The Mechanisms Of Ammonium/Nitrate On Banana Growth And Fusarium Wilt

Fusarium oxysporum f. sp. cubense race 4 is the causal agent of banana (Musa. spp.) Fusarium wilt, a soil-borne disease that can cause severe losses in yield and quality of banana. Currently, the pathogenic mechanism of Fusarium wilt is putted down to jamming of xylem or systemic toxicity. However, the question of why Fusarium caused wilt occurs remains unanswered. Experiments were conducted to investigate the effects of different nitrate/ammonium ratios and different pH values on the growth of Fusarium oxysporum f. sp. cubense of banana wilt disease. The penetration through plant cell walls by pathogen is mimicked in this experiment to illustrate the penetration mechanism of banana Fusarium wilt. Hydroponics experiments were conducted to investigate the effects of nitrate/ ammonium ratio on the growth of banana plants and invasion of banana Fusarium oxysporum f. sp. Cubense. The results showed that,1. The results show that in the treatments with different nitrate/ammonium ratios, the growth of Fusarium oxysporum f. sp. cubense is strongly restrained at the low pH value (pH=4). At the same pH value, the pathogen growth is significantly inhibited by ammonium as the sole nitrogen source (100% ammonium), and the diameter of the colonies is less than 4 cm. When the ammonium concentration is increased, the pathogen growth is depressed and thoroughly inhibited by ammonium over 5 mmol/L. The penetration through plant cell walls by pathogen is mimicked in this experiment, and it is observed that the pathogen could not penetrate the cellophane membrane when ammonium is the only nitrogen source. In conclusion, the ammonium is convinced to restrain the Fusarium oxysporum f. sp. cubense growth, and its penetration process through the host plant cell wall.2. In comparison with the treatments of sole nitrogen resource, under the treatment of 75% nitrate+25% ammonium (75% N+25% A), the biomass of banana plants and the content of N, P, K in plants were the highest amongst all the treatments. The rhizospheric pH was decreased strongly under the 100% ammonium treatment, while the pH increased with the addition of nitrate in the root medium. After inoculation of Fusarium oxysporum f. sp. Cubense, the population of pathogen in rhizosphere was increased by the application of ammonium nutrition, the population of pathogen in rhizosphere was increased by the application of ammonium nutrition, The Fusarium Oxysporum wilt diesease incidence was seriousily when the ammonium ratio reached 100%. In conclusion, sole ammonium nutrition could depress the growth of banana plants, and also it can possitive Fusarium oxysporum f. sp. Cubense infected.3. The number of pathogen in nitrate grown plant was significantly lower than ammonium grown plant after Fusarium oxysporum f. sp. cubense inoculation. Root exudates cinnamic acid and citric acid from ammonium grown plant significantly increased spore germination of Fusarium oxysporum f. sp. cubense as compared to nitrate grown plant. Root exudates esters from nitrate grown plant significantly increased the lecture seed root growth and resistence the spore germination of Fusarium oxysporum f. sp. cubense as compared to ammonium grown plant.