BP Singh

70 S.R. BhatQuarantine procedures for in vitro culture and exchange ofgermplasm are well established for important crops such aspotato, banana, sweet potato, yams and can be adopted for othercrops as well (FAO/IBPGR, 1989).3. . Salvaging diseased material. As stated above, in vitrocultures are usually free from bacterial and fungal contaminations.Even plants infected with viruses and other obligate parasites canbe salvaged through 'meristem culture'. Although White (1934)recorded for the first time the absence of viruses in culturesinitiated from root apices of infected material, it was Morel andMartin's (1952) work with shoot apex culture of dahlia whichdemonstrated the significance of 'meristem culture' for viruselimination. The exact reason for' the absence of viruses inmeristematic zone is unclear. However, meristem culture techniqueis now well established and success has been reported in over 100plant species. Even seed borne virus (pea seed borne mosaic virus)has been eliminated through' meristem culture (Kartha andGamborg, 1978). A modification of this technique called 'in vitro,'_l!P~~9g!~ging~. w"a~ ._g~vi~ed by Navarro .. ~t. al . . (197~) for' theelimination of viruses in citrus .. which is currently in wide use.,_, ...For most of the problem crops ,meristem culture is now usedto establish clean cultures. The plantlets derived from meristemculture need to be tested for ascertaining virus-free status. Thesuccess rate may range from 10-80%. However, once the materialis cleaned it can be rapidly multiplied and can be maintainedindefinitely in disease-free state through tissue culture.4. Assistance in transport : Recalcitrant seeds and vegetativepropagules (cuttings, budwoods) are highly perishable and aredifficult to transport over long distances. Similarly, bulbs,suckers, grafts and seedlings are delicate and need excessivepacking and care during transport. Such bulky materials aredifficult to handle and hence limit exchange by restricting thenumber of samples and also the nU:p1ber of replicate~. By resortingto in vitro culture, recalcitrant seed species and clonal materialscan be easily transported. Over 200 culture tubes (each with3-4 shoots) can be packed in 0.75 cubic feet (approx.O.02 m 3 ) boxand will weigh less than 5 kg. In vitro cultures can withstandrigors of transport and survive at ambient temperatures (IS-30°C)for 3-4 weeks. Even in germplasm collection in vitro techniques