Growth and physiological responses of sorghum cultivars exposed to excess H⁺ and the herbicide metolachlor

Abstract

The growth responses of six grain sorghum (Sorghum bicolor (L.) Moench) cultivars exposed to single and (or) combined treatments of the herbicide metolachlor (2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methlethyl)acetamide) and excess H+ were investigated under growth chamber conditions. The sorghum cultivars tested were '38M', '58M', 'GP-10', 'SC574', 'SC283' (inbred lines), and 'Funk G522DR' (F1 hybrid). Shoot lengths were measured on seedlings from each cultivar grown for 14 days in white quartz flintshot sand treated with metolachlor at 0, 0.25, 0.5, 1.0, and 2.0 mg/kg. Pots were watered with 100 mL of 0.1 M acetate at pH 6.0, 5.5, 5.0, 4.5, or 4.0 on alternate days. A sorghum mutant ('58M') shown to have enriched gibberellin levels and '38M', a second sorghum mutant, were essentially immune to either metolachlor (2 mg/kg) or excess H+ concentration (pH 4.0). 'Funk G522DR' was sensitive to both excess H+ concentrations and metolachlor, and interactions between these two stresses were evident. The remaining cultivars were intermediate in response to both excess H+ concentration and metolachlor. Glutathione contents and glutathione S-transferase activities of the metolachlor-resistant 'GP-10' and the metolachlor-sensitive 'Funk G522DR' were comparable. Thus, enriched gibberellin levels may be a major factor in the differential response of the tested sorghum cultivars to metolachlor and (or) excess H+ stresses. Phenological response in relation to multiple stresses is discussed. Key words: pH, metolachlor, gibberellin, acid soil.

Short‐term phytotoxicity in Brassica napus (L.) in response to pre‐emergently applied metazachlor: A microcosm study

“…Reductions in crop shoot length have been observed in Sorghum sp. under the influence of the chloroacetamide metolachlor . Although the timing of appearance of the leaves of B. napus seedlings seemed not to be influenced by metazachlor (Figure ), the surface of the leaves and the petiole length were noticeably reduced (Supplemental Data, Figure S1) and could be linked with an insufficient capacity of light capitation for photosynthesis and therefore reduced shoot weight.…”

Efeito da irrigação inicial na profundidade de lixiviação do herbicida s-metolachlor em diferentes tipos de solos

“…Todavia, vários trabalhos científicos, como os de van Rensburg & van Dyk (1986), Burgard et al (1993) e Oliveira Júnior (1998), demonstraram não haver efeito do pH sobre a adsorção de herbicidas não-iônicos, como o s-metolachlor. No entanto, Wilkinson & Duncan (1993) concluíram que cultivares de sorgo previamente conhecidos como tolerantes ao metolachlor tiveram sua tolerância diminuída em solos mais ácidos. Segundo esses autores, esse fato não está ligado a mudanças na adsorção do herbicida ao solo, mas sim à influência negativa do excesso de H + na degradação do metolachlor na planta.…”