Screening Of EMS Mutation Conditions And Construction Of EMS Mutant Library In Watermelon M08

Watermelon（Citrullus lanatus（Thunb.）matsum.&Nakai.）is a horticultural crop originated in Africa and widely cultivated all over the world,which has important edible and economic value.Germplasm resources are the basis of breeding,and excellent germplasm resources are the key to watermelon breeding and functional gene research.Therefore,it is of great practical significance to find and select excellent mutant materials by mutation,create watermelon mutant library and enrich the diversity of existing resources.This test for watermelon‘M08’material,the mutagenic effects of’M08’under different EMS treatment combinations were studied by seed soaking method and seedling dropping method,and the watermelon mutant library was constructed.By investigating the agronomic characters of M₁ and M₂ plants,mutants with important agronomic characters were screened,which provided important materials for breeding new watermelon varieties and analyzing watermelon functional genomics.The main results are as follows:1.Selection of EMS mutation conditions:（1）The optimum conditions for EMS mutation treatment seeds were as follows:soak coat opened gourd seeds in warm soup for 4 h,and then soak seeds in 1.5%EMS for 12 h or 1.0%EMS for 24 h.（2）It was considered that 0.5%EMS at cotyledon spreading stage was the best mutation condition.2.Construction of M₁generation population of watermelon:（1）5000 seeds of watermelon’M08’were soaked in 1.5%EMS for 12 hours,and 3464 seedlings were produced（1786 of them had no growth point and died later）,and 749 M₁ generation plants with good growth were finally obtained;There were 15 variation types in M₁ generation population,and the total variation rate was 20.96%,of which the mutation rate of leaves was the highest,which was11.36%;（2）720 seedlings were treated by dropping seedling method,and 689 seedlings survived in M₁ generation;The mutant population contained 10 variation types,and the total variation rate was 19.30%.3.Phenotypic identification of M₁ generation mutant of watermelon:2 mutants with leaf color variation:M₁-1,the leaf color turns yellow and turns yellow green in the later stage of growth;M1-5,the specific performance is that the leaf color changes from yellow to green with plant development,but it does not return to the normal plant color.The peel color of young melon is also light yellow in the early stage and normal in the later stage.There were 2plants with leaf type variation:M₁-2,which showed that the leaves narrowed and the wavy sawtooth of the leaf margin deepened;M₁-7 shows irregular shape,the number of cracks is reduced to 2-3,the blade becomes thinner and the blade edge becomes smooth.Fruit type variation:M₁-3,from oval to spindle.Pericarp variation:M₁-4,pericarp bands became irregular patches.Flower sex variation plant:M₁-6,strong male plant,female flower only appears at the 32nd node of the main vine.4.Population construction and phenotypic observation of watermelon M₂ generation:the M₂ generation seed bank was constructed by strictly selfing M₁ generation plants,including940 lines（443 lines were obtained by seed soaking method and 497 lines were obtained by seedling dropping method）.132 lines were randomly selected and 20 plants were planted for phenotypic observation.At this stage,13 variation types were observed,the total phenotypic mutation rate was 5.21%.5.Phenotypic observation and photosynthetic characteristics analysis of M₁-5 virescent mutant in M₂ generation population:in stage I,the content of photosynthetic pigment was low and the leaves were yellow;In period II,the content of photosynthetic pigment increased significantly,and the leaf color changed from yellow to green,but it will not return to normal leaf color.With the accumulation of photosynthetic pigment,the photosynthetic ability of the post green mutant can be restored and can grow normally.