| The methods of resistance evaluation of citrus somatic hybrids to citrus foot rot, the resistant mechanism and Phytophthora parasitica toxin were studied in this paper. The results were as follow:1. The results of evaluation from inoculating citrus branches and leaves with the mycelia of P.parasitica showed that there was a significantly positive relationship between two results. The method that citrus leaves were inoculated with P.parasitica could be used to evaluate the resistance of citrus to foot rot.2. The results of evaluation from treating citrus young leaves with P.parasitica toxin and inoculating citrus leaves with the mycelia, showed that there was a significantly positive relationship between two results. The method that citrus young leaves were treated with P.parasitica toxin could be used to evaluate the citrus somatic hybrid resistance to foot rot.3. Branches and leaves inoculated with P.parasitica mycelia, and the young leaves trended with the toxin, were to evaluated the resistance of citrus somatic hybrids to foot rot. The results indicated that Trifoliate orange + Sour orange was high resistant (HR), Sour orange + Lime, Trifoliate + Cleopatra mandarin, Severinia -f Hamlin sweet orange. Flying dragon trifoliate orange + Hamlin sweet orange. Trifoliate orange + Page tangelo resistant (R), Sour orange + Microcitrus , Sour orange + Cleopatra mandarin moderate resistant, the others susceptible.4. The relationship between phenylpropanoid metabolism and the resistance of citrus to P.parasitica was studied. The results showed that the contents of the products from phenylpropanoid metabolism i.e. lignin, phenoid and citrus phytoalexin DMC, etc., hi resistant citrus tissues were higher than susceptible ones. After citrus was infected by P.parasitica, the contents of these products in resistant tissues rose faster, and peak values higher, than the susceptible ones. In healthy citrus tissues, the activities of PAL, a key enzyme in phenylpropanoid metabolism, were higher in resistant types than in susceptible ones. After inoculating citrus with the pathogen, the PAL activities in resistant types rose sharply to a peak. The relationships between the resistance of citrus to P.parasitica and PO, PO isoenzyme and PPO were also studied.5. The methods of DMC purification and detection, the relationship between the resistance of citrus and the contents of DMC, and the effect of DMC on the mycelial growth of P.parasitica were studied. The results indicated that there were DMC whether in healthy citrus tissues or in infected tissues, whether in the branches or in the leaves. The contents of DMC hi resistant types were higher than in susceptible ones. The contents of DMC were higher in the branches than in the leaves. DMC could significantly inhibited the mycelial growth of P.parasitica in vitro.6. PR-proteins existed in citrus, this proteins in citrus Included chitinase and P-1, 3- glucanase. After infection, there were difference of PR-proteins between resistant and susceptible citrus. The activities of chitinase and P-1, 3-glucanase in resistant citrus rose faster than that hi susceptibe citrus. Chitinase and P-1, 3-glucanase coeffect on P.parasitica mycelia and lead to expand and burst, inhibit the growth of P. parasitica mycelia.7. The optimum conditions for toxin production of P.parasitica were 62 medium, pH4-6, 25-28 , and culturing for 28 days.8. The bioactivities of P.parasitica toxin were studied. The results showed that P.parasitica toxin was toxic to the plants of different family and was a kind of NHST. Citrus with different resistant types were susceptibility to the toxin. The PAL, PO, and PPO activities in citrus leaves were induced byP.parasitica toxin.9. The methods for purificating P.parasitica toxin were studied. Sephadex G-50 and G - 200 could be used to purify the toxin. The toxin could dissolve in methyl alcohol, ethyl alcohol and heated acetone. It was P - D -glucosidase, heat stable and susceptible to Tryptin and HC1. The toxin co...
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