| In this paper, two common B. napus cultivars 'Zhongyou821' (P1) and 'HZ21-1' (P1) were crossed to a white-flowered resynthesized B.napus line, 'HW243' (P2). Six generations (P1, P2, F1, RF1, F2, B2, B2) of the two combinations, i.e., 'Zhongyou821×HW243' and 'HZ21-1×HW243', were grown at two locations, Ya'an and Kangding (altitude 2650m), for investigations on the heredity of the white flower character. The flower color was observed with 'naked eye', 'pigment extraction' and 'petal scanning', respectively. And the genetic rules of white flower character were analysed. BSA (bulked segregant analysis) was used to identify the SSR molecular markers linked to the white flower character in the combination 'Zhongyou821×HW243'. The main results were summarized as follow:1. Observations with naked eyes showed that there was no obvious difference in flower color between the reciprocal F1 hybrids. The petal color of F1 hybrids was milky, slightly inclined to the white flower parent. In F2, the flower colors could be classified into three types, i.e., white, milky and yellow. The ratio of white: milky: yellow flowered plants was 1:11:4. In B1, the flower colors were classified into two types, i.e., milky and yellow, the ratio of milky: yellow flowered plants was 1:1. In B2, the flower colors were classified two types, i.e., white and milky, the ratio of white: milky flowered plants was 1:3.2. The process of pigment extraction from the flower petals was made with seven different solvents, including dH2O, anhydrous alcohol, acetone, petroleum ether, aether, methanol and chloroform. The effect was the best with anhydrous ethanol, without significant influence by pH and temperature on the extraction effect. We used absolute alcohol as the solvent for the systematic investigations in this experiment. The extracted solutions were tested with a visible/ultra-violet spectrophotometer at variable wavelengths. It was found that the wavelengths 439nm and 469nm showed the biggest difference among P1, P2 and F1. The wavelength 439nm was used for the systematic analysis in this experiment. It was shown that the absorbance values between the reciprocal F1 hybrids were not significantly different, but significant differences were observed among individual plants in the segregating generations. Based on the absorbances in P1, P2 and F1, the values in F2 could be classified into 3 groups, i.e., 0-0.1 (close to white flower P2), 0.1-0.5 (close to milky flower F1, RF1) and 0.5-2 (close to yellow flower P1). With Chi-square test, the ratio of white: milky: yellow flowered plants was 1∶11∶4 in the F2. In B1, the ratio of milky: yellow flowered plants was 1∶1. In B2, the ratio of white: milky flowered plants was 1∶3. These results were consistant with those estimated with eye method.3. With the flower petal scanning method, the characteristic parameter B for color in the CIE RGB system and the characteristic parameter b in the CIE Lab system were shown to be effective. In this experiment the parameter B of CIE RGB system was applied to the genetic analysis. The resluts indicated that B values of CIE RGB between the reciprocal F1 hybrids were not significantly different, but big significant difference was observed among individual plants in the segregating generations. Based on the B values in F2, 3 groups of plants could be divided, i.e., 0-100 (close to P1, yellow flowered), 100-195 (close to F1, RF1, milky flowered) and 195-255 (close to P2, white flowered). With Chi-square test, the ratio of white: milky: yellow flowered plants in F2 was 1∶1∶4. In B1, the ratio of milky: yellow flowered plants was 1∶1. In B2, the ratio of white: milky flowered plants was 1∶3. The results were consistant with those estimated with both eye method and pigment extraction method.4. Based on the results observed with 'naked eye', pigment extraction and petal scanning, respectively, it can be speculated that the white flower character in this study was controlled by two pairs of incompletely dominant, interacting nucleic genes. The white flower color was incompletely dominant over the yellow color. It is presumed that the genotype of the white flower parent was W1W1W2W2, the genotype of the yellow flower parent was w1w1w2w2, and the genotype of the F1 hybrid was W1W1W2W2. In the yellow flowered offspring the homozygous recessive gene pair w1w1 acted epistatically over the dominant gene W2, restricting the expression of the W2 allele at the other locus.5. With 600 pairs of SSR primers the DNA molecular polymorphism was tested in the cross combination 'Zhongyou821×HW243'. Ninty (90) pairs of SSR primers produced polymorphism between the two parents. The percentage of polymorphic SSR markers was 15%. Six (6) pairs of SSR primers produced polymorphism between the two bulks. The amplified product of primer 'B36' (Na12-G03) in the yellow flower plants and the white flower plants in F2 indicated that B36 was strongly linked to the white flower character.6. White flower character in B.napus was a complex character. The milky white flower in the segregating hybrid offspring showed a variation in whiteness. This might be resulted from the variable numbers of dominant white flower genes in the genotype. Meanwhile, minor genes in the background might also be responsible. However, further investigations are necessary for a better understanding about the genie actions of the white flower character.7. In present study consistent results were obtained with 'naked eye', 'pigment extraction' and 'petal scanning'. However, the 'naked eye' method might be easily influenced by a number of factors, such as visual difference in human, light intensity in the field and the visual fatigue of the observer, etc. So it is always necessary to make repeated observations or multiple-people observations in order to reduce errors. The methods by pigment extraction and petal scanning were objective and stable, so they were better than the 'naked eye' method. And the petal scanning method in present experiment is the simplest and the most economic method for flower color observations.
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