Cytology And Seed Biology Of Sorghum Halepense And Its Three Related Species

Sorghum halepense is one of the world's top ten vicious weeds, as second-class dangerous plant pests in China. S. almum, S. sudanense and S. bicolor are three relatives of S. halepense. It is difficult to identify them because of their morphological similiarity. In order to effectively distinguish them, we studied their cytology and seed biology. The main results are as follows:1. The seeds of Sorghum halepense, S. almum, S. bicolor and S. sudanense are very similar, especially for S. halepense and S. almum. It is difficult to identify by morphological appearance. Sorghum halepense and S. almum's caryopsis are relatively small, while those of S. bicolor and S. sudanense are relatively larger. Concerning the 1000-caryopsis Weight of the caryopsis, the largest is S. bicolor, secend is S.sudanense, and then are S.almum and Sorghum halepense, respectively.2. The effects on seed germinations of Sorghum halepense and S. almum by temperature are more significant than the other two crop species: S. bicolor and S. sudanense. The seeds of the two crop species germinate evenly. The seed germination of the weedy species S. halepense and S.almum was more sensitive to conditions, revealing their better adaptation to condition changes.3. Our observation on the karyotypes showed that the somatic chromosome number of S. sudanense, S. bicolor, S. halepense and S. almum are 2n = 20, 2n = 20, 2n = 40 and 2n = 40, respectively; their chromosome number X = 10, which coincided with the proviously reported chromosome base number of the genus sorghum plants X=10. The karyomorphology of these four species of the genus Sorghum were also studied. The karyotypes of S. halepense and S.almum were 2B and 1B, and both belong to asymmetric type, while those of S. bicolor and S. sudanense were 2A and 1A, respectively, and both belong to symmetrical karyotype.4. Our comparisons on the chromosomes, karyons, cells and mosis rates of these four species showed that the largest average hromosome projection area was S. sudanense, followed by S. bicolor and S.almum, S. halepense was the smallest; on the size of cells and karyons, the largest was S.sudanense, followed by S. bicolor, and then were S.almum and S.halepense, respectively. Under temperatures from 25℃to 35℃, the mosis rate of the apical meristematic zone cells of S. sudanense was the smallest, while that of S. halepense were the largest at various temperatures. The relationship among the chromosomes, karyons, cells, seed sizes and mosis rates in four plants supported the viewpoint that the plants with lower DNA C-values are of higher invasiveness.5. As a assistant method, the principal component analysis based on the seed ultraviolet spectra of these four species could be applied to identify the seeds of S. halepense and those of the other three related species.Based on the indices of seed biology, cytology and ultraviolet spectra, we could improve the preciseness in identification of the seeds of S. halepense and those of the other three relatives.