Preliminary Research on Radiation Breeding of Pteroceltis tatarinowii Maxim

Chengxiu LI Tiantian CHENG Zhongkui SUN Yu YAN Lin ZHANG

Abstract In order to explore the effect of radiation breeding on new germplasm innovation of  Pteroceltis tatarinowii , the dry seeds of  P. tatarinowii  from Lingyan Temple were used as test materials in this study, which were irradiated by 60Co-γ rays with different radiation doses. The results showed that the emergence rate decreased with the increase of radiation dose, the emergence rate of low dose below 200 Gy decreased slowly, and the emergence rate of high dose above 200 Gy decreased sharply; when the radiation dose ranged from 100 to 200 Gy, the mutagenic effect of  P. tatarinowii  seeds was the best; and radiation obviously affected the leaf color and leaf shape of seedlings. This study provides original materials for the cultivation of new  P. tatarinowii  varieties and the study of color-changing mechanism.

Key words  Pteroceltis tatarinowii  Maxim.; 60Co-γradiation; Seedling emergence

Received: August 2, 2021  Accepted: October 8, 2021

Supported by "Innovation Driving and Leading Promotion of Seedling and Flower Industry in Mount Tai" of Industrial Upgrading Project of Science and Technology Park in Shandong Province (2019YQ012); "Collection, Preservation and Accurate Identification of Germplasm Resources of Precious Timber Tree Species" of Shandong Provincial Agricultural Elite Varieties Project (2019LZGC01804).

Chengxiu LI (1964-), female, P. R. China, senior engineer, devoted to research about garden flowers.

*Corresponding author.

Pteroceltis tatarinowii  Maxim. is a deciduous tree from Pteroceltis and Ulmaceae, also known as Tuanpishu, Diaopiyu or Yipu. It is a unique fiber tree species in China and a national rare and endangered tree species, mainly distributed in 19 provinces such as Anhui, Zhejiang and Fujian.  P. tatarinowii  has strong adaptability, with calcium preference. Meanwhile, it is fond of living in limestone mountains, and can also grow in granite and sandstone areas.  P. tatarinowii  stem bark and branch bark fiber are high-quality raw materials for manufacturing famous painting and calligraphy Xuan paper at home and abroad; the woodiness of  P. tatarinowii  is solid, dense, tough and wear-resistant, which can be used for furniture, farm tools, drawing boards and joinery; and seeds can be pressed for oil. In addition,  P. tatarinowii  is a unique single genus plant in China, which has important academic value for studying the phylogeny of Ulmaceae.

Radiation breeding is a breeding method which has been widely used in recent years, α-ray, β-ray, γ-ray, Χ-ray, neutron and other physical factors are often used to treat organs with strong meristem ability, such as seeds, bud tips and branches, so as to change their genetic materials and produce various mutations［1］. Then, excellent plants that meet the demand of people are selected from the mutated individuals for cultivation, thus obtaining new varieties. Radiation mutation breeding is a common breeding method for ornamental horticulture and tree breeding. According to the data, the new varieties bred by γ-ray radiation account for 56.5% of the total new varieties of ornamental plants［2］. However, there are few successful examples of radiation mutagenesis in  P. tatarinowii  breeding, which brings inconvenience to radiation breeding and reduces radiation mutation rate. Therefore, in this study,  P. tatarinowii  seeds were mutated with 60Co-γ ray, and the radiation variation of  P. tatarinowii  seeds was preliminarily explored, aiming at improving radiation efficiency of  P. tatarinowii  seeds, enriching special germplasm resources of  P. tatarinowii  seeds, and promoting the breeding process of new varieties of  P. tatarinowii  seeds.

Materials and Methods

Experiment time and place

The seeds of fine individual  P. tatarinowii  in Lingyan Temple, which were selected by  P. tatarinowii  research group of Taishan Forestry Research Institute in Tai’an City, were collected in early September 2020, and then put into a net bag to dry naturally in the shade.

