The Floral Biology, Breeding System, and Interspecific Hybridization of Salvia spp.
Date Issued
2015
Date
2015
Author(s)
Hsu, Chun-Yi
Abstract
Salvia L. is a large genus comprised of 900 species of annual, biennial, or perennial herbs, or shrubs. Although about 140 species are in cultivation, only a few salvias are commonly found in commerce and gardens. Interspecific hybridization could contribute more Salvia cultivars. Salvia coccinea Juss. ex Murr., yellow-flowered Taiwan-endemic S. nipponica Miq. var. formosana (Hayata) Kudo, S. patens Cav., and S. splendens Sell. ex Roem. & Schult were collected and studied. The objectives of the study were to determine the floral structure, pollination system, in vitro pollen germination, and hybridization crossability. Pollen tube and nutlet growth were observed after self- or interspecific pollination. Interspecific hybrids of S. coccinea × S. splendens were obtained, and progeny traits were investigated. Observation revealed that S. coccinea ‘Snow Nymph’ had homostylic flowers and immovable stamens. Salvia nipponica var. formosana had typical lever-like stamens, with fertile theca concealed in the upper lip and the sterile lower connective arm restricted access to nectar. Salvia splendens ‘Vista Red’ had pin and homostylic flowers and immovable stamens. Salvia coccinea ‘Snow Nymph’ and S. splendens ‘Vista Red’ could set seeds without pollinators, while S. nipponica var. formosana must require pollinators for pollination. All these three salvias were self-compatible. Supplement of sucrose and polyethylene glycol-3350 (PEG) in the modified Brewbaker and Kwack medium with 0.1% casein hydrolysate could improve pollen germination and tube growth of Salvia. Highest pollen germination was recorded in medium containing 5%-10% sucrose + 30% PEG for S. coccinea ‘Snow Nymph’, 10% sucrose + 20% PEG for S. nipponica var. formosana, 0% or 10% sucrose + 20% PEG for S. splendens ‘Vista Red’. However, pollen of ‘Vista White’ germinated well with media containing 0%-15% sucrose + 30% PEG or 10% sucrose + 20% PEG. The optimum osmotic potential for pollen germination ranged from -2.45 to -1.42 MPa. In these three salvias investigated, sucrose benefited but was not necessary for pollen germination. Effect of flower age on pollen germination rate was measured with medium containing 10% sucrose + 20% PEG. In both S. coccinea ‘Snow Nymph’ and S. splendens ‘Vista White’, pollen had the highest germination rate at 1 day after anthesis. In S. nipponica var. formosana, pollen had the highest germination rate at anthesis. Highest germination rate of S. splendens ‘Vista Red’ was obtained at 1 and 2 d after anthesis. Stigma had became receptive at anthesis in S. coccinea ‘Snow Nymph’, S. nipponica var. formosana, and S. splendens ‘Vista Red’, indicating these plants were not protandrous. Among all cross combination tested in this study, pollen tubes were observed in the style base at 1 d after pollination when S. coccinea ‘Snow Nymph’, S. nipponica var. formosana, or S. splendens ‘Vista Red’ were crossed with S. coccinea ‘Snow Nymph’, S. nipponica var. formosana, S. patens ‘Blue Angel’, or S. splendens ‘Vista Red, respectively. Pollen tubes of S. coccinea ‘Snow Nymph’ were arrested on stigma of S. nipponica var. formosana. Pollen tubes of S. patens ‘Blue Angel’ were not observed in style base of S. nipponica var. formosana until 2 d after pollination. Mature seeds were obtained only when S. coccinea ‘Coral Nymph’ or ‘Snow Nymph’ as female parents crossed with S. splendens ‘Vista Red’ or ‘Vista White’. Nutlets did not enlarge when S. nipponica var. formosana was crossed with S. patens ‘Blue Angel’ or S. splendens ‘Vista Red’. In most cross combinations, hybrid nutlets showed only partial development indicating that post-fertilization barriers existed. The megagametophyte of S. nipponica var. formosana was, but those of S. splendens and S. coccinea were not, surrounded by a differentiated integumental cell layer. Selfed-embryo and endosperm of S. nipponica var. formosana developed slower than S. splendens and S. coccinea. Most hybrid embryo and endosperm aborted and resulted in basal shrinking and/or browning nutlet at 8-16 d after pollination. Nearly-mature embryo was obtained in S. coccinea ‘Coral Nymph’ or ‘Snow Nymph’ as female parent crossed with S. splendens ‘Vista Red’. Embryo reached globular to early-heart stage in S. coccinea ‘Coral Nymph’ or ‘Snow Nymph’ as female parent crossed with S. nipponica var. formosana. Embryo most reached torpedo stage in S. splendens ‘Vista Red’ crossed with S. coccinea ‘Coral Nymph’ or ‘Snow Nymph’. In contrast, embryo and endosperm aborted 4 d after pollination when S. splendens ‘Vista Red’ crossed with S. nipponica var. formosana. Hybrid weakness was observed in S. coccinea × S. splendens progenies. In this study, only progenies of S. coccinea ‘Snow Nymph’ × S. splendens ‘Vista Red’ and S. coccinea ‘Snow Nymph’ × S. splendens ‘Vista White’ grew and flowered. Both hybrid progenies had new plant and inflorescence appearance. Most flower characteristic traits of both hybrid progenies were between two parents. The selected progenies had more nodal florets than S. splendens. Both hybrid progenies had green with gray-orange, red or purple calyx and orange-red corolla. Corolla had white blotch in progenies of S. coccinea ‘Snow Nymph’ × S. splendens ‘Vista White’. Both hybrid progenies had pollen polymorphism with low fertility and could not set seed after self-pollination or backcross with both parents.
Subjects
crossability
embryo development
pollen
pollination mechanism
polyethylene glycol (PEG)
Type
thesis
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