Glyphosate-resistant hairy fleabane (Conyza bonariensis) exhibits a larger number of trichomes and altered stomatal density relative to the susceptible counterpart

Following the adoption of Roundup Ready crops, glyphosate spraying frequency increased, while the use of other herbicide modes of action was neglected. Herbicide-resistant biotypes were reported in three major Conyza species in Brazil, including Conyza bonariensis, increasing growers' bottom line. Considering that leaf surface structures affect proper herbicide deposition, uptake, and performance, this study aimed to characterize epicuticular surface components in glyphosate-resistant (R) and -susceptible (S) C. bonariensis. Conyza spp. seeds were collected in 36 locations in Brazil, and plants were subjected to resistance screening tests by spraying glyphosate at 720 and 1440 g ae ha-1 (0.5X and 1X the label recommended rate, respectively). For resistance level characterization, C. bonariensis biotypes with contrasting responses were selected for glyphosate dose-response assays. Leaf tissues for epicuticular surface analysis were harvested from newly-obtained R and S biotypes at two growth stages. Histological cuts were made on a leaf area of 25 mm² with a blade. Samples were fixed in Karnowsky solution, gradually changed to 100% ethanol, critical-point dried with CO2, and coated with gold, followed by stomatal and trichome density quantification using scanning electron microscopy. Results indicated a poor control with glyphosate in 33 of 36 Conyza spp. biotypes, and a high (31.5) resistance factor was calculated after dose-response trials. Leaf surface analysis indicated that C. bonariensis leaves are amphistomatic and exhibit tectorial trichomes. A higher number of trichomes and altered stomatal density (number.mm²) were quantified in R compared to the S counterpart, potentially reducing glyphosate uptake and effectiveness.

Efecto antibacteriano in vitro de exudados foliares de tabaco contra dos bacterias fitopatógenas / In vitro antibacterial effect of tobacco leaf exudates against two bacterial plant pathogens

Los productos naturales son una alternativa para el control de microorganismos que ocasionan enfermedades en los cultivos. Este trabajo tuvo como objetivo evaluar diferentes solventes para la obtención de extractos crudos a partir de exudados foliares de líneas de tabaco, y el efecto in vitro de estos extractos contra dos bacterias fitopatógenas: Xanthomonas campestris (Xc) y Pectobacterium carotovorum (Pc). Se evaluaron solventes con polaridades entre 3.1 y 6.2 (diclorometano, n-butanol, acetato de etilo, metanol y etanol 90 %). El etanol 90 % se seleccionó como mejor solvente y como sustituto del diclorometano por su mayor rendimiento. Los extractos etanólicos crudos se obtuvieron a partir de exudados foliares de diez líneas de tabaco seleccionadas. La diversidad de la composición química de los extractos etanólicos se reveló por cromatografía en capa delgada. La actividad antibacteriana se evaluó por el método de difusión en agar con discos de papel de filtro y la medición del diámetro del halo de inhibición. Se observó inhibición para todos los extractos contra Xc destacándose los correspondientes a las líneas Nic 1061 "TI 1738" y Nic 1016 "Incekara" hasta 5 µg de extracto crudo seco /disco, con un mayor rendimiento para la línea Nic 1061. El extracto de la línea Nic 1015 fue el único con actividad contra Pc hasta 5 µg de extracto crudo seco por disco. Estos resultados sugieren un uso potencial de los extractos crudos de las líneas Nic 1061 y Nic 1015 "TI 1341" como un agente efectivo para la protección de cultivos contra estas bacterias.

