Creation Of A New Anti-clubroot Loose-curd Cauliflower Germplasm With Green Stem By Using Molecular Marker-assisted Selection

Clubroot is a soil-borne disease caused by Plasmodiophora brassicae Woron（Plasmodiophora brassicae Woron）.At present,more than 60 countries in the world are affected by clubroot disease,resulting in a serious decline in the production of cauliflower crops or even no harvest,which brings great challenges to industrial development and farmers’income.Cauliflower（Brassica oleracea var.botrytis L.）can be divided into two categories:compact-curd cauliflower and loose-curd cauliflower in terms of main commodity characters.When the loose-curd cauliflower matures,the flower bulbs are loose,the stems are green,and the white stems are green.The taste is crisp and tender.Compared with traditional compact-curd cauliflower,it is beautiful and delicious,and it has become the main type of cauliflower consumption in China.Which has become the main characters of cauliflower consumption in China.However,the loose-curd cauliflower varieties that produce general green-stemmed loose-curd cauliflower are often not high-yielding,and high-yield loose-curd cauliflowers often have insufficient green stems and fail to meet the needs of consumers.Therefore,the breeding of high-yielding loose-curd cauliflower varieties with high yield is the main breeding direction of loose-curd cauliflower at present.With the rapid prevalence of loose-curd cauliflower in domestic cities in recent years,the clubroot disease is also increasing.Most of the loose-curd cauliflower is resistant to clubroot.Due to the rapid spread of clubroot disease and difficult prevention and control,the clubroot is generally lacking in disease-resistant varieties.At present,researchers believe that the most economical and effective way to prevent control the disease is to breed resistant varieties.Therefore,it is particularly necessary to screen disease-resistant resources,mine disease-resistant genes,and create disease-resistant germplasm.This research mainly focused on the field phenotype investigation of loose-curd cauliflower materials,BSA sequencing of loose-curd traits,In Del markers screening,molecular marker screening and field identification of anti-clubroot,and the creation of anti-clubroot germplasm resources.The main results were as follows:（1）The white stem compact-curd cauliflower F90 and green stem loose-curd cauliflower S120 and their hybrid F₂ populations were used as basic materials,the phenotype was investigated in the field,and 40 individual plants of the loose-curd cauliflower and the compact-curd cauliflower were selected for BSA re-sequencing and analysis.Finally,two In Del-linked markers related to the loose-curd traits of cauliflower located in the region of chromosome 1 were obtained,and these two markers were verified in extreme individual plants randomly selected in the F₂ segregating population.The results showed that the agreement between these two In Del markers and the extreme individual plant phenotype survey results in the field was as high as 96.37%.To a certain extent,the results reflect the differences between loose-curd and compact-curd traits in In Del markers.Can better select in the early generations of loose-curd cauliflower,Which can shorten the breeding time and improve the breeding efficiency.These results provide important marker resources and theoretical references for high-quality cauliflower production and molecular marker-assisted breeding of loose-curd traits.（2）Using the published 23 pairs of closely linked molecular markers to screen 12cabbage seed materials collected by the research group,the results show that the marker BSA7 can amplify specific characteristics in the anti-clubroot material‘Kale ZZH’.The900bp band indicates that the anti-clubroot material‘Kale ZZH’may be related to the Crr1resistance gene.Furthermore,‘Kale ZZH’was amplified and sequenced using the sequence of Crr1 and homology analysis was performed.The results showed that the amino acid sequence of‘Kale ZZH’had a high homology of 98.66%with the Crr1 gene.It is proved that theanti-clubroo of‘Kale ZZH’is related to the Crr1 gene.（3）The high-yield F₂ single plant‘LB04-97’with green stems isolated after crossing the white stem compact-curd cauliflower F90 and green stem loose-curd cauliflower S120 was used as the male parent,and the female parent‘Kale ZZH’was used as the female parent to obtain the F₁ generation.After self-separation,the F₂ generation population was formed,and the F₂ generation population was subjected to artificial inoculation resistance identification and molecular marker identification.Studies have shown that the results of the two identification methods are consistent,and the comprehensive use of the two methods makes the identification results more accurate and credible,and further verifies the accuracy and stability of the marker BSA7.（4）Use‘LB04-97’as the male parent to backcross the F₁ generations of‘Kale ZZH’and‘LB04-97’,and perform inoculation resistance identification and molecular marker identification at the seedling stage of the BC₁ generation single plant.The traits and phenotypes were identified,and finally two new broccoli germplasms with root disease resistance and green stem loose-curd cauliflower traits were obtained.The combination of artificial inoculation resistance identification,molecular marker identification and field phenotype identification creates new anti-clubroot materials for cauliflower,which provides basic services for subsequent disease-resistant breeding.