ABSTRACT

Rice bran application is practically used by Japanese organic rice farmers as a common measure in controlling Monochoria vaginalis, a known weed in organic rice production. To elucidate the inhibitory mechanisms of rice bran application on M. vaginalis germination, we focused on volatile fatty acids (VFAs) and aromatic carboxylic acids (ACAs) as organic acids produced through rice bran decomposition in the soil, which can possibly suppress M. vaginalis germination. Both solo solutions of 1 mM VFAs (propionic or isobutyric acid) and 0.2 mM ACAs (3-phenylpropionic or 4-phenylbutyric acid) exhibited M. vaginalis germination suppression, especially at pH 4.6, the lowest pH tested. In the 0.5–3 mM VFA solutions at pH 4.6, germination was strongly suppressed in the order of isobutyric > propionic > butyric > acetic acid. With the 0.05–0.2 mM ACA solutions at pH 4.6, the germination was strongly suppressed in the order of 3-phenylpropionic > 4-phenylbutyric > 2-phenylpropionic acid. Benzoic acid did not exhibit significant germination suppression. The solutions of 0.5 mM VFAs and 0.05 mM ACAs exhibited no suppression when applied separately; however, the certain mixture of a VFA and an ACA at the aforementioned concentration, for example, 0.5 mM isobutyric acid and 0.05 mM 3-phenylpropionic acid, exhibited significant germination suppression. These results showed the several combinations of VFAs and ACAs at even non-effective concentrations synergistically suppressed M. vaginalis germination.

Abbreviations:2PPA: 2-phenylpropionic acid; 3PPA: 3-phenylpropionic acid; 4PBA: 4-phenylbutyric acid; ACA: aromatic carboxylic acid; EC: electrical conductivity; M. vaginalis: Monochoria vaginalis; VFA: volatile fatty acid

摘要

日本有机稻农实际上使用米糠作为控制阴道单壁菌的常用措施，这是一种有机稻生产中的已知杂草。为了阐明施用米糠对阴道分枝杆菌萌发的抑制机制，我们重点研究了土壤中米糠分解产生的挥发性脂肪酸（VFA）和芳香族羧酸（ACA），它们可能抑制阴道分枝杆菌的萌发发芽。1 mM VFA（丙酸或异丁酸）和 0.2 mM ACA（3-苯基丙酸或 4-苯基丁酸）的单独溶液均显示阴道分枝杆菌萌发抑制，尤其是在 pH 4.6（测试的最低 pH）下。在 pH 4.6 的 0.5-3 mM VFA 溶液中，发芽受到强烈抑制，顺序为异丁酸 > 丙酸 > 丁酸 > 乙酸。在 pH 4.6 的 0.05–0.2 mM ACA 溶液中，萌发被强烈抑制，顺序为 3-苯基丙酸 > 4-苯基丁酸 > 2-苯基丙酸。苯甲酸没有表现出显着的发芽抑制。0.5 mM VFAs 和 0.05 mM ACAs 的溶液单独使用时没有表现出抑制作用；然而，上述浓度的 VFA 和 ACA 的某些混合物，例如 0.5 mM 异丁酸和 0.05 mM 3-苯基丙酸，表现出显着的发芽抑制。M.阴道发芽。

缩写：2PPA：2-苯基丙酸；3PPA：3-苯基丙酸；4PBA：4-苯基丁酸；ACA：芳香族羧酸；EC：电导率；M.阴道：阴道单绒毛菌；VFA：挥发性脂肪酸