Trichome Density Research Articles

Helicoverpa armigera preference and performance on three cultivars of short-duration pigeonpea (Cajanus cajan): the importance of whole plant assays.

Helicoverpa armigera is a major pest of pigeonpea (Cajanus cajan). Efforts to develop pigeonpea varieties resistant to H. armigera attack have been met with limited success, despite reports of high levels of resistance to H. armigera in wild relatives of pigeonpea and reports of low to moderate levels of resistance in cultivated varieties. Here we examined H. armigera oviposition preference and larval performance on whole plants of three cultivars of short-duration pigeonpea: a susceptible control (ICPL 87) and two cultivars with purported host-plant resistance (ICPL 86012 and ICPL 88039). In our no-choice oviposition experiment, H. armigera laid similar numbers of eggs on all three cultivars tested, but under choice conditions moths laid slightly more eggs on ICPL 88039. Larval growth and development were affected by cultivar, and larvae grew to the largest size (weight) and developed fastest on ICPL 86012. Moths laid most of their eggs on floral structures, sites where subsequent early instar larvae overwhelmingly fed. Experimentally placing neonate larvae at different locations on plants demonstrated that larvae placed on flowers experienced greater survival, faster development, and greater weight gain than those placed on leaves. The type and density of trichomes (a potential resistance trait) differed among cultivars and plant structures, but larvae selected to feed at sites where trichomes were absent. Future work examining host-plant resistance against H. armigera should incorporate the behavioural preference of moths and larvae in experiments using whole plants as opposed to bioassays of excised plant parts in Petri dishes. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

The Molecular, Morphological and Genetic Characterization of Glyphosate Resistance in Conyza bonariensis from South Africa.

Six Conyza bonariensis (L.) Cronquist populations were screened in a pot experiment at the University of Pretoria's Hatfield experimental farm to evaluate and confirm the degree of glyphosate response. Resistance factors ranged from 2.7- to 24.8-fold compared to the most susceptible biotype. Partial sequencing of the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene found no mutation at the Thr102, Ala103 or Pro106 positions. EPSPS mRNA expression levels in glyphosate-resistant biotypes (Swellendam and Piketberg seed sampling sites) were comparable or lower than those in susceptible biotypes (George and Fauresmith sites). Additionally, the highest expression level was reported in the susceptible Fauresmith biotype. These results indicate that glyphosate resistance in the tested resistant biotypes is not caused by target-site mutations and EPSPS gene amplification. Leaf surface characteristics can influence the spread and subsequent absorption of glyphosate. The study established non-significant results in the amount of leaf wax and insufficient mean separations in cuticle thickness and trichome density data. Therefore, the observed differences in response of biotypes to glyphosate treatment could not be attributed conclusively to differences in the leaf morphological characteristics investigated. Results from the inheritance study were consistent with glyphosate resistance being inherited in an incompletely dominant manner when plants were treated with glyphosate herbicide at 900 g ae ha-1.

Screening of advanced sugarcane genotypes against rust mite

In the screening trial, among the nineteen sugarcane genotypes screened for the reaction to sugarcane rust mite, Abacarus sacchari, only 2 genotypes (009-64 and 0961-07) harboured >1 mites /2 cm2 leaf area while remaining all the genotypes harboured <2 mites/2 cm2 leaf area for the entire crop duration. Morphological characters of genotypes revealed that interveinal distance, leaf area and trichome density were found to influence the A. sacchari negatively. The genotype with high phenol and lower amount of total sugar, reducing sugar, crude protein was found with the lower level of incidence of mites. The study on the role of leaf nutrient on the mite population revealed that genotype with higher potassium content and lower nitrogen levels were found with the minimum incidence of A. sacchari.

