Caracterização de genótipos de arroz utilizados no Brasil quanto à tolerância à salinidade no estádio de plântula

Rice production (Oryza sativa L.) is among the most economically important activities in the world. However, soil and salinity coming from irrigation water reduce rice yield. Therefore, the identification and/or development of salt-tolerant rice genotypes is a strategy to minimize this problem. The development of new genotypes depends on the presence of genetic diversity, and understanding the heritability of a desired trait can help in the selection process. Thus, this study aimed to identify superior genotypes, analyze the genetic diversity and estimate the heritability for salinity tolerance at the seedling stage in rice genotypes used in Brazil. For this, seedlings of 69 genotypes were kept in hydroponic solution with 40 mM NaCl (4 dSm-1) for seven days. Shoot length, root length, shoot dry weight, and root dry weight) were evaluated and the results were converted into relative performance. Tolerant and moderately salt-tolerant genotypes were identified at the seedling stage, which can be used in breeding programs and can be cultivated in high salinity areas. Principal component analysis showed the presence of genetic diversity for salinity response. Finally, it was shown that most of the observed variation is of genetic origin, which can make the breeding process less difficult.O arroz (Oryza sativa L.) é uma espécie com grande importância econômica no mundo. A salinidade do solo ou da água reduz a produtividade da cultura. Por isso, a identificação e/ou desenvolvimento de genótipos de arroz com tolerância à salinidade é uma estratégia para minimizar esse problema. O desenvolvimento de novos genótipos depende da presença de variabilidade genética, e o conhecimento da herdabilidade da característica de interesse pode auxiliar no processo de seleção. Dessa forma, esse estudo teve como objetivo identificar genótipos superiores, analisar a variabilidade genética e estimar a herdabilidade para tolerância a salinidade no estádio de plântula em genótipos de arroz utilizados no Brasil. Para isso, plântulas de 69 genótipos foram mantidas em solução hidropônica acrescida de 40mM de NaCl (4 dSm-1) durante sete dias. Foram avaliados comprimento de parte aérea, comprimento de raiz, peso seco de parte aérea, e peso seco de raiz e os resultados foram convertidos em desempenho relativo.  Foram identificados genótipos tolerantes e moderadamente tolerantes à salinidade no estádio de plântula, os quais podem ser utilizados em programas de melhoramento e cultivados em áreas com ocorrência desse estresse. A análise de componentes principais mostrou a presença de variabilidade genética para resposta à salinidade. Finalmente, foi demonstrado que a maior parte da variação observada nos caracteres é de origem genética, o que pode tornar o processo de melhoramento menos difícil

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

Wheat blast: The last enemy of hunger fighters

Abstract Effective strategies for disease control are crucial for sustaining world food production and ensuring food security for the population. Wheat blast, a disease caused by the pathogen Magnaporthe oryzae pathotype Triticum, has been a concern for cereal producers and researchers due to its aggressiveness and rapid expansion. To solve this problem, the development of resistant varieties with durable resistance is an effective, economical and sustainable way to control the disease. Conventional breeding can be aided by several molecular tools to facilitate the mining of many sources of resistance, such as R genes and QTLs. The identification of new sources of resistance, whether in the wheat crop or in other cereals are an opportunity for efficient wheat breeding through the application of different techniques. Since this disease is still poorly studied in wheat, knowledge of the rice Magnaporthe pathotype may be adapted to control wheat blast. Thus, genetic mapping, molecular markers, transgenic approaches, and genomic editing are valuable technologies to fight wheat blast. This review aimed to compile the biotechnological alternatives available to accelerate the development of improved cultivars for resistance to wheat blast

Avaliação do efeito de pigmentos fenólicos na germinação de arroz sob condições de baixa temperatura

