| The evolution of62wheat varieties cultivated widely in Shandong province since1950was evaluated by SSR markers. With the development of production and the changes of thedisease, Shandong province has experienced wheat8times turnover. Changes in grain yield,harvest index (HI) and photosynthetic parameters of eight landmark wheat cultivars widelyplanted in Shandong province at different eras were investigated in the fields. The mainresults are as follows:1. Changes of genetic diversity in wheat varieties replacementThe results revealed that all24pairs of SSR markers were highly polymorphic, and100alleles were amplified with the average of4.167per marker. The mean polymorphisminformation content (PIC) was0.527with a range from0.200to0.723. The genetic diversityindexes ranged from0.225to0.761with the average of0.582. There were significantdifferences in site polymorphism among these three genomes, and the average richness ofallelic variation in each genome was D＞B＞A. The genetic diversity index and thepolymorphism information content index of genome B were similar to that of genome D, buthigher obviously than that of genome A. The average genetic richness, genetic diversity indexand genetic distance in1950s were all higher, and each of them was3.042,0.531and0.596respectively. Then they decreased slowly until they rebounded in1980s and reached the peakwith the values of3.250,0.560and0.616respectively. After that they decreased sharplyagain. The genetic similarity coefficients of62wheat cultivars varied from0.580to0.940with the mean of0.723. All wheat cultivars could be clustered into7groups at0.719according to the method of UPGMA. The clustering result was mostly consistent with themain parental lines and their derivatives for wheat breeding on different period in Shandongprovince. the results showed that the wheat breeding in Shandong province, as well asthroughout China，has been based on core parental lines since1950. Because of the creation and application of the endemic germplasm, genetic diversity of wheat cultivars released inShandong province had even been the highest in all the wheat regions of China, especially in1980s. But it declined sharply after1980s. Therefore more efforts should be made to broadenthe wheat breeding base and conserve wheat germplasm.2. Changes of photosynthetic characteristics and yield componentsThe grain yield and HI showed a significant linear improvement in Shandong provincewith the cultivars changed, however the biomass did not increase obviously. The chlorophyllcontent (Chl a and Chl b), light saturated photosynthetic rate (Pn)，stomatal conductance (Gs),carboxylation efficiency (CE)，photochemical efficiency (ΦPSII) of photosystem II (PSII), andrespiratory rate (R) of flag leaves from all historical cultivars reached their maximal valuesbetween flowering date and10days after anthesis (DAA), then declined gradually, anddeclined sharply after about10～20DAA. The intercellular CO2concentration (Ci) and thenon-photochemical quenching (NPQ) increased persistently after the flag leaves were fullexpanded. The decrease of Pn was not caused by stomatal factors. The carboxylase activity ofribulose bisphosphate carboxylase oxygenase (Rubisco) was crucial for the earlier reductionof Pn after flowering rather than chlorophyll content, while the chlorophyll degradation, ΦPSIIand NPQ played important roles in further reduction at the late duration of grain filling. Thephotosynthetic characteristics improved with the cultivar evolution derived from both theincrease in chlorophyll content, Pn, Gs, CE and ΦPSIIand their longer duration, and whichmay be the physiological basis of the grain yield improvement. However, the respiratory ratealso enhanced with the cultivar change and which was disadvantage to yield increase. |
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