<i style="">In vitro </i>germplasm preservation through regenerative excised root culture for conservation of phytodiversity<i style=""></i>

Abstract

<i style="">In vitro </i>preservation of germplasm becomes imperative for those plant species in which application of conventional methods is infructuous. Of the 4 methods of <i style="">in vitro </i>preservation of germplasm, viz., cryopreservation, slow growth shoot culture, normal growth culture and regenerative excised root culture, the last method has some advantages over the others in case of certain plant species, particularly the palms. Its main advantages are: Practicability and low cost because of no requirement of agar-agar, of light as well as of strict maintenance of temperature besides easy exchange of germplasm across the International boundaries without damage in transit. However, all these 4 methods have certain shortcomings, which necessitate adoption of a composite approach involving all of them to achieve the main goal of conservation of phytodiversity. In general, durations of germplasm preservation <i style="">in vitro</i> through cryopreservation and slow growth shoot culture have ranged from a few weeks to about 2 yrs depending on the plant species concerned. In certain plant species, the normal growth culture had afforded germplasm preservation for considerably long periods of time, viz., more than 27 yrs in <i style="">Dioscorea floribunda </i>and<i style=""> D. deltoidea</i> and 32 yrs in <i style="">Citrus grandis,</i> albeit with a danger of cultures getting infected during frequent subcultures. In contrast, the duration of germplasm preservation through regenerative excised root culture ranged from 6 to 24 yrs. The method of regenerative excised root culture had been demonstrated to preserve germplasm of a number of plant species, including herbaceous annuals and perennials and trees, viz., <i style="">Solanum khasianum</i> (spiny and spineless), <i style="">S. torvum, S. surattense, Atropa belladonna, Kalanchöe fedtschenkoi, Rauvolfia</i> <i style="">serpentina</i>, <i style="">Populus deltoides</i> and <i style="">Dalbergia latifolia.</i> A similar possibility existed in case of <i style="">Shorea robusta, Cocos nucifera</i> and <i style="">Elaeis guineensis</i>, roots of which though established in long-term culture, the regenerant differentiation in their explants was most sporadic. For establishing excised root cultures of different plant species, modifications of various nutrient media, viz., Murashige and Skoog (1962), Street (1954), Street and McGregor (1952) and White (1943) were used in liquid state, while for inducing regenerant differentiation, some other modifications of the same media except of White as well as of Schenk and Hildebrandt (1972) medium were employed, using different cytokinins, viz., BAP, 2iP, Z and TDZ with auxins, viz., IAA, NAA and 2, 4-D and also certain growth inhibitors/retardants, viz., ABA, CCC and ancymidol as also a polyamine, putrescine. In all cases, agarified media were used except in <i style="">R. serpentina, </i>which required the liquid state of medium for regenerant differentiation, while in <i style="">S. khasianum </i>and <i style="">A. belladonna</i>, caulogenesis took place in agarified morphogenic medium and embryogenesis in the liquid state of medium. Further, whilst in <i style="">R. serpentina </i>and <i style="">A. belladonna</i> plantlets were produced via embryogenesis, in rest of the plant species through caulogenesis. Plants regenerated through long-term excised root culture were true-to-type, which was substantiated by tracing their origin from the pericycle tissue of root explants. The root-regenerated plants fared well under field conditions save <i style="">A. belladonna,</i> plants of which could be grown in potted soil only in controlled physical conditions.<b style=""></b>