Phenotyping Olive Cultivars for Drought Tolerance Using Leaf Macro-Characteristics

This work investigates the relationships between leaf traits and olive response to water stress through two complementary field experiments in order to screen genotypes for drought tolerance. The first experiment consisted of the phenotyping of 32 olive varieties for 11 leaf morpho-physiological traits during a fruit set phase under well-watered conditions. In the second experiment, the yield and vegetative responses of five representative varieties to the withholding of irrigation during the whole fruit growth period were assessed to identify leaf traits that are associated with olive resilience plasticity and that could be used as drought tolerance markers. The results highlighted large phenotypic variability for leaf area (LA, 2.9–9.5 cm2), petiole elasticity (8.0–36.0°), water loss in detached leaves (WLDL, 3.6–11.6%), stomatal density (222.6–470.1 no mm−2), stomatal length (11.4–18.7 µm), trichome density (120.5–204.4 no mm−2), trichome width (103.6–183.4 µm), leaf contents in cuticular wax (CWC, 44.7–606.2 µg cm−2), and soluble sugars (SSC, 15.8–536.9 mg gdw−1). Among these leaf traits, WLDL displayed a significant correlation with the yield stability index (r = −0.973) and water use efficiency (r = −0.939), suggesting its use as relevant drought tolerance phenotypic marker. Likewise, LA, SSC, and CWC were singled out as second-level drought tolerance markers, being strongly correlated with stability of leaf size and leafing intensity in response to water stress. Cluster analysis highlighted 12 distinct levels of drought tolerance within the studied olive collection. Based on the four identified phenotypic markers, “Lechin de Sevilla” alongside “Picholine Marocaine” were found to be the most drought-tolerant varieties, while Frantoio was the most sensitive. This study provides the first, unprecedented, insights into the usefulness of leaf phenotyping in olive drought tolerance screening, with a focus on structural and functional leaf traits.

Structural Disparity of Avocado Rootstocks In Vitro for Rooting and Acclimation Success

Improving clonal rootstock propagation of avocado has been a major industry/research challenge globally for many decades. Tissue culture has been a focus for clonal propagation with substantial advancements in recent years. In the process of tissue culture, avocado rootstocks display differences in rooting and acclimation capacity. Such differences may relate to the specific structural characteristics of the rootstock. This study aimed to investigate the structural difference during tissue culture in two rootstocks ‘Reed’ and ‘Velvick’, with differing rooting and acclimation capacity. Histological investigations were carried out of stem vasculature, leaves and roots of tissue cultured plantlets. Quantitative parameters; stomatal index, stomatal density, trichome density, vein-islet density and vein termination density were also analysed. Prominent fascicular cambium and fewer phloem fibres in stems positively correlated with rooting capacity. Acclimation success positively correlated to the presence of fully differentiated secondary xylem in root. Presence of smaller epidermal cells, high stomatal density and reduced vein termination density was associated with reduced acclimation success. These findings will support optimisation strategies for micropropagation of not only difficult-to-root and difficult-to-acclimate avocado rootstocks, but also, other woody perennials experiencing similar problems.

Effect of Organic Matter Fertilizers on the Composition of Volatiles, Morphometrical and Anatomical Parameters of Essential Oil-Bearing Thymus × citriodorus Cultivated in an Open Field Conditions

Thymus × citriodorus (Lamiaceae) is medicinal, essential oil-bearing hybrid, synthesizing significant amounts of geraniol. This hybrid is suitable for cultivation in an open ground in the Baltic region; therefore, increasing the yield and amounts of bioactive compounds by organic matter fertilization during organic farming is realized. The aim of the present study was to evaluate the effect of fertilization with liquid cattle dung and humus on the quantitative and qualitative composition of essential oils as well as on biomass for some morphometrical and anatomical parameters of Thymus × citriodorus that were grown in open ground for two years. Each fertilization treatment was carried out on four replications, and four separate experimental plots were used as control plots. For anatomical investigations, the impress method and light microscopy were used. The essential oils were isolated by hydrodistillation and analyzed by GC-FID and GC-MS. The results showed somewhat different effects of liquid cattle dung and humus on the investigated parameters of hybrid in the first (warmer and drier) and second (rainier and cooler) experimental years. Liquid cattle dung had positive effects on biomass, height and the area covered by plants and on the number and length of inflorescences as well as on the density of stomata in the lower epidermis in the first year, but in the second experimental year, effects were observed on the length of inflorescences only. The effect of humus on the density of glandular trichomes in the upper epidermis of leaves was positive in the first year, but negative in the second experimental year. Moreover, in the second experimental year, humus affected negatively the height of plants and the percentage of the essential oil. The conclusion was that although it is fertilized with the same organic fertilizers, different climatic conditions in different years can influence chemical, anatomical and morphometrical parameters of plants growing in an open ground.

