| Pennisetum longissimum var. intermedium is a new species of Pennisetumlongissimum, found and named by Chen Shouliang and Jin Yue in1984, is a perennialherbaceous plant of axial root type of Gramineae Pennisetum distributed in Yunnan,Sichuan, Guizhou, Hunan and Gansu province. Four new strains of Pennisetumlongissimum var. intermedium have been selected by Lanzhou Institute of Husbandryand Pharmaceutical Sciences of CAAS through introduction and domestication formany years, they have the characteristics of high yield, strong seed viability, easycultivation and disease resistance with average height of1.8m~1.9m, hay yieldreaching up to1.60×104kg/hm2and crude protein content exceeding18%. Thegrowth performance, phallic character, cytological features and stress resistance of thefour new strains of Pennisetum longissimum var. intermedium had been investigatedin this thesis. Meanwhile, the genetic diversity analysis of25wild strains fromYunnan and4new domesticated strains had been conducted in order to providescientific basis for development and utilization of germplasm resources of Pennisetumlongissimum var. intermedium and new variety selection. The main results are asfollows:(1) The blooming and pollinating performance of Pennisetum longissimum var.intermedium had been investigated among3early mature strains. It was shown thatthey mainly flowered from7:00am to11:00am with flowering peak occurring from8:00am to10:00am. The strain No.1started to bloom at7:00am and finished at11:00am; the blooming of strain No.2started at7:30am and ended at11:30am; thestrain No.3started at7:30am and finished at11:00am. The florescence of the strainNo.1, No.2and No.3were13d,20d and15d, respectively. There was only oneflowering peak for strain No.1and No.2with a “low-high-low” trend While twoflowering peaks were observed for strain No.3showing“low-high-low-sub-high-low” trait. The flowering of Pennisetum longissimum var. intermedium was not onlyregulated by its bioclock, but also influenced by temperature variations and humidity.The temperature of20℃to25℃was suitable for pollen germination. When relative humidity was high, pollen shedding was delayed or even no pollen shedding. Thepollen is nearly spherical or ellipsoidal. There was significant ruga on the surface ofpollen. The extine had graininess like fish scale. The average diameter, polar andequatorial axial length was47.1μm,45μm and52μm, respectively, with averagelength/width ratio of0.86. Moreover, the applications of blooming and pollinatingperformance of Pennisetum longissimum var. intermedium in crossbreeding and therelationship between pollen morphology and fructification percentage were alsodiscussed.(2) The statistics and karyotype analysis of chromosome of root tip cell of fournew strains of Pennisetum longissimum var. intermedium during mitosis metaphasewere conducted through root tip squash method. It was shown that Pennisetumlongissimum var. intermedium is tetraploid plant with basic chromosome number of9.The total number of chromosome of four new strains was36. The minisome atcentromere among congener were highly homologous. The karyotype formulae ofstrain No.1and No.3was2n=4x=36=17m+1sm. While the karyotype formulae ofNo.2was2n=4x=36=16m+2sm and2n=4x=36=18m (1SAT) for the strain No.4. Thekaryotype of four new strains was karyotype asymmetry belonged to Stebbins’1Btype with minor variation of index of karyotypic asymmetry. The strain No.1andNo.3had close genetic relationship with minor difference of karyotype, which wassignificantly different from the strain No.2and No.4.(3) The phenotypic diversity of25wild accessions from Yunnan and4domesticated cultivation accessions in Gansuof Pennisetum longissimum var.intermedium were analyzed based on16phenotypic traits in order to provide basicdata for selecting the related characters and excellent resources. The results showedthere were highlysignificantdifferences in phenotypic traits within29accessions(P＜0.01). Theaverage variation coefficient and the range of16phenotypic traitswere17.58%and0.31～51.60respectively, which showed there was relatively highervariation and discrete degree of morphological characters in the species. The principalcomponent analysis of phenotypic traits indicated the traits involving leaf length, spikelet length, spikelet width, peduncle length and internode length were the mainfactors account for phenotypic variations. The variation of seed traits such asgerminationpercentage and seed setting rate was lower, with stable genetic. Thecluster analysis showed29tested accessions were divided into3groups in general,each group included9,12and8accessions respectively. Geneticdifferentiation ofphenotypic traits wasn’t in accordance with geographical distribution, but mainly dueto the interaction of genetic and environmental factors. According to above results,the protectionmeasures of germplasm resources and the selection strategies ofbreeding parents for Pennisetum longissimum var. intermedium were presented.