Relative response of explant material of Anacardium occidentale L. to in vitro culture

Abstract

The task of developing intact plants from tissues of woody plants has been attempted and success reported in a few crop species, mostly with explant tissues such as shoot tips, intermodal region, leaf parts, from seedlings, In vitro methods, if standardised, can facilitate rapid multiplication of, and therefore, expansion of area under high yielding material of crops like cashew. In such an exercise, the selection of explant material assumes utmost importance. The present studies were, therefore, aimed at examining the relative response of different explant materials of cashew to in vitro culture. During the initial period of study, fungal and bacrerial contamination was a major problem, which was reduced to some extent in the further trials, by surface - sterilisation. Among the surface – sterilants used, mercuric chloride gave good results. Contamination was severe with bleaching powder. conditions . Interference of polyphenols was observed during certain stages of the study. The oxidised polyphenols were found to diffuse into the medium. The problem was overcome by including antioxidants (activated charcoal, polyvinyl pyrolidine, ascorbic acid, citric acid and combinations of these) in the media. Murashige and skoog (MS) medium, Schenk & Hildebrandt (SH) medium, Lin and Staba (LS) medium and Woody Plant Medium (WPM), supplemented with growth factors like gibberellic acid (GA), naphthalene acetic acid (NAA), kinetin and 2,4-D were tried. Among the media tested, SH gave better results, followed by MS, LS and WPM. New green buds were found to develop when the culture establishment studies were carried out with MS basal, supplemented with kinetin and NAA at (1 mg/1 + 10-1 mg/1). (1 mg/1 + 0.5 mg/1) and (2 mg/1 + 10-1 mg/1). However, these cultures showed symptoms of drying soon after subculturing. Callus development was observed when shoot tips were cultured in MS + Kinetin + NAA at 2 mg/1 + 1 mg/1, respectively and MS + Kinetin + 2, 4-D at (0.5 mg/1 + 1.0 Mg/1), (1.0 mg/1 + 4.0 mg/1) and (2.0 mg/1 + 1.0 mg/1). Comparatively better results were observed with SH + Kinetin and 2, 4-D. The cultures were hampered with browning which was overcome, to a certain extent, with pre – culture treatments and additives. Percentage survival was fair on pre – culture treatment with ascorbic acid at 150 mg/1, 300 mg/1 and citric acid at 75 mg/1. Callusing was also observed and the rate ranged from fair to good with citric acid at 150 mg/1 and with combination of ascorbic acid and citric acid at 150 mg/1 each. Callusing, ranging from poor to fair, resulted with SH + kinetin and 2, 4-D at (1 mg/1 + 1 mg/1). (1 mg/1 + 2 mg/1) and 2 mg/1 + 4 mg/1), respectively. Survival ranged from 33 to 66 per cent, with Lin and staba medium supplemented with kinetin + NAA and kinetin + 2, 4 – D. The results were same when the basic medium was changed to WPM. The explants were cultured in liquid media. But none of the cultures could give any positive results. Shoot tips were found to be the most responding explant among the many tried in different media. Among the combinations of growth substances tried, kinetin + 2, 4 – D was found to give good results when kinetin was used at a low and 2, 4 – D at a high concentration. Response of cashew explants to in vitro culture can be improved by further modification of the medium and culture conditions.