Experimental treatment

The harvested  P. tatarinowii  seeds of each plant were divided into 6 parts on average, and treated with 60Co-γ radiation in Shandong Quangang Radiate Technology Development Co., Ltd. in early March, 2021. According to the radiation research results of related woody tree species, the radiation doses were set as 0 (CK), 100, 200, 300, 400 and 500 Gy, respectively, and the cobalt source radiation dose was 1.5 Gy/min, with 300 seeds treated for 3 times.

Determination index and method

The irradiated seeds were stored in sand, sown in plug plates after seed germination, and placed in random groups. When two true leaves grew, the emergence rate and mutation rate were counted.

Data analysis

Excel 2010 software was used for data statistics, SPSS 22.0 was used for correlation regression analysis, analysis of variance and multiple comparative analysis, and the mean for three repetitions of data using was adopted.

Results and Analysis

Effects of radiation treatment on emergence rate of  P. tatarinowii  seeds

The seedling emergence rate of  P. tatarinowii  was about 65%, and the average seedling emergence rate in the CK group reached 67.26% in this study. Radiation reduced the seedling emergence rate of  P. tatarinowii , and showed a significant downward trend with the increase of radiation dose. There were significant differences among 6 treatments. When the radiation dose ranged from 100 to 500 Gy, the relative emergence rates of seeds under radiation stress decreased significantly, which were 56.32%, 45.68%, 21.06%, 7.52% and 3.69%, respectively.

Effects of radiation treatment on seed mutation rate of  P. tatarinowii

Radiation dose had significant effect on seedling mutation rate of  P. tatarinowii . When radiation dose was 0, 300, 400, 500 Gy, the seedling mutation rate was 0. Only when radiation dose was 100, 200 Gy, the mutation rate was 1.22% and 1.88%, respectively. The whole mutation rate was low, which indicated that radiation should be further studied in breeding new  P. tatarinowii  varieties.

Morphological analysis of radiation seedlings

When the radiation surviving plants grew to a certain height, they were transplanted to the field for continuous observation. Among them, the radiation plants grew weakly as a whole, and died constantly. The most intuitive differences among the surviving radiation plants were in leaf color and leaf shape (Figu. 1), in which the leaves appeared white spots in different degrees, and the leaves changed pale. After radiation, the leaf area of the plants was obviously reduced compared with the control, and the serrations of the leaf edges became larger.

Discussion and Conclusions

The emergence rate of  P. tatarinowii  seeds was significantly reduced by 60Co-γ radiation, and there were significant differences among treatments. The emergence rate decreased slowly when the radiation dose was below 200 Gy, but decreased obviously when the radiation dose was greater than 200 Gy, which was the same as that of most woody plant seeds. Previous studies have shown that the amount of oxygen free radicals produced by radiation with different seed water content is different, the damage to genetic material is different, and different tree species show different radiation sensitivity, so their emergence rate and radiation dose are different. The radiation mutation rate of  P. tatarinowii  seeds is lower than that of  Osmanthus fragrans, Verniciafordii, Paeonia lactiflora  and  Ailanthus altissima ［3］. The influence of radiation on seedlings is not only reflected in the emergence rate, but also the most intuitive performance in its external morphology. Xiong  et al. ［4］ found that the uniformity of emergence decreased and the root development was inhibited when irradiating  Osmanthus fragrans  seeds. Li Zhineng  et al.  irradiated  Platanus acerifolia  seeds and found that the plant height, fresh weight and root length of seedlings decreased. Yi Lisa  et al.  irradiated the seeds of  Camellia oleifera  in Guangning and observed that the growth of seedling height and ground diameter was inhibited to a certain extent. Yang  et al. ［5］ held that radiation caused obvious changes in branches and leaves of Kuerle Sweet Pear to a certain extent. In this study,  P. tatarinowii  seedlings showed changes in leaf color and leaf type. Among them, there are some high-quality specific variations, which provide original materials for breeding new  P. tatarinowii  varieties and studying the discoloration mechanism of  P. tatarinowii . However, these specific germplasms need further observation and propagation, which can be determined as effective radiation only after the morphology remains stable after 1 or 2 generations of radiation stabilization.

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