Mycorrhization of the Commercially Important Micropropagated Plants

Abstract

In the last few years, urbanization and changes in eating habits have caused a significant shift toward the consumption of fresh fruits, leafy green salads, and vegetables. This has been followed by a growing commercialization of ornamental plants. These products come from a labor- and capital-intensive activity, where chemical inputs play an essential role but also brings with it a set of problems linked to the degradation of the natural environment and resource base. The present review presents new developments in the potential use of biological tools such as arbuscular mycorrhizal fungi (AMF), which should ensure adequate levels of food production with satisfactory reduction of chemical fertilizer and pesticides, in the context of technologies needed for sustainable agriculture. The potential of mycorrhizal fungi as biofertilizers and bioprotectors to enhance crop production is well recognized, but not well exploited because of the current agronomic practices, with their implications for the environment. To clarify a few salient points, we discuss a case experiment conducted on tissue culture-raised plantlets in association with mycorrhizal fungi grown in a controlled growth house (phytotron) and then transferred to the field for follow-up response under natural conditions.

For rooting, the genetic, developmental, positional, and physiological conditions of the microcutting are essential. Propagation in vitro offers an excellent possibility to study the factors that determine the rooting ability of a shoot. The major leap forward in the study of rooting was made 60 years ago with the discovery of the effect of auxin. (Thimann and Went, 1934). Since then, progress has been slow and no other major factor has been found to achieve rooting of recalcitrant crops. It has been postulated that redirection of research is required. We have established the positive influence of endomycorrhizal fungi (possibly Glomus mosseae Schenck and Perez) on the excessive root proliferation in the maize seedlings in in situ experiments. Evidence was documented for the secretion of growth-promoting metabolites like indole acetic acid (IAA) and kinetin on associative growth and development of maize roots and fungal symbionts. Such a study under controlled conditions with micropropagated plants will allow identification of the promoters involved and accurate determination of which step in the rooting process is blocked in recalcitrant crops. This review highlights such a novel approach for future biotechnology.

Key Words:

• tissue culture
• micropropagated plants
• mycorrhizal fungi
• arbuscular mycorrhizal fungi (AMF)
• vesicular arbuscular mycorrhizae (VAM)
• inter- and intraradical mycelium