Studies were conducted on specific core collections constructed on the basis of different traits and sample size by the method of stepwise cluster with three sampling strategies based on genotypic values of cot-ton. A total of 21 traits (11 agronomy traits, 5 fiber traits and 5 seed traits) were used to construct main core collections. Specific core collections, as representative of the initial collection, were constructed by agrono-my, fiber or seed trait, respectively. As compared with the main core collection, specific core collections tended to have similar property for maintaining genetic diversity of agronomy, seed or fiber traits. Core collections developed by about sample size of 17% (P2=0.17) and 24% (P1=0.24) with three sampling strategies could be quite representative of the initial collection.

A genetic model with genotyp

A priming method called sand priming was developed using sand as a priming solid matrix in present experiment. Seeds were mixed with sands that contained 3.8% (v/w) water and sealed in plastic box and then were primed at 18℃ for 72h. Four varieties of rice were used to investigate the effect of sand priming on germination of direct-sown rice (Oryza sativa L.) in the laboratory. The results showed that the energy of germination, germination percentage, germination index and vigor index were improved in four varieties. Meanwhile, seedling height, root length, number of root and root dry weight were significantly higher than the nonprimed controls. Field experiments showed that the seed establishment and yield in sand primed seeds were significantly increased by 19.8%-22.9% and by 9.8%-31.2%, respectively as compared to soaked seeds without priming. It is indicated that sand priming method may help to improve seedling establishment in direct-sown rice and possible to be used in the field croo oroduction.

Seed germination and seedling development at different Pb concentrations in three rice varieties (Jiayu 293, Jiayu 948 and Xieyou 963) were investigted. The method of qualitative trait combining with quantitative trait by orthogonal polynomials was applied to analyze rice seed vigour by regression model. Seeds from different rice varieties showed different sensitivities to Pb poison, in the Pb concentration of 100--700mg/L, Pb had significant inhibitory effects on root length and shoot height, and the restraint would aggravate along with the increase of Pb concentration. However, Pb had no inhibitory effect on root dry weight and shoot dry weight, indicating that different physiological characteristics had different sensitive re-actions to Pb. The gained predicting equation of regression could predict the effects on rice seed vigour at different Pb concen-trations.