Citrus post-bloom fruit drop (PFD) is caused by Colletotrichum acutatum and C. gloeosporioides species complexes and frequently occurs in São Paulo (SP) state, Brazil. The environmental requirements for conidial germination and appressorium formation have been already determined in vitro; however, the environmental conditions for infection in citrus flowers remain unknown. C. acutatum is considered the main species complex causing PFD in citrus, but a survey of the pathogen’s prevalence has never been performed in SP state. The aims of this study were to assess the influence of different temperatures and wetness periods on infection of flowers by C. acutatum and C. gloeosporioides in potted citrus trees, and to determine the prevalence of both pathogens in different SP regions and sweet orange varieties. Environmental requirement trials were conducted in 2- to 3-year-old potted sweet orange trees. Flowers at different development stages (R2, R4 and R5) were inoculated with C. acutatum and C. gloeosporioides, and the trees were incubated at 18 or 24 °C for wetness periods of 6, 8, 12, 16 or 24 h. The percentages of inoculated flowers with PFD lesions and persistent calyces were calculated. The prevalence of both pathogens in SP regions was assessed in samples of diseased flowers collected at 16 commercial orchards of ‘Natal’, ‘Valencia’ and ‘Pera’ sweet oranges. The species complex was confirmed by isolation and PCR with species complex-specific primers. Blossom blight and persistent calyx incidences were higher in flowers inoculated with C. acutatum than in those inoculated with C. gloeosporioides. Incubation periods ranged from 2 to 5 days, and from 5 to 6 days for C. acutatum and C. gloeosporioides, respectively. In SP, irrespective of the region and sweet orange variety, C. acutatum was isolated from more than 80% of symptomatic flowers. We concluded that C. acutatum is not only more aggressive than C. gloeosporioides for causing PFD but also more prevalent in SP orchards.

柑橘花后果实掉落（PFD）是由切菜炭疽菌和C. gloeosporioides物种复合物引起的，并经常发生在巴西圣保罗（SP）州。在体外已经确定了分生孢子萌发和ress形成的环境要求。然而，柑橘花感染的环境条件仍然未知。切皮衣藻被认为是导致柑橘中PFD的主要物种，但从未在SP状态下进行过病原体流行情况调查。这项研究的目的是评估不同温度和湿度时期对切花衣藻和球孢C. gloeosporioides的花朵感染的影响。在盆栽柑桔树中，并确定不同SP地区和甜橙品种中两种病原体的流行情况。在2至3岁的盆栽甜橙树中进行了环境要求试验。在不同发育阶段的花朵（R2，R4和R5）上接种了满角油杆菌和球孢梭菌，然后将树木在18或24°C下孵育6、8、12、16或24 h。计算了具有PFD病变和持续性花萼的接种花的百分比。在“ Natal”，“ Valencia”和“ Pera”甜橙的16个商业果园中采集的病花样品中评估了SP区的两种病原体的患病率。通过分离和使用物种复合物特异性引物的PCR确认了物种复合物。接种C. acutatum的花比接种C. gloeosporioides的花的花枯病和持久的花萼发生率高。钝角隐孢子虫和球孢梭菌的潜伏期为2至5天，而潜伏期为5至6天， 分别。在SP中，无论区域和甜橙种类如何，从超过80％的有症状花朵中分离出A. acutatum。我们得出的结论是，在导致PFD方面，切角梭菌不仅比角孢梭菌更具侵略性，而且在SP果园中更普遍。