibereno e a sua relação com tricomas glandulares e com a resistência a artrópodos-pragas se mantiveram ao longo dos retrocruzamentos, evidenciando a possibilidade de obtenção de plantas resistentes via seleção indireta para alto teor de zingibereno nos folíolos.

Delayed induced responses of birch glandular trichomes and leaf surface lipophilic compounds to mechanical defoliation and simulated winter browsing

Changes in morphology and chemistry of leaf surface in response to herbivore damage may increase plant resistance to subsequent herbivore attack; however, there is lack of studies on induced responses of glandular trichomes and their exudates in woody plants and on effects of these changes on herbivores. We studied delayed induced responses in leaf surface traits of five clones of silver birch (Betula pendula Roth) subjected to various types of mechanical defoliation and simulated winter browsing. Glandular trichome density and concentrations of the majority of surface lipophilic compounds increased in trees defoliated during the previous summer. This induced response was systemic, since control branches in branch defoliated trees responded to the treatments similarly to defoliated branches, but differently from control trees. In contrast to defoliation treatments, simulated winter browsing reduced glandular trichome density on the following summer and had fewer effects on individual surface lipophilic compounds. Moreover, constitutive density of glandular trichomes was negatively correlated with induced total amount of lipophilic compounds per trichome, indicating a trade-off between constitutive and induced resistance in silver birch. Induced changes in leaf surface traits had no significant effect on leaf damage by chewers, miners and gall mites, but increased susceptibility of birch trees to aphids. However, leaf damage by chewers, miners and gall mites in defoliated (but not in control) trees was correlated with concentrations of some fatty acids and triterpenoids, although the direction of relationships varied among herbivore species. This indicates that induction of surface lipophilic compounds may influence birch resistance to herbivores. Our study thus demonstrated both specificity of elicitation of induced responses of birch leaf surface traits by different types of damage and specificity of the effects of these responses on different types of herbivores.

Methyl Jasmonate Application Induces Increased Densities of Glandular Trichomes on Tomato, Lycopersicon esculentum

This study was designed to address whether applications of methyl jasmonate (MJ) or Benzothiadiazole (BTH) to cultivated tomato, Lycopersicon esculentum, induced elevated densities of defense-related glandular trichomes on new leaves. Four-leaf tomato plants were sprayed with MJ, BTH, or control solutions, and the density of type VI glandular trichomes on new leaves was subsequently determined at 3, 7, 14, 21, and 28 d. At 7, 14, and 21 d, the density of type VI glandular trichomes on new leaves was significantly higher on MJ-treated plants than on BTH- or control-treated plants. At 7 and 14 d after treatment, the mean density of glandular trichomes on new leaves of MJ-treated plants was ninefold higher than on leaves of control-treated plants. We observed entrapment of immature western flower thrips in trichomes on MJ-treated plants at higher rates than on BTH or control plants. Studies to evaluate potential trade-offs between reductions in pest populations by increased trichome density and possible negative impacts of trichome induction on biological control agents are needed.

Bacterial Colonization of the Phyllosphere of Mediterranean Perennial Species as Influenced by Leaf Structural and Chemical Features

