Reproduction of Meloidogyne morocciensis (Tylenchida: Meloidogynidae) in weeds found in Brazil.

Weeds can be hosts of root-knot nematodes of the genus Meloidogyne. The importance of the species Meloidogyne morocciensis parasitizing many crops is recognized, but their reproductive capacity in weeds is not known. The present study hypothesizes the ability of M. morocciensis to parasitize and reproduce in different weed species found in Brazil. The objective was to evaluate the reproduction of M. morocciensis in 36 weed species. The plants were individually inoculated with 5,000 eggs and second stage juveniles and kept in greenhouse for 60 days. The experimental design was completely randomized with twelve replications. The root system of each plant was evaluated for gall index (GI), final nematode population (PF), number of nematode/g of root (NNGR) and reproduction factor (RF). It was verified that M. morocciensis has the capacity to parasite 36 weed species belonging to 16 different botanical families, confirming the hypothesis proposed. From the 36 species evaluated, 77.8% (28) were susceptible (FR ≥ 1.0) to M. morocciensis. The present study is the first to identify different weeds as hosts of M. morocciensis, evidencing its polyphagous habit, indicating species of plants with high capacity to multiply this nematode and that need more attention during the integrated management of these pathogen.

Negative cross-resistance to clomazone in imazethapyr-resistant Echinochloa crus-galli caused by increased metabolization.

Herbicide resistance is frequently reported in E. crus-galli globally with target and non-target site resistance mechanism to acetolactate synthase (ALS)-inhibiting herbicides. However, resistance to certain herbicides can result in increased sensitivity to other herbicides, a phenomenon called negative cross-resistance. The objective of this study is to identify the occurrence of negative cross-resistance (NCR) to the pro-herbicide clomazone in populations of E. crus-galli resistant to ALS inhibitors due to increased metabolization. Clomazone dose-response curves, with and without malathion, were performed in imazethapyr-resistant and -susceptible E. crus-galli biotypes. CYPs genes expression and antioxidant enzymes activity were also evaluated. The effective dose to reduce 50% (ED50) of dry shoot weight obtained in the clomazone dose-response curves of the metabolic based imazethapyr-resistant and -susceptible biotypes groups were 22.712 and 58.745 g ha-1, respectively, resulting in a resistance factor (RF) of 0.37, indicating the occurrence of NCR. The application of malathion prior to clomazone increased the resistance factor from 0.60 to 1.05, which indicate the reversion of the NCR. Some CYP genes evaluated were expressed in a higher level, ranging from 2.6-9.1 times according to the biotype and the gene, in the imazethapyr-resistant than in -susceptible biotypes following clomazone application. Antioxidant enzyme activity was not associated with NCR. This study is the first report of NCR directly related to the mechanism of resistance increased metabolization in plants. The occurrence of NCR to clomazone in E. crus-galli can help delay the evolution of herbicide resistance.

First report of rice root-knot nematode, Meloidogyne graminicola, infecting Juncus microcephalus in Brazil.

Juncus microcephalus plants showing symptoms of root-knot nematode infestation were observed in the municipality of Agudo, Rio Grande do Sul state, Brazil. Based on morphological observation, esterase phenotypes, and molecular analyses of rDNA-ITS and D2-D3 regions of 28S rDNA, the causal agent of the observed symptoms was identified as Meloidogyne graminicola. Pathogenicity of M. graminicola was confirmed by fulfilling modified Koch's postulates. To our knowledge, this is the first report of M. graminicola in J. microcephalus in Rio Grande do Sul State, Brazil.

Host status of morning-glory (Ipomoea spp.) to Meloidogyne species.

Weeds can be hosting and alternative multipliers of root-knot nematodes (Meloidogyne spp.). Among the main weeds, species of the genus Ipomoea stands out for their cosmopolitan presence and the negative impact on crops. In addition, they can behave as hosts and promote the reproduction of pests, diseases, and nematodes. However, the ability of Meloidogyne nematodes to infect morning-glory (Ipomoea spp.) is little understood. In this context, the objective was to evaluate the reproduction of M. arenaria, M. enterolobii, M. ethiopica, M. hapla, M. incognita, M. javanica, M. luci, and M. morocciensis in I. grandifolia, I. hederifolia, I. nil, I. purpurea, and I. quamoclit. Plants were individually inoculated with 5,000 eggs and second-stage juveniles and kept in a greenhouse for 60 days. The design was completely randomized with six repetitions. After this period, the root system of each plant was evaluated to gall index (IG) and reproduction factor (RF). It was verified that the eight species of Melodoigyne have the capacity to parasitize I. grandifolia, I. hederifolia, I. nil, I. purpurea, and I. quamoclit, showing the susceptibility of these weeds to the plant-parasitic nematodes. The highest RF were observed for M. enterolobii with values of 12.5 and 12.9 for I. quamoclit and I. hederifolia, respectively. While M. arenaria obtained the lowest values, with RF ≤ 4.0 for all species of Ipomoea. Thus, weed species of the Ipomoea genus are potential hosts and multipliers of root-knot nematodes, making it important to be considered in integrated management strategies for these plant-parasitic nematodes.

