The Reproductive Biology And Potential Enemy Of Solanum Rostratum (Solanaceae) In Xinjiang

Solanum rostratum Dunal. is an annual weed with strong ability for invasion, and its style, which is deflected either to the left or right of the main floral axis, presents enantiostyly. This species exerts its influence on crops and pastures through competition for water, nutrients and light throughout the growing season. It is a nuisance due to the sharp spines which can stick to skin, hair and mucous membranes of livestock, and thus may lower the quality of their skin and hair. Leaves, berries and roots of S. rostratum contain cholinesterase inhibitory substances, which can cause livestock poisoning and even death. In addition, plant diseases and insect pests on the S. rostratum can also be spread. In this paper, the distribution of this species in Urumqi County, the characteristics of flowering phenology, breeding system, pollination ecology, reproductive allocation, fruit/seed-set and the potential enemies at two observation sites were observed and compared. The main results were as follows:1) The four populations of S. rostratum were found in Urumqi, Xinjiang and it distributed in open disturbed sites such as desert pastures of the 850-1160 meters elevation.2) The flowering amplitude curves at population, individual and inflorescence level were similar at two observation sites; the mean longevity of single flower in two floral morphs was almost identical; the floral morph ratios at plants and inflorescences levels approached 1:1. But there were considerably differences in the onset, peak of flowering date and duration time at population and individual levels, while the number of flowers and duration time at inflorescence level was different at two observation sties.3) Each flower containing 5 stamens, including 1 large pollinating stamen and 4 small feeding stamens. The large stamen was deflected opposite to the style, while the small stamens were not deflected. The stamens presented heteranthery because there were significant differences in the length and width of filament and anther between the large and small stamens. Large stamen had more pollen grains than each small stamen, while the total pollen grains and ovules in each flower were equal. The pollen longevity and stigma receptivity were just overlapped, the period of highest pollen vigor was just that of the strongest stigma receptivity. Dynamic curves of pollen viability of the large and small stamens in two morphs were similar. P/O value, bagging experiments, the observation of self-pollen germination on the stigma and the estimating of out-crossing index indicated that this species was self-compatible, but mainly out-crossing, so its breeding system belongs to facultative outcrossing.4) The pollination of S. rostratum was entomophily. Halictus quadricinctus Fab. was its main pollinator in Liuhuanggou population and presenting a low-high-low trend at different stages of peak flowering date, while Halictus sp. was main pollinator in experiment farm and presenting a gradually decline trend at different stages of peak flowering date. Furthermore, flowers of S. rostratum were also visited occasionally by No. 1 of Syrphidae and Xylocopa latipes Drury at two observation sites. Although H. quadricinctus was larger than Halictus sp., but the visiting behavior, visiting frequencies and activating times of two species were similar at two observation sties. The retention time of H. quadricinctus and Halictus sp. on plant were significantly correlated with the temperature and relative humidity in some time at two observation sites. 5) The plants favored to allocate a great proportion of resources to reproductive activities, and the reproductive allocation could reach to 44.56%, the large fruits (seeds) production ensured enough propagules for dispersal. Subglobose berry was enclosed by spiny calyces tightly and each fruit contained 8-68 seeds. Fruits and seeds of most plants break off from calyces during autumn, while some plants can break at the soil surface during autumn and berries and seeds could be dispersed by wind.6) There were various insect pests on the S. rostratum during the whole growth season, including Leptinotarsa decemlineata (Say), Mylabris axillavis Billberg and butterfly. L. decemlineata mostly gnawed the fresh and tender leaves, buds and opened flowers; M. axillavis mainly quickly gnawed the whole flower including corolla, pistil and stamens; larval of butterfly mainly damaged stamens and fresh fruits. So these insect pests may be the potential enemies of S. rostratum in Xinjiang.