In this study, we assessed various leaf structural and chemical features as possible predictors of the size of the phyllosphere bacterial population in the Mediterranean environment. We examined eight perennial species, naturally occurring and coexisting in the same area, in Halkidiki (northern Greece). They are Arbutus unedo, Quercus coccifera, Pistacia lentiscus, and Myrtus communis (evergreen sclerophyllous species), Lavandula stoechas and Cistus incanus (drought semi-deciduous species), and Calamintha nepeta and Melissa officinalis (non-woody perennial species). M. communis, L. stoechas, C. nepeta, and M. officinalis produce essential oil in substantial quantities. We sampled summer leaves from these species and (1) estimated the size of the bacterial population of their phyllosphere, (2) estimated the concentration of different leaf constituents, and (3) studied leaf morphological and anatomical features and expressed them in a quantitative way. The aromatic plants are on average more highly colonized than the other species, whereas the non-woody perennials are more highly colonized than the woody species. The population size of epiphytic bacteria is positively correlated with glandular and non-glandular trichome densities, and with water and phosphorus contents; it is negatively correlated with total phenolics content and the thickness of the leaf, of the mesophyll, and of the abaxial epidermis. No correlation was found with the density of stomata, the nitrogen, and the soluble sugar contents. By regression tree analysis, we found that the leaf-microbe system can be effectively described by three leaf attributes with leaf water content being the primary explanatory attribute. Leaves with water content >73% are the most highly colonized. For leaves with water content <73%, the phosphorus content, with a critical value of 1.34 mg g(-1) d.w., is the next explanatory leaf attribute, followed by the thickness of the adaxial epidermis. Leaves higher in phosphorus (>1.34 mg g(-1) d.w.) are more colonized, and leaves with the adaxial epidermis thicker than 20.77 microm are the least colonized. Although these critical attributes and values hold true only within the Mediterranean ecosystem studied and the range of observations taken, they are important because they provide a hypothesis to be tested in other Mediterranean ecosystems and other biomes. Such comparative studies may give insight as to the general properties governing the leaf-microbe system.

Resistência de genótipos de batata ao pulgão

Avaliou-se a resistência (e antibiose) de genótipos de batata, comerciais e em fase de melhoramento, ao pulgão Myzus persicae, em ensaios efetuados com plantas em vasos, sem chance de escolha, em Jaboticabal (SP). Foram efetuados seis experimentos, utilizando-se um total de 16 genótipos, a saber: 'Achat', 'Apuã', 'Aracy', 'Aracy Ruiva', 'Bintje', 'Ibitu Açu', 'Itararé', 'N 140-201', 'NYL 235-4', '288.719-13', '288.764-26', '288.776-3', '288.776-6', '288.794-19', '288.801-6' e '288.814-7'. Em cada experimento foram utilizadas combinações variadas dos mesmos. Nos dois primeiros experimentos as plantas foram infestadas com 30 pulgões adultos por planta, distribuídos em três folhas, com três avaliações realizadas em semanas subseqüentes à infestação, contando-se o número de indivíduos por planta. O terceiro experimento foi conduzido aprisionando-se duas fêmeas adultas no interior de pequenas gaiolas fixadas na face abaxial dos folíolos, em número de dez por planta, avaliando-se a reprodução do pulgão após sete dias, em dois plantios. No quarto experimento efetuou-se a infestação da planta com 15 pulgões, avaliando-se o crescimento da população na planta toda durante três semanas consecutivas. No quinto experimento foi avaliada a descendência de uma única fêmea adulta por folíolo e no sexto experimento avaliou-se o peso dos pulgões aos sete dias de vida. Os tricomas glandulares presentes nos folíolos e a funcionalidade dos mesmos também foram avaliados. A cultivar 'Ibitu Açu' apresentou elevado grau de antibiose a M. persicae; os genótipos '288.776-3' e '288.794-19' também apresentaram esse tipo de resistência, em grau moderado; '288.719-13' e '288.764-26' foram resistentes ao pulgão, provavelmente devido à presença de tricomas glandulares funcionais, dos tipos A e B, em seus folíolos (antixenose); entre os mais suscetíveis destacaram-se 'Bintje' e '288.801-6'.

Leaf surface traits: overlooked determinants of birch resistance to herbivores and foliar micro-fungi?