(4) The genetic diversity of the29accessions of Pennisetum longissimum var.intermedium from Gansu and Yunnan were analyzed by ISSR makers.10primerswere selected from50primers which had clear, stable polymorphic bands. A total of72loci were obtained, including62polymorphic loci, the percentage of polymorphicloci (PPL) was87.4%. The mean observed number of alleles (Na), effective numberof alleles (Ne), Shannon information index (I) and Nei’s genetic index (H) were1.8611,1.7428,0.5610and0.3959, respectively. The genetic similarity (GS)coefficient ranged from0.236to0.903, indicating enriched genetic diversity. Clusteranalysis with UPGMA method showed that the29tested accessions were divided into4groups at the level GS0.51, but there was no significant positive correlationbetween genetic and geographic distance among the germplasms studied. The resultof this research was the first time to reveal genetic diversity and variation ofP.longissimum var. intermedium at the molecular level, which provided theoreticaland data evidence for the introduction, domestication, conservation and exploitationof wild P. longissimum var. intermedium germplasm resources.(5) The physiological characteristics of Pennisetum longissimum var.intermedium seedlings under three treatments of PEG-6000, low temperature and saltstress were studied using simulation adversity stress method. Their resistance,ecological adaptability were analyzed and evaluated comprehensively. The resultsshowed that,①With the increasing PEG concentration, soluble protein contentincreased first, then decreased and finally increased, soluble sugar increased first and then decreased, the maximal value was observed at5%PEG The content of MDAsharply increased first, then remained stable and significantly decreased finally, with amaximal value at5%PEG. The activity of SOD sharply decreased first, thenincreased slowly before increased significantly, with a minimal value at5%PEG anda maximal value at20%PEG.②The content of soluble protein and soluble sugar,the activity of SOD increased at first and then decreased under low temperature stress.The content of proline increased with decreasing temperature and MDA showed anincreasing trend.③With the increasing salt concentration, the soluble proteincontent increased first and then decreased; while the content of soluble sugar, prolineand MDA increased. SOD activity showed a slight increase at first, then slowlyreduced before declining rapidly. The correlation analysis revealed that the content ofproline was significantly negatively correlated with soluble sugar under PEGtreatment. With4hours low temperature stress, the content of MDAwas significantlypositively correlated with soluble sugar and proline content. Under NaCl treatment,the content of soluble sugar was significantly positively correlated with MDA andproline, the activity of SOD was significantly negatively correlated with soluble sugarand MDA, which was significantly positively correlated with soluble protein content.To sum up, the physiological dynamic changes of Pennisetum longissimum var.intermedium reflects its adaptive response to stresses and injury.(6) In Qinwangchuan saline soil region of Gansu province, the phenologicalphase, growing rate, leaf area and tiller number of4Pennisetum longissimum var.intermedium wild and cultivated new strains were studied comparatively with fieldtrials, and the production performance were evaluated comprehensively with greysystem theory. The result showed that strain No.1, No.2and No.3sprouted quicklyand matured early, their growth period was about147d; strain No.4had the growthperiod of160d. Strain No.1was the fastest-growing one, its plant heights in eachgrowth period were significantly higher than the other three materials, and reached themaximum (187.94cm) at blooming stage. Strain No.3grew more slowly, its heightwas only150.51cm at rippen stage. During the early to midium-term, leaf area andstem diameter of all the test were increased progressively, then leveled off and even declined after heading stage. Strain No.1, No.2and No.4changed consistently andsignificantly higher than the strain No.3. Strain No.2’s tillering ability was thestrongest, followed by strains No.1, No.3and No.4in turn. The strain No.1and No.2had better somprehensive performance, with15300kg/hm2and14700kg/hm2hayyield. Fast growing rate, strong tillering ability, high hay yield and early maturitywere observed for strain No.1and No.2, which were suitable for wide planting in theQinwangchuan saline soil region.In conclusion, Pennisetum longissimum var. intermedium is crosspollinated,withsignificant ruga on surface of pollen, while the extine had graininess. The totalnumber of chromosome was36with karyotype asymmetry of Stebbins’1B type.There was rich genetic diversity among29strains of Pennisetum longissimum var.intermedium. The genetic differentiation was mainly influenced by combined impactof genetic and environmental factors without showing geographical distributionregulation. The proline, soluble protein, soluble saccharides, MDA content and SODactivity changed under stress, correlations among them were observed. Thecomprehensive evaluation found that the strain No.1and No.2had betterperformances among four new strains of Pennisetum longissimum var. intermedium,which were suitable for cultivation in arid, semi-arid region and salinized zone ofcentral Gansu province. |
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