Phenotypic Characteristics of Strawberry Floral Organs in Response to Botrytis cinerea Infection and Methods for Gray Mold Resistance Evaluation

Strawberry (Fragaria × ananassa) gray mold, caused by the pathogen Botrytis cinerea, is a commercially devastating disease. This pathogen infects multiple tissues and organs of strawberry, with floral organs as the main primary infection sites. However, the resistance of floral organs among different strawberry germplasm to gray mold remains unclear. The present study aims to investigate the response characteristics of strawberry floral organs to B. cinerea infection, establish an in vitro floral inoculation method for evaluating gray mold resistance, rapidly identify the gray mold resistance differences among strawberry germplasm, and to screen out resistant and susceptible resources.

In this study, detached flowers of strawberry resistant/susceptible cultivars ‘Yanli’ and ‘Benihoppe’ were used as experimental materials, and inoculated with conidia of B. cinerea strain Bc05.10 to identify the phenotypic characteristics of different tissues and the disease index of stamens. Floral organs of 31 strawberry cultivars were inoculated in vitro with Bc05.10 conidia to determine the stamen disease index. The field incidence of gray mold was surveyed, and a correlation analysis between the stamen disease index and field incidence was performed.

Brown lesions first appeared on the stamens of two cultivars; as the inoculation time prolonged, the lesions spread from the anthers to the filaments, and eventually extended to the sepals. The disease index of stamens in ‘Benihoppe’ was significantly higher than that in ‘Yanli’. At 4 hours post-inoculation (hpi), the conidial germination rate on the stamens of ‘Yanli’ (20.30%) was significantly lower than that of ‘Benihoppe’ (80.42%). A total of 31 strawberry cultivars were evaluated for gray mold resistance by inoculating conidia of Bc05.10 onto the stamens of detached flowers. Among them, ‘Qiaojiaren’ ‘Yayohime’ ‘Fenjiaren’ and ‘Guangdian’ were identified as resistant cultivars, while ‘Benihoppe’ ‘Tianshi No. 8’ ‘Toyonoka’ and ‘Fenyu’ were highly susceptible cultivars. Field investigation on the natural incidence of gray mold revealed that the floral organs of ‘Yanli’ ‘Jingyu’ ‘Mengzhiying’ ‘Jingshuo’ and ‘Fenjiaren’ had the lowest field incidence, while ‘Tochiotome’ ‘Nyohō’ and ‘Benihoppe’ had the highest field incidence. The correlation coefficients between the field incidence of different cultivars and the disease index at 12 hpi and 24 hpi were r=0.565 (P=0.035) and r=0.610 (P=0.021), respectively, showing significant positive correlations; no significant correlation was observed between the field incidence and the disease index at 36 hpi (r=0.328, P=0.252). Additionally, the cumulative disease index at 12 hpi + 24 hpi showed a highly significant positive correlation with the field disease incidence (r=0.713, P=0.004).

A rapid evaluation system of strawberry resistance to gray mold was established by using isolated stamens as inoculation materials. It accurately assessed the resistance level of floral organs of different strawberry germplasm resources to gray mold, thereby providing a new method and reference for the screening of resistant strawberry resources.