ABSRACT: A major limitation in large scale application of micropropagation technology is high mortality experienced by in vitro raised plants during laboratory to land transfer. This study was aimed at investigating the best concentration of Naphthalene acetic acid (NAA) on in vitro rooting and also develop protocol for successful plant acclimatization with high survival rate. Date palm plantlets were rooted on Murashige and Skoog (MS) basal medium with different NAA concentrations (0.0, 0.1, 0.5 1.0, 1.5 and 2 mg/l) without activated charcoal. Result showed that all the NAA concentrations supported root formation. The optimal initiation and growth of roots of the plantlets were observed at NAA concentration of 1.0 mg/l (87 %) and least with Basal MS without NAA (47 %). Results also showed that root number and lengths increased with increasing NAA concentrations up to 1.0 mg/l and decreased thereafter. The culture mixture of peat moss + soil (2:1) gave the highest survival percentage of 80 % for plant acclimatization. This investigation had shown that accurate assessments of responses to medium at various stages should be considered as specific requirement for successful plant acclimatization.

The success of in vitro culture techniques is always hampered by microbial contamination. The present study was carried out to develop an efficient protocol for date palm explants sterilization for successful somatic embryos induction and plantlets formation of some date palm varieties. The shoot tips were treated with different sterilizing agents at different concentrations and durations of exposure. The use of ethanol (70%), sodium hypochlorite (3.5% & 70%) and mercuric chloride (0.2%) with or without addition of Tween-20 had different effects on decontamination of the date palm explants. The percentage of explants contaminated with bacteria for sterilants 1, 2 and 4 was 18.8%, 6.3% and 6.3% respectively while 25%, 37.5%, 31.25% and 6.25% were contaminated with fungi for sterilants 1, 2, 3 and 4 respectively. Under the conditions used, a combination of antioxidants (Citric and Ascorbic acids at 100mg/l), 0.2% mercuric chloride and 3.5% sodium hypochlorite solution with 3 drops/100ml of Tween-20 helped in the reduction of chlorosis, contamination and die-back in the shoot tip explants. The explants were further cultured in appropriate media for callus initiation and subsequent somatic embryo induction. Optimal embryogenic callus was obtained from the shoot explant of sterilant number 4 which had the minimal contamination and die-back of all the cultures. After 3 subcultures, the somatic embryos formed were multiplied for shoot development. From this study, we established that the use of appropriate surface sterilant at suitable concentration and duration of exposure of date palm explant to it is indispensable for maximum responses of in vitro cultures. Keywords: Date palm, Microbial contamination, Sterilizing agents, in vitro, Somatic embryos

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