Distribution pattern of arthropods on the leaf surfaces of Acacia auriculiformis saplings

Acacia auriculiformis A. Cunn. Ex Benth. (Fabaceae), a non-native pioneer species in Brazil with fast growth and rusticity, is used in restoration programs. Our goal was to assess during a 24-month survey the pattern of arthropods (phytophagous insects, bees, spiders, and predator insects) on the leaf surfaces of A. auriculiformis saplings. Fourteen species of phytophagous, two of bees and eleven of predators were most abundant on the adaxial surface. The values of the ecological indexes (abundance, diversity, and species richness) and the rarefaction, and k-dominance curves of phytophagous, bees and arthropod predators were highest on the adaxial leaf surface of A. auriculiformis. The k-dominance and abundance of Aleyrodidae (Hemiptera) (both leaf surfaces), the native stingless bee Tetragonisca angustula Latreille (Hymenoptera: Apidae) (both leaf surfaces) and the ant Brachymyrmex sp. (adaxial surface) and Pheidole sp. (Hymenoptera: Formicidae) (abaxial surface) were the highest between the taxonomic groups of phytophagous, bees, and predators, respectively on A. auriculiformis saplings. The ecological indexes and rarefaction, abundance, and k-dominance curves of phytophagous insects, bees, and predators were highest on the adaxial leaf surface. The preference of phytophagous insects for the adaxial leaf surface is probably due to the lower effort required to move on this surface. Understanding the arthropod preferences between leaf surfaces may help to develop sampling and pest management plans for the most abundant phytophagous insects on A. auriculiformis saplings. Also, knowledge on the preference pattern of bees and predators may be used to favour their conservation.

Arthropod fauna on the abaxial and adaxial surfaces of Acacia mangium (Fabaceae) leaves

Acacia mangium (Willd., 1806) (Fabales: Fabaceae) is a fast growing, rustic, pioneer species, with potential to fix nitrogen, and for programs to recover degraded areas. The objective was to evaluate the distribution and the functional diversity of interactions and the K-dominance of arthropod groups on A. mangium saplings. The number of individuals of eleven species of phytophagous insects, three bee species, and fourteen natural enemy species were highest on the adaxial leaf surface of this plant. Abundance, diversity and species richness of phytophagous insects and natural enemies, and abundance and species richness of pollinators were highest on the adaxial A. mangium leaf surface. The distribution of five species of sap-sucking hemipterans and six of protocooperating ants (Hymenoptera), with positive interaction between these groups, and three bee species (Hymenoptera) were aggregated on leaves of A. mangium saplings. Aethalion reticulatum (L.) (Hemiptera: Aethalionidae) and Bemisia sp. (Hemiptera: Aleyrodidae); Brachymyrmex sp. and Camponotus sp. (Hymenoptera: Formicidae); and Trigona spinipes Fabricius (Hymenoptera: Apidae) were the most dominant phytophagous insects, natural enemies, and pollinators, respectively, on A. mangium leaves. Knowledge of preferred leaf surfaces could help integrated pest management programs.

TcTI, a Kunitz-type trypsin inhibitor from cocoa associated with defense against pathogens

Protease inhibitors (PIs) are important biotechnological tools of interest in agriculture. Usually they are the first proteins to be activated in plant-induced resistance against pathogens. Therefore, the aim of this study was to characterize a Theobroma cacao trypsin inhibitor called TcTI. The ORF has 740 bp encoding a protein with 219 amino acids, molecular weight of approximately 23 kDa. rTcTI was expressed in the soluble fraction of Escherichia coli strain Rosetta [DE3]. The purified His-Tag rTcTI showed inhibitory activity against commercial porcine trypsin. The kinetic model demonstrated that rTcTI is a competitive inhibitor, with a Ki value of 4.08 × 10–7 mol L−1. The thermostability analysis of rTcTI showed that 100% inhibitory activity was retained up to 60 °C and that at 70–80 °C, inhibitory activity remained above 50%. Circular dichroism analysis indicated that the protein is rich in loop structures and β-conformations. Furthermore, in vivo assays against Helicoverpa armigera larvae were also performed with rTcTI in 0.1 mg mL−1 spray solutions on leaf surfaces, which reduced larval growth by 70% compared to the control treatment. Trials with cocoa plants infected with Mp showed a greater accumulation of TcTI in resistant varieties of T. cacao, so this regulation may be associated with different isoforms of TcTI. This inhibitor has biochemical characteristics suitable for biotechnological applications as well as in resistance studies of T. cacao and other crops.

