American Journal of Plant Sciences, 2012, 3, 567-571 doi:10.4236/ajps.2012.35068 Published Online May 2012 (http://www.SciRP.org/journal/ajps) 567 Photoperiod Affects in Vitro Flowering in Wild Peanut Arachis paraguariensis Olubunmi Aina, Kenneth Quesenberry, Maria Gallo Department of Agronomy, University of Florida, Gainesville, USA. Email: ainab@ufl.edu Received March 5 th , 2012; revised March 22 nd , 2012; accepted April 12 th , 2012 ABSTRACT Arachis paraguariensis, a wild peanut species, is a potential experimental system for studying the molecular mecha- nisms of flowering in the genus Arachis. The present study was carried out to investigate the effect of photoperiod on in vitro reproductive behavior of five genotypes of A. paraguariensis. Day-lengths of 12, 16 and 24 h were tested to monitor in vitro flowering using growth chambers kept at 26˚C ± 1˚C and 60% ± 5% relative humidity under an illumi- nation of 40 μmol·m –2 ·s –1 . Flowering percentage of plantlets ranged from 35% to 93%, 20% to 75%, and 5% to 53% for 12, 16 and 24 h day-lengths, respectively. Genotype PI 262842 displayed the highest frequency of flowering under all the day-length treatments but in vitro flower bud initiation was delayed. The highest mean flowering percentage of 65% across all the genotypes for plantlets exposed to 12 h photoperiod is indicative that flowering induction actually oc- curred. The results presented in this paper provide evidence for photoperiodic flowering response as well as the occur- rence of short day-length-enhanced flowering in A. paraguariensis. Keywords: Flower; Tissue Culture; Day-Length; Photoperiod; Peanut; Arachis; In Vitro 1. Introduction Several wild Arachis species constitute important sources of novel genes for improving cultivated peanut (Arachis hypogaea L.). Of significant importance is Arachis para- guariensis Chodat & Hassl., a perennial wild relative of the peanut having novel traits including disease [1,2], insect [3], and nematode [4] resistance. Low fruiting ef- ficiency due to asynchronous flowering and pod forma- tion is a persistent problem within the genus Arachis that often results in considerable seed-yield losses and low germination rates [5,6]. Although photoperiod sensitivity within the genus Arachis is widely reported [7,8], the specific role of environmental factors in the regulation of its reproductive performance is poorly understood. For example, results from field studies focusing on the ef- fects of photoperiod on flowering in cultivated peanut were inconsistent due to differential responses among different cultivars [9,10]. Gaining a proper understanding of the molecular basis for flowering mechanisms should enable the plant breeder to efficiently manipulate reproduction processes for achieving significant impacts on yield and other impor- tant traits. In vitro flowering, a common phenomenon in several plant species offers an ideal experimental system for studying these mechanisms. Additionally, tissue cul- ture techniques such as in vitro fertilization, peg culture and embryo rescue can be explored as a means of over- coming the long existing hybridization barriers between cultivated peanut and several of its wild relatives. In vitro tissue explants for plant regeneration are grown on nutrient medium inside confined vessels; there- fore, precise control of all environmental factors is ex- pected. Nevertheless, seasonal effects of explant collec- tion and culture initiation on plantlet regeneration have been reported for many species [11-15]. Furthermore, different cytokinins, sucrose concentrations, photoperiod, and subculture time have been used to promote in vitro flowering [4,11]. Flowering in vitro has been observed in a few Arachis spp., however, the photoperiodic flowering response in tissue culture is relatively rare and poorly understood. Still et al. [16] and Li et al. [17] reported the occurrence of flowering in tissue culture of A. para- guariensis, but the environmental and genetic factors involved were not investigated. In this study, a factorial experiment in a completely randomized design with sub-sampling was replicated two times to investigate the influence of photoperiod on in vitro flowering of five genotypes of A. paraguariensis. 2. Materials and Methods 2.1. Explant Source Seeds of five genotypes of A. paraguariensis used for Copyright © 2012 SciRes. AJPS