Nutrient utilization in liquid/membrane system for watermelon micropropagation

Abstract

Watermelon [Citrullus lanatus (Thunberg) Matsumura and Nakai] proliferating shoot meristems from established shoot cultures were inoculated on modified Murashige and Skoog salts medium supplemented with 10 μM 6-benzyladenine (BA) for shoot proliferation and on similar medium supplemented with 1 μM BA and 10 μM gibberellic acid (GA3) for shoot elongation. Agar-solidified medium and microporous polypropylene membrane rafts in liquid medium were used to support the tissues. Growth over culture time of proliferating and elongating tissues in liquid and agar-solidified media were compared. Nutrient depletion in liquid medium was monitored and quantified using ion selective electrodes. Tissue fresh weights in both proliferation and shoot elongation media were greater in liquid than in agar-solidified medium. Relative dry matter content, however, was greater in agar-solidified than in liquid medium. More shoots elongated in agar-solidified than in liquid medium. The numbers of buds or unelongated shoot meristems, however, were comparable for both the liquid and agar-solidified medium. Proliferating and elongating tissues in liquid medium used Ca++ and K+ minimally. NO 3 − was utilized but not depleted by proliferating tissues. NH 4 + , however, was depleted. Most of the NH 4 + was utilized by the proliferating tissues within 21 days of culture when growth rate was greatest. At 35 days, residual Ca++, K+, NO 3 − , and NH 4 + in proliferation medium were 81.0%, 67.8%, 55.7%, and 1.2% of initial levels, respectively. NO 3 − and NH 4 + in shoot elongation medium were depleted. The greatest NO 3 − and NH 4 + utilization was observed during the first 14 days of culture when the largest growth rate was obtained. The residual Ca++, K+, NO 3 − , and NH 4 + in shoot elongation medium at 38 days were 63.5%, 37.9%, 21.2%, and 24.3% of initial concentrations, respectively. At the end of experiment, 72.3% and 42.8% of initial sugars were still remaining in the shoot proliferation and shoot elongation medium, respectively.