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Article first reported by Alternaria sp. Marigold leaf spot caused by the large area in the central and western regions of Gansu Province. As can be seen from the survey results, marigold leaf spot generally occurred in Wuwei City, Gansu Province, Huangyangzhen Gulang County and Silver City Jingtai County marigold cultivation base incidence rates are generally between 23% to 95% in disease index of 5.75 to 48.5. The severity of disease around quite different, Silver City Jingtai County disease occurs more serious, Wuwei City Huangyangzhen followed Gulang County, the incidence is relatively light. Detailed description of the symptoms of the disease: leaves, stems, and spend the formation of brown, purple-brown, round or irregular lesion, lesion central off-white or yellow-white, serious lesion color deepened, connected into a piece of dry leaves , stem necrosis. Pathogenic strains isolated from the marigold different predilection conidiophores solitary or clustered, straight or bent to one side, light brown, separated. Conidia size of 18.26 ~ 24.90 × 8.81 ~ 11.61μm, average 21.58 × 10.21μm, shaped pour sticks, long oval, spindle, etc., early light color, after was brown, dark brown, 2 to 4 diaphragm, 0 to 3 the mediastinum, separated at the constriction. Beak shorter, columnar, size, 2.74 ~ 4.5 × 2.4 ~ 4.16μm, separated. According to the morphological characteristics of the isolated strains, although there are some differences in colony color, but in the main morphological characteristics is not a significant difference, considered to belong to the same kind. Access to relevant literature, identified as the Alternaria (Alternaria sp.) The biological measurement results: Alternaria fungi (Alternaria sp.) Can make good use of sucrose, maltose, starch and glucose utilization better use of poor lactose; better utilization of nitrogen source to glycine and potassium nitrate. growth and sporulation also relatively high, the other poor; optimal growth conditions: 25 ° C the pH6.04 conditions pathogen growth under the best and most sporulation; sufficient sunlight is conducive to sporulation; several different colonies growing on the medium, 5% ML best PSA sporulation poor on Czapek medium and 0.1% DM use; conidia germination at 25 ℃ best; non-water droplets, even The relative humidity of 100% germination rate is only about 25% of the water droplets in the germination rate, relative humidity below 90% to almost not germinate. The identification of the carrier rate and carrier types for different varieties of marigold seeds. The results show that the external between different varieties carry fungal species are quite different seed carried on the surface of the dominant flora Alternaria fungi (Alternaria sp.) And fungi (Fusarium species of Fusarium sp.) Imported coated surface of the seed is not isolated to any fungi, the seeds do better disinfected; 2005, the highest infection rate of the F1 hybrids, 40%. The seed infection site test results show that the pathogens are parasites on the seed coat, accounting for more than 90% of the carrier rate, carrier rate is different because of the different varieties of performance. The seed epidermis can also be contaminated, but the infection rate was significantly lower than the seed coat, the marigold seeds of different varieties of embryo and endosperm without pathogens. Seed disinfection results show that 0.1% AgNO3 for different varieties of marigold seeds have a 100% disinfection effect, external seed can kill any pathogens; at 55 ° C hot water soaking, 50 ° C hot water soaking and 50% iprodione (Iprodione have) wp750 times higher disinfection, disinfection effect in more than 80%, you can effectively control the occurrence and development of the pathogen; 58% of metalaxyl - Mn-Zn (Metalaxyl) of wp750 times and 47% Jiarui agricultural (of Kasumin-Bordeaux) wp1000 times disinfection effect is not ideal, is not suitable for used as a seed treatment. Indoor Bacteriostatic Test, 50% iprodione (Iprodione) wettable powder the best antibacterial effects (EC50 = 1.3249mg/ml)., 75% chlorothalonil (Chlorothalonil) the WP has good suppression bacteria effect (EC50 = 3.5316mg/ml), the effect of both fungicides significantly higher than the other agents, is ideal virusicides; WP 70% thiophanate (Thiophanate-Methyl) and 58% metalaxyl - MnZn (Metalaxyl) wettable powder inhibitory effect is not ideal, almost can not suppress the pathogen (Alternaria sp.) growth. The field control results show that: 50% iprodione (Iprodione) WP 800 times control effect best, the absolute control effect reached 76.54%, can promote the use of production. However, from a cost-effective point of view, 63% of polymicrobial clear WP (Carbendazim-Chlorothalonil) and 75% chlorothalonil WP (Chlorothalonil) is the ideal chemical control of marigold leaf spot.
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