| Cucumber(Cucumis sativus L.)is a worldwide vegetable crop that has been grown for more than 3,000 years.The utilization of heterosis is the major way for the breeding of modern varieties.To breed the excellent hybrid F1,we need to obtain a large number of stable inbred lines.Induction of haploid/double haploid plants in vegetable crops by irradiated pollen combined with embryo culture is an important means of modern plant breeding,and a large number of homozygous inbred lines can be obtained quickly in a short period of time,thus accelerating the breeding process of hybrid F1 varieties.However,this technique still has many problems,such as the sensitivity of pollen grains to radiation dose,large workload of embryo rescue and lower haploid yield,and poor reproducibility of some results.To optimize the technology system of cucumber haploid induction using radiation pollen pollination and accelerate the breeding process,4 different genotypes of cucumber were used as test varieties for pollen(‘18393’,‘18026’,‘18394’,and‘18011’).The effects of radiation doses(150 Gy,175 Gy,and 200 Gy)on the pollen viability,pollen tube growth,and fruit setting rate of the tested varieties were analyzed.In addition,3 different genotype combinations were used as the test varieties(’19532 × 19026’,’19465 ×19026’,and ’19026 × 19464’).We analyzed the effects of different radiation doses(175 Gy and 200 Gy)on the number of full seed,plant regeneration rate,and haploid induction rate of the test varieties,and investigate the ploidy levels of regenerated plants by flow cytometry and chloroplast count of guard cells.Further,the types of seeds suitable for embryo rescue and its location were determined by comparing the haploid induction rates of different fruit parts and seeds of different states.The major conclusions are as follows:Influence of 60Co-y irradiation on pollen viability,pollen tube growth and fruit setting rate of different genotypes of cucumberIn this study,y radiation had no significant effect on the outer wall and appearance of pollen grains of 4 tested materials,but the activity and germination rate of radiation pollen of 4 tested materials at 3 radiation doses were significantly lower than that of unradiated pollen.Among them,the pollen vigor and germination rate of ’18026’ were lower than those of the other three tested materials.In addition,the results of in vivo pollen germination and pollen tube elongation observation showed that the pollen of the four tested materials could germinate normally on the stigma and form pollen tube at different radiation doses,but the pollen tube growth rate decreased with the increase of radiation dose,and there was no significant difference between the four tested materials.For the fruit setting rate,the analysis results of the four tested materials showed that there was a significant difference between the radiation pollen setting rate and the unradiated pollen setting rate.Among them,the decrease value of ’18393’ fruit setting rate was the largest,26.09%(200 Gy),and the decrease value of ’18026’ fruit setting rate was the smallest,10.63%(200 Gy).In conclusion,the resistance of ’18026’ pollen to 60Co-y rays was higher than that of the other 3 tested materials,mainly manifested in the viability and fruit setting rate of pollen,which could be considered as a pollen donor for subsequent haploid study experiments.Study on the induction of haploid plants using irradiated pollens in cucumberA total of 89 haploid plants were obtained in this study,of which 85 were derived from semi-full seeds and flat seeds.By comparing the haploid induction rate of seeds in different parts of fruit and different states,it was found that haploid production was easier in semi-full and flat seeds of the fruit head.The number of full seeds,plant regeneration rate and haploid induction rate of 3 genotype combinations(’19026×19464’)were significantly higher than those of other combinations,indicating that the genotype combination was suitable for this technique to induce haploid of cucumber.Meanwhile,it was found that the formation pathway of regenerated plants mainly included embryoid pathway and callus pathway. |