Morphology and Anatomy of Leaf, Stem and Petiole of Luvunga crassifolia Tanaka (Rutaceae)

Luvunga crassifolia is an underutilized plant in the Citrus family. Other than brief morphological descriptions, there are no published reports on other identification features of this plant. Thus, the current study was aimed to investigate macroscopic and microscopic diagnostic features of L. crassifolia leaves, stems, and petioles. Macroscopic characterization, optimization of histological procedure, and histochemical analyses of differential stains were carried out on the leaves, stems, and petioles of L. crassifolia. The histological method was optimized by modifying the following parameters: number of fixation days, dehydration duration with degraded series of ethanol or butanol, clearing duration, and infiltration duration. After infiltration, embedding and sectioning of the tissues were performed. Histochemical analyses were carried out using differential stains to identify the cellular components in leaf, stem and, petiole tissue sections. This study showed that L. crassifolia leaves are amphistomatic. Pellucid dots were observed on both adaxial and abaxial leaf surfaces. Secretory cavities, xylem, phloem, and pericyclic fibers were found in the cross-sections of leaf, stem, and petiole. Calcium oxalates were present in the leaf and stem sections, while trichomes were detected in stem and petiole sections. The information obtained from this study will be helpful for the identification and future taxonomic-related studies of this plant species.

First Report of Coleosporium helianthi infecting Helianthus verticillatus (Whorled Sunflower)in the United States

Helianthus verticillatus, the whorled sunflower, is an endangered species found only in the southern United States (Trigiano et al. 2021) that is being developed for ornamental uses. This sunflower species requires little to no maintenance, produces spectacular floral displays from September into October, and attracts numerous potential pollinators including many native bees (Strange et al. 2020). In June and July of 2021, chlorotic, irregularly shaped spots were observed on the adaxial surface of mature leaves of two vegetatively produced clones of H. verticillatus (Trigiano et al., 2021) at three locations in Knoxville, TN. In September, yellow (4A, Royal Horticultural Society Color Chart) sori were abundant on abaxial surfaces and more rarely on the adaxial leaf surfaces of both clones at all locations. Globose-to-cylindrical, yellow urediniospores were 23.7µm (20-32) x 18.9 (16-22) µm (n = 30) with irregular, verrucose ornamentation. The morphology and dimensions of the urediniospores were similar to other Coleosporium species (e.g., C. asterum, Back et al., 2014). Telia were waxy, red-brown (167A; B) and developed in October with colder temperatures. Cylindrical teliospores were sessile, 1-celled, thin-walled with basidia ca. 93 µm (70-117) x 25 µm (19-29), consistent with spores of C. helianthi (Cummins, 1978). DNA was obtained from urediniospores using a Phire kit (ThermoFisher Scientific, Waltham, MA) and the 28S rDNA region was amplified using the NL1 and NL4 primers (Back et al. 2014) (Genbank accession # OL364847) as well as ITS 1-4 primers (White et al. 1990) (GenBank accession OL364848). For comparison, DNA sequences were also obtained from authentic C. helianthi on H. divaricatus in the Arthur Fungarium at Purdue University (#PURN11678; GenBank accession OL364846) using the protocols of Aime et al. (2018). 28S sequences shared 99.65% (568/570 bp) identity. To test Koch’s postulates, seven healthy detached leaves were lightly brushed on both leaf surfaces with leaves with uredia producing urediniospores. The leaves were incubated adaxial side up in 9-cm-diameter Petri dishes on moistened filter paper at ambient laboratory conditions. A similar number of healthy leaves were brushed with healthy leaves, incubated in the laboratory and served as the control treatment. After 7-10 days, uredia with urediniospores formed primarily on the abaxial leaf surface, but a few were present on the adaxial surface of leaves treated with urediniospores, whereas the leaves in the control remained healthy. Molecular, morphological and infectivity studies identified C. helianthi as the pathogen. Coleosporium helianthi occurs on the commercial sunflower, H. annuus, and several wild sunflower species, including H. tuberosum (Jerusalem artichoke) and H. microcephalus (small-headed sunflower), among others in the southern U.S. (Farr and Rossman 2021). Coleosporium species are heteroecious and mostly macrocyclic rusts (McTaggart and Aime, 2018) with aecia and aeciospores typically found on pines (Pinus spp.). Although H. verticillatus is very susceptible to rust infection and it probably reduces photosynthetic capability, it does not appear to adversely affect flowering in the fall. The disease primarily degrades the aesthetic appeal of the plant but does not require control measures. To our knowledge, this is the first report of C. helianthi infecting H. verticillatus. Voucher material is deposited in the Arthur Herbarium (#PURN23470).

