Effects of soil-applied ground leaves of Melia azedarach L. on acclimatization of bacteria-contaminated rooted plum shoots

Plantlet transfer from mixotrophic in vitro conditions to ex vitro environment is a critical stage of micropropagation. Bacteria contaminations can negatively affect plant micropropagation. Extracts from various tissues of Meliaceae spp. have shown biocide effects against some bacteria strains. The present work aims to evaluate the effect of melia (Melia azedarach L.) ground leaves on acclimatization of the plum hybrid MRS2/5 (Prunus cerasifera x P. spinosa) free of cultivable bacteria or in vitro-contaminated with Sphingomonas paucimobilis or Bacillus circulans. Plantlets were acclimatized in a growth chamber (24±2 °C, 16-h photoperiod, 70 moles PAR m-2 s-1) in a peat medium enriched with ground melia leaves, harvested in late summer, ground and added to peat at 0, 20 and 40 g fw kg-1 (first experiment) or 0, 5 and 10 g fw kg-1 (second experiment). Shoot length and weight, root weight and leaf chlorophyll content of ‘MRS 2/5’ were detected 4 weeks after plant transfer ex-vitro. Plantlets contaminated with Sphingomonas paucimobilis showed a decrease in shoot and root weight, shoot length and leaf chlorophyll content. The addition of 5 g kg-1 melia leaves significantly increased shoot length and weight, leaf K and B compared to the control, regardless of the contaminating bacteria. Moreover, the addition of 20 g kg-1 of melia leaves enhanced leaf chlorophyll, with no effect on shoot and root fresh weight. The highest rate of melia (40 g kg-1) caused the death of almost all plants. These results indicate that the addition to substrate of Melia azedarach ground leaves at 5 g kg-1 can improve acclimatization of micro propagated ‘MRS 2/5’ plantlets.