In Rio Grande do Sul, the main rice producer State in Brazil, low temperatures can occur during germination and seedling establishment, and in some cases, during the reproductive stage. When low temperatures occur in the early developmental stages cause delay in germination, resulting in a non-homogeneous growing. In reproductive stage, low temperatures cause spikelet sterility, directly interfering with plant yield. Researchers have shown that some phenolic compounds such as proanthocyanidins and anthocyanin are associated with low temperature tolerance in plants due to their antioxidant capacity. The red and black color in the seeds of some rice genotypes is conferred by the phenolic compounds proanthocyanidins and anthocyanin, respectively. Therefore, tis study aimed to verify whether rice genotypes with red or black seeds are more tolerant to low temperatures during germination. In this study, five rice genotypes were tested, two present seeds without pigmentation and with contrasting response to low temperature tolerance (BRS Bojuru - tolerant and BRS Pampeira - sensitive), two genotypes with red seeds (BRS 902, SCS 119 Rubi) and one black seed genotype (SCS 120 Ônix). As expected, the genotypes with pigmented seeds had a greater total phenolic compounds content. However, under low temperature conditions, the genotypes with pigmented seed showed a similar response to the sensitive genotype. Therefore, the presence of proanthocyanidins and anthocyanin in the seed of the studied genotypes does not provide tolerance to low temperatures during germination.No Rio Grande do Sul, principal estado produtor de arroz do Brasil, baixas temperaturas podem ocorrer durante a germinação e estabelecimento de plântulas, e em alguns casos, durante o estádio reprodutivo. Quando baixas temperaturas ocorrem no estádio inicial de desenvolvimento causam atraso da germinação, resultando em um crescimento não homogêneo. No estádio reprodutivo, baixas temperaturas podem ocasionar esterilidade das espiguetas, interferindo diretamente na produtividade da planta. Pesquisas têm mostrado que alguns compostos fenólicos como as proantocianidinas e antocianinas estão associadas com tolerância a baixa temperatura em plantas devido sua capacidade antioxidante. A coloração vermelha e preta nas sementes de alguns genótipos de arroz é conferida pelos compostos fenólicos proantocianidinas e antocianinas, respectivamente. Portanto, o objetivo desse estudo foi verificar se os genótipos de arroz com sementes vermelhas ou pretas são mais tolerantes a baixas temperaturas durante a germinação. Neste trabalho, cinco genótipos foram testados, dois com sementes sem pigmentação e com resposta contrastante para tolerância a baixa temperatura (BRS Bojuru - tolerante e BRS Pampeira - sensível), dois genótipos com sementes vermelhas (BRS 902, SCS 119 Rubi) e um genótipo com sementes pretas (SCS 120 Ônix). Como esperado, os genótipos com sementes pigmentadas têm maior conteúdo de compostos fenólicos totais. Entretanto, sob condições de baixa temperatura, os genótipos com semente pigmentada mostraram resposta similar ao genótipo sensível. Dessa forma, a presença de proantocianidinas e antocianinas nas sementes dos genótipos estudados não confere tolerância a baixas temperaturas durante a germinação.  

Efeitos de ácidos orgânicos na germinação e crescimento inicial de Brassica napus L. var. oleifera

Canola (Brassica napus L. var. oleifera) is cultivated in the Southern Brazil as an alternative winter crop in the rotation system. No-tillage and hydromorphic soils favor the formation of aliphatic organic acids with short chain and low molecular weight, as acetic, butyric, and propionic acids. These acids may cause negative effects on the canola production. Thus, this study aimed to evaluate the response of five canola hybrid genotypes under the effect of acetic, butyric and propionic acids on the germination and initial phase of seedling growth. The results showed the characters evaluated respond differently to treatments applied within the same genotype. Therefore, the selection of a genotype with a resilient performance for the characters evaluated under stress is complex. Nevertheless, a sensitive profile response was observed in Hyola 433 genotype under different organic acids. Furthermore, acetic acid showed no negative impact on germination and initial growth of the genotypes.A Canola (Brassica napus L. var. oleifera) é cultivada no Sul do Brasil como uma alternativa para a estação fria no sistema de rotação de culturas. O sistema de plantio direto e a ocorrência de solos hidromórficos favorece a formação de ácidos orgânicos alifáticos com cadeia curta e baixo peso molecular, como os ácidos acético, butírico e propiônico. Estes ácidos podem causar efeitos negativos na produção de canola. Assim, este estudo teve por objetivo avaliar a resposta de cinco genótipos híbridos de canola sob o efeito dos ácidos acético, butírico e propiônico na germinação e na fase inicial do crescimento da plântula. Os resultados demonstraram que os caracteres avaliados respondem de forma diferente em relação aos tratamentos aplicados dentro do mesmo genótipo. Dessa forma, a seleção de um genótipo que manteve um comportamento padrão nos caracteres avaliados sob estresse é dificultado. Entretanto, em uma visão geral, o genótipo Hyola 433 manteve respostas características de sensibilidade nos caracteres avaliados em relação aos ácidos utilizados. Ainda, foi detectado que o ácido acético teve menor efeito na germinação e na fase inicial de crescimento dos genótipos estudados

Can WRKY transcription factors help plants to overcome environmental challenges?

