Detection and identification of Phoma macdonaldii in sunflower seeds imported from Argentina

Abstract

China has been importing sunflower hybrid seeds for commercial planting from other countries in recent years. Tianjin Entry-Exit Inspection and Quarantine Bureau isolated nine fungal strains similar to Phoma macdonaldii, which causes black stem, from Argentine sunflower seeds. Isolations were made from the debris in with seed not from the seed were slow-growing on PDA, velutinous or flocculent form, irregular on the edge, milk white to ivory color. These isolates were observed for appearance of pycnidia containing guttulate conidia on PDA and on sterile filter paper. DNA extractions from mycelia of the isolates were amplified by ITS1/ ITS4 and ActF1/R1 primers. Compared with the sequences in the NCBI database, these sequences had a similarity of 98–100% with Phoma macdonaldii. All isolates were tested on four true-leaf sunflower seedlings using hypocotyls inoculation. Typical black oval lesions were found on the stem after 7 d and black pycnidia were found on the lesions. Based on the morphological characteristics, sequences analysis and pathogenicity test, these nine isolates were identified as Phoma macdonaldii. This is the first intercept record of Phoma macdonaldii from imported sunflower seeds in China.