Systematic Study And Seed Dormancy And Germination Characters Of Iris Spieces In Sichuan

Iris L. is a large genus in Iridaceae and involves about 300 species in the world. Because of its beautiful and specially shaped, it is preferable in viewing and admiring as garden plants. Species of Iris are herbs perennial and distributing in the north temperate regions (Goldblatt 1990). There are 60 species,13 varieties, and 5 forms in China, which is a distribution center of Iris (Zhao 1985). The taxonomic status of Iris species are still under discussion today. The main dispute is focus on:(1) the interspecific relationships of I. lactea Pall.and I. lactea var. chinensis (Fisch) Koidz.. Based on their geographical and morphological differences, Zhao (1985) treated I. lactea var. chinensis as a variety of I. lactea. But, Gao (1985) suggested that I. lactea var. chinensis should be a homonymy of I. lactea, not a variety of I. lactea. (2) the relationship among I. sichuanensis Y. T. Zhao, I. leptophylla Lingelsh.and I. goniocarpa Baker. Their morphological characteristics, except the size of leaf, are similar to each other. The taxonomic classification of these three species is always mixed up. Based on the size of leaf, Zhao (1985) suggested that I. sichuanensis and I. leptophylla should be two independent species. However, according to the similar flower and geographic distribution of I. sichuanensis and I. leptophylla, Gao (1985) suggested that I. sichuanensis should be a homonymy of I. leptophylla. (3) the relationship among I. japonica Thunb.,I. confusa Sealy andI. wattii Baker. Zhao (1980) reported that the flowers and fruits of I. confusa were similar to those of I. japonica, while the vegetative parts of I. confusa were similar to those of I. wattii. Waddick (1994) suggested that I. japonica and I. confusa may be the variants of a same species. The relationship between I. confusa and I. wattii were still uncertain (Waddick and Zhao 1992). In order to investigate the relationships of I. lactea, I. lactea var. chinensis; I. sichuanensis, I. leptophylla, I. goniocarpa, I. japonica, I. confusa and I. wattii, morphology, cytology, pollen morphology, and nrDNA internal transcribed spacer (ITS) sequences analysis were used in this study. The stigma receptivity, seed dormancy and germinaton characters of Iris species were also investigated in this study for provide some new theory evidence with propagation and breeding for Iris genus. The main results are as follows:1. A cladistic analysis based on 27 morphologic characters of 7 taxa and 1 variety in Iris species was presented. Maximum parsimony analysis of the aligned sequences yielded 4 maximally parsimonious trees. The results indicated that:(1)I. lactea was closely related to I. lactea var. chinensis; (2)I. sichuanensis was related to I. leptophylla than that to I. goniocarpa; (3) I. japonica had a more close relationship with I. wattii than that with I. confusa.2. Karyotype analysis of 9 taxa and 1 variety in the genus Iris were investigated in this study. The karyotypes of I. sichuanensis, I. leptophylla, I. goniocarpa, I. lactea, I. confusa and I. germanica were reported firstly in this study. The karyotype formulate were: I. sichuanensis,2n=26=12m(4SAT)+12sm(2SAT)+2st;I. leptophylla,2n=26=14m(2SAT) +10sm(4SAT)+2st;I. goniocarpa,2n=26=12m+12sm+2st(2SAT).I. lactea,2n=40= 28m+10sm+2st;I. confusa,2n=32=8m+18sm+6st;I. germanica,2n=40=16m+20sm+4st. The karyotypes of I. chrysographes, I. tectorum and I. lactea var. chinensis were also carried out. I. chrysographes,2n=40=18m+22sm(2SAT); I. tectorum,2n=28=16m +12sm+6st(6SAT);I. lactea var. chinensis,2n=40=18m+16sm+6st(6SAT). The results showed as follows:(1)I. wattii, I. confusa and I.japonica are three independent species; (2) I. sichuanensis, I. leptophylla and I. goniocarpa are three independent species with close relationships; (3) it is reasonable to treat I. lactea var. chinensis as a variety of I. lactea.3. Pollen morphologies of 11 taxa and 1 variety in Iris were investigated under scanning electron microscope. The results showed that (1) except the width of spine, the shape and size of pollen grains, shape of aperture, extine sculpture of I. lactea and I. lactea var. chinensis were similar. (2) the shape of pollen grains, extine sculpture and width of spine of I. leptophylla, I. sichuanensis and I. goniocarpa were highly approximate and no aperture was found among the three species. The pollen grain of I. goniocarpa was smaller than those of I. leptophylla and I. sichuanensis. (3) pollen of I. japonica and I. confusa had similar size and shape, and no grains existed in the meshes of these two species. The shape of pollen grains in I. japonica was suboblate while that in I. confusa was subspheroidal. (4) I. wattii was distinctly different from I. japonica and I. confusa in pollen size and exine ornamentation, suggesting that I. wattii had relatively distant relationship with I. japonica and I. confusa. We discussed briefly the pollen morphological characteristic and evolutionary trend of the five subgenus of Iris.4. To estimate the phylogenetic relationships of Iris species, nuclear ribosomal internal transcribed spacer (ITS) of 10 taxa and 1 variety were analyzed. I. lactea var. chinensis and I. lactea collected from one place were clustered in same clade. The other two species of I. lactea var. chinensis and I. lactea collected from different place were clustered in to two sub-clades. The result indicated that geography differentiation existed in I. lactea var. chinensis and I. lactea. I. leptophylla, I. sichuanensis and I. goniocarpa in one clade. Within this clade,I. leptophylla and I. sichuanensis were clustered in the same sub-clades. The results suggested that I. leptophylla have more close relationship with I. sichuanensis than that with I. goniocarpa. I. japonica and I. confusa were clustered in one clade, and I. wattii was single clustered in one clade. The recults suggested that the relationship of I. japonica and I. confusa were more closely than those with I. wattii.5. Pollen viability and stigma receptivity of 11 taxa and 1 variety of Iris were were estimated in this study. The results indicated that:(1) The best time of pollen viability was appeared in 12:00—14:00 and the best time of stigma receptivity was appeared in 10:00—14:00. (2) All of the anther and stigma colour could not show the pollen viability and stigma receptivity ability.6. Seed dormancy in four Iris species were carried out in this study. The results indicate that:(1) the 4 species of I. tectorum, I. lactea, I. confusa and I. chrysographes were not have physical dormancy; (2) all four Iris species were light sensitive seeds, a light requirement for I. lactea, I. confusa and I. chrysographes for seed germination were very necessary; (3) the seed coat had inhibitory effects on I. lactea, I. confusa and I. chrysographes, they all have physiological dormancy phenomena.7. Seed germination in four Iris species were carried out in this study. The results indicate that:(1) seed coat was the biggest resistance for seeds to germination in I. lactea, I. confusa and I. chrysographes. In I. tectorum endosperm was the biggest resistance for seed germination; (2) in I. tectorum seed coats had promoted effects on seed germination; (3)I. lactea and I. confusa adapted well to environment. The optimum substratum for I. tectorum seed germination was clay soils; (4) alternating temperatures 20/30℃were more suitable for I. lactea, I. confusa and I. chrysographes seeds germination; (5) 4℃stratification have no obvious effect for promote seed germination.