| Sweet sorghum, as C4 crop, having a rapid growth rate and more significant yield potential, is known as"high energy crop". Developing sweet sorghum is significant in maintaining the safety of energy, food and environment in consideration of the exploitation of bio-energy made from the resource of no-maple food nowadays. There is a great source of sweet sorghums in China, while the study on its physiological characteristics related to is relative few and late. Our research is aimed to reveal the difference of biological characteristics of different sugar yield potential types of sweet sorghum, so as to provide some theory for the breeding and cultivation of sweet sorghum in obtaining high sugar yield. The experiment was conducted at the maize Sci-tech zone of Shandong Agricultural in 2006 and in 2007. In order to illustrate the genotype differences and the correlation ship between sugar yield and the plant agronomic traits, characteristics of DM accumulation and partition, as well as the differences in nitrogen and phosphorus accumulation and utilization, 30 conventional sweet sorghum varieties with wide genetic backgrounds collected from both domestic and abroad are grown in field experiment respectively, under a lower density (15 000 plant·ha-1) condition in order to optimize the plant growth development. The main results were as followed:1,There were significantly differences in soluble sugar content and the sugar yield potential per plant with the 30 sweet sorghum varieties under experiment. The average sugar content was 35.39%, the variation coefficient (CV) in sugar yield per plant was 81.65%, which was larger that of sugar content. The average sugar yield was 219.54g·plant-1. The ratio for number of high SY varieties to total number was only 26.7%, showing a large improvement space in high yield breeding of sweet sorghum. Among the Cultivars under experiment Rio,M81E,Honey,Smith,Roma,Ramada and Cowley performed better either in sugar content or sugar yield, and in lodging resistance and anti-insect and diseases compared to other Cultivars.2,The differences in the main agronomic traits of plant were remarkable among the tested cultivars. High-yielding sweet sorghum cultivars had a tall plant height, especially in the main stem height, larger numbers of nodes and tillers, more green leaves at maturity, and a higher value in leaf thickness, leaf stay-green and the whole period duration, while the variation in the length of panicle and peduncle were little. Therefore, by improving the main stem length and stem diameter, strengthening the capacity in leaf carbohydrate producing, meanwhile selecting those Cultivars with longer growth period according to the local phonological period, decrease the peduncle length so as to improve the plant lodging resistance are important for acquiring high biomass output.3,There were great differences in characteristics of DM accumulation and distribution of the tested Cultivars. In Cultivars with high SY productivity, the whole plant and all the parts of the plant, stalk, leaf, sheath and panicle, showed relatively high DM productivity. With regard to the DM distribution ratio of various organs, the higher SY type tend to have a larger ratio of stalk DM weight to whole plant, while a smaller ratio of panicle DM weight both at heading and maturing stages, the ratio of leaf or sheath DM weight was almost similar at maturing stage, though it is significantly lower at heading stage. Thus sweet sorghum with high SY productivity are characterized with strong DM productivity, especially in enlarging the leaf source, meanwhile, the DM partitioned to stalk sink increased but those partitioned to panicle sink decreased significantly, so the nutrient requirement between the two sinks: stalk and panicle remained a relative balance so as to acquired a high biomass and high SY.4,There were significantly differences in characteristics of accumulation and production efficiencies within nitrogen (N) and phosphorus (P) with the tested 30 sweet sorghum varieties. The CV in both N content and total N accumulation (TNA) were 14.78% and 50.27%, respectively, while the CV in both P content and total P accumulation (TPA) were 17.88% and 38.99%, respectively. The high SY type maintained lower level in either N or P content; however, both the TNA and TPA were significantly larger than the other two types. The deviation in both N DM production efficiency (NDMPE) and N sugar yield production efficiency (NSYPE) were also obvious, and the CV were 15.48% and 47.24%, respectively, while the deviation in both P DM production efficiency (PDMPE) and P sugar yield production efficiency (PSYPE) were 19.90% and 49.98%, respectively. The high SY type usually had a high value in either N or P production efficiency.In Cultivars with higher SY, more nitrogen distributed in stalk, leaf than in panicle, while the nitrogen level in both stalk and leaf were lower than those low-SY type and mediate-SY type. The nitrogen content in either stalk or leaf and sheath was significantly lower in high-SY type as compared with the low and mediate types, but for nitrogen content of panicle the high-SY type was higher than the mediate one, with nearly equivalent to that of the low-SY type. As far as the nitrogen distribution was concerned, it was that stalk was prior to leaf and sheath, with panicle took the least participation in nitrogen accumulation. Results by both correlation analysis and path analyses indicated that the correlation coefficient between SY and DM accumulation, nitrogen productivity efficiency for SY was significantly positive; further these two items exerted direct effect on SY, however, the nitrogen content of whole plant behaved in a contrary direction, i.e., the higher nitrogen content the lower SY obtained. The difference in phosphorus distribution and content of various organs and the correlation analysis and path analysis with SY had a similar trend with nitrogen mentioned above. Increased ability of absorption in both nitrogen and phosphorus meanwhile, while sustaining relative low plant nitrogen and phosphorus level as well as high productivity efficiency for sugar yield are all the primary characteristics of sweet sorghum varieties for producing high sugar yield.5,Plants with all tillers increased total sugar yield significantly in our experiment compared to the ones with all tiller removed at either the optimum cultivating density (75000 plant·ha-1) or lower plan density (37500 plant·ha-1). That could be ascribed to the remarkable incensement of stalk biomass of the tillers, which could compensate the decrease of main stem at some extent compared to the single plant without tillers, so the additive biomass by both main stalk and tiller overweight the one with single stalk. Meanwhile sugar content in the stalk between tiller and main stem is roughly the same at the higher density compared to that of the single stalk. The sugar content in the main stem deceased significantly than that of single stalk at lower density, but the sugar content in the tillers approached or even exceeded that of single stalk. Anyway the sugar yield gained by remaining tillers could enhance the mass sugar productivity at some extent in contrast to that gained by the single stalk. |
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