Selection tools for reducing generation time of geophytic herbaceous perennials

Abstract

Lengthy generation times in herbaceous perennials (1 to 5-10+ years from seed to flowering) impede the rate of progress flower breeders can make during breeding and/or domestication of floricultural crops. Geophytic herbaceous perennials, i.e., those with over-wintering underground storage organs (rhizomes, bulbs, corms, tubers etc.), have the added complication of the need for meristem size for vegetative to reproductive phase change competency and increased flower bud number. Consequently, these and other factors necessitate that most geophytic floricultural crops are primarily vegetatively (asexually) propagated. The University of Minnesota Flower Breeding and Genetics program has focused>20 years to reduce the generation time in many geophytic crops, including monocots (Gladiolus, Lilium, Iris) and dicots (Chrysanthemum), using a suite of selection techniques from seed germination onwards to flowering. Our objectives are to compare the selection techniques which have accomplished these goals: time (week) of seed germination, rate of subsequent growth, contractile root formation (corm and bulb crops), leaf number, leaf unfolding rates, stem elongation, stem and inflorescence height, internode number and length, propagule formation (size, weight), visible bud date and flowering, and flower number. Germinating seedlings were tooth picked each week with a different color each week to designate germination weeks (G1 for week 1, etc.) which enabled selecting and transplanting only the earliest germinators/generation. In most crops (Gladiolus, Iris, Chrysanthemum), seed germination during weeks 2-4 after sowing (G2-G4) was highly correlated with visible bud dates and flowering, even if early generations flowered after Year 1. In Lilium, however, G1-G2 seedlings had earlier flowering than those in G3-G8. Incorporation of these techniques along with fast cycling within geophytic breeding programs can enhance the rate of progress made per generation, particularly when the annual cycle is reduced to 3-4 months instead of 12. Comparative analyses of traits within and among each crop allows for creating crop-specific strategies to reduce generation time and maximize gain from selection.