Selection of Suitable Type of Nozzles for Development of Electrostatic Induction Nozzle

The electrostatic induction mechanism, which superimposes charges on pesticide spray droplets, creates an impact on deposition and wraparound effect on leaf surfaces Smaller droplets have a higher capability to charge accumulation over the surface of the droplet as compared with larger droplets. This paper studied the effect of nozzle type (flat fan, hollow cone, and full cone nozzle), orifice area (1 and 1.5 mm2), and operating pressure (3-5kg cm-2) on spray droplet characteristics on soil bin. Water-sensitive papers were analysed by image analysis software to get the droplet characteristics. The smallest droplets of a hollow cone, flat fan, and full cone were 130, 142, and 279.76 µm respectively produced at 5kg cm-2 and orifice opening 1 mm2. With an increase of pressure droplet size and relative span was decreased for all selective nozzle. From the selected nozzles, the lowest relative span of 0.89 was found with a hollow cone nozzle at 5 kg cm-2 pressure and orifice size of 1 mm2. Among all the selected nozzles hollow cone nozzle produced the smallest droplet sizes and lowest relative span for all selected parameters.

Polarity in cuticular ridge development and insect attachment on leaf surfaces of Schismatoglottis calyptrata (Araceae)

The plant cuticle is a multifunctional barrier that separates the organs of the plant from the surrounding environment. Cuticular ridges are microscale wrinkle-like cuticular protrusions that occur on many flower and leaf surfaces. These microscopic ridges can help against pest insects by reducing the frictional forces experienced when they walk on the leaves and might also provide mechanical stability to the growing plant organs. Here, we have studied the development of cuticular ridges on adaxial leaf surfaces of the tropical Araceae Schismatoglottis calyptrata. We used polymer replicas of adaxial leaf surfaces at various ontogenetic stages to study the morphological changes occurring on the leaf surfaces. We characterized the replica surfaces by using confocal laser scanning microscopy and commercial surface analysis software. The development of cuticular ridges is polar and the ridge progression occurs basipetally with a specific inclination to the midrib on Schismatoglottis calyptrata leaves. Using Colorado potato beetles as model species, we performed traction experiments on freshly unrolled and adult leaves and found low walking frictional forces of insects on both of these surfaces. The changes in the micro- and macroscale morphology of the leaves should improve our understanding of the way that plants defend themselves against insect herbivores.

