Eficiência de indutores e antibióticos no controle da podridão-mole em couve-chinesa

Abstract

The production of Chinese cabbage (Brassica pekinensis) may be limited by occurrence of diseases, among which the soft rot caused by Pectobacterium carotovorum subsp. carotovorum (Pcc). The effect of inducers and antibiotics on the disease control was studied in laboratory, greenhouse and field. In the first paper acibenzolar-S-metil (ASM) (0.025 g L-1), Ecolife® (2 mL L-1), Agro-Mos® (2 mL L-1) and calcium oxide (0.22 g L-1) were evaluated for in vitro bacterial growth inhibition; epidemiological components, incidence (INC), incubation period (PI), disease final severity (SEVF), diasease index (IDO) and area under disease curve progress (AUPDC); enzymatic activity of peroxidase and polyphenoloxidase and physiological cost of induction. Under greenhouse and field conditions inducers were sprayed seven days after transplant, and seven days after induction strain Pcc120 was inoculated by pricking, except for enzymatic activity and physiological cost experiments. In vitro Pcc120 was not inhibited by any tested product. The INC was not reduced in any experiment. In greenhouse SEVF was reduced by 47.5% by Agro-Mos® and ASM which also reduced IDO by 35.1 and 45.3% respectively and AUDCP. Induced resistance was confirmed by negative antibiosisagainst pathogen and increase of peroxidase and polyphenoloxidase activities in treated plants. In field only ASM confirmed greenhouse results by reducing disease intensity. There was no physiological cost for plants sprayed with ASM or Agro-Mos®. In the second paper it was evaluated the in vitro sensibility of Pcc to bactericides, and the effect of Mycoshield® (oxitetracycline 20%) at 3.0 and 1.5 g L-1, and yeasts (Rh1 and Rh2 - Rhodotorula spp. and Sc1 - Saccharomyces cerevisae at 108 cel mL-1) to control the disease in greenhouse and field. Plants were sprayed with Mycoshield® and yeasts seven days after transplant and inoculated seven days and 12 h after treatment, respectively. In all experiments INC, PI, SEVF, IDO and AUDPC were evaluated. In vitro 40 Pcc isolates were resistant to copper sulfate and sensitive to oxitetracycline, streptomycin, oxitetracycline+ streptomycin and oxitetracycline + copper sulfate all at 0.2 g L-1. Six Pcc isolates were significantly more inhibited by MycoshieldÒ than by Agri-Micina® (oxitetracycline 1.5% + streptomycin 15%), but there was no inhibition by Kasumin® (kasugamicin 2%). In greenhouse MycoshieldÒ at 3.0 g L-1 reduced SEVF and IDO until 47.4 and 19.0%. The yeast Sc1 reduced SEVF and AUDCP till 27.6 and 39.3% respectively, while Rh1 reduced AUDCP until 33.5%. In field MycoshieldÒ reduced IDO, SEVF and AUDCP by 14.4; 15.5 and 28.9% respectively; while Rh1 reduced IDO by 8.8% and Sc1diminished the AUDCP by 15.7%. The reduction of disease intensity and low physiological cost of induction indicate the potentiality of ASM in an integrate management program of Chinese cabbage soft rot. On the other hand MycoshieldÒ and yeasts showed low efficiency for controlling disease in field.