Stephen K. O'Hair

In vitro growth of Carica papaya L. cotyledons

Abstract Lamina and midrib explants taken from cotyledons of axenically-grown Carica papaya L. seedlings were cultured on modified Murashige and Skoog (MS) basal medium containing half-strength major salts and chelated iron, 30 g l −1 sucrose, 8 g l −1 Difco Bacto agar and all possible combinations of benzylaminopurine (BA) and naphthaleneacetic acid (NAA), each of which was used at 13 concentrations between 0.0 and 15.0 mg l −1 . Optimum growth regulator concentrations for callus induction and maintenance from midrib (0.3–2.0 mg l −1 BA with 0.5–3.0 mg l −1 NAA) and lamina (0.6–3.0 mg l −1 BA with 1.2–5.0 mg l −1 NAA) explants were determined from a prediction model. The medium and environmental factors for adventitious root and shoot formation on these explants were also determined.

Net CO2 assimilation of taro and cocoyam as affected by shading and leaf age

Taro and cocoyam were grown outdoors in either full sun or under 40% shade. Leaves were tagged as they emerged and the effect of leaf age on net CO2 assimilation rate (A) was determined. The effects of shading on A, transpiration (E), stomatal conductance for CO2 (gc) and H2O (gs), and water use efficiency (WUE) were also determined for leaves of a single age for each species. The effect of leaf age on A was similar for both species. Net CO2 assimilation rates increased as leaf age increased up to 28 days with the exception of a sharp decline in A for 21 day-old leaves which corresponded to unusually low temperatures during the period of leaf expansion. A generally decreased as leaves aged beyond 28 days. Cocoyam had higher A rates than taro. Leaves of shade-grown plants had higher rates of A and E for both species at photosynthetic photon flux densities (PPFD) up to 1600 μmol s−1 m−2. Shade-grown leaves of cocoyam had greater leaf dry weights per area (LW/A) and a trend toward higher gc and gs than sun-grown leaves. Shade leaves of taro had greater gc and g3 rates than sun-grown leaves. The data suggest that taro and cocoyam are highly adapted to moderate shade conditions.

In vitro plant regeneration from corm callus of Amorphophallus rivieri Durieu

Abstract Corm explants of Amorphophallus rivieri Durieu were cultured on Murashige and Skoog (MS) medium modified by the use of half-strength major salts with 200 mg l −1 NH 4 NO 3 and various concentrations and combinations of benzyladenine (BA) and α-naphthaleneacetic acid (NAA). Optimum growth regulator combinations for inducing adventitious shoots from corm callus were 2.0–10.0 mg l −1 BA and 0.1–0.3 mg l −1 NAA. Axillary bud development from these regenerated shoots was stimulated in liquid MS medium containing 3.0 mg l −1 zeatin, 0.01 mg l −1 gibberellic acid (GA 3 ) and 0.3 mg l −1 NAA. Shoots were rooted on modified MS medium with 1.0 mg l −1 NAA. Rooted plantlets were successfully established under greenhouse conditions.