Determination of Seed Germination Requirements in Nolana sp.

Abstract

Nolana is a diverse genus native to coastal deserts of Peru and Chile, with great potential for developing new ornamental cultivars. Low germination has been an obstacle to breeding efforts at the University of New Hampshire (UNH). Nolana fruits are comprised of unusual sclerified mericarps, each containing one or more embryos. Germination occurs with opening of funicular plugs on the mericarps. Under normal greenhouse conditions at UNH, germination success in eight Nolana species (N. adansonii, N. aticoana, N. humifusa, N. laxa, N. ivaniana, N. plicata, N. elegans, and N. rupicola) ranged from 0 to 0.05 seedlings/mericarp. We analyzed mericarp morphology, imbibition, and the effect of chemical and environmental germination treatments. SEM showed that soaking treatments create physical changes in mericarp morphology, exposing tracheid tubes in the funicular plugs. Mericarps were soaked in dye to track imbibition, confirming that this occurs through the tracheid tubes, and that additional scarification is not required. The following chemical treatments were unsuccessful in increasing germination: 0.1 N HNO3, 0.2 KNO3, conc. H2SO4, 10 mM or 1 μM ethephon. Gibberellic acid (1000 ppm) effectively increased germination in some species (up to 0.47 seedlings/mericarp). Mericarps stored dry for 2 years had significantly higher germination than fresh mericarps (0.55 seedlings/mericarp). Mericarps of N. aticoana were subjected to after-ripening treatments. Mericarps stored for 7 weeks at 35 °C and 75% RH showed significantly higher germination (0.36 seedlings/mericarp) than mericarps stored dry, or stored moist for 1-6 or 8-12 weeks. Our findings facilitate development of larger hybrid populations, thus increasing the efficiency of Nolana breeding programs.