Abstract:

To explore the pathogenic species of watermelon anthracnose in western Hunan, and provide a theoretical basis for watermelon anthracnose prevention and control, we took the diseased leaves of watermelon grown in the Science and Technology Park of Xiangxi Vocational and Technical College for Nationalities as the research objects, isolated and purified the pathogen of the disease, and conducted morphological observation, Koch's rule verification, 18S rDNA-ITS sequence analysis and the biological characteristics analysis. The colony of strain C913 was round, hyphae of villiform and neatly arranged. It was white at first and then grayish white. The conidia discs were arranged in a ring shape, and there were orange-red conidia clusters. The conidia are cylindrical, blunt at both ends, single cell, with a septum in the middle, and the size was (9.8~17.5) µm× (4.5~5.9) µm. The 18S rDNA sequence was 100% similar to the four Colletotrichum gloeosporioides included in GenBank. The hyphae could grow normally when the temperature was 10-37℃, but the growth rate of the hyphae was the fastest at 25℃, and the colony diameter was 78.28 mm. The growth slowed down when the temperature was less than 10℃ or greater than 37℃. The hyphae spores could grow under the condition of pH 5-11. The hyphae grew fastest when the pH was 6 and the colony diameter was the largest, 84.62 mm. The colony diameter with glucose and sucrose as the carbon source medium was significantly higher than that of other treatments, 63.4 mm and 62.2 mm, respectively; while lactose was not conducive to the growth of mycelium (P<0.01), which was 33.1 mm, and 19.06% less than that of the control. (NH₄)₂SO₄ obviously inhibited the growth of C913 hyphae. According to the morphological characteristics of the strain and the results of 18S rDNA-ITS sequence analysis, the strain C913 was identified as Colletotrichum gloeosporioides of the genus Colletotrichum of the subphylum Coelospora. The pathogen is found on diseased leaves of watermelon for the first time. When the temperature is 20-31℃ and pH is 6, it is the most suitable condition for mycelial growth, and when the temperature is 25-31℃ and pH is 9, it is the most suitable condition for sporulation. The colony diameter is the largest in the medium with glucose and sucrose as carbon sources, and the colony diameter is in the order of peptone>NaNO₃>glycine>glutamic acid>agar>(NH₄)₂SO₄.

Key words: watermelon anthracnose, 18S rDNA-ITS, biological characteristics, Colletotrichum gloeosporioides, colony diameter