Previous studies on the mechanisms of birch resistance to herbivores and foliar micro-fungi (both pathogenic and endophytic) have focused mainly on the role of internal leaf chemistry. In the present study, we examined genetic correlations between leaf surface traits (glandular trichome density and total concentrations of surface flavonoid aglycones) and occurrence of three species of foliar micro-fungi, one pathogenic rust (Melampsoridium betulinum) and two endophytic fungi (Fusicladium sp. and Melanconium sp.), and performance of autumnal moth larvae (Epirrita autumnata) in two birch species, Betula pubescens ssp. czerepanovii and B. pendula. The performance of autumnal moth larvae on B. pubescens ssp. czerepanovii was negatively correlated with density of glandular trichomes (RGR: r=−0.855; pupal mass: r=−0.709). In addition, rust infection was negatively correlated with trichome density in B. pendula (r=−0.675) and with epicuticular flavonoid aglycones in B. pubescens ssp. czerepanovii (r=−0.855). The frequency of the endophytic fungus Fusicladium sp., was related to epicuticular flavonoid aglycones (r=−0.782), while another endophytic fungus, Melanconium sp., showed no associations with any of the studied variables in B. pubescens ssp. czerepanovii. Our results indicate that leaf surface traits may be at least as important determinants of herbivore performance and micro-fungi abundance in birch as leaf internal chemistry.

Glandular-haired alfalfa resistance to potato leafhopper (Homoptera: Cicadellidae) and hopperburn: development of resistance indices.

Eight proprietary genotypes of glandular-haired alfalfa, Medicago sativa L., supplied by two different companies, were compared for the degree and types of resistance to the potato leafhopper, Ernpoasca fabae (Harris), and hopperburn. A tube cage no-choice bioassay was developed to test leafhopper mortality, feeding, settling preferences, severity of hopperburn symptoms (in this case, defined as both yellowing and stem growth reduction), and trichome density and type on feeding sites. Leafhopper mortality was both strongly and significantly associated with feeding and leaf trichome density; decreased hopperburn symptom severity was weakly, although significantly, associated with increased mortality. To quantify hopperburn in terms of both yellowing and stem growth reduction, we developed a ranking system that reduces overall hopperburn expression to a single number that considers the varying responses to both types of symptoms. Great variability in leafhopper settling, leafhopper mortality, and stem glandular trichome density was detected among alfalfa genotypes, suggesting that genotypic differences may be based on the concentration and/or chemical constituency of the trichome exudates. We postulate that, among variably resistant genotypes of glandular-haired alfalfa, differences among leafhopper responses and hopperburn severity are linked to forced movement from the stems to the leaves as refuge feeding sites. Principal component analysis was performed to reduce the 10 variables down to five biologically significant factors. Scores for these factors were then used to develop resistance indices for potato leafhopper resistance, hopperburn resistance, and an overall glandular-haired alfalfa resistance index.

Pod Surface Characteristics in Wild and Cultivated Vigna Species and Resistance to the Coreid Bug Clavigralla tomentosicollis Stal. (Hemiptera: Coreidae)

Several Vigna species were used to determine the role of pod trichomes and pod toughness in the resistance of cowpea to feeding damage by the coreid bug Clavigralla tomentosicollis Stal. The scanning electron microscopy study revealed the presence of glandular and non-glandular trichomes on the pod wall of all test genotypes. The cultivated genotypes TVu 1890, TVu 3354 and IT84S-2246 of the V. unguiculata ssp. unguiculata showed significantly lower (P<0.05) densities of glandular trichomes than accessions of the wild Vigna species (TVnu 72, TVnu 151, and TVnu 707). All pods were similar with respect to the density and length of non-glandular trichomes. The two wild accessions TVnu 151 and TVnu 707 of the V. unguiculata ssp. dekindtiana had low pod, strength similar to that of the susceptible genotype IT84S-2246, and also showed high seed damage levels comparable to that of this susceptible genotype. These accessions of the subspecies dekindtiana contrasted with the wild and resistant accession TVnu 72 of the V. vexillata species which suffered minor seed damage in spite of its low pod strength. The association between high pod strength and low seed damage was found only in the two cultivated genotypes TVu 1890 and TVu 3354. Our results suggest that tough pod wall and high density of glandular trichomes can be combined to achieve enhanced resistance to C. tomentosicollis in cultivated Vigna genotypes.