| Crop breeding via mutations is an effective method to obtain new traits especially in the condition that the genetic diversity available of the crop is limited. EMS is one of the widely used chemical mutagens for the mutation breeding via its interaction with DNA enabling heritable changes of the genome and thus the production of new varieties. However, the expression of such mutation of EMS in high ploidy crops is estimated to be lower due to more complex genomic organization than that in haploids and diploids, and the mutation breeding efficiency is sometimes not acceptable. In the present work, we applied EMS to tetraploid potato variety Solatium tuberosum L. cv Zhongshu 2 , and analyzed the efficiency of EMS caused mutation in cultivated high ploidy potato crop.Stem segments were collected from virus free potato in vitro plantlets and the explants of terminal buds, axillary buds, and callus-axillary bud complexes were treated with 1% EMS solution for 4h. Explants without treatment were used as control. The explants were then cultured in a B5 basal medium. After 4 subcultures, the seedlings were further transferred to soil and grew in greenhouse for 2 gernerations. After the EMS treatment and during the development of the treated plants and their further generations via tubers, morphological and physiological data were collected in categories of shoot color, leaf shape, dwarf, stem diameter, flower development, tuber production, tuber color, total dry material of tubers, plant cold tolerance. Statistic analyses were conducted with SAS model.1. We observed that the plant individuals showed different tolerance to EMS, and morphological changes occurred in plant height, leaf shape, shoot and tuber color, and flower bud development. The EMS treatment caused a color change, i.e., from green to white, in axillary bud explants. After 20 days of in vitro culture, the explants became green and 20% of them started growth after 20-50 days of culture.2. In the 4 populations of clones originated from the axillary bud explants, changes of plant height, stem diameter, numbers of tubers produced, and the formation of flower bud were observed and were significantly different from the control. Changes of stem and leaf morphology and color also occurred, among which leaf shape and color changes and changes in the formation of flower bud maintained so far in the 2nd generation via tubers in greenhouse. The tuber dry weight and starch content did not show significant changes, however, the content of reducing sugar showed a 3-fold increase than the control.a) In the 2nd generation via tubers in greenhouse, in a sudden 2~3days -4°C condition, the plants of control group showed 6.19% lethality and 75.53% of occurrence of red spots and abnormal growth thereafter;in the leaf-shape changed mutation population, however, only 28% of the plants showed red spots, and none of them died.b) We conclude that EMS is efficient to cause various mutations in potato tetraploid materials, and many mutated characters show a stable heredity via tuber-based generations. Mutations in potato leaf morphology and color, tubers reducing sugar content, and flower buds formation are the most valuable mutations obtained in the present work. Among the morphological mutations, leaf-shape mutations show a high correlation to plant cold tolerance, indicating that a physiological mutation exists leading to the observed cold tolerance. The mutated leaf-shape, in this case, can be used as a morphological marker for potato cold resistant breeding.
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