BP Singh

LIse of Tissue Culture Techniques in Exchange 69blackberry, grapes etc. are routinely exchanged as in vitro cultures.Use of tissue culture techniques at various steps in germplasmexchange and the resulting benefits are briefly discussed below:1. Preparation of material : Availability of material for supply isoften limited and it usually takes a year (for annuals) before theindent can be honoured. In perennial crops it may take evenlonger. In many c10nally propagated crops multiplication rate isvery low (5-10 times per year) and may require special skills andresources. Recourse to tissue culture can alleviate this problem.Rapid multiplication through in vitro culture is already beingpracticed on a commercial scale for many important crops.Further, tissue culture multiplication has been reported for over1000 plant species.Since tissue culture is carried out under controlledconditions, material can be multiplied at any time of the year. Thus,rapid multiplication through in vitro culture can save time andmake material available in adequate quantity to the indentor.2. Assistance in quarantine. Exchange of germplasm alwayscarries the risk of introduction of pests, pathogens, weeds etc.These may be present as mixtures (e.g., weed seeds) or borneexternally or internally. There are numerous instances ofaccidental introduction of unwanted organisms during germplasmexchange. Whereas seed material is more easily accessible forquarantine inspection and sanitisation h'eatments, bulky vegetativepropagules· (suckers, corms, bulbs etc.) and plantlets are difficultto screen effectively. Undesirable organisms have been known toescape through quarantine net especially in materials with soil ,roots, or external coverings (sheaths, husks).Tissue culture involves surface sterilization and cultureunder aseptic conditions. Almost all insects, pests, bacteria andfungi borne externally are eliminated during surface sterilization.Since tissue culture medium contains sugars, vitamins andnutrients, bacteria and fungi, if present, will grow and show upas contaminants in the medium. Similarly, presence of insects andnematodes can be easily detected. Thus when clean. cultures areestablished and used for exchange the risk of introduction ofunwanted organisms is greatly redu.ced. Q~y ()bligate parasitesare giffkult, to detect in, in vitro c.ultures and need speCial attention.