Photosynthetic Characteristics Of Apple Germplasm Resources

The photosynthetic characteristic is the core index that reflects the function of plant physiology. To determine the photosynthetic characteristic of the apple germplasm resources is the prerequisite and foundation of selecting and utilizing the high quality germplasm resources. In controlled environment conditions, the photosynthetic characteristic index of 18 apple germplasm resources from Xinjiang and 34 wild apple accessions are determined with the photosynthetic instrument, Li—6400, to analyze and determine the dynamics of different photosynthetic resources, as well as the correlation of different parameters. Selecting 6 wild resources with the different levels of net photosynthetic rate from the 34 wild apple accessions, the determination, observation and research are done with the related parameters of the daily variation of the photosynthetic index, light response curves, CO2 response curves, chlorophyll fluorescence, chlorophyll, the RuBP carboxylase content, stomas and chloroplast, as well as the leaf cells and the ultrastructure of chloroplast.1. The photosynthesis parameters of 18 apple germplasm resources from Xinjiang were obviously different and there was a significant correlation between different Pn and Gs, Tr. The chlorophyll content of unit mass of fresh leaves was not obviously relative to Pn. Among the 18 apple germplasm resources, M. niedzwetzkyana Dieck., M. prunifolia Mill. and M. prunifolia (Wild.) Mill.had high total capacity of photosynthesis, while M. pumila Mill. and M. niedzwetzkyana Dieck. had a relatively low capacity of photosynthesis.2. The results showed that the photosynthesis parameters of 34 wild apple accessions were obviously different and there was a significant correlation between different Pn and LUE, Gs, WUE, Tr. The chlorophyll content of unit mass of fresh leaves was not obviously relative to Pn. Among the 34 wild apple accessions, M. spectebilis Borkh and M. asiatica Nakai had high total capacity of photosynthesis, while M. sieversii (Ledeb.) Roemer and M. sikkimensis (Hook. f.) Koehne had a relatively low capacity of photosynthesis.3. The diurnal variation of 6 wild apple resources presents different curves. M. spectebilis Borkh. and M. asiatica Nakai show unimodal curve, while M. prunifolia (Willd.)Borkh.,M. tiaojinensis Cheng et Jiang,M. sieversi(iLedeb.)Roemer and M. sikkimensi(sHook. f.)Koehne show bimodal curve.The daily mean values of the 6 wild apple resources'net photosynthetic rate, ordered from high to low are: M. spectebilis Borkh.,M. asiatica Nakai,M. prunifolia (Willd.)Borkh.,M. tiaojinensis Cheng et Jiang,M. sieversii(Ledeb.)Roemer,M. sikkimensis(Hook. f.)Koehne.The characteristics of chlorophyⅡfluorescence, the number of intracellular chloroplast, the shapes and arrangements of palisade tissue, the shapes of chloroplast as well as the stacking level of grana lamella play a crucial role on photosynthetic capacity of apple germplasm resources, while the content of ribulose diphosphate carboxylase (RuBP carboxylase) has a significant impact on apple leaves'photosynthetic capacity. Under normal conditions, M. spectebilis Borkh. and M. asiatica Nakai have high photosynthetic capability; M. prunifolia(Willd.)Borkh. and M. tiaojinensis Cheng et Jiang take the second place; M. sieversii(Ledeb.)Roemer and M. sikkimensis(Hook. f.)Koehne are low in photosynthetic capability. M. asiatica Nakai is a typical kind of wild resources that owns high photosynthetic capacity and potential, while M. sikkimensis(Hook. f.)Koehne is a typical wild resource that has low photosynthetic capacity and potential.