Studies On Biological Mechanism And Screen The Mutant Of Resistance To Phomopsis Stem Blight Of Asparagus (Asparagus Officinalis L.)

Asparagus (Asparagus officinalis L.) is a dioecious, herbaceous perennial species in the family Liliaceae (lily) and it is also an important vegetable for exported purpose in China. The phomopsis stem blight caused by phomopsis aspasagi(Sacc) Bubak is a destructive disease of asparagus in many parts of the world such as China, Japan, America, Brazil, France. The incidence of the disease is 50% 100%, and the rate of stem blight is 10% 30%, all of asparagus die away when the disease is very serious. Asparagus commercial fields are often made a clean sweep because of the phomopsis stem blight in china.The aims in the present study are to demonstrate the effects of Si and chitin on the growth of disease-resistance and to investigate the possible mechanism by which Si and chitin increases the tolerance to this disease in Asparagus officinalis seedlings. On the other hand, the effect of Ethyl methyl sulfonate (EMS) treatment on the proliferation and regeneration of in vitro callus from Asparagus officinalis seedling was studied using three varieties, 'UC800', 'Guanjun' and 'Shuofeng', which provided the basis of screening the mutant with biotic and abiotic resistance in asparagus breeding program. The main results are presented as following:1. The PDA medium with NaCl and Na₂SiO₃ at different level was used to culture Phomopsis aspasagi(Sacc) Bubak in the experiment. The growth of mycelium wasn't inhibited on medium containing NaCl compared with control, but that was obviously inhibited on the medium with Na₂SiO₃ when its concentration was above 6 mmol/L. Morever, the inhibition was more significant with the increase of the Na₂SiO₃ concentration in the medium.2. Hydroponic culture experiment were conducted with asparagus cultivars to investigate the effects of Si and inocultation with phomopsis aspasagi (Sacc) Bubak. The results showed that the inoculation of phomopsis aspasagi(Sacc) Bubak enhanced the activity of catalase (CAT), guaiacol peroxidase (G-POD), superoxide dismutase (SOD), phenylalanine ammonia-lyase (PAL), polyphenoloxidase (PPO). chitinase andβ-1.3-glucanase activity, while Si supply increased the activity of CAT, SOD, G-POD, PAL, PPO, chitinase andβ-1.3-glucanase in vivo of inoculation plants. The disease index was significantly decreased by Si-supply after inoculation, and the relative against efficiency was 39.33%. Theaddition of Si improved the ability of resistance to phomopsis stem blight.3. To investigate the effects of chitin on induction of the tolerance of phomopsis stem blight in asparagus, different asparagus cultivars were used and inocultated with phomopsis aspasagi (Sacc) Bubak in seedlings. The results showed that the inoculation of phomopsis aspasagi(Sacc) Bubak enhanced the activity of catalase (CAT), guaiacol peroxidase (G-POD), superoxide dismutase (SOD), polyphenoloxidase (PPO) activity, while chitin supplement increased the activity of CAT, SOD, G-POD and PPO in vivo of inoculation plants. The effect of the time supplying chitin on activity of antioxidant systema enzyme was significantly different and the change was the most obvious when supplied the chitin in 2 days after inoculation. The disease index significantly reduced with chitin-supply, and the relative against efficiency was respective 39.33%, 45.45% and 23.68%when supplied the chitin 2 days before inoculation, the day of inoculation and 2 days after inoculation. So we concluded that chitin addition improved the ability of resistance to phomopsis stem blight.4. The proliferation rate and growth rate of the callus was found to be significantly different among different genotypes, and the proliferation rate of the variety 'Shuofeng' was the highest. The callus was obviously inhibited on the medium containing 0.5% EMS, and more significantly on the higher concentration of 0.7% EMS. The effect was depended on the genotypes, and the callus from 'Guangjun' was most susceptible to EMS treatment among three test varieties. The regeneration rate of the in vitro callus was significantly affected by the combinations of different plant growth regulators in the media and the highest rate with 61.8% was found in percent of bulblet when cultured in the MS media containing with 1 mg·L^-1 KT. When compared with different genotypes, the variety 'Guanjun' was most easy for induction the stem. The combination of in vitro callus culture and EMS treatment will provide a potential tool for screening the mutant with biotic and abiotic resistance in asparagus breeding program.