Pathogen Identification And Effect Of Chemical Control Of Phalaenopsis Sp. Root Rot Disease In Changchun

The root rot disease is one of the serious diseases on Phalaenopsis sp. and is widespread in Changchun in recent years. The purpose of this paper is to isolate, identify the pathogen of this disease and study on its biological characteristics and chemical control. For determining the pathogen of Phalaenopsis sp. root rot disease, the author collected 317 disease roots and isolated 240 fungal and bacterial strains in 2004-2006. Six fungal species were identified with the Koch's postulates from these isolates, Fusarium solani, F. oxysporum, F. graminearum, Rhizoctonia solani, Pythium. sp. The results showed that Fusarium solani is the main pathogen of Phalaenopsis sp. root rot disease in changchun, and the others may enhance the occurrence of this disease.The results of the biological studies on Fusarium solani showed that the favorable temperature for mycelia growth and conidia germination is at 10～35℃and the optimum temperature was 25℃for mycelia growth and conidia production. The optimum temperature for spore germination was 30℃; rate of conidial germination in 24h was 93.5%; the optimum temperature for sporogenesis was 25℃and Fusarium solani did not produce spores under 5℃. Colony growth condition and the rate of spore germination were best under the treatment of 12h alternation of darkness and light. Under 16h darkness and 8h light colony diameter was smallest. Continuously under the dark condition produced the spore quantity most greatly for 9.8×10⁶/ml, under the continual illumination condition produces the spore quantity slightly for 4.2×10⁶/ml.There's no obvious influence on the colony growth of Fusarium solani at different pH. Conidia could germinate at pH range 3～11 and highest rate of conidial germination is at pH 4～7. The spore quantity was greatest for 13.125×10⁶个/ml at pH 7.11. Best carbon resources was fructose and the colony diameter was 6.37cm 5days after inoculation; The rate of conidia germination was 59.7% in 2% agarose and 57.21% in amylum, both of which are higher than in the other carbon sources. The lowest rate of conidia germination was 1.44% in fructose. The highest sporulation was 12.24×10⁶个/ml in 2% rnaltobiose. Agarose inhibited hyphae growth and sporulation. Among different nitrogen sources, NH₄NO₃ was good for hyphea growth and the colony diameter was 6.67cm in 5 days. The highest rate of conidia germination was 82.1% in CK and the lowest was 27.5% in FeNH₄(SO₄)₂ NaNO₃ reduced hyphae growth and sporulation. Ventilation seriously influenced on the hyphae growth. The average growth quantity of hyphae was 725.6mg in shaking cultivation and 483.1 mg in static cultivation. After 20h the rate of conidia germination was 77.1% in the condition of sealing and 82.33% in ventilating. The lethal temperature of spores was at 57℃for 10minutes.Using the toxicity of thirteen fungicides and its concentrations were determined by testing the conidial germination rate and colony growth. The results indicated that conidial germination rate was effectively inhibited by 50% Carbendazim, 25%Azoxystrobin, 10% Difenoconazole, 50% Tucsukin in100mg/L concentration. The best effect reach 100% by Carbendazim. The EC50 of the four kinds of fungicides were 4.7760mg/L,7.2670mg/L,7.8206 mg/L, 9.9099 mg/L individually. Mixture of four fungicides in the given concentration was tested and screened five synergetic combinations: Carbendazim: Tucsukin(9∶1), Carbendazim: Tucsukin(8∶2), Carbendazim: Tucsukin(1∶9), Azoxystrobin: Difenoconazole(9∶1) and Azoxystrobin: Difenoconazole(3∶7). The lowest EC50 was 3.2848mg/L on Azoxystrobin: Difenoconazole(3∶7) under five concentration gradients. The experiment result in laboratory was coincided with in field trails.The prevented effect of fungicides [Azoxystrobin:Difenoconazole (3∶7) (9∶1 ), Carbendazim: Tucsukin (1∶9) (8∶2) (9∶1), 25% Azoxystrobin, 50% Carbendazim,] was 100%. The treaty effect of fungicides[Carbendazim: Tucsukin(1∶9)(8∶2)] was 40%.