Effect of Emitter Modifications on Spray Performance of a Solid Set Canopy Delivery System in a High-Density Apple Orchard

Optimally configured solid set canopy delivery systems (SSCDS) can provide adequate spray performance in high-density apple orchards with a minimized risk of off-target pesticide drift. SSCDS configured in a shower-down emitter arrangement have been reported to be the simplest and most economical system. However, existing off-the-shelf emitters used in shower-down configurations have resulted in minimal deposition in lower canopy zones. Therefore, this study was focused on the modifications of off-the-shelf emitters to obtain a desirable spray pattern for adequate spray deposition in all the canopy zones. The modifications include redesigning the impact plate of two existing micro-emitters. Field tests were conducted to evaluate the spray performance of SSCDS with the non-modified emitters (treatment: SD1 and SD3) and contrast the results with modified emitters (treatment: SD2 and SD4). While the treatments SD1 and SD3 had off-the-shelf emitters with swivel plate and static spreader, respectively, the treatment SD2 and SD4 had similar emitters with modified impactor plates. In each treatment block, the apple canopy was divided into six zones and sprayed with a 500 ppm fluorescent tracer solution. Mylar cards and water-sensitive paper samplers were placed on the adaxial and abaxial leaf surfaces in each canopy zone to quantify spray deposition and coverage, respectively. The SSCDS treatments retrofitted with modified emitters, i.e., SD2 and SD4, were observed to have uniform and numerically higher deposition and coverage compared to SD1 and SD3. The SSCDS treatment with modified static spreader (i.e., SD4) resulted in the highest overall spray deposition (1405.7 ± 156.4 ng cm−2 [mean ± standard error]) with improved mid (1121.6 ± 186.9 ng cm−2) and bottom (895.6 ± 149.3 ng cm−2) canopy deposition. Overall, the proposed emitter modification assisted in improved SSCDS spray performances and may be a way forward toward large-scale emplacements of such systems.

Interaction of surfactants with barley leaf surfaces: time-dependent recovery of contact angles is due to foliar uptake of surfactants

Main conclusion Time-dependent contact angle measurements of pure water on barley leaf surfaces allow quantifying the kinetics of surfactant diffusion into the leaf. Abstract Barley leaf surfaces were sprayed with three different aqueous concentrations (0.1, 1.0 and 10%) of a monodisperse (tetraethylene glycol monododecyl ether) and a polydisperse alcohol ethoxylate (BrijL4). After 10 min, the surfactant solutions on the leaf surfaces were dry leading to surfactant coverages of 1, 10 and 63 µg cm−2, respectively. The highest surfactant coverage (63 µg cm−2) affected leaf physiology (photosynthesis and water loss) rapidly and irreversibly and leaves were dying within 2–6 h. These effects on leaf physiology did not occur with the lower surfactant coverages (1 and 10 µg cm−2). Directly after spraying of 0.1 and 1.0% surfactant solution and complete drying (10 min), leaf surfaces were fully wettable for pure water and contact angles were 0°. Within 60 min (0.1% surfactant) and 6 h (1.0% surfactant), leaf surfaces were non-wettable again and contact angles of pure water were identical to control leaves. Scanning electron microscopy investigations directly performed after surfactant spraying and drying indicated that leaf surface wax crystallites were partially or fully covered by surfactants. Wax platelets with unaltered microstructure were fully visible again within 2 to 6 h after treatment with 0.1% surfactant solutions. Gas chromatographic analysis showed that surfactant amounts on leaf surfaces continuously disappeared over time. Our results indicate that surfactants, applied at realistic coverages between 1 and 10 µg cm−2 to barley leaf surfaces, leading to total wetting (contact angles of 0°) of leaf surfaces, are rapidly taken up by the leaves. As a consequence, leaf surface non-wettability is fully reappearing. An irreversible damage of the leaf surface fine structure leading to enhanced wetting and increased foliar transpiration seems highly unlikely at low surfactant coverages of 1 µg cm−2.