Photosynthesis and chlorophyll fluorescence of Iranian licorice (Glycyrrhiza glabra l.) accessions under salinity stress.

While salinity is increasingly becoming a prominent concern in arable farms around the globe, various treatments can be used for the mitigation of salt stress. Here, the effective presence of Azotobacter sp. inoculation (A1) and absence of inoculation (A0) was evaluated on Iranian licorice plants under NaCl stress (0 and 200 mM) (S0 and S1, respectively). In this regard, 16 Iranian licorice (Glycyrrhiza glabra L.) accessions were evaluated for the effects on photosynthesis and chlorophyll fluorescence. Leaf samples were measured for photosynthetic pigments (via a spectrophotometer), stomatal and trichome-related features (via SEM), along with several other morphological and biochemical features. The results revealed an increase in the amount of carotenoids that was caused by bacterial inoculation, which was 28.3% higher than the non-inoculated treatment. Maximum initial fluorescence intensity (F0) (86.7) was observed in the ‘Bardsir’ accession. Meanwhile, the highest variable fluorescence (Fv), maximal fluorescence intensity (Fm), and maximum quantum yield (Fv/Fm) (0.3, 0.4, and 0.8, respectively) were observed in the ‘Eghlid’ accession. Regarding anatomical observations of the leaf structure, salinity reduced stomatal density but increased trichome density. Under the effect of bacterial inoculation, salinity stress was mitigated. With the effect of bacterial inoculation under salinity stress, stomatal length and width increased, compared to the condition of no bacterial inoculation. Minimum malondialdehyde content was observed in ‘Mahabad’ accession (17.8 μmol/g FW). Principle component analysis (PCA) showed that ‘Kashmar’, ‘Sepidan’, ‘Bajgah’, ‘Kermanshah’, and ‘Taft’ accessions were categorized in the same group while being characterized by better performance in the aerial parts of plants. Taken together, the present results generally indicated that selecting the best genotypes, along with exogenous applications of Azotobacter, can improve the outcomes of licorice cultivation for industrial purposes under harsh environments.

Parallel Differentiation and Plastic Adjustment of Leaf Anatomy in Alpine Arabidopsis arenosa Ecotypes.

Functional and structural adjustments of plants in response to environmental factors, including those occurring in alpine habitats, can result in transient acclimation, plastic phenotypic adjustments and/or heritable adaptation. To unravel repeatedly selected traits with potential adaptive advantage, we studied parallel (ecotypic) and non-parallel (regional) differentiation in leaf traits in alpine and foothill ecotypes of Arabidopsis arenosa. Leaves of plants from eight alpine and eight foothill populations, representing three independent alpine colonization events in different mountain ranges, were investigated by microscopy techniques after reciprocal transplantation. Most traits clearly differed between the foothill and the alpine ecotype, with plastic adjustments to the local environment. In alpine populations, leaves were thicker, with altered proportions of palisade and spongy parenchyma, and had fewer trichomes, and chloroplasts contained large starch grains with less stacked grana thylakoids compared to foothill populations. Geographical origin had no impact on most traits except for trichome and stomatal density on abaxial leaf surfaces. The strong parallel, heritable ecotypic differentiation in various leaf traits and the absence of regional effects suggests that most of the observed leaf traits are adaptive. These trait shifts may reflect general trends in the adaptation of leaf anatomy associated with the colonization of alpine habitats.

Physicochemical Properties of Sugarcane Cultivars Affected Life History and Population Growth Parameters of Sesamia nonagrioides (Lefebvre) (Lepidoptera: Noctuidae).

