Nichos de sobrevivência de Pseudomonas savastanoi pv. glycinea, agente causal do crestamento bacteriano da soja (Glycine max L.)
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2022-01-28
Autores
Melo, Luana Laurindo de
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Universidade Estadual Paulista (Unesp)
Resumo
Pseudomonas savastanoi pv. glycinea (Psg), agente causal do crestamento bacteriano, causa prejuízos severos à cultura da soja (Glycine max L.), e o conhecimento de seus nichos de sobrevivência é de elevada importância para o manejo eficiente da doença. Apesar de ser recorrente nas regiões produtoras de soja do Brasil, há poucas informações disponíveis sobre a ecologia de Psg. Desta forma, os objetivos deste trabalho foram avaliar em condições de campo: I) a sobrevivência de Psg como células livres em quatro tipos de solo; II) a sobrevivência de Psg na filosfera e rizosfera de 12 espécies de plantas cultivadas utilizadas em rotação com a soja; e em condições de casa de vegetação: III) a colonização endofítica de plantas cultivadas por Psg. Para avaliar a sobrevivência no solo, dez experimentos foram realizados e, após a infestação, as avaliações foram realizadas a cada dois dias até a não recuperação de células viáveis da bactéria. Foram conduzidos três experimentos para avaliação da sobrevivência de Psg na filosfera e rizosfera de Avena sativa (aveia branca), Avena strigosa (aveia preta), Crotalaria juncea (crotalária), Glycine max (soja), Helianthus annuus (girassol), Hordeum vulgare (cevada), Lolium multiflorum (azevém), Phaseolus vulgaris (feijão comum), Raphanus sativus (nabo forrageiro), Sorghum bicolor (sorgo), Triticum aestivum (trigo) e Zea mays (milho), com avaliações a cada sete dias, por até 70 dias. Para a colonização endofítica, dois experimentos foram conduzidos com as mesmas espécies de plantas cultivadas, com dois métodos de inoculação de Psg, com e sem ferimentos nas plantas. As avaliações ocorreram a cada 14 dias, pelo máximo de 70 dias. O isolado Soj. 1462 de Psg, patogênico à soja, e resistente a 100 μg.mL-1 de rifampicina, foi utilizado em todos os experimentos, e os períodos de sobrevivência da bactéria foram confirmados por PCR com primers específicos. Nos solos, Psg apresentou uma baixa sobrevivência com períodos inferiores a dois dias, em todos os experimentos. Na filosfera, os maiores períodos de sobrevivência de Psg foram em soja (70 dias), e aveia branca, aveia preta, azevém, girassol e sorgo (35 dias). Na rizosfera, os maiores períodos de sobrevivência de Psg foram verificados para aveia branca, aveia preta, azevém, cevada, milho, soja e trigo (28 dias). Para a colonização endofítica, em plantas com ferimentos, os maiores períodos médios de sobrevivência (PMS) foram verificados em soja (70 dias), aveia branca, aveia preta e azevém (63 dias), e sorgo (49 dias). Nas plantas inoculadas sem ferimentos, os maiores PMS foram em azevém e soja (70 dias), aveia branca e aveia preta (49 dias), e sorgo (42 dias). Com base nesses resultados, o solo não é um nicho favorável para a sobrevivência de Psg, assim como a rizosfera das plantas avaliadas. O cultivo de aveia branca, aveia preta, azevém, cevada, girassol, milho, sorgo e trigo em rotação/sucessão à soja, em áreas com histórico de crestamento bacteriano não é recomendado. Nessas áreas, o indicado é o plantio de crotalária, feijão comum e nabo forrageiro para redução do inóculo bacteriano.
