Abstract: A variety of plant diseases and damage by certain pests in agricultural and horticultural plants can be efficiently controlled without substantial chemical injuries by applying a plant-protecting composition which comprises (a) 1 part by weight of a chitosan hydrolyzate having an average molecular weight of 10,000 to 50,000, obtained by acid hydrolysis or enzymatic hydrolysis of chitosan and (b) 0.25 to 4 parts by weight of acetic acid. Any possible chemical injury to plants caused by applying the composition can be further reduced when the composition is admixed with a deproteinized juice of alfalfa leaves.

Abstract: A novel species of acetic acid bacteria belonging to the genus of Acetobacter, to which a scientific name of Acetobacter altoacetigenes MH-24 (FERM BP-491) is given. The bacteria can grow in a culture medium containing at least 4 w/v % of acetic acid with a pH of 3.5 at the highest. Pure samples of species have been isolated and used for the fermentation production of vinegar without undertaking the conventional inoculation process using the prior art seed vinegar to provide a high-quality vinegar of high acetic acid concentration such as white vinegar, with high production efficiency.