ENVIRONMENTAL MANAGEMENT FOR OPTIMIZING MICROPROPAGATION

Abstract

Many factors can influence the success of any horticultural enterprise, but micropropagation lends itself to successful management because conditions can be controlled by the practitioner. This discussion will assume biotic factors are controlled and will therefore focus primarily on factors influencing the stock plant as an explant source and on explant performance. 1. Environment Under Which the Stock Plant is Grown. One of the most important of these factors is light. Light quantity/intensity affects photosynthesis of leafy cultures and has impact on other physiological processes e.g. endogenous hormone levels, which in turn influence explant performance in vitro. Light quality, especially red and far-red light, also affects hormone levels and subsequent in vitro results. Photoperiod affects stock plant morphology, which also relates to explant responses during subsequent culture. Temperature under which the stock plant is grown can also affect explant performance (see Ko, others). Relationship to stock plant morphology and physiology will also be discussed with regard to nutrition and growth regulating chemicals. Our research on Priming the explant for culture success will also be emphasized. 2. Environment Under Which the Explant is Cultured. Manipulation of the physical environment has dramatic effects on explant response in vitro. Numerous examples of the influence of light exist including exclusion of light, different amounts of light (intensity, photoperiod) and manipulating light quality. Of special interest are studies by Economou and Read (and others) demonstrating the effects of light quality and quantity on subsequent in vitro performance. Effects of culture temperature, gaseous environment (see works of Kozai, for example), physical condition of the medium and contaminants all influence in vitro culture success. The chemical environment, i.e., the composition of the culture medium, is perhaps the most studied aspect of tissue culture and micropropagation. Many have attempted to devise a medium containing precise amounts of macro- and micronutrients, organic constituents and growth regulators (Hildebrandt, Murashige and Skoog, deFossard), with no uniform protocol accepted by micropropagators to date. An innovative approach developed in our lab will be presented, along with an evaluation of the advantages and disadvantages of various media and their methods of development. 3. Environment Under Which Micropropagated Plants are Acclimatized. Specialized examples from our lab will be discussed for this topic.