In Vitro Reproductive Development of Peanut, Arachis hypogaea L., as Influenced by Plant Growth Regulators, Sucrose and pH1
Q. L. Feng, H . E. Pattee*, and H. T. Stalkef
Research on in vitro embryo culture in Arachis has the objective ofrescuinginterspecific hybridembryos which abort before they reach maturity. This study explored effects ofthe three exogenous plant growth regulators 1naphthaleneacetic acid (NAA), gibberellic acid (GA,), and 6-benzylaminopurine (6-BAP); sucrose; and medium pH on in vitro fruit and embryo development ofA. hypogaea L. by culturing 10-d-old peg tips. Results indicated that medium containing 0.5 to 1.0 mg L NAA was optimal for in vitro pod formation and embryo development. GA, did not have a significant influence and 6-BAP had negative effects on both in vitro fruit and embryo development. High concentrations of 6-BAP and NAA induced callus which inhibited ovary enlargement and embryo development. Sixty g L-' sucrose was the best concentration for ovary enlargement and embryo development. Acidic medium was needed for in vitro reproductive development with pH 4.5-6.5 the most favorable. A pod formation frequency of 81%, a seed production rate of 90% (from pods recovered in
vitro), and plant recovery of 33% were obtained for a medium containing 1.0 mg L-' NAA and 0.5 mg L-' GA, plus 60 g L-' sucrose at pH 5.8. In vitro-recovered cotyledonaryembryos between 4 and 10mm long germinated precociously into seedlings at relatively higher frequencies than morphologicallymature embryos which produced more vigorous plants. Key Words: Embryo, ovule, pod, peg, in vitro culture, tissue culture.
'This research was partially supported by the North Carolina Agric. Res. Sew., Raleigh, NC 27695-7643and the Peanut CRSP, USAID grant DAN4048-G-SS-2065-00.Recommendations neither represent an official position nor policy of the NCARS or USAID. =Grad. Res. Asst., Dept. of Crop Science; Prof., USDA-ARS, Dept. of Botany; and Prof., Dept. of Crop Science, respectively, North Carolina State Univ., Raleigh, NC 27695-7625. *Corresponding author. Peanut Science (1995) 22:135-141
Peanut is a valuable leguminous crop because seeds contain high percentages of protein and oil. Cultivated peanut is susceptible to many diseases, insects and nematodes, whereas many wild species of Arachis have high levels of resistances. However, introgression of wild germplasm to cultivated peanut is restricted because interspecific hybridization is difficult (5).Embryo abortion occuring soon after fertilization often is the cause for failure of interspecific hybridization (6,7,11,12), and in vitro culture of embryos is an approach to rescue hybrids. Studies by Bajaj et al. ( I ) , Ozias-Akins ( l o ) , Sastri et al. (17), and Stalker and Eweda (20) indicated that rescuing heart-shaped embryos of interspecific hybrids is possible. However, since abortion often occurs at a stage prior to the heart shape (11,12), improved in vitro techniques are needed to rescue proembryos.
Previous work has resulted in multicellular globular embryos derived from one- to two-celled proembryos of selfed A. hypogaea L. (8,13,14). Ziv and Sagar (23) achieved in vitro growth of A. hypogaea ovules and obtained viable young seedlings by a two-step process. M a t u r e seeds w e r e obtained from several-celled proembryos of A. hypogaea and A. duranensis Krapov. and W . C. Gregory by Feng et al. (2,3), but at a very low frequency. The objective ofthis research was to evaluate effects of plant growth regulators, sucrose, and medium p H on in vitro reproductive growth and development in A. hypogaea.
Materials and Methods
Plants of A. hypogaea cv. NC 6 were grown in 15 x 15-cm pots in a greenhouse at North Carolina State University, Raleigh, NC during the summer of 1994. Selfed flowers were marked daily at anthesis with colored tags, and elongating aerial pegs were collected 10 d later. Pegs were rinsed in running tap water for 5 min,...
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