Natural products are an alternative to control microorganisms that cause diseases in crops. This work aimed to evaluate different solvents for obtaining crude extracts from tobacco leaf exudates and to determine in vitro effect of these extracts against two phytopathogenic bacteria: Xanthomonas campestris(Xc) and Pectobacterium carotovorum(Pc). Crude extracts from ten tobacco lines using solvents with polarities between 3.1 and 6.2 (dichloromethane, n-butanol, ethyl acetate, methanol and ethanol 90%) were obtained. Ethanol 90% was selected as the best solvent for obtaining extracts from tobacco leaf exudates and as a substitute of dichloromethane due to the best yield. The chemical composition diversity of the ethanolic extracts was revealed by thin-layer chromatography. The antibacterial activity was evaluated by agar disk diffusion method recording the inhibition zones. Growth inhibition was observed for all extracts against Xc, and the better activity corresponded to the lines Nic 1061"TI 1738" and Nic 1016 "Incekara" until a minimal amount of 5 µg/ disc, with higher yield in case of the line Nic1061 . Only the extract of the line Nic 1015 was able to inhibit the growth of Pc until a minimal inhibitory concentration of 5 µg/disc. These results suggest a potential use of crude extracts from lines Nic 1061 and Nic 1015 "TI 1341" as an effective agent for the crop protection against Xc and Pc respectively.

UV-B Resistant Yeast Inhabit the Phyllosphere of Strawberry.

The increase on the worldwide influx of solar ultraviolet radiation (UV-B) has inflicted a considerable challenge, due to its deleterious effects to live beings and pose a special threat to phyllosphere communities. However, UV-B influence on epiphytic yeasts associated with agricultural crops remains limited. Main aim of the present study was to determine the effect of ultraviolet-B radiation on the epiphytic yeast populations associated with strawberry under field conditions. Thus, strawberries (Fragaria x ananassa Duchesne cv. Oso Grande) were grown under three different treatments: a) environmental UV-B, b) enhanced UV-B and c) decreased UV-B; thereafter, their yeast epiphytic populations were analyzed by T-RFLP prior to yeast isolation, identification and in vitro test for the sensitivity against UV-B. Our results demonstrated that UV-B radiation did not significantly affect the strawberry epiphytic yeast populations. However, isolates directly exposed to radiation, generally revealed morphological abnormalities and a diminishing value in the percentage of survival, although they remained constant after 240 min of exposure. The increase in UV-B radiation was not sufficient to affect the dynamics and composition of epiphytic yeast communities from strawberry, there was a clear morphotype shift towards the selection of pigmented isolates.

Leaf surface characters applied to Lauraceae taxonomy in a Seasonal Forest of Southern Brazil

The goal of this work was to test if the macro and micro morphological analysis of the leaf surface could provide vegetative diagnostic characters for some of the most common Lauraceae species in Southern Brazilian Seasonal Forests. The leaf printing technique with universal instantaneous adhesive was used for the epidermical microscopical analysis and external macroscospical analyses of leave were made. Microscopic evaluation revealed the visibility and contours of anticlinal walls of epidermical cell and stomata and shape of guard-cells. Macroscopic evaluation showed the absence or presence of characters such as hairiness, domatia and scents. The results showed that analyzed characters, together with other diagnostic characteristics, could contribute in taxonomic delimitation of some common Lauraceae species in the Southern Brazil.

Este trabalho teve por objetivo testar se a análise macro e micro morfológica da superfície foliar poderia prover caracteres diagnósticos vegetativos para algumas das espécies mais comuns de Lauraceae encontradas em Florestas Estacionais do sul do Brasil. Utilizou-se a técnica de impressão foliar com adesivo instantâneo universal para a análise microscópica da epiderme e procederam-se análises externas macroscópicas das folhas. Microscopicamente, foram utilizados a visibilidade e os contornos das paredes anticlinais das células epidérmicas, bem como a visibilidade dos estômatos e o formato de suas células-guarda. Macroscopicamente, verificaram-se a presença ou ausência de caracteres como pilosidade, domácias e odores. Os resultados obtidos no trabalho mostraram que os caracteres analisados, juntamente com outras características diagnósticas, podem contribuir na delimitação taxonômica de algumas espécies da família comuns no sul do Brasil.