Pseudomonas savastanoi pv. glycinea (Psg), the causal agent of bacterial blight, causes severe damage to soybean (Glycine max L.), and knowledge of the survival niches is important for the efficient management of the disease. Although it is recurrent in the soybean producing regions in Brazil, there is little information available on the ecology of Psg. Thus, the objectives of this work were to evaluate under field conditions: I) the survival of Psg as free cells in four soil types; II) the survival of Psg in the phyllosphere and rhizosphere of 12 crops used in rotation with soybean; and under greenhouse conditions: III) the endophytic colonization of Psg in crops. To evaluate the survival of Psg in the soil, ten experiments were carried out and, after soil infestation, evaluations were performed every two days until the nonrecovery of viable cells of the bacterium. Three experiments were conducted to evaluate Psg survival in the phyllosphere and rhizosphere of Avena sativa (white oat), Avena strigosa (black oat), Crotalaria juncea (sunn hemp), Glycine max (soybean), Helianthus annuus (sunflower), Hordeum vulgare (barley), Lolium multiflorum (ryegrass), Phaseolus vulgaris (common bean), Raphanus sativus (forage turnip), Sorghum bicolor (sorghum), Triticum aestivum (wheat), Zea mays (maize), with evaluations every seven days for up to 70 days. For endophytic colonization, two experiments were conducted with the same crops, with two inoculation methods, with and without injuries in the plants. The evaluations took place every 14 days, for a maximum of 70 days. The strain Soj. 1462 of Psg, pathogenic to soybean, and resistant to 100 µg.mL-1 of rifampicin was used in all experiments, and the survival periods of the bacterium were confirmed by PCR with specific primers. In the soils, Psg had a low survival with periods of less than two days, in all the experiments. In the phyllosphere, high survival periods of Psg were verified in soybean (for 70 days), and white oat, black oat, ryegrass, sunflower, and sorghum (for 35 days). In the rhizosphere, the highest survival periods were verified for white oat, black oat, ryegrass, barley, maize, soybean, and wheat (28 days). For endophytic colonization, in plants with injuries, the highest average survival period (ASP) were verified in soybean (70 days), white oat, black oat and ryegrass (63 days), and sorghum (49 days). In plants inoculated without injury, the highest ASP were obtained in ryegrass and soybean (70 days), white oat and black oat (49 days), and sorghum (42 days). Based on these results, the soil is not a survival niche of Psg, as well as the rhizosphere of the evaluated crops. The cultivation of white oat, black oat, ryegrass, barley, sunflower, maize, sorghum, and wheat in rotation/succession to soybean, in areas with a history of bacterial blight is not recommended. In these areas, it is recomended the cultivation of crotalaria, common bean and forage turnip to reduce bacterial inoculum.
Pseudomonas savastanoi pv. glycinea (Psg), the causal agent of bacterial blight, causes severe damage to soybean (Glycine max L.), and knowledge of the survival niches is important for the efficient management of the disease. Although it is recurrent in the soybean producing regions in Brazil, there is little information available on the ecology of Psg. Thus, the objectives of this work were to evaluate under field conditions: I) the survival of Psg as free cells in four soil types; II) the survival of Psg in the phyllosphere and rhizosphere of 12 crops used in rotation with soybean; and under greenhouse conditions: III) the endophytic colonization of Psg in crops. To evaluate the survival of Psg in the soil, ten experiments were carried out and, after soil infestation, evaluations were performed every two days until the nonrecovery of viable cells of the bacterium. Three experiments were conducted to evaluate Psg survival in the phyllosphere and rhizosphere of Avena sativa (white oat), Avena strigosa (black oat), Crotalaria juncea (sunn hemp), Glycine max (soybean), Helianthus annuus (sunflower), Hordeum vulgare (barley), Lolium multiflorum (ryegrass), Phaseolus vulgaris (common bean), Raphanus sativus (forage turnip), Sorghum bicolor (sorghum), Triticum aestivum (wheat), Zea mays (maize), with evaluations every seven days for up to 70 days. For endophytic colonization, two experiments were conducted with the same crops, with two inoculation methods, with and without injuries in the plants. The evaluations took place every 14 days, for a maximum of 70 days. The strain Soj. 1462 of Psg, pathogenic to soybean, and resistant to 100 µg.mL-1 of rifampicin was used in all experiments, and the survival periods of the bacterium were confirmed by PCR with specific primers. In the soils, Psg had a low survival with periods of less than two days, in all the experiments. In the phyllosphere, high survival periods of Psg were verified in soybean (for 70 days), and white oat, black oat, ryegrass, sunflower, and sorghum (for 35 days). In the rhizosphere, the highest survival periods were verified for white oat, black oat, ryegrass, barley, maize, soybean, and wheat (28 days). For endophytic colonization, in plants with injuries, the highest average survival period (ASP) were verified in soybean (70 days), white oat, black oat and ryegrass (63 days), and sorghum (49 days). In plants inoculated without injury, the highest ASP were obtained in ryegrass and soybean (70 days), white oat and black oat (49 days), and sorghum (42 days). Based on these results, the soil is not a survival niche of Psg, as well as the rhizosphere of the evaluated crops. The cultivation of white oat, black oat, ryegrass, barley, sunflower, maize, sorghum, and wheat in rotation/succession to soybean, in areas with a history of bacterial blight is not recommended. In these areas, it is recomended the cultivation of crotalaria, common bean and forage turnip to reduce bacterial inoculum.
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Palavras-chave
Filosfera, Colonização endofítica, Rizosfera, Solo, Soja, Phyllosphere, Endophytic colonization, Rhizosphere, Soil, Soybean