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

HERBICIDE RESISTANT WEED MANAGEMENT USING SENSITIVITY ANALYSIS OF THE WEED POPULATION GROWTH CURVE

Strategies to prevent herbicide weed resistance are rarely practiced by farmers. As a consequence, herbicide resistant weed biotypes (HRWB) have been increasing worldwide in the past decades. This paper aims to analyze the weed population growth curve and to propose a strategic plan for prevention and management of HRWB. The existing weed control methods are organized considering the sensitivity analysis of the population growth at each phase of the logistic growth curve. This analysis indicates that tactics directed to reduce the population growth rate are most appropriate for HRWB management, mainly at the initial phase of the resistant weed population growth. This epidemiological approach provides evidence to the importance of early detection and management of HRWB

Evolution of imidazolinone-resistant weedy rice in Malaysia: the current status

Weedy rice (Oryza sativa f. spontanea or O. sativa complex) has become a severe threat to Malaysian rice (Oryza sativa L.) granaries after the direct-seeding method of rice cultivation was introduced in the late 1980s. Since then, researchers have studied the biology and ecology of weedy rice and espoused the evolutionary theory of the origin of Malaysian weedy rice. This review paper aimed to synthesize the body of knowledge about weedy rice and the evolution of herbicide-resistant (HR) weedy rice in Malaysia. The imidazolinone (IMI) herbicide component of the Clearfield® Production System (CPS) rice package is among the most effective tools for weedy rice control. However, dependence solely on this technology and farmers’ ignorance about the appropriate use of IMI herbicides with the CPS rice package have resulted in the evolution of IMI-resistant (IMI-R) weedy rice. This has reduced the efficacy of IMI herbicides on weedy rice, ultimately nullifying the benefit of CPS rice in affected fields. At present, it is assumed that IMI-R weedy rice populations are widely distributed across the rice granaries in Malaysia. Therefore, it is important that integrated management measures be adopted comprehensively by Malaysian rice growers to curb the spread of IMI-R weedy rice problem in Malaysia, especially in fields planted with CPS rice. This review focuses on the biology of Malaysian weedy rice, the history of the establishment of weedy rice in Malaysian rice fields, the impact of HR rice technology on the evolution of IMI-R weedy rice in Malaysia, the distribution of resistant weedy rice populations across Peninsular Malaysia rice granaries, the weedy rice resistance mechanisms, and weedy rice management. The synthesis of all this information is helpful to researchers, policy makers, the private agricultural industry, advisers to farmers, and proactive farmers themselves with the goal of working toward sustainable rice production

Rapid reduction of herbicide susceptibility in junglerice by recurrent selection with sublethal dose of herbicides and heat stress

Global climate change, specifically rising temperature, can alter the molecular physiology of weedy plants. These changes affect herbicide efficacy and weed management. This research aimed to investigate the combined effect of heat stress (HS) and sublethal doses of herbicides (four active ingredients) on adaptive gene expression and efficacy of herbicide on Echinochloa colona (L.) Link (junglerice). Three factors were evaluated; factor A was E. colona generation (G0-original population from susceptible standard; G1 and G2 were progenies of recurrent selection), factor B was herbicide treatment (florpyrauxifen-benzyl, glufosinate-ammonium, imazethapyr, quinclorac and nontreated check) and factor C was HS (30 and 45 ◦C). The herbicides were applied at 0.125× the recommended dose. Recurrent exposure to HS, combined with sublethal doses of herbicides, favors the selection of plants less susceptible to the herbicide. Upregulation of defense (antioxidant) genes (APX: Ascorbate peroxidase), herbicide detoxification genes (CYP450 family: Cytochrome P450), stress acclimation genes (HSP: Heat shock protein, TPP: Trehalose phosphate phosphatase and TPS: Trehalose phosphate synthase) and genes related to herbicide conjugation (UGT: UDP Glucosyltransferase) was significant. The positive regulation of these genes may promote increased tolerance of E. colona to these herbicides

A Novel Single-Site Mutation in the Catalytic Domain of Protoporphyrinogen Oxidase IX (PPO) Confers Resistance to PPO-Inhibiting Herbicides

Protoporphyrinogen oxidase (PPO)-inhibiting herbicides are used to control weeds in a variety of crops. These herbicides inhibit heme and photosynthesis in plants. PPO-inhibiting herbicides are used to control Amaranthus palmeri (Palmer amaranth) especially those with resistance to glyphosate and acetolactate synthase (ALS) inhibiting herbicides. While investigating the basis of high fomesafen-resistance in A. palmeri, we identified a new amino acid substitution of glycine to alanine in the catalytic domain of PPO2 at position 399 (G399A) (numbered according to the protein sequence of A. palmeri). G399 is highly conserved in the PPO protein family across eukaryotic species. Through combined molecular, computational, and biochemical approaches, we established that PPO2 with G399A mutation has reduced affinity for several PPO-inhibiting herbicides, possibly due to steric hindrance induced by the mutation. This is the first report of a PPO2 amino acid substitution at G399 position in a field-selected weed population of A. palmeri. The mutant A. palmeri PPO2 showed high-level in vitro resistance to different PPO inhibitors relative to the wild type. The G399A mutation is very likely to confer resistance to other weed species under selection imposed by the extensive agricultural use of PPO-inhibiting herbicides

Herbicide Physiology and Environmental Fate

Herbicides are crucial tools for weed management in agriculture [...

