Elaborate Report of Allium sativum Clove Brown Rot Caused by Fusarium solani in China

In September 2023, brown rot disease was observed on cloves of garlic (Allium sativum) variety "Zipi-1" (purple skin) collected from Jinxiang County, China during scientific research at the Beijing Academy of Agricultural and Forestry Sciences after being planted in nutrient soil for approximately 2 weeks in a growth chamber maintaining 22℃, 60% