| Cassava (Manihot esculenta Crantz) is one of an important economic crop in the tropics of China, and the foodstuff and biomass energy industries based on the cassava root were the important component of the tropical agricultural economy. The Phytophthora root rot (PRR) disease, an international disease on cassava, seriously influences the quality and production of cassava root in the cassava plantation of Africa, America and Asia. In China, the new type of PRR caused by Phytophthora palmivora is rarely investigated. Therefore, this study focused on the survey of disease symptom, pathogen isolation and identification, the prevention and treatment fungisides screening, the evaluation and utilization of disease-resistance properties of cassava varieties, and the differential gene expression analysis of the disease-resistance and susceptible varieties affected. The main results are as follows:On the survey of disease symptoms showed that the PRR was the most serious fungi disease in present at the cassava plantations of China, which was found in Danzhou of Hainan; Baoshan of Yunnan and Zhanjiang of Guangdong province. The harvest lost 80 percent or more by causing of PRR in some serious infected plantations.The pathogen, isolated from the diseased roots being infected by PRR with tissue isolation methods, had been identified as Phytophthora palmivora by pathogenicity determination, morphologic observation, the basic biological properties determination and ITS sequence analysis. And the optimum growth conditions of PRR are 28℃, pH 5, D-saccharose and ammonium acetate as carbon and nitrogen source, in OA medium in addition alternating of light and dark. And the lethal temperature is 50℃ for 10 min.Based on one Pytophthora palmivora strain came from HaiNan province,15 fungicides were screened in laboratory by hypha growth rate method.56% mancozeb·8% oxadixyl WP, 5% flumorph·45% phosethyl-Al WP and 15% metalaxyl·10% propamocab hydrochloride were found to have the lowest EC50 value and best inhibition of Pytophthora palmivora isolates, whereas 72.2% propamocab hydrochloride had the highest EC50 value but poor inhibition.56% mancozeb·8% oxadixyl WP,5%flumorph·45%phosethyl-Al WP and 15% metalaxyl·10% propamocab hydrochloride were suggested to be used for field control of cassava root rot disease.The PRR disease-resistance of 58 varieties domestic cassava was evaluated with the in vitro incubation method. The results showed that 6 varieties were identified into class 1 resistance,16 were identified into class 2,11 as class 3,16 as class 4, and 9 as class 5 of 58 varieties in total. The germplasm resources with good agronomic characters and high resistance to PRR as the parents were sexctual hybridized in the field within 96 hybrid combinations, and 318 seeds of F1 have been obtained.144 pairs of selective amplification primer, the differentially expressed genes from the roots after inoculated with Phytophthora palmivora (CRHN01) by cDNA-AFLP technique. The result showed that 125 transcript derived fragments (TDFs) displayed altered-expression patterns after inoculation by 144 primer pairs. The 75 TDFs were cloned and sequenced; of which 60 had known functions and 15 were related with unknown protein through Blastx searching the GenBank database. The 44 TDFs may have an effect on the interactions of Manihot esculenta Crantz with Phytophthora palmivora, which were homologous to genes involved in some means of physiological and biochemical such as metabolism, protein synthesis, signal transduction, disease defense, protein destination and storage, transporters et al. |
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