Abstract WRKY transcription factors (TFs) are responsible for the regulation of genes responsive to many plant growth and developmental cues, as well as to biotic and abiotic stresses. The modulation of gene expression by WRKY proteins primarily occurs by DNA binding at specific cis-regulatory elements, the W-box elements, which are short sequences located in the promoter region of certain genes. In addition, their action can occur through interaction with other TFs and the cellular transcription machinery. The current genome sequences available reveal a relatively large number of WRKY genes, reaching hundreds of copies. Recently, functional genomics studies in model plants have enabled the identification of function and mechanism of action of several WRKY TFs in plants. This review addresses the more recent studies in plants regarding the function of WRKY TFs in both model and crop plants for coping with environmental challenges, including a wide variety of abiotic and biotic stresses

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

Florpyrauxifen-Benzyl Selectivity to Rice

Florpyrauxifen-benzyl (FPB) is a new class of auxinic herbicide developed for selective weed control in rice. This study aimed to evaluate the effect of environmental conditions, P450 inhibitors, rice cultivar response, and gene expression on FPB selectivity in rice. Field experiments established in a randomized block design showed that rice plant injury due to two FPB rates (30 and 60 g ai ha−1) was affected by planting time and rice stage at herbicide application. The injury was higher at the earliest planting season and more in younger plants (V2) than larger (V6 and R0). However, no yield reduction was detected. Under greenhouse conditions, two dose-response experiments in a randomized block design showed that spraying malathion (1 kg ha−1) before FPB application did not reduce herbicide selectivity. The addition of two P450 inhibitors (dietholate and piperonyl butoxide, 10 g a.i. seed-kg−1 and 4.2 kg ai ha−1, respectively) decreased the doses to cause 50% of plant injury (ED50) and growth reduction (GR50). However, it seems not to compromise crop selectivity. BRS Pampeira cultivar showed lower ED50 and GR50 than IRGA 424 RI. A growth chamber experiment was conducted in a completely randomized design to evaluate the gene expression of rice plants sprayed with FPB (30 and 60 g ai ha−1). Results showed downregulation of OsWAKL21.2, an esterase probably related to bio-activation of FPB-ester. However, no effect was detected on CYP71A21 monooxygenase and OsGSTL transferase, enzymes probably related to FPB degradation. Further research should focus on understanding FBP bio-activation as the selective mechanism

Recurrent Selection with Low Herbicide Rates and Salt Stress Decrease Sensitivity of Echinochloa colona to Imidazolinone

Weeds represent an increasing challenge for crop systems since they have evolved adaptability to adverse environmental conditions, such as salinity stress. Herbicide effectiveness can be altered by the quality of water in which the weed is growing. This research aimed to study the combined effect of salt stress and recurrent selection with a sublethal dose of imidazolinone herbicides in the shifting of the sensitivity of Echinochloa colona (L.) Link (junglerice) to imidazolinone herbicides. This study was divided into two experiments; in experiment I, three recurrent selection cycles were conducted in Pelotas/RS/Brazil with imazapic + imazapyr at 0.125× the field rate; and in experiment II, three recurrent selection cycles were conducted in Fayetteville/AR/USA with imazethapyr, at 0.125× the recommended dose. Salt stress was implemented by irrigation with 120 mM sodium chloride (NaCl) solution. The effective dose for 50% control of the population (ED50) values increased from the field population to the second generation (G2) after recurrent selection with a sublethal dose of imidazolinone combined with salt stress, supporting the hypothesis of reduced susceptibility by the combination of these abiotic factors. Recurrent exposure to a sublethal dose of imazapic + imazapyr or imazethapyr, combined with salt stress, reduced susceptibility of Echinochloa colona (L.) plants to imidazolinone herbicides

The Genetic Control of SEEDSTICK and LEUNIG-HOMOLOG in Seed and Fruit Development: New Insights into Cell Wall Control

Although much is known about seed and fruit development at the molecular level, many gaps remain in our understanding of how cell wall modifications can impact developmental processes in plants, as well as how biomechanical alterations influence seed and fruit growth. Mutants of Arabidopsis thaliana constitute an excellent tool to study the function of gene families devoted to cell wall biogenesis. We have characterized a collection of lines carrying mutations in representative cell wall-related genes for seed and fruit size developmental defects, as well as altered germination rates. We have linked these studies to cell wall composition and structure. Interestingly, we have found that disruption of genes involved in pectin maturation and hemicellulose deposition strongly influence germination dynamics. Finally, we focused on two transcriptional regulators, SEEDSTICK (STK) and LEUNIG-HOMOLOG (LUH), which positively regulate seed growth. Herein, we demonstrate that these factors regulate specific aspects of cell wall properties such as pectin distribution. We propose a model wherein changes in seed coat structure due to alterations in the xyloglucan-cellulose matrix deposition and pectin maturation are critical for organ growth and germination. The results demonstrate the importance of cell wall properties and remodeling of polysaccharides as major factors responsible for seed development