Simple SummaryThe sugarcane stem borer, Sesamia nonagrioides (Lefebvre), is the most important pest of sugarcane in Iran and some other regions of the world. Variation in the resistance of six commercial sugarcane cultivars to S. nonagrioides was investigated using the oviposition preference, life history, and population growth parameters. Moreover, the physical and biochemical properties of the tested sugarcane cultivars were estimated to understand any possible correlation between the insect’s parameters and the physiochemical features of the cultivars tested. The physicochemical properties of sugarcane cultivars significantly affected S. nonagrioides oviposition behavior, life history, and population parameters. Based on the obtained results, the resistant cultivar, SP70-1143, could be recommended for cultivation in sugarcane fields where the risk of S. nonagrioides damage is usually high.The use of resistant cultivars is an efficient management strategy against S. nonagrioides. The effects of different sugarcane cultivars, CP48-103, CP57-614, CP69-1062, CP73-21, SP70-1143, and IRC99-02 were evaluated on the oviposition preference (free-choice assay), life history, and life table parameters of S. nonagrioides at 27 ± 1 °C, 60 ± 5% RH and a photoperiod of 16: 8 (L: D) h. The longest and shortest developmental times were on cultivars SP70-1143 and CP48-103, respectively. The oviposition preference of S. nonagrioides was the highest on cultivars CP48-103 and CP69-1062, and negatively correlated with the shoot trichome density and shoot rind hardness of the cultivars. The highest intrinsic rate of increase of S. nonagrioides was on cultivar CP48-103 and the lowest was on cultivar SP70-1143. The shortest mean generation time was on CP48-103 and the longest was on SP70-1143. The results indicate that cultivars CP48-103 and CP69-1062 were susceptible, and cultivar SP70-1143 was partially resistant against S. nonagrioides. This information could be useful for developing integrated management programs of S. nonagrioides, such as the use of resistant cultivars to reduce the damage caused by this pest in sugarcane fields.

A novel regulatory complex mediated by Lanata (Ln) controls multicellular trichome formation in tomato.

Trichomes that originate from plant aerial epidermis act as mechanical and chemical barriers against herbivores. Although several regulators have recently been identified, the regulatory pathway underlying multicellular trichome formation remains largely unknown in tomato. Here, we report a novel HD-ZIP IV transcription factor, Lanata (Ln), a missense mutation which caused the hairy phenotype. Biochemical analyses demonstrate that Ln separately interacts with two trichome regulators, Woolly (Wo) and Hair (H). Genetic and molecular evidence demonstrates that Ln directly regulates the expression of H. The interaction between Ln and Wo can increase trichome density by enhancing the expression of SlCycB2 and SlCycB3, which we previously showed are involved in tomato trichome formation. Furthermore, SlCycB2 represses the transactivation of the SlCycB3 gene by Ln and vice versa. Our findings provide new insights into the novel regulatory network controlling multicellular trichome formation in tomato.

Comparative transcriptome analysis reveals key pathways and genes involved in trichome development in tea plant (Camellia sinensis).

Trichomes, which develop from epidermal cells, are considered one of the important characteristics of the tea plant [Camellia sinensis (L.) O. Kuntze]. Many nutritional and metabolomic studies have indicated the important contributions of trichomes to tea products quality. However, understanding the regulation of trichome formation at the molecular level remains elusive in tea plants. Herein, we present a genome-wide comparative transcriptome analysis between the hairless Chuyeqi (CYQ) with fewer trichomes and the hairy Budiaomao (BDM) with more trichomes tea plant genotypes, toward the identification of biological processes and functional gene activities that occur during trichome development. In the present study, trichomes in both cultivars CYQ and BDM were unicellular, unbranched, straight, and soft-structured. The density of trichomes was the highest in the bud and tender leaf periods. Further, using the high-throughput sequencing method, we identified 48,856 unigenes, of which 31,574 were differentially expressed. In an analysis of 208 differentially expressed genes (DEGs) encoding transcription factors (TFs), five may involve in trichome development. In addition, on the basis of the Gene Ontology (GO) annotation and the weighted gene co-expression network analysis (WGCNA) results, we screened several DEGs that may contribute to trichome growth, including 66 DEGs related to plant resistance genes (PRGs), 172 DEGs related to cell wall biosynthesis pathway, 29 DEGs related to cell cycle pathway, and 45 DEGs related to cytoskeleton biosynthesis. Collectively, this study provided high-quality RNA-seq information to improve our understanding of the molecular regulatory mechanism of trichome development and lay a foundation for additional trichome studies in tea plants.

