| As Faboideae plants, Medicago sativa, Coronilla varia and Lotus cornioulatous are important leguminous forages, which are typical allogamy and their seed production mainly depends on the pollinators. In this paper, the functional groups of pollinator and seeding characteristics of these leguminous forages were studied in Hexi corridor, Northwest China. The results are as below:1. From 2011-2012, insects visted M. sativa, C. varia and L. cornioulatous were investigated. The results showed that there were 22 kinds of diptera, belonging to 4 orders and 11 families, respectively. According to the frequency of these insects, Megachile abluta, Megachile spissula, Xylocopa valga, Andrena parvula and Anthophora melanognatha were principle pollinators of alfalfa. Apis sinensis, Melitta sinensis, Bombus agrorum, Megachile abluta, Megachile spissula, Xylocopa valga and Anthophora melanognatha were principle pollinators of C. varia. And Anthidium florentinum, Apis sinensis, Megachile abluta, Andrena parvula, Anthophora melanognatha were principle pollinators of L. cornioulatous. The diurnal foraging activities of these nine principle pollinators exhibited two visiting peaks at 10:00-12:00 and 16:00-18:00, respectively. Such visiting dynamics fitted optimal pollination time and dynamic of flowers among three forage crops. The results above indicated a complementary relationship among these principle foragers. The number of pollen carried, visiting frequency and landing times of these visitors were correlated with their body sizes. These forage crops shared some pollinators, which were belong to general pollination system.2. The rate of podding and seeding were investigated during different flowering stages (early flowering, full-blossom and late flowering) of three leguminous forages. There were significant differences (p<0.01) of podding rates but no difference of seeding rates. And the rate of podding of full-bloom stage of M. sativa, C. varia and L. cornioulatous were 58.68%,77.05% and 58.15% respectively, which was significantly higher than those of early and late flowering stages. Furthermore, the rate of podding was positively correlated with number of pollinators, which increased 8.85% as 100 pollinators increased. However, there was no correlation between rate of seed set and pollinators. Under self-pollination and cross-pollination conditions, podding rate were significantly lower than those under open pollination (p<0.01), which indicated that the number of pollinators were positively correlated with podding rate, while seeding rate is no correlation with them. The index of self-compatibility of M. sativa was the lowest (0.50), while C. varia and L. cornioulatous were 1.04 and 1.52. The relative reproductive success is RRSC. varia (0.14)> RRSL. comioulatous (0.09)> RRSM. sativa (0.06). The results suggested that lower compatibility was much limited by pollen resources.3. The pollen tube growth and embryonic development were observed in M. sativa, C. varia and L. cornioulatous. The results showed that 1) In M. sativa, pollen grains germinated 2h after pollination and pollen tube reached the ovary after 8h. The rate of ovule fertilization was up to 75% and remained unchanged 24h after pollination. Forty-eight hours after pollination, pollen tubes were still observed to grow to the ovary.2) In the case of C. varia and L. cornioulatous, pollen tubes reached the ovule and the percentage of ovule fertilization was up to 89%. Eight hours after pollination, the percentage of ovule fertilization reached 96%-100%. These results indicated that number of pollen tubes could meet the demand of double fertilization in M. sativa, C. varia and L. cornioulatous. The percentage of seed abortion in M. sativa, C. varia and L. cornioulatous were higher as 87.67%,78.00% and 81.33%, respectively. And random abortive position of seed in one pod was also observed. Furthermore, fluorescence observation of callose deposition on the ovule confirmed the randomness of female sterility happened in three leguminous forages.The results showed that the pollination insect species are abundant in Hexi corridor, but seeding rate is still lower. The paper indicates that the the number of pollinators decide to pod, while seeding rate is not different, there are enough pollen counts with pollinators in natural condition and it can meet the demand of the three plants, so pollen counts is not main reason to limit to seed, while it is correlated with the genetic characteristic. The study provided an important basis theory for futher to study the genetic characteristic of the leguminous plants and to improve the seed yield.In conclusion, the number of pollinators is enough for these leguminous forages in Hexi corridor. And numbers of pollen grain loaded on the stigma is not limited factors for seed set in three leguminous forages. Low seeding rate was mainly due to the ovule abortive, it was a mechanism to adapt to the environment, which was decided by its genetic characteristics. |
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