Competitividade de Biótipos de Picão-Preto (Bidens subalternans) Resistente e Suscetível aos Inibidores da ALS

The continuous use of ALS-inhibiting herbicides has led to the evolution of herbicide-resistant weeds worldwide. Greater beggarticks is one of the most troublesome weeds found in the soybean production system in Brazil. Recently, a greater beggarticks biotype that is resistant (R) to ALS inhibitors due to Trp574Leu mutation in the ALS gene was identified. Also, the adaptive traits between susceptible (S) and R to ALS inhibitors biotypes of greater beggarticks were compared. Specifically, we aimed to: (1) evaluate and compare the relative growth rates (RGR) between the biotypes; (2) analyze the seed germination characteristics of R and S biotypes under different temperature conditions; and (3) evaluate their competitive ability in a replacement series study. The experiments were conducted at the University of Arkansas, USA, in 2007 and at Universidade Federal do Rio Grande do Sul (Federal University of Rio Grande do Sul), Brazil, in 2008. Plant proportions for replacement series studies were respectively 100:0, 75:25, 50:50, 25:75 and 0:100, with a total population of 150 plants m-2. There was no difference in RGR between R and S biotypes. The R-biotype germination rate was lower than that of the S biotype. However, at low temperature conditions (15 oC), the reverse was observed. In general, there is no difference in the competitive ability between R and S greater beggarticks biotypesO uso contínuo de herbicidas inibidores da ALS tem levado à evolução de plantas daninhas resistentes mundialmente. Picão-preto é uma das mais importantes plantas daninhas no sistema de produção de soja no Brasil. Recentemente, foi identificado um biótipo de picao-preto resistente (R) aos inibidores da ALS devido à mutação Trp574Leu no gene ALS. Também, foram comparadas características adaptativas entre biótipos de picao-preto suscetível (S) e R aos inibidores da ALS. Especificamente, os objetivos deste trabalho foram: (1) avaliar e comparar o crescimento relativo (RGR) entre os biótipos; (2) analisar características da germinação das sementes dos biótipos R e S sob diferentes condições de temperatura; e (3) avaliar suas habilidades competitivas em um estudo em série de substituição. Os experimentos foram conduzidos na University of Arkansas, EUA, em 2007 e na Universidade Federal do Rio Grande do Sul, Brasil, em 2008. Para os estudos de série de substituição as proporções de plantas dos biótipos foram, respectivamente: 100:0, 75:25, 50:50, 25:75 e 0:100, com uma população total de 150 plantas m-2. Não se verificou diferença no RGR entre os biótipos R e S. A taxa de germinação do biótipo R foi menor que a do biótipo S. Porém, sob baixas condições de temperatura (15 oC), foi observada a situação oposta. Em geral, não há diferença na habilidade competitiva entre os biótipos R e S de picão-pret

Competitividade de Biótipos de Picão-Preto (Bidens subalternans) Resistente e Suscetível aos Inibidores da ALS

The continuous use of ALS-inhibiting herbicides has led to the evolution of herbicide-resistant weeds worldwide. Greater beggarticks is one of the most troublesome weeds found in the soybean production system in Brazil. Recently, a greater beggarticks biotype that is resistant (R) to ALS inhibitors due to Trp574Leu mutation in the ALS gene was identified. Also, the adaptive traits between susceptible (S) and R to ALS inhibitors biotypes of greater beggarticks were compared. Specifically, we aimed to: (1) evaluate and compare the relative growth rates (RGR) between the biotypes; (2) analyze the seed germination characteristics of R and S biotypes under different temperature conditions; and (3) evaluate their competitive ability in a replacement series study. The experiments were conducted at the University of Arkansas, USA, in 2007 and at Universidade Federal do Rio Grande do Sul (Federal University of Rio Grande do Sul), Brazil, in 2008. Plant proportions for replacement series studies were respectively 100:0, 75:25, 50:50, 25:75 and 0:100, with a total population of 150 plants m-2. There was no difference in RGR between R and S biotypes. The R-biotype germination rate was lower than that of the S biotype. However, at low temperature conditions (15 oC), the reverse was observed. In general, there is no difference in the competitive ability between R and S greater beggarticks biotypesO uso contínuo de herbicidas inibidores da ALS tem levado à evolução de plantas daninhas resistentes mundialmente. Picão-preto é uma das mais importantes plantas daninhas no sistema de produção de soja no Brasil. Recentemente, foi identificado um biótipo de picao-preto resistente (R) aos inibidores da ALS devido à mutação Trp574Leu no gene ALS. Também, foram comparadas características adaptativas entre biótipos de picao-preto suscetível (S) e R aos inibidores da ALS. Especificamente, os objetivos deste trabalho foram: (1) avaliar e comparar o crescimento relativo (RGR) entre os biótipos; (2) analisar características da germinação das sementes dos biótipos R e S sob diferentes condições de temperatura; e (3) avaliar suas habilidades competitivas em um estudo em série de substituição. Os experimentos foram conduzidos na University of Arkansas, EUA, em 2007 e na Universidade Federal do Rio Grande do Sul, Brasil, em 2008. Para os estudos de série de substituição as proporções de plantas dos biótipos foram, respectivamente: 100:0, 75:25, 50:50, 25:75 e 0:100, com uma população total de 150 plantas m-2. Não se verificou diferença no RGR entre os biótipos R e S. A taxa de germinação do biótipo R foi menor que a do biótipo S. Porém, sob baixas condições de temperatura (15 oC), foi observada a situação oposta. Em geral, não há diferença na habilidade competitiva entre os biótipos R e S de picão-pret