Induction Of Polyploidy Germplasm Resources Of Morus Mongolica And Preliminary Evaluation Of Resistance Of Polyploid Morus Notabilis

Mulberry is a perennial woody plant in the mulberry family,and is a tree species with many uses.The innovation development of mulberry germplasm resources is an important basis for cultivating high-yielding and high-quality mulberry varieties and for achieving sustainable development of sericulture.Polyploid mulberry varieties are not only high yielding and of high quality,but also have wide adaptability and strong stress resistance.Breeding polyploid mulberry lines is an effective way to improve mulberry varieties.In this study,Morus mongolica Schneid.(2n = 4x = 28)was used to establish tissue cultures.Then,the tissue cultured M.mongolica plants were treated with colchicine to induce polyploid.Polyploid plants with stable ploidy levels(2n = 8x = 56)were isolated and purified from the mixoploids,and their characters were evaluated.The traits of polyploids of Morus notabilis Schneid.(2n = 4x = 28)were also measured under different degrees of salt stress,and their resistance levels were preliminarily identified.The main findings are summarized below.1.Polyploid induction and identification of germplasm resources of M.mongolicaWinter buds of germplasm resources of M.mongolica were induced to form adventitious buds under the following tissue culture conditions: M535 medium(containing adenine sulfate)+ 1.0 mg/L 6-benzyl adenine + 30 g/L sucrose + 7 g/L agar.After obtaining tissue-cultured M.mongolica materials,polyploid was induced by applying colchicine at 1.0 g/L for 16 h,24 h,and 48 h,and at 2.0 g/L for 24 h,36 h,48 h,60 h,and 72 h.The tissue-cultured seedlings of M.mongolica showed milder toxicity symptoms when treated with 1.0 g/L colchicine than when treated with 2.0 g/L colchicine.Many seedlings died in the 2.0 g/L colchicine treatment,so this treatment was unsuitable for polyploid induction in tissue-cultured seedlings of M.mongolica.After colchicine induction,multiple mixoploids were obtained.Three polyploid plants(2n = 8x = 56)were screened by continuous cutting and separation.2.Determination of traits of polyploid M.mongolica and M.notabilisThe stomata and leaf structure of polyploid M.mongolica(2n = 8x = 56)and M.notabilis(2n = 4x = 28)were observed,and the relative chlorophyll content was determined.After doubling the number of chromosomes,the leaves of polyploid M.mongolica and M.notabilis were thickened,there were more abundant stomata on the lower epidermis,the stomatal density per leaf area decreased,and the relative chlorophyll content in the leaves increased significantly.3.Preliminary identification of stress resistance phenotypes of M.notabilis polyploidsPolyploids of M.notabilis and M.notabilis were treated with sodium chloride at concentrations of 0 mmol/L,50 mmol/L,100 mmol/L,and 150 mmol/L.After 15 days,plants in the control group were growing well,whereas those in the salt stress groups showed poor growth,with yellowed leaves.Peroxidase activity,catalase activity,and proline content,which are indicators of stress resistance,increased with increasing salt concentrations in the M.notabilis polyploids,and were higher than their corresponding contents in diploid M.notabilis.The polyploids showed strong salt resistance.The content of malondialdehyde,an indicator of membrane damage,was lower in polyploid M.notabilis than in diploid M.notabilis,and the polyploids showed milder leaf damage under salt stress.In summary,the polyploids of M.notabilis showed enhance resistance to salt stress.