In Vitro Induction And Identification Of Tetraploid In Malus Zumi And Its Evaluation Of Stress-tolerance

Malus zumi was an exellent apple rootstock with characteristics of extensive adaptability, powder mildew resistance, scab resistance, cold resistance and salt and alkali resistance. The adaptability and stress resistance would usually be enhanced after polyploidization. In this study, the tetraploid of Malus zumi was induced in vitro. The morphological and physiological characters were compared between tetraploid and diploid, and some stress tolerance of the tetraploid subculture plantlets were primarily evaluated. The major results were as followed:1. The tetraploid of Malus zumi was obtained from leaves cultured in inducing medium with colchicines for thirty days. The best inducing medium was MS+NAA0.25mg/L+TDZ2.0mg/L+ Fructose 30g/L+ Agar 6.2g/L+ Colchicine 50mg/L.2. No tetraploid was obtained from shoots cultured in propagation medium with colchicine. When colchicine concentration was lower than 50mg/L, its effect on growth was invisible. When colchicine concentration was 100mg/L, the height, multiplication coefficient and growth increment were lower than the control, but no death occurred. One variation shoot was found in the forepart, but re-mutation occurred later on.3. Compared to the diploid, the tetraploid showed dereased multiplication coefficient, total growth increment, leaf shape index, chlorophyll a content, chlorophyll b content, total chlorophyll content, but increased leaf thickness, leaf water content and stem diameter, and all the differences were significant. The difference of their rooting rate and roots number were not significant, but the root of tetraploid was thicker than the diploid. In the water cultrue treatment, the leaf shape index and leaf thickness of the tetraploid plant were also lower than that of diploid significantly.4. The results of hormone level showed that: hormone content of the leaves both in diploid and tetraploid, whatever from test-tube plantlets or water cultivated seedlings, ABA was the highest, and the same result in new roots of water cultivated seedlings. Chromosome doubling did not result in significant difference in hormone level except increased ZR in the leaves of water cultivated seedlings.5. The SOD and POD activities of teraploid were significantly higher than that of diploid, while no difference was found in the content of MDA and free proline.6. The salt-resistance between tetraploid and diploid was compared. The results showed that tetraploid had lower injury index, relative reduction of multiplication coefficient and total growth increment than diploid, which indicated increased salt resistance in tetraploid.7. The drought-resistance between tetraploid and diploid was compared. The results showed that tetraploid had higher multiplication coefficient and total growth increment than diploid, which indicated increased drought resistance in tetraploid.8. The Fe-deficient-resistance between tetraploid and diploid was compared. The results showed that tetraploid had higher multiplication coefficient and total growth increment, but lower relative reduction percent of Chlorophyll a, b and total Chlorophyll content than diploid, which indicated increased Fe-deficient- resistance in tetraploid.