Alteration in Light Spectra Causes Opposite Responses in Volatile Phenylpropanoids and Terpenoids Compared with Phenolic Acids in Sweet Basil (Ocimum basilicum) Leaves.

Basil (Ocimum basilicum, cv. Dolly) grew under three different light spectra (A, B, and C) created by light-emitting diode lamps. The proportions of UV-A, blue, and green-yellow wavelengths decreased linearly from A to C, and the proportions of red and far-red wavelengths increased from A to C. Photosynthetic photon flux density was 300 μmol m–2 s–1 in all spectra. The spectrum C plants had highest concentrations of phenolic acids (main compounds: rosmarinic acid and cichoric acid), lowest concentrations and emissions of phenylpropanoid eugenol and terpenoids (main compounds: linalool and 1,8-cineole), highest dry weight, and lowest water content. Conversely, spectra A and B caused higher terpenoid and eugenol concentrations and emissions and lower concentrations of phenolic acids. High density of peltate glandular trichomes explained high terpenoid and eugenol concentrations and emissions. Basil growth and secondary compounds affecting aroma and taste can be modified by altering light spectra; however, increasing terpenoids and phenylpropanoids decreases phenolic acids and growth and vice versa.

Insight into the effect of low temperature treatment on trichome density and related differentially expressed genes in Chinese cabbage.

Trichome is important for help plant resist adversity and external damage. However, it often affects the appearance and taste of vegetables. In the present study, the trichome density of leaves from two Chinese cabbage cultivars with and without trichomes treated at low temperature are analyzed by biological microscope, and the differentially expressed genes related to trichomes formation were screened through transcriptome sequencing. The results showed that the number of leaves trichomes was reduced by 34.7% at low temperature compared with room temperature. A total of 661 differentially expression genes effecting trichomes formation were identified at the CT vs C, LCT vs LC, CT vs LCT. Several differentially expression genes from every comparison group were enriched in plant hormone signal transduction and amino acid biosynthesis pathway. Combined with the central genes obtained by WGCNA analysis, five candidate genes Bra029778, Bra026393, Bra030270, Bra037264 and Bra009655 were screened. qRT-PCR analysis verified that the gene expression differences were in line with the trend of transcriptome data. This study not only found possible new key genes and laid a foundation for revealing the molecular mechanism regulating the formation of trichome in Chinese cabbage, but also provided a new way to study plant surface trichomes.

Impacts of elevation on plant traits and volatile organic compound emissions in deciduous tundra shrubs.

The northernmost regions of our planet experience twice the rate of climate warming compared to the global average. Despite the currently low air temperatures, tundra shrubs are known to exhibit high leaf temperatures and are increasing in height due to warming, but it is unclear how the increase in height will affect the leaf temperature. To study how temperature, soil moisture, and changes in light availability influence the physiology and emissions of climate-relevant volatile organic compounds (VOCs), we conducted a study on two common deciduous tundra shrubs, Salix glauca (separating males and females for potential effects of plant sex) and Betula glandulosa, at two elevations in South Greenland. Low-elevation Salix shrubs were 45% taller, but had 37% lower rates of net CO2 assimilation and 63% lower rates of isoprene emission compared to high-elevation shrubs. Betula shrubs showed 40% higher stomatal conductance and 24% higher glandular trichome density, in the low-elevation valley, compared to those from the high-elevation mountain slope. Betula green leaf volatile emissions were 235% higher at high elevation compared to low elevation. Male Salix showed a distinct VOC blend and emitted 55% more oxygenated VOCs, compared to females, possibly due to plant defense mechanisms. In our light response curves, isoprene emissions increased linearly with light intensity, potentially indicating adaptation to strong light. Leaf temperature decreased with increasing Salix height, at 4 °C m-1, which can have implications for plant physiology. However, no similar relationship was observed for B. glandulosa. Our results highlight that tundra shrub traits and VOC emissions are sensitive to temperature and light, but that local variations in soil moisture strongly interact with temperature and light responses. Our results suggest that effects of climate warming, alone, poorly predict the actual plant responses in tundra vegetation.