First report of Meloidogyne javanica (Nematoda: Meloidogynidae) infecting Scoparia dulcis, a medicinal plant in Brazil.

Medicinal plants Scoparia dulcis showing symptoms caused by root-knot nematodes were detected in the municipality of Cachoeira do Sul, Rio Grande do Sul State, Brazil. Based on the morphological, esterase phenotypes, and molecular analyses of the mitochondrial DNA region between the cytochome oxidase subunit II and 16S rRNA genes (mtDNA) and species-specific sequence characterized amplified region (SCAR), the causal agent of the observed symptoms was identified as Meloidogyne javanica. Pathogenicity was confirmed by fulfilling a modified version of Koch's postulates. To our knowledge, this is the first report of M. javanica infecting S. dulcis in Brazil.

Snorkeling Strategy: Tolerance to Flooding in Rice and Potential Application for Weed Management.

Flooding is an important strategy for weed control in paddy rice fields. However, terrestrial weeds had evolved mechanisms of tolerance to flooding, resulting in new 'snorkeling' ecotypes. The aim of this review is to discuss the mechanisms of flooding tolerance in cultivated and weedy rice at different plant stages and the putative utility of this trait for weed management. Knowledge about flooding tolerance is derived primarily from crop models, mainly rice. The rice model informs us about the possible flooding tolerance mechanisms in weedy rice, Echinochloa species, and other weeds. During germination, the gene related to carbohydrate mobilization and energy intake (RAmy3D), and genes involved in metabolism maintenance under anoxia (ADH, PDC, and OsB12D1) are the most important for flooding tolerance. Flooding tolerance during emergence involved responses promoted by ethylene and induction of RAmy3D, ADH, PDC, and OsB12D1. Plant species tolerant to complete submersion also employ escape strategies or the ability to become quiescent during the submergence period. In weedy rice, the expression of PDC1, SUS3, and SUB1 genes is not directly related to flooding tolerance, contrary to what was learned in cultivated rice. Mitigation of flooding tolerance in weeds could be achieved with biotechnological approaches and genetic manipulation of flood tolerance genes through RNAi and transposons, providing a potential new tool for weed management.

Pigmentos fotossintéticos em azevém suscetível e resistente ao herbicida glyphosate / Photosynthetic pigments in Italian ryegrass susceptible and resistant to the herbicide glyphosate

O objetivo deste trabalho foi quantificar o teor de pigmentos fotossintéticos em biótipos de azevém (Lolium multiflorum) suscetíveis e resistentes ao glyphosate, por dois diferentes métodos, bem como, estabelecer uma correlação entre o índice de clorofila obtido pelo equipamento portátil e a metodologia clássica (clorofila extraível). Um experimento foi conduzido em casa de vegetação e laboratório da Universidade Federal de Santa Maria, Campus de Frederico Westphalen - RS - em esquema fatorial 2X4, em que o fator A equivaleu aos biótipos de azevém (resistente e suscetível a glyphosate) e o fator B a estádios de desenvolvimento das plantas (afilhamento, vegetativo I e II, e reprodutivo). O biótipo de azevém suscetível apresentou maiores teores de clorofila a, b, total e carotenoides, inferindo em um maior potencial competitivo frente ao biótipo resistente ao herbicida. A determinação do teor de clorofila pelo determinador portátil apresentou alta correlação com o método clássico de determinação de pigmentos fotossintéticos, podendo, assim, ser usado com precisão na avaliação deste, proporcionando economia de tempo bem como do uso de reagentes.

The aim of this study was to quantify the content of photosynthetic pigments in ryegrass (Lolium multiflorum) susceptible and resistant to glyphosate, by two different methods, as well as the correlation between chlorophyll content obtained by portable and classical methodology (chlorophyll extractable). An experiment was conducted in a greenhouse and laboratory of the Federal University of Santa Maria, Frederico Westphalen Campus - RS in a 2X4 factorial scheme, where factor A was equivalent to ryegrass (resistant and susceptible to glyphosate) and factor B to the developmental stages of plant (tillering, vegetative I and II and reproductive stage). The susceptible ryegrass biotype showed higher contents of chlorophyll a, b, and total carotenoids, inferring a superior competitive potential to the herbicide-resistant biotype. The determination of chlorophyll by portable determinato showed high correlation with the classical method of determination of photosynthetic pigments, and can thus be used to assess this accurately, saving time, as well as the use of reagents.