Induction Of Dihaploid From Tetraploid Potato Cv.cooperation 88 And Its Mechanisms

Potato(Solanum tuberosum L.),which is an annual herb belonging to the Solanaceae family,has a wide range of cultivation and strong adaptability,and propagates asexually mainly through tubers.Due to its high nutritional value,potato is the world’s third largest food crop after wheat and rice.China is the largest producer of the potato in the world.Potato has a variety of chromosome ploidy,generally,its cultivar is tetraploid.However,there are many potatoes with other chromosome ploidies in nature,such as diploid,triploid,pentaploid,hexaploid and octoploid.Among these potatoes,diploids not only account for the largest proportion but also have different excellent traits,which are important germplasm resources in potato breeding.In fact,the tetraploid potato is characterized by single species,narrow genetic background and poor gene resources,while the wild diploid shows a simple genetic background and has a series of excellent traits such as disease resistance and insect resistance.However,due to differences in chromosome ploidy and hybridization incompatibility,the cultivated tetraploid cannot be directly used to cross with the wild diploid,which then hampers the utilization of the abundant wild diploid resources in nature.To solve this problem,the tetraploid cultivar must be induced to produce dihaploid firstly.The dihaploid then can be directly hybridized with wild diploid to obtain the excellent traits.In this study,the tetraploid Cooperation 88(C88,as the maternalplant)was crossed with the diploid IVP101(as the paternalplant)for the induction of parthenogenesis.Based on this,we identified the dihaploids from about 1600 offspring population and preliminary discussed the mechanism of the reduction of chromosome ploidy.The main contents of this study include the following aspects:(1)Successfully generated 820 aseptic seedlings of the offspring population.(2)Improved the method of analyzing potato chromosome ploidy by flow cytometry,and detected the chromosome ploidy of the offspring population using this improved method.(3)Partially identified the chromosome ploidy of the offspring population by the method of stoma guard cell chloroplast counting.(4)Partially identified the chromosome ploidy of the offspring population by the method of root tip chromosome counting.(5)Surveyed and analyzed the phenotypic traits of some offspring populations.(6)Identified the cytoplasm types and SSR markers of some offspring populations.(7)Preliminarily explored the mechanism of chromosome ploidy reduction of the offspring population.Through the above experiments,a set of experimental materials of offspring population from the parthenogenesis of C88 was finally obtained,including diploid,triploid,tetraploid,polyploid and even mixoploid,which can be used in subsequent experiments.In addition to the normal euploidy,aneuploidy,polyploidy and mixoploidy were also detected in the offspring population induced by parthenogenesis,of which the mechanism of the dihaploid induction was complex.Preliminarily,we speculated the underlying mechanism of dihaploid induction from the perspective of gamete formation and the pollen size of the parents.We think that parthenogenesis,hybridization,gene elimination,and gene introgression are involved in the dihaploid induction.In addition,in this study,dihaploids were detected in the offspring population with embryo patches,while the triploids and tetraploids were also detected in offspring population without embryo patches,suggesting that embryo patch labeling could not be used as the only standard to identify dihaploids.Furthermore,cytoplasmic types and SSR markers were also detected in some offspring population.The results of cytoplasmic types showed that most of the cytoplasmic types of the offspring population followed the law of maternal inheritance,but some of those were not,especially in the mitochondrial types.The results of SSR markers showed that most of the offspring population showed a high genetic relationship with the female parent,and they may be directly developed from the gamete of the female parent,while a small number of offspring population were formed with the introgression of the male parent genomes.