Study On Reproductive And Ecological Characteristics Of Hemarthria Compressa Cv. Guangyi

Whipgrass(Hemarthria compressa(L.f.) R.Br.) is a perennial tropical grass with rhizomes and stolons of the family Poaceae,mostly distributed in tropical,subtropical and temperatural areas.Two varieties,'Guangyi' and 'Chonggao',play important roles in the husbandry industry and ecological reconstruction in the south china,due to its special agronomic characteristics such as long-term use,fast growth rate,high yields,wide adaptabilities and stand hardness stresses.But the main disadvantage of wihpgrass is its low sexual reproductivity,which means it can not produce seeds,just propagated in vegetative way.So explore the reason of low fecundity is important.The objective of the study was to find the reason of low fecundity of the 'Guangyi' from several aspects,such as pollination biology,breeding system,embryo,and reproductive allocation.Through two years study,the main results are as follows.The pollen viability of 'Guangyi' was detected by methods of iodine-iodide kalium, triphenyltet razolium chloride(TTC),and oxide-enzyme method.The results showed that the method of TTC was suitable for detection of pollen viability of H.compressa and qualitative analysis.Checked the pollen germination of 'Guangyi' by using TTC under different temperature conditions,the pollen viability lost quickly in high temperature(40℃) condition,lower temperature could not keep the viability for a long time,but could delayed the viability loss,that means lower temperature could be the sufficient way to keep the pollen viability of H.compressa.Pollen germination rate was checked by pollen germination in vitro showed that the pollen viability was 65.67%when temperature was 27℃,much lower than other grasses, and the life-span was no more than 4 hours.Environmental factors were related to the stigma receptivity H.compressa,there was significant difference(p＜0.01) for the plant stigma receptivity between the greenhouse (average temperature was 27℃,average relative humidity was 65%) and the field(average temperature was 25℃,average relative humidity was 75.9%) conditions.The stigma receptivity was 1-5 days and 1-3days after blooming in the greenhouse and in the field, respectively.'Guanyi' belong to the reproduction system of oligate xenogamy.It could not produce seed by self-pollination.The pollen-ovule ratio was 87465/1.The flowering period of 'Guangyi' was from July to August.There had two stages to flower during one day,that was 6:00-8:00 am and 15:30-19:00 pm,among them,from 16:00-18:00 pm,the pollen grains collected was highest in the study.Wind speed affected the distances of the pollen grains distributions.When the wind speed was 0 to 1-5,or 12-19 km/h respectively,the pollen grains distributed within the circle of 5m,or 21m from the pollen grain originate place,respectively.In the areas of pollen covered,the plant stands comes from the same mother plant,so the cross-pollination in the same plant stand was common.The dilemma between the pollen distribution characteristics and reproduction system of 'Guangyi' was one of the reasons of lower seed-rate.The megasporogenesis and female gametophyte of 'Guangyi' didn't have genital obstacle in their development,but the aborted ratio was little bit high in the development of microspore and male gametophyte.The archesporial cell originated from a single cell and developed directly into megaspore mother cell.The dyad was formed after the first division,and meiosisⅡ,resulting in a linear tetrad.The development of the female gametophyte conformed to the Polygonum type.The meiosis of the microspore mother cell was of the successive type and decussate tetrads were formed.The maturate pollen grains contained 3 cells a large vegetative cell and two sperms.The maturate anther wall had four layers,from outside to inner side were epidermis,endothecium,middle lamella,and tapetum.The tapetum is secretery type.After checking,the aborted rate of microspore mother cell in meiosisⅠwas 5.7%,10%of the tapetum collapse advance caused abort.The allocation of the biomass in 'Guangyi' was exceeding inequality.In the process of sexual growth,vegetative modules and rhizomes had absolute predominant position,and the biomass for the ears contented less than 3%of total biomass.The low investment in sexual reproduction of H.compressa was the main reason for its low seed production.There were others reasons limited the seed set of H.compressa,but we still not known. There need further research on the process of fertilization,embryogenesis,seed formation and environmental influence etc.,to explore the secret of no-seed of 'Guangyi'.After know the real reason which cause no-seed,use some new high-techs to improve the seed set,at the same time,control the diseases and insect pests were also important.