Preliminary results on the use of Melia azedarach fruit extracts as antimicrobial agents in the micropropagation of Zantedeschia

Bacterial contamination can be a great problem for in vitro plant tissue culture. The present study investigates the antimicrobial activity of fruit extracts of Melia azedarach on some bacterial isolates (\u2018spot agar test\u2019) and contaminants of in vitro shoots of Zantedeschia aethiopica, and the influence of the extracts on shoot growth. The shoots were grown on a proliferation medium (ZP) consisting of basal MS composition and BA 3 mg/L. Bacterial strains were isolated from various micropropagated plants, and identified as Sphingomonas paucimobilis (Sp), Bacillus circulans (Bc), Kocuria kristinae (Kk), and A17 (under identification). Forty gram fruit pulp and skin of Melia were homogenized in 100 ml distilled water (PA extract) or 50% ethanol (Et-OH) solution (PE extract). PEE was obtained from PE by Et-OH evaporation. Variable amounts (0, 1, 5, 10 and 20%) of PE and PEE fruit extracts and Et-OH solution were added to ZP, and their influence on shoot growth was evaluated. Zantedeschia shoots were inoculated with different bacterial strains and grown on standard ZP medium to allow bacteria spread. Shoots were treated with 10% PEE and subcultured again on ZP. Shoot homogenates were then processed for bacteria counts (colony forming units, cfu/ g fresh tissue). PE and PEE at 1% positively affected shoot growth; however, growth decreased as the extract amount increased. No growth, and severe yellowing occurred with 20% PEE, and even shoot death with PE at the same level. PEE was the most active extract, having a bactericidal activity against all the bacterial isolates, except Sp, while the Et-OH solution had no antimicrobial activity. PEE also strongly reduced Bc and Kk development in contaminated Zantedeschia shoots. These results suggest that fruit extracts of M. azedarach represent a promising alternative to antibiotics as antimicrobial treatments for bacteria-contaminated in vitro grown ornamental plants