Endogenous auxin level is a critical determinant for in vitro adventitious shoot regeneration in potato (Solanum tuberosum L.)

Endogenous levels of indole-3-acetic acid (IAA) were determined in the internodal explants of Indian tetraploid potato cultivars (cvs) viz., Kufri Sutlej (K.Sutlej) and Kufri Giriraj (K.Giriraj). Seven fold higher level of endogenous IAA was recorded for cv K.Sutlej over cv K.Giriraj. As a result, perhaps there was a callusing response from the cut end of the internodal explants of both the cvs in the MS basal medium. The extent of callusing was relatively higher in cv K.Sutlej when compared to that in K.Giriraj. The callusing response was inhibitory to shoot morphogenesis. Inclusion of an established anti-auxin, 2,3,5-tri-iodobenzoic acid (TIBA) in the regeneration medium facilitated a high frequency adventitious shoot regeneration response with lower cytokinin levels. Murashige and Skoog (MS) medium containing TIBA at 2.5?mg?l^?1 and 0.25?mg?l^?1 zeatin evoked a 100% regeneration response (4.5 shoot buds per explant) in cv K.Sutlej within 20?C25?days. However, in cv K.Giriraj, which had lower levels of endogenous IAA, 80% regeneration response (1.4 shoot buds per explant) was recorded in an extended period of 40?C45?days on a medium containing 0.5?mg?l^?1 TIBA and 0.1?mg?l^?1 zeatin. Although, TIBA and zeatin induced shoot bud formation, it failed to support sustained growth of the regenerated shoots in cv K.Giriraj. Hence, 0.01?mg?l^?1 ??-naphthaleneacetic acid (NAA) with a relatively higher concentration of zeatin (1.0?mg?l^?1) were used for sustained shoot regeneration (3.3 shoot buds per explant) within 25?days. From our results, it is evident that there was a difference in the requirement of exogenous zeatin levels required to induce a regeneration response in two cultivars of potato and this is attributed to the variable levels of endogenous IAA.