High-frequency in vitro flowering, hand-pollination and fruit setting in ten different cultivars of Capsicum spp. (C. annuum, C. chinense, and C. frutescens): an initial step towards in vitro hybrid production

Abstract

We developed an efficient method for inducing high-frequency in vitro flowering and fruiting in 10 cultivars (Cap-1 to -10) of three different species of Capsicum (C. annuum, C. chinense, and C. frutescens) collected from diverse geographical regions of India and Mexico. Shoot tips of in vitro germinated seedlings were cultured on MS media supplemented with different concentrations of 6-benzylaminopurine (BAP) alone or in combination with silver nitrate or silver thiosulphate. Low BAP concentration was a good inducer of flower buds in vitro. Synergism between silver ions and cytokinin improved flower induction. Flowering frequency improved significantly when silver nitrate or silver thiosulphate was supplemented with optimum BAP. Maximum responses, 7.5 ± 0.20 (in Cap-1) to 15.8 ± 0.27 (in Cap-5) flowers, were induced in the medium containing 0.75 mg l−1 BAP and 30 μM silver thiosulphate within 60 days of culture. Both in vitro hand-pollination and high sucrose concentration (5.0–6.0 %) in the medium improved fruit setting. In general, fruits were very small (mini-fruit) and seedless; however, three cultivars (Cap-3, -5, and -6) produced normal fruits with seeds. On an average, 144 days were required from seed implantation to fruit ripening. The frequency of meiotic abnormalities was higher in flowers produced in vitro than in those produced in vivo, and pollen viability was relatively lower in the in vitro flowers than in the in vivo flowers. The present protocol offers a repeatable system for studying the physiological mechanism of flowering and fruiting as well as providing the basis for further investigation for rapid in vitro cross-breeding programmes in Capsicum spp. for commercial hybrid production.