IN VITRO PRODUCTION OF MICROTUBERS FOR CONSERVATION OF POTATO GERMPLASM: EFFECT OF GENOTYPE, ABSCISIC ACID, AND SUCROSE J. GOPAL*, ANJALI CHAMAIL, AND DEBABRATA SARKAR Division of Crop Improvement, Central Potato Research Institute, Shimla-171 001, Himachal Pradesh, India (Received 19 May 2003; accepted 3 February 2004; editor F. Engelmann) Summary With the objective of using microtubers for conservation of potato germplasm, the main effects of genotype, abscisic acid (ABA), and sucrose level, and of their interactions on biomass production, microtuberization, microtuber dormancy, and dry matter content, were studied. ABA decreased both microtuber production and microtuber dormancy, whereas higher concentrations (60 – 80 g l 21 ) of sucrose promoted biomass production, microtuber production as well as microtuber dry matter content. Microtubers stored under diffused light had longer dormancy than those kept continuously in the dark. Interactions among various factors conditioned the main effects for some characters. In vitro performance of the genotypes studied was related to their known performance under in vivo conditions for most of the characters. Microtubers produced on media devoid of ABA and containing high sucrose concentrations and N 6 -benzyladenine (44.38 mM) could be stored for 12 mo. under diffused light at 6 ^ 18C. Key words: in vitro conservation; microtuber dormancy; microtuberization; Solanum tuberosum L. Introduction In vitro production of microtubers by serial culture of individual nodes with axillary buds is routinely used for disease-free seed production in potato (Gopal et al., 1998a). Microtubers are also convenient for handling, storage, and transport of germplasm (Thieme, 1992). Microtubers displaying enhanced dormancy seem to be advantageous for potato germplasm conservation since these can be stored for longer periods without having recourse to specialized infrastructure and stringent maintenance vis-a ` -vis regeneration schedule as required for conventional storage of microplants in vitro (Gopal et al., 2003). Performance of the crop raised from microtubers is affected by their dormancy (Gopal et al., 1997). Of all the different growth regulators, abscisic acid (ABA) is considered to be the principal dormancy-inducing agent. ABA levels in potatoes are generally highest in freshly harvested (deeply dormant) tubers, and decline as sprouting initiates (van den Berg et al., 1991; Suttle and Hultstrand, 1994). However, there appears to be very little information available on the effect of ABA on microtuber dormancy when supplied exogenously in the (micro- tuber) induction medium. There are conflicting reports on the role of ABA in potato tuberization; it has been identified as promoting (Abdullah and Ahmad, 1980; Andre et al., 1998) as well as inhibiting (Palmer and Smith, 1969; Hussey and Stacey, 1984) tuberization. Koda and Okazawa (1983) reported that ABA increased the rate of tuberization when its concentration was increased in combination with 2% sucrose, but the tubers thus formed characteristically ceased their development at the bulking stage. The level of sugar in the induction medium, especially sucrose, as well as the genotype also affect microtuberization (Koda and Okazawa, 1983; Andre et al., 1998; Gopal et al., 1998a). However, little is known about the effect of sucrose on microtuber dormancy (Choi et al., 1994; Coleman and Coleman, 2000). In addition, it would be interesting to study the effect of possible interactions between the genotype, ABA, and sucrose on microtuber production and subsequent dormancy release. How these factors affect total biomass production during microtuberization and subsequent microtuber dry matter content has also not been reported. Therefore, in the present investigation, the main effects of genotype, ABA, and sucrose, and the effects of their interactions on potato microtuberization vis-a ` -vis microtuber dormancy and dry matter partitioning, were studied in relation to the usefulness of microtubers for the conservation of potato germplasm in vitro. Materials and Methods Genotypes. Three potato (Solanum tuberosum L.) cultivars with variable tuber dormancy, i.e., short (Kufri Badshah), medium (Kufri Chandramukhi), and long (Kufri Sindhuri) were used in the present study. These cultivars also vary for foliage maturity, tuber size, number of tubers, tuber dry matter, etc. (Gopal and Kang, 1988; Gopal et al., 1992). In vitro microtuber production. Disease-free plants of the above genotypes were multiplied and maintained in vitro on MS (Murashige and Skoog, 1962) medium supplemented with 30 g l 21 sucrose under standard culture conditions (16 h light/8 h dark photoperiod from cool white fluorescent lamps with a light intensity of 20 mmol m 22 s 21 at 24 ^ 18C). Single-node cuttings (SNCs) dissected from 6 – 8-wk-old axenic plantlets *Author to whom correspondence should be addressed: Email: jai_gopal@cpri.hp.nic.in or jai_gopal@rediffmail.com In Vitro Cell. Dev. Biol.—Plant 40:485–490, September – October 2004 DOI: 10.1079/IVP2004540 q 2004 Society for In Vitro Biology 1054-5476/04 $18.00+0.00 485