Growing of potato microplants in the presence of alginate-silverthiosulfate capsules reduces ethylene-induced culture abnormalities during minimal growth conservation in vitro

Alginate capsules containing anionic complex silverthiosulfate (STS) [Ag(S2O3)23-] were placed in the culture tubes over minimal growth media for studying whether STS could be used at higher concentrations to sustain ethylene-inhibiting effect during conservation of microplants in six potato (Solanum tuberosum L.) genotypes in vitro. Different concentrations of STS (0.1, 0.5, 1.0, 2.0, 3.0 and 4.0 mM) were incorporated into the alginate capsules, and 12 alginate-STS capsules were tested in semisolid (7 g l−1 agar) minimal growth medium containing 20 g l−1 mannitol and 40 g l−1 sucrose. This indirect supplementation of STS through alginate capsules rendered reduced total availability of STS in the minimal growth medium as compared to when it was directly supplemented in the medium at a given concentration. Growing of microplants in the presence of alginate-STS capsules improved the microplant growth and reduced the culture abnormalities over a period of 16 months under minimal growth conditions. Most significant improvement in microplant growth was in terms of green leaf production and leaf senescence. Vitrification, flaccidity and other growth abnormalities, viz., leaf loss, abnormal stem swelling and necrosis were not observed when the microplants were conserved in the presence of alginate-STS capsules. To foster optimum microplant growth and reduce culture abnormalities, potato microplants could favourably be maintained in the presence of 0.5–1.0 mM alginate-STS capsules during minimal growth conservation. Higher concentrations of alginate-STS capsules (>1.0 mM) were in general detrimental to potato microplant growth and survival during prolonged storage in vitro. Release kinetics of STS from the alginate-STS capsules, its distribution in the medium and accumulation of silver in potato microplants were studied using 110mAg. The release rate of STS from the capsules was found to be directly proportional to the concentrations of alginate-STS capsules. A distinct concentration gradient of 110mAg in the medium with increasing depth from top to bottom, and its accumulation in the potato microplants may be attributed to the improved anti-ethylene action of STS at higher concentrations through alginate capsules.