Study On The Reproductive Biology Of The Desert Plant Peganum Harmala

In this study,we explored the flower characteristics,phenology,heterostyly,breeding system,the number and the type of main pollinators,and the main factors influencing the pollination of the desert plant Peganum harmala using field observation and experimentation,aiming to reveal its reproductive biological characteristics and ecological adaptation strategies.The main results of this study were as follows:1.Peganum harmala produced single flowers,which were white when bloom.The flower season of the population was from mid-May to late-July(about 80 d),and the peak flowering period last for 19 d;The flower season of single flower last 2-3 d.The 15 anthers dehisced gradually,which indicated that it was of dichogamy;Pollen viability and stigma receptivity at different flowering stages and on the day of flowering were of synchronism.The flowering order of the plant was from bottom to top.Five nectaries appeared at the base of the ovary.These characteristics greatly enhanced male function and prolonged the male stage of the flower,so that the plant had long-lasting pollen dispersal and the ability to attract pollinators,reducing the risk of pollination failure due to high temperature and drought.2.There were heterotype styles in P.harmala.The long-style flowers("L" type)were the majority in the population,and the short-style flowers("S" type)occupied only a small proportion.There were differences between the two kinds of flowers.Compared with the flower characteristics of the "S" type,the corolla of the "L" type was slightly larger,stamens of the "L" type were longer.The stamen of the "L" type was equal to or slightly higher than the stigma,but the stamen of the "S" type was significantly higher than stigma with a range of more than 3 mm;The color of the stigma of the "L" type was green,and the surface depression was deep;the color of the stigma of the "S" type was yellowish green,and the surface depression was slightly shallow.The ovary size of the "L" type flower was bigger than that of the "S" type,and the color of the "L" type flower was darker.The micromorphology of pollen grains and stigma of the two types of flowers was different.The germination ditch of pollen grains of the "L" type flowers was wider than that of the "S" type flowers.The stigma was in the shape of triangular,with fine fluff on the three edges.The stigma surface of the "L" type was rougher than that of the "S" type.Field surveys also found that the stigma of some flowers was extremely short and tended to degenerate.It is preliminarily speculated that the pistil of some flowers had gradually degenerated,and the flower developed into male flowers.3.Herkogamy was found in P.harmala with a range of 0.067 ± 0.0047 cm.The outcrossing index was 5.According to Dafni,the breeding system was out-crossing and self-compatible,sometimes demanding for pollinators.Pollen and ovule ratio was 15443.9 ±1407.051,and its breeding system was obligate xenogamy according to Cruden.The results showed that the seed set rate of the cross pollination was the highest(92.5%),and the seed set rate of the artificial self-pollination and natural pollination reached more than 80%.The analysis showed that P.harmala applied a mixed mating model of self-mating and cross-breeding to guarantee the reproduction.Apomixis did not exist in the plant.4.The main pollinating insects of P.harmala was Hymenoptera.The effective pollinating insects included Apis mellifera,Megachile sp.,Melittidae and Scolia sp.Each of them had a variety of behaviors,and they had significant difference in the proportion of insects carrying powder,the visiting frequency and the stay time.In the desert environment,the temperature was the main factor influencing the pollination of P.harmala,and the temperature changes in one day determined the variations of the pollen vitality,stigma receptivity,the number of pollinating insects,and the nectar amount.There was a significant positive correlation between the nectar amount and the number of pollinating insects in one day.The results showed that 12:00 and 18:00 were the best time for the pollination of the insects,when the temperature was suitable for insects' activity,and the nectar amount was also abundant.In addition,the high temperature triggered the closure of the corolla,to avoid the pollen grain inactivation caused by high temperature.Corolla closure,delayed flowering,and the decrease in the number of pollinating insects caused by the cold rainy weather,were the results of the plant adapting to climate and pollinating insects.In conclusion,P.harmala flowers have heterostyly and gradual anther dehiscence,with a mixed breeding system of selfing and outcrossing.The outcrossing depends on pollinators,and temperature is an important factor affecting successful pollination.Heterostyly indicates that the pistil has degenerated,which may lead to andromonoecy.