Callus formation impedes adventitious rhizogenesis in air layers of broadleaved tree species

Abstract

Callusing and root induction in air layering was evaluated aim- ing at evolution of procedure for mass clonal propagation of mature ortets of five tropical broadleaf species differing in their potential for adventi- tious root formation in shoot cuttings as: Anogiessus latifolia < Boswellia serrata < Dalbergia latifolia < Gmelina arborea < Dalbergia sissoo. Two experiments were conducted in rainy season during consecutive years; without application of growth regulators in the first year and with growth regulators (T 1 - water, T 2 - 100 ppm indole-3-acetic acid, T 3 -100 ppm thia- mine- HCl and T4 -combination of T 2 + T 3 ) in the next year. Air layered branches were detached from the trees to record percentage of alive air- layers, callusing and rooting (%) as well as root number and root length. Response to air layering was found to be highly variable in five tree spe- cies but appeared to be feasible procedure for clonal propagation of mature ortets of B. serrata and D. sissoo with 100% (in auxin + thiamine treat- ment) and 83.3% (in auxin treatment) success, respectively. Maximum cal- lusing (%) was found in D. latifolia while no callusing was observed in D. sissoo, which is most easy-to-root among all five species. Callus forma- tion impedes adventitious rhizogenesis in air layers as significant negative correlation of callusing (%) and adventitious root formation was record- ed in air layers of five tropical broadleaved tree species. Application of exogenous auxin alone or in combination with thiamine circumvents cal- lusing to ensure direct development of roots for successful air layering. Keywords auxin, callusing, girdling, rooting, thiamine.