Study On Physiological Change And Genetic Heritance Of Oillseed Rape (Brassica Napus L.) Germplasm In The Presence Of Oxalic Acid

Oilseed rape (Brassica napus L.) is one of the most worldwide cultivated oil plants, especially growing in China, Canada, India, and European Union. However, the quantity and quality of oilseed rape has been greatly affected by Sclerotinia sclerotiorum. At present, it is still impossible to obtain such a Oilseed rape which is immune from 5. Sclerotiorum because of severe symptoms, difficult control measures and complicated nosogenesis. The toxin of oxalic acid is known as one of the most important pathogenic factors in the process of causing the pathogenicity of 5. Sclerotiorum. Therefore the plants' reactions to the presence of oxalic acid have been identical with the resistance /tolerance to S. Sclerotiorum. A wide range of differences in tolerance to the oxalic acid have been found in B. napus cultivars/strains. It is important to cultivate some highly resistant/tolerant germplasm through Screening and evaluating resistance/tolerance to oxalic acid, and now it has become very urgent to seek some methods to evaluate the tolerance to 5. sclerotiorum in oilseed rape (B. napus L.) rapidly, effectively and exactly. Unfortunately, it has still unknown to both the physiological mechanism of toxicity hazard and the genetic mechanism of toxic tolerance difference, consequently, it has severely holden back the progress in the field of plant breeding in resistance/tolerance to S. Sclerotiorum. In the present research, firstly, it has been conducted an experiment on germination of oilseed rape with oxalic acid solution treatment instead of sterilized water, and the oilseed rape (B. napus L.) tolerance to oxalic acid could be screened rapidly through the relative vigor index (RVI). several rapeseed (B. napus L.) materials with different oxalic acid tolerant were infected with S. sclerotiorum mycelia to test the reliability of measures on the evaluating the rapeseed (B. napus L.) tolerance. Secondly, solutions of oxalic acid at different concentration (0, 1, 2 mmol/L) have been prepared and applied to the oxalic acid submerged root method during the three leaf stages of GH01, several physiological indices have been analyzed with different time intervals after treatment. At the same time, several oilseed rape (B. napus L.) materials with different oxalic acid tolerance have been treated with solution of oxalic acid (2mmol/L) and different physiological levels among materials have been investigated in a fixed time to reveal physiological mechanism on disease resistance. Finally, 5 oilseed rape (B. napus L.) materials with different oxalic acid tolerance have been used to make diallel cross (5×5), and their hybrid seedlings have been treated with solution of oxalic acid (2mmol/L) and their relative seedling height have been investigated to study the genetic tolerance to oxalic acid in F₁ plants. Several main results are as follows:1. Characterization and rapid evaluation for oxalic acid tolerance in oilseed rape (B. napus L.) germplasm: The germination rate and seedling height were measured after 4 days' germination of oilseed rape (B. napus L.) in 2mmol/L oxalic acid solution treatment instead of sterilized water, the oilseed rape (B. napus L.) tolerance to oxalic acid could be screened rapidly through the relative vigor index (RVI). The forty-six lines of oilseed rape (B. napus L.) germplasm were selected from different pedigree resources to test the oxalic acid tolerance during seed germination in 2mmol/L oxalic acid solution treatment. The average of relative germination rate (RGR) and relative seedling height (RSH)were 78.22 % and 66.85 % respectively, and the average relative vigor index was 53.13%, there were significant difference of the oxalic acid tolerance among different oilseed rape lines. Twenty-six lines of oilseed rape (B. napus L.) with different oxalic acid tolerant were infected with S. sclerotiorum mycelia, the correlation between the necrosis lesion length and the RVI was significant. The results indicated that the germination in oxalic acid was an effective method to evaluate the tolerance to S. sclerotiorum in oilseed rape (B. napus L.).2. The physiological change of oilseed rape (B. napus L.) in the presence of the treatment of oxalic acid solution: solutions of oxalic acid at different concentration (0, 1, 2 mmol/L) have been prepared and applied to the oxalic acid submerged root method during the three leaf stages of GH01, the content of soluble substances and the activities of several enzyme have been investigated with different time intervals. The results have shown that both soluble protein and soluble carbohydrate have increased all the time. However, activities of pathogenesis-related protein enzyme, such as superoxide dismutase, PPO, POD, MDA ,their activities increased in the earlier stage until reached a maximal level, then decreased in the later stage, therefore the change of enzymes' activities with time have been bell-shaped with different curve degree. Besides, oilseed rapes' (B. napus L.) physiological reactions to the solutions of oxalic acid on the concentration of 2mmol/L was stronger than those on the concentration of 1mmol/L, correspondingly, the line trend of activities change in the presence of the solutions of oxalic acid on the concentration of 2mmol/L was more curved than those on the concentration of 1mmol/L. several oilseed rapes (B. napus L.) with different oxalic acid tolerant were treated with solution of oxalic acid (2mmol/L) and different physiological levels among materials were investigated in a fixed time, except from MDA, there were no significant correlations between all other physiological indices and oxalic acid tolerance index. 3. Genetic study on resistance/tolerance to oxalic acid in oilseed rape(B. napus L.): five oilseed rape(B. napus L.) varieties, including three high tolerance and two low tolerance, was used to make diallel cross (5×5), their hybrid seedlings have been treated with solution of oxalic acid (2mmol/L) and their relative seedling height were investigated to study the genetic tolerance to oxalic acid in F₁ plants. The results showed that ,besides nuclear inheritance, the resistance was also attributed to maternal inheritance. The interactions of genes were quite complicated, including dominance effect and addictive effect. Oilseed rapes' (B. napus L.)resistance to oxalic acid were partial dominance, materials with different oxalic acid resistance had different degree of dominance, the dominance level of the resistance materials xinong Changjiao×[(D57×O20)×85-64]F₇ was 31.53%, and that of III-227×(D57×O20)F₁₀ was 5.92%.both general and special combining abilities were important for the resistance/toerance. general combining ability of Youyan Number 2×84-24016 was highest and III-227×(D57×O20)F₁₀ was lowest. The cross of [Xinong Changjiao×[(D57×O20)×85-64]F₇]×[Yellow-seed Ganlan×[(D57×O20)×85-64]F₆] was highest special combining ability, and was considered as optimum combination.