Vol. 84 No: 6

Title:
In vitro propagation of 'Arka Ravi' chrysanthemum on growth regulator-free medium harbouring endophytic bacteria

Authors:
P. THOMAS, BINDU PANICKER, T. JANAKIRAM and B.N. SATHYANARAYANA

pp: 653-659

Abstract:
To develop a micropropagation protocol for the elite chrysanthemum cultivar, ‘Arka Ravi’, in vitro cultures were established using surface-sterilised nodal microcuttings (1.0 – 1.2 cm) on semi-solid MS medium. Microbial contamination was observed in 22% of cultures during the initiation phase. Cultures that were devoid of obvious contamination were transferred to culture bottles containing MS medium supplemented with 30 g l^-1 sucrose, 2.5 g l^-1 Phytagel^® and either benzyl adenine (BA) or kinetin (KIN) supplied at 0, 1, 5, 10, or 20 μM, and were monitored, over eight in vitro passages, for their growth and microbial association. Shoot-tip and nodal microcuttings yielded a single shoot, coupled with rooting, in medium devoid of BA or KIN which was the best medium for continuous micropropagation. Rooting was inhibited with increasing concentrations of BA or KIN, and one or more shorter shoots with condensed internodes were induced, resulting in low rates of propagation. Culture indexing (i.e., testing the medium and tissue from visibly clean cultures using enriched bacteriological media) revealed quiescent endophytic bacteria associated with 80 – 100% of such cultures. Three distinct colony morphotypes were isolated and were identified as Ralstonia, Enterobacter, and Methylobacterium spp., based on their 16S rRNA gene sequences. These endophytes did not interfere with normal micropropagation, but tended to grow actively and outgrow older cultures, especially at higher cytokinin concentrations. Stable micropropagation of ‘Arka Ravi’ chrysanthemum for ≥ 2 years, with their resident endophytic bacteria in a covert form, was achieved on basal MS medium with > 90% shoot growth and rooting, a four-to-five-fold propagation rate at each 2 – 3 week sub-culture cycle, and with > 90% establishment of rooted plantlets ex vitro. These results suggest that in vitro cultures of chrysanthemum often harbour endophytes with no obvious indications of their presence or with possible hidden effects during micropropagation.

Full text: JHSB Subscribers     ISHS members & other users
(PDF 912300 bytes)

Translate:

Go back to previous page