Resistance to Mirid Bug Creontiades Biseratense (Distant) in Cotton

A field experiment was carried out in the AICRP on Cotton, Haradanahalli Farm, Chamarajanagar, Karnataka to know the association of morphological characters of 15 cotton genotypes (different resistance category) influencing resistance to mirid bug, Creontiades biseratense. Cotton morphological parameters viz., trichome density on leaves, squares and midvein showed a significance difference with the genotypes and the higher incidence of mirid bug was recorded on genotypes having more trichome density. Similarly, genotypes having higher boll rind thickness and length of petiole recorded the higher incidence. of C. biseratense. There was a significant positive correlation between C. biseratense incidence and trichomes on leaves (r = 0.90**), trichomes on squares (r = 0.89**), trichomes on midvein (r = 0.91**), boll rind thickness (0.80**) and length of petiole (r = 0.60*). However thickness of leaf showed the non-significant negative difference among the genotypes (r = -0.03).

Influence of Plant Growth Regulators on Glandular Trichome Density and Steviol Glycosides Accumulation in Stevia rebaudiana.

With the advent of modern lifestyles, diabetes-related comorbidities attributed the importance of low-caloric natural sweetener plants such as Stevia rebaudiana. This plant is the viable source of steviol glycosides (SGs) and other economically important secondary metabolites. Glandular trichomes (GTs) play the role as a reservoir for all secondary products present in the plant species. Therefore, the present study was carried out to evaluate the influence of different plant growth regulators (PGRs) on GT density and its impact on the SG content. The direct shoot regeneration system was developed on Murashige and Skoog (MS) + benzyl aminopurine (BAP) (1.0 mg/L) + naphthaleneacetic acid (NAA) (0.5 mg/L), and MS + BAP (1.5 mg/L) + NAA (0.5 mg/L) from nodal and leaf explants, respectively. Among the combination of PGRs used, MS medium fortified with BAP (1.0 mg/L) and 2,4-dichlorophenoxyacetic acid (2,4-D) (0.5 mg/L) played a significant role in increasing the GT density on leaf and stem tissues of S. rebaudiana. Furthermore, high-performance thin-layer chromatography and gas chromatography–mass spectrophotometry data confirmed a notable rise in SGs and other valuable secondary metabolites. Thus, the protocol developed can be used for the propagation of stevia with an improved metabolic profile at a large scale.

GENOTYPICAL VARIATIONS AND ASSOCIATION BETWEEN GRAM POD BORER (HELICOVERPA ARMIGERA) AND PHYSIO-MORPHOLOGICAL TRAITS IN GRAM (CICER ARIETINUM L.)

Chickpea (Cicer arietinum L.) commonly known as gram is a widely cultivated grain legume crop in the Leguminosae (Fabaceae) family. Gram pod borer (Helicoverpa armigera) is known as the most damaging pest of chickpea that damages various parts of plants at different growth stages. Various physio-morphological characteristics tend to affect the infestation of pod borer as pod wall thickness, pod trichomes density, and pod color. For this purpose, research was conducted in the field area of Entomological Research Institute, AARI, Faisalabad. Nine Kabuli chickpea genotypes i.e. PCK-15001, PCK-15019, PCK-16010, PCK-16027, PCK-17001, PCK-17007, PCK-17018, PCK-17030, and NOOR-2019 were sown under RCBD design having three replications. The results showed that the genotype “PCK-17030” had a significantly highest population of pod borer of 0.97larvae/plant and showed the highest pod damage of 7.39% while the genotype“PCK-16027” was the lowest infested with 0.69 larvae/plant of pod borer. On the other hand, the genotype “Noor-2019” showed the lowest pod damage of 6.42%. It is, therefore, concluded that pod wall thickness and density of pod trichomes had a negative relation to the damage of pod borer. As regards pod color, it was observed that there was the maximum pod borer damage in the genotypes having green colored pods as compared to the genotypes having pods with yellowish brown streaks.

