Gladioli are herbaceous perennials with long, sword-like leaves and tall spikes of showy, colorful flowers. Numerous cultivars have been bred with extended vase life, floral novelty, or extended flowering periods. Recent focus has included transformation for potential creation of a genetically modified organism (GMO) cultivar. Most of the Gladiolus spp. are originally from South Africa, although they are widely distributed to as far north as Russia and into the Mediterranean. Winter-hardy species from Russia include G. imbricatus and G. palustris. It has been reported that several species are adaptable to cultivation. Modern G. hybrids are derived from S. African species. Modern gladioli are primarily grown as summer-growing cut flowers and tender annuals.
There are several environmental factors that affect the winter hardiness trait, including low temperatures, variable snow/ice cover, low light periods, and secondary invasion by pathogens. Winter hardiness is a necessary trait for herbaceous perennials growing in northern climates and is important for floriculture crops as well as consumers. Underground storage organs in geophytes, e.g., corms, bulbs, tubers, rhizomes, etc., allow herbaceous perennials to survive cold winters. The underground structure of perennial Gladiolus is a corm or fleshy storage stem from which shoots and roots grow. Gladiolus is a genus that has not been studied to any great extent in the area of winter hardiness. Most or all cultivars are ‘non-hardy’ in Minnesota and other northern latitudes.
Hence a group of researchers including Neil O. Anderson, Janelle Frick, Adnan Younis and Christopher Currey from University of Minnesota from various universities of USA (University of Minnesota, Arkansas and Purdue university) and Pakistan (University of Agriculture Faisalabad), carried out a research to investigate the Heritability of Cold Tolerance/Winter Hardiness in Gladiolus. There were three inter-related research objectives for this study. First, selected cultivars and selections of Gladiolus xgrandiflorus were to be tested to determine the range of cold tolerance at temperatures of 0°C to –10°C for all corm tissues and their subsequent regrowth potential. The second objective was to determine the nuclear DNA genetic variation (using intersimple sequence repeats, ISSRs) of the tested genotypes in comparison with wild species and other hybrids. Third, the heritability (h2) of cold tolerance was to be assessed in hybrids derived from crossing tested winter hardy and non-hardy parents.
The gladiolus breeding program at the University of Minnesota is part of a larger project in the Herbaceous Perennial Breeding Program to revolutionize geophytes. Gladiolus which are winter hardy or cold tolerant in USDA Zones 3-4 would allow this crop to overwinter in northern growing conditions and eliminate the need to dig the corms each fall and replant the subsequent spring. In recent years, due to the lack of adequate snow cover and cold temperatures the breeding program has had to supplement field overwintering over successive winters with laboratory freezing tests—a routine procedure widely used for woody and herbaceous perennial plants. Our studies with USDA Z4 winter hardy chrysanthemums and gaura have shown that herbaceous perennial crowns and root systems must tolerate temperatures of –10°C (Z4) or –12°C (Z3) to survive Minnesota winters. Most likely this is the case for gladiolus; although to the best of our knowledge, there have not been prior laboratory freezing tests of gladiolus corms for this purpose.
A range in response was found among tested gladiolus genotypes for tissue damage after laboratory freezing (Experiment 1). ‘King’s Gold’, for instance, was ‘non-hardy’ at 0°C to – 10°C (dead roots/shoots). ‘Great Lakes’ was intermediate with living root/shoot tissues at 0,-3°C only whereas ‘Lady Lucille’ had living roots (0 to -6°C) and apical meristems (-3°C). LT50s = -10°C for stem tissues in most genotypes; all were severely damaged or dead at -12°C. The apical meristem is more sensitive to freezing than roots, which are likewise more sensitive than stem tissue (corms) to freezing. The genetic variation (ISSRs) for the tested genotypes ranged across a wide spectrum of the gladiolus genome (Experiment 2); no correlation with ability of tissues to survive cold temperatures was found, except Sel’n. VT-03 (USDA Z3) and G. dahlenii. No transgressive hybrid segregants for corms occurred with greater hardiness than the parents (Experiment 3). In general, crosses with ≥1 hardy parent (hardy x hardy, non-hardy x hardy) had significantly greater numbers /lengths of living roots/shoots than non-hardy x non-hardy hybrids. In all crosses at -10°C, -12°C, no living roots, root initials, apical meristems occurred. Hybrids with ≥1 hardy parent had greater numbers / lengths of living roots and shoots than the non-hardy x non-hardygroup. The highest number of roots occurred in hardy x hardy crosses (at 0°C, -3°C) and non-hardy x hardy (-6°C); root lengths, in some cases, exceeded parental values. Root number is barely heritable for hardy x hardy hybrids but more so with non-hardy parents. Root length had a wider range of heritability. Heritability of corm ratings is likewise low. A significantly greater number of shoots in progeny (all crossing groups) than the parents were found at the 0°C, -3°C, and -6°C temperatures, although heritability remained low. While selected progeny are hardy to -6°C, this is not within the minimum range required for herbaceous perennial survival in USDA Z3-4. Further breeding and selection for increased cold tolerance would be required for gladiolus to reliably survive winter conditions in northern latitudes.
Neil O. Anderson, Janelle Frick, Adnan Younis and Christopher Currey (2012). Heritability of Cold Tolerance (Winter Hardiness) in Gladiolus xgrandiflorus, Plant Breeding, Ibrokhim Y. Abdurakhmonov (Ed.), ISBN: 978-953-307-932-5, InTech, Available from:http://www.intechopen.com/articles/show/title/heritability-of-cold-tolerance-winter-hardiness-in-gladiolus-xgrandiflorus