First Report of Rhizopus Head Rot of Sunflower Caused by Rhizopus arrhizus (syn. R. oryzae) in Xinjiang and Gansu Provinces of China

Abstract

Sunflower (Helianthus annuus) is an important oil crop widely grown in the Northwest of China. During 2015 and 2017, a survey on cultivated sunflower was undertaken in Northwest of China. Head rot of sunflower was observed in Changji County, Xinjiang Province in July 2015 and in Guazhou County, Gansu Province in July 2017. Brown water-soaked spots occurred and gradually spread on the back of the flower head and extended down the sepals and peduncles. The receptacle became soft and pulpy. White mycelial mats with numerous black spots were found on the back of the flower head and in the vicinity of infected achenes. The infected heads were collected in 2015 and 2017, respectively. Symptomatic tissues were surface sterilized with 0.5% sodium hypochlorite for 3 min and rinsed three times with autoclaved distilled water. Small pieces from symptomatic tissues were plated on potato dextrose agar (PDA) at 28°C. Within 3 days, colonies with abundant aerial and black sporangia were formed. Four isolates from Xinjia...