Morphological and biochemical resistance to Helicoverpa armigera (Lepidoptera: Noctuidae) in tomato

Tomato (Solanum lycopersicum L.) production in the tropics suffers from depredation by the tomato fruit borer, Helicoverpa armigera (Hübner), causing severe economic losses. Development of H. armigera resistant tomato cultivars in India is very limited due to lack of good sources of resistance for breeding. Use of insect resistant cultivars could reduce indiscriminate use of insecticides. A total of twenty-two tomato genotypes were assessed under field conditions for resistance to H. armigera during 2017–18 and 2018–19. Morphological and biochemical factors associated with the expression of resistance to this pest in tomato were estimated and considered as potential markers of resistance. The six genotypes, Kashi Sharad, Pb Barkha-1, DVRT-1, Pb Barkha-2, DVRT-2 and Pusa Rohit, were least infested by H. armigera with fruit weight loss ranging from 4.63 to 8.71 percent and were classified as resistant. Expression of resistance was associated with higher trichome density on leaves and calyxes, higher fruit pericarp thickness, higher phenol content in leaves and fruits, and lower soluble sugar and protein contents in leaves and fruits. Resistant genotypes of tomato with these factors may be used as sources of resistance in future breeding programs to enhance resistance to H. armigera in commercially cultivated tomato varieties.

THE EFFECT OF CONCENTRATION AND FREQUENCY OF GIBERELLINS ON THE GROWTH OF ARTEMISIA ANNUA Linn

Artemisia is one of the plants that can be used as an alternative medicine for malaria. The Artemisia plant contains secondary metabolites in the form of artemisinin compounds that function as antimalarials. One of the efforts that can be done to increase the growth of Artemisia annua. plants is by using a growth regulator of gibberellins (GA3). Using a Randomized Block Factorial Designs (RBFD) with the first factor being the concentration of 50 mg.L-1 (K1), mg.L-1(K2), 150 mg.L-1 (K3), 200 mg.L-1 (K4). The second factor has 3 frequencies, 1 time giving 7HSPT (F1), 2 times giving 7HSPT and 14HSPT (F2), and 3 times giving 7HSPT, 14HSPT and 30HSPT (F3). In addition, there were plants that were not given GA3 control (without treatment). Parameters observed were plant height, leaf area, glandular trichome density, and plant dry weight. The results showed that the administration of gibberellins (GA3) with different concentrations and frequencies on plant height, leaf area, glandular trichome density, and dry weight of A. annua plants had no significant effect. Plants have not been able to grow properly because the provision of gibberellins that have not been active stimulates all plant tissues and directly seeps through the roots, stems and leaves.

Resistance of True Citrus species to Diaphorina citri

Host genetic resistance is a promising strategy for the management of Diaphorina citri Kuwayama (Hemiptera: Psyllidae), and consequently Huanglongbing (HLB). To date, no study has investigated the resistance to D. citri in the clonal and vegetatively propagated plants of the Microcitrus, Eremocitrus, and Atalantia genera. This study assesses Near and True Citrus genotype antixenosis and antibiosis against D. citri, with trichome density and volatile emission as possible mechanisms of resistance. All genotypes were oviposited by D. citri, however, 8 of 14 genotypes were less oviposited than Citrus × sinensis 'Valencia' (susceptible control). Diaphorina citri nymphs had lower nymphal viability in E. glauca (31%) and M. warburgiana (58%) than that in Citrus × sinensis (77%). The behavioral assay showed that 30% of D. citri nymphs in the last instars evaded E. glauca shoots, whereas no nymphs evaded Citrus × sinensis shoots. A higher trichome density was observed in E. glauca shoots compared to the other genotypes. Chemical analysis revealed differences in the volatile profiles of E. glauca and Citrus × sinensis. Eremocitrus glauca and M. warburgiana genotypes were more resistant to D. citri than Citrus × sinensis. Higher trichome density in the shoots may negatively influence the development of D. citri nymphs. Eremocitrus glauca volatiles may also be involved in their resistance to D. citri. © 2022 Society of Chemical Industry.