The first recording of gummy stem blight disease caused by didymella bryoniae(stagonosporopsis cucurbitacearum ) on watermelon crop in Iraq

Abstract

This study was conducted in the laboratory of mycotoxins in the Department of Plant Protection / College of Agricultural Engineering Sciences / University of Baghdad. The results of the field survey of gummy stem blight showed the presence of symptoms of spotting and death on the shoot and damage to fruits in the fields of watermelon for some province, Diwaniyah, Sulaymaniyah, Kut, and Salah Al-din. These symptoms were represented by the appearance of spots and cankers on the stems, leaves in a dark brown color with cracks in the stems and fruits, and resulted in a gummy material in black or brown color. The purification results of the fungus isolation showed that it appears in a white to the green olive and then to the dark color on the top side of the colony. As for the colonial lower side, it shall be olive in color to black in the form of concentric rings, where the isolates were similar to the Stagonosporopsis cucurbitacearum. The strongly virulent isolate (I11) was determined after proving its high efficacy in re-infection and giving the same symptoms and was diagnosed in the beginning depending on the morphological characteristics. The Pycnidia was observed on the affected parts (crown area) under the optical microscopy, Chlamydospores were also observed by testing under the optical microscopy. Furthermore, the results indicated the superiority of the nutrient medium V8A to stimulate the fungus over the formation of Pycnidia for the strongly virulent isolate (I11) which was formed on the colony. In addition, it was clear under optical microscopy and are signs considered diagnostic for the fungus, compared to other methods such as exposure to ultraviolet light alternating with the dark hours, and the method of scraping the surface of the colony that did not show any efficiency in stimulating the fungus to form its reproductive parts. Molecular diagnosis using polymerase chain reaction (PCR) technology was also based on the ITS4 region sequence of DNA, where the results of the nucleotide sequence showed that the strongly virulent isolate of the stagonosporopsis cucurbitacearum. The isolate was stored in the Gen-Bank under the accession number (MT102262), and the results showed a 98% match with the global isolates. Therefore, this fungus was recorded as the causative agent of gummy stem blight disease on the watermelon crop, and in general, this is the first recording of S.cucurbitacearum and the first report on gummy stem blight disease on the watermelon crop in Iraq. Furthermore, the other strongly virulent isolate D4, that was isolated from the watermelon farms in Diwaniya Province, symptoms of cankers were observed on the stem and crown area with black gummy material similar to the gummy material caused by gummy stem blight disease on the watermelon crop and caused by the fungus D. bryoniae (S. cucurbitacearum). Besides, the presence of microsclerotia at the injury site was also partially diagnosed, and it was observed that M. phaseolina was the cause of charcoal rot disease on some vegetables, and its nucleotide sequence was stored with the accession number MT102264. In addition to the isolates of other accompaniment fungi (13), also diagnosed and stored the nucleotide sequence for each isolate in the GenBank under the global accession number for each one.