Study On Genetic Diversity And Physiological Mechanism Of High Photosynthetic Efficiency Of Sweet Sorghum Germplasms

Genetic diversity about phenotypic and DNA level and photosynthetic physiological characteristics,physiological mechanism of high photosynthetic efficiency were studied for72Sweet Sorghumgermplasms in this paper, in order to provide theoretical foundation and reference indexs for sweetsorghum breeding and cultivation physiology. The main results were as follows:1. Phenotypic characters analysis showed that genetic diversity indexes（1.6333） is the highest for graincolor among14qualitative character; the lowest one was for in leaf color of seedling and seed settingform, the average diversity indexes is0.7460. The quantitative character such as main panicle length,stem diameter, brix, grain weight per spike, stem juice extraction,1000grain weight, plant height, panicleweight and whole growth period had greater coefficient of variability, range from7.85％to53.01％, allquantitative character tested showed great diversity indexes, ranging from1.7331to2.1383with an averageof2.0061, which showed this collection of sweet sorghum germplasm had great genetic diversity. Clusteranalysis showed that all72germplasms were divided into4groups. correlation analysis result showed thatplant height, strong stem, more internode numbers and high brix and appropriate growth period which thesecharacters should be emphasis choosen, and grain characters and yield needn’t more attention duringbreeding sweet sorghum varieties.2. A total of20SSR primers from50SSR primers performed polymorphism and91alleles loci weredetected. The average number of alleles per SSR was3.45with a range from2to5. The value of allelicpolymorphic information content （PIC） ranged from0.2859to0.6652, on an average of0.5057per SSRmarker. The genetic similarity coefficient ranged from0.2001to1.000with a average of0.5599. Thecluster analysis grouped the72sweet sorghum cultivars and lines into2main groups. Group A included69accessions and group B included only3accessions. Group A was again sub-divided into sub-groups Ithrough XI. The accessions of sweet sorghum with similar agronomic trait was mostly clustered one group.3. The biological yield was highly significant correlated with net photosynthetic rate （Pn）（R=0.933）, andsignificant correlated with PEP and LAI（R=0.775,0.743）, there was no significant correlation with othercharacters. Brix was significant correlated with Pn, Tr, PEP and LAI（R=0.685,0.679,0.747,0.691）, therewas no significant correlation with other characters.Kernel yield had no significant correlation with allcharacters.“LT05”,“LT02”,“Xingaoliang No.3”,“MN-94” was high biological yield, high brix and highphotosynthetic efficiency of Sweet Sorghum Strain. The Pn could be effectively used as a selection indexfor high photosynthetic efficiency Sweet Sorghum breeding.4. There was significant difference in Pn, transpiration rate（Tr）, cond（Gs）, Intercellular CO2concentration（Ci）, Coefficient of variance was30.47%,29.98%,39.86%,66.21%respectively. correlation analysis indicated that biological yield was highly significant correlated with Pn, Gs, and significantcorrelated with Tr. There were mainly higher Chlorophyll A（Chla）, Chlorophyll B（Chlb）, Chl, Nitrogencontent（LNCa）, Total protein content（TP）, PEP, LAI in Early, middle, late high photosynthetic efficiencystrain. These sweet sorghum strain had great photosynthetic diversity. Besides Pn continue as selectionindex for high photosynthetic efficiency Sweet Sorghum breeding, Gs, Tr, Chl, Chla, Chlb, PEP, LNCa, TPbe used as a effectively selection index.5. The curves of diurnal variation of Pn of XinGaoLiang No.3and TLF-1had two peaks and an obviousmidday depression, Pn of XinGaoLiang No.3higher TLF-1, it had shorter depression; The control factorsof Pn had different in different time, the variation of Pn was mainly induced by non-stomatal factors in a.m.,but by stomatal factors in p.m. There were significant correlation in RH, Tleaf, Tr, Gs, Ci with Pn. It was animportant cause of that XinGaoLiang No.3had shorter photosynthetic midday depression and netphotosynthetic rate in postulation period, so its stalk sugar content higher TLF-1．6.The curve of the variation of Pn was “parabla” in the stage of growth of XinGaoLiang No.3, Itreached peak value in heading period. The direct influence order was ambient CO₂concentration （Ca）>photosynthetical active radiation（PAR）>Ci. Ca and PAR were direct ecological factors, Ci wasphysiological restrainable factor, It influenced the change of Gs andTr, thereby to Pn.7. The average value of Pn, Tr, Gs, Ci, water use efficiency （WUE） and SPAD value（SPAD） insaline-alkaline land were very significantly inferiored to control land, the difference of late growth periodturned out bigger. The biological yield of XinGaoLiang No.3and XinGaoLiang No.9was inferiored to57.8%and76.5%respectively, the sugar brix was inferiored to38.5%and100.0%respectively of twosweet sorghum varieties in saline-alkaline land. Pn was highly significant correlated with PAR, Ta, Ca insaline-alkaline land. In the post the main limiting factors is non-stomata. Salt tolerance ability of“Xingaoliang No.3” higher “Xingaoliang No.9”. In order to develop sweet sorghum in saline-alkaline land,It was primary to choose salt tolerance sweet sorghum variety, secondly, the economic benefits, ecologicalbenefits, land qulity must been considered.