Vol. 75 No: 1

Title:
Explant, medium and vessel aeration affect the incidence of hyperhydricity and recovery of normal plantlets in triploid watermelon

Authors:
PIOUS THOMAS, J.B. MYTHIL and K.S. SHIVASHANKARA

pp: 19-25

Abstract:
Hyperhydricity or glassiness was a frequent problem during the micropropagation of triploid watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) 'Arka Manik' and this was influenced by level of BA, explant, medium and vessel aeration. High BA (5-10 mM) gave multiple shoots and led to high incidence and intensity of hyperhydricity while the use of low BA (1 μM) facilitated single-shoot growth with relatively low hyperhydricity. Hyperhydric cultures generally exhibited varying degrees of glassiness on subculturing or failed to grow at all. Shoot tip and upper nodal segments from lowly hyperhydric shoots on 1 μM BA medium often showed normal growth on subculturing while lower nodes tended to give glassy growth. Delaying subculturing thus contributed to hyperhydricity. Rugini olive (RO) basal medium showed better culture growth and less hyperhydricity than MS medium. Use of more gelling agent (phytagel 2.5 g vs. 3 g ^-1 or agar 8 vs. 10 g ^-1), substitution of agar (10 g ^-1) for phytagel (3 g ^-1), incorporation of osmotic agents mannitol and sorbitol (500 mg ^-1 each) in the medium or improving vessel aeration using caps with a 1.25 or 2.5 cm diameter opening covered with cotton bunk or cellulose nitrate filter (0.2 mm pore size) individually helped in reducing hyperhydricity to some extent. Provision for aeration was relatively superior to other approaches but more aeration (2.5 cm diameter) led to faster medium dehydration and growth limitation. Hyperhydricity/glassiness could be checked effectively with satisfactory growth by adopting a combination of low BA (1 μM), osmotic agents, agar gelling and vessel aeration (1.25 cm diameter cotton bunks) using RO or MS basal medium. Hyperhydric stock cultures could be salvaged or reverted to give normal growth by employing this approach coupled with better aeration (1.25 cm filter or 2.5 cm bunks) and selective use of shoot tip and upper nodal segments. Attempts to improve the propagation rate through multiple shoot induction using 5-10 μM BA after solving the hyperhydricity problem indicated that single-shoot growth using shoot tip and nodal cuttings in the presence of low BA (1 μM) was superior to the former, giving better net multiplication and normal plants.

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