Morphology, Physiology, Heredity And Molecular Markers Of Yellow Leaf Mutant YL-1in Cabbage (Brassica Oleracea L.var. Capitata)

Cabbage (Brassica oleracea L. var. capitata) is an important vegetable crop belonging to genusBrassica of Cruciferae family and is widely cultivated throughout China. The mutation of leaf-coloroccurs at a relatively high frequency in plantae, including different types of yellow, albino, stripes andso on, while yellow is the main type. Leaf yellow mutant is not only the ideal material to explore themechanism of plant photosynthesis, chlorophyll biosynthetic pathway, chloroplasts function and geneticlaws, but also can be used as seedling marker trait in heterosis utilization. Leaf yellow mutant YL-1wasdiscovered in2010with low plant vigor and small plant expansion in our preliminary observation, butits physiological characteristics is unclear. So far, however, there has been no report about cabbageyellow leaf mutant. Therefore, it is necessary to research on the morphology, physiological, genetic, andmolecular markers of cabbage yellow leaf mutant, which could provide theoretical and practical basisfor the use of marker traits in seedling stage and the revelation of the mutation mechanism in cabbage,and even other vegetable crops.Yellow leaf mutant (YL-1) and its near isogenic line WT708were used to compare their differencein plant vigor, main agronomic traits at mature stage, and the photosynthetic pigment content underdifferent temperature. The photosynthetic pigment content, photosynthesis indicators, chloroplastultrastructure and chlorophyll fluorescence parameters were measured. The F2, BC populationsgenerated from the hybrid of yellow leaf YL-1and the normal leaf kale inbred11-192were used toinvestigate the inheritance and map the yl-1gene. The results were as follows:1. Agronomic traits and heterosis ofYL-1compared with WT708Mutant YL-1can grow with yellow leaf, but its maximum length and width of the outer leaves,height and plant expansion were at least26.97%、30.32%、21.12%and27.53%lower than WT708,respectively. Although YL-1can form a head, but its weight is only39.00%of WT708. Yellow leaf wasaffected by temperature and low temperature could increase the lack of chlorophyll. YL-1and WT708were hybridized respectively with the same cabbage inbred material (2209,704) to compre theirheterosis. For the same type of combinations of either YL-1or WT708, they showed no significantdifference on leaf color, plant vigor and head weight. Therefore, YL-1can be used to makecombinations which has the same heterosis with WT708.2. Analysis of photosynthetic characteristics and chlorophyll fluorescence of YL-1The measurement of photosynthetic pigments content, chloroplast ultrastructure and chlorophyllfluorescence parameters indicated that YL-1is deficient for the total chlorophyll, but its chlorophyllcontent was partially recovered in the latter stage. YL-1had fewer chloroplasts and base grains, lessgrana lamellae stacked pile and irregular arrangement of base grains. At the head-forming stage, YL-1has more grana lamellae stacked pile and grains, but still significantly less than WT708. Thephotosynthesis indicators of YL-1were significantly lower than WT708throughout the entire growthperiod. The chlorophyll fluorescence parameters Fo, Fm, Fo’, Fv/Fm, Fv’/Fm’, ФPSⅡ, QP, QNand ETR inYL-1were significantly lower than WT708. It is suggested that the cause of yellow leaf in YL-1is the reduction of chlorophyll content and abnormal chloroplast structure, and thereby the efficiency decreaseof solar energy capturing and photosynthetic rate.3. Genetic analysis and gene mapping of yellow leaf gene yl-1YL-1and normal leaf inbred kale11-192were used as parents to make six generations (P1, P2,F1,F2, BC1P1, BC1P2) for genetic analysis. Ratio of the number of normal leaf plants versus yellow leafplants in F2population was2.94:1, and1.08in BC1population, which fits the ratio of3:1or1:1bychi-square analyses. Thus, yellow leaf trait was considered to be controlled by a single nuclear recessivegene, named as yl-1. According to the genome re-sequenced data of the existing cabbage and kale,180pairs of InDel markers were designed, and the yl-1gene was preliminarily mapped on the firstchromosome with BSA method. Then191pairs of InDel markers were developed according to thegenome re-sequenced data of YL-1and11-192forfine mapping. Two InDel markers closely linked toyl-1were obtained based on409yellow leaf F2individuals. The yl-1gene was located between InDelmarker BCYM560and BCYM898, with the genetic distance of1.22cM and0.49cM.