|
The black-spot disease on dongzao jujube occurred severely recently. It was reported that the percentage of the diseased fruits reached more than 20%, and could reach as high as 80% in some areas in 2003. However the pathogens, occurrence and the control method of the disease were unknown. In our research, the symptoms characteristics on the diseased fruits were described, the biological characteristics of the pathogens and occurrence of the disease were studied, the fungicides and biocontrol agents for controlling the disease were selected. The main results showed as following.1. Disease symptoms: At the beginning stage of the disease, there are several white spots on the fruits and afterwards the color of spots become black. The spots are almost round, the diameters of them are about 1mm and some reach 3mm. Some spots can fall off when the fruits are mature .2. According to the morphological characteristics and size of acervulus, conidiophore and chlamydospore, the pathogens were identified as Coniothyrium fucsidulum Sacc, Phoma pomirum Thum. and Alternaria alternate (Fr.) Keissler. Coniothyrium sp. and Phoma sp. could infect the dongzao jujube fruits singly and jointly, but Alternaria sp. could only infect fruits jointly with the other pathogens.3. For the mycelial growth of Coniothyrium sp., the optimum temperature was 25-30 ℃, pH was 7 and the treatment of continuing light has significant effect on the mycelial growth. The optimum sporulation temperature was 25~30℃, the optimum pH was 9-10 and the treatment of continuing light has significant effect on sporulation. The optimum temperature for conidial germination was 26-30℃, the optimum pH value was 8-9, when relative humidity reached 100% or water, the percentage of conidial germination was the highest, the conidia can not germinate under 85%, and nutrition has no selective effect on conidial germination. For the mycelial growth of Phoma sp., the optimum temperature was 25-30℃, the optimum pH value was 7, the treatment of alternate light and darkness has significant effect on the mycelial growth. For the sporulation, the optimum temperature was 26~30℃, the optimum pH value was 6-7, the treatment of darkness have significant effect on sporulation. For the conidial germination, the optimum temperature was 26-30℃, the optimum pH value was 7-9, the conidia can not germinate under 85% RH. For themycelial growth of Alternaria sp., the optimum temperature was 25-32°C, the optimum pH value was 7, the treatment of continuing light has significant effect on mycelial growth. For the sporulation, the optimum temperature was 25~30°C, the treatment of darkness have significant effect on sporulation. For the conidial germination, the optimum temperature was 15~35°C, the optimum pH value was 7-9, the conidia can not germinate under 85%, and nutrition has no selective effect on conidial germination.4. Occurrences: The beginning of infection stage of the black-spot disease was in the last ten-day of June and the high infection stage was from the last ten-day of July to the first ten days of August. The rate of infection during the growth stage of the fruit was higher than during the ripe stage. Rainfall and humidity were the key factor which affected the disease severity in one year, but temperature was not an important factor .5. Using growth rate method, seven fungicides are test for their toxicity to main pathogens of the disease in lab. Three ones are chosen which have good restraining effect to three pathogens . In addition, 157 biocontrol agents are test in lab. and three isolates should significant control effect in lab. In the same time, the biocontrol effect of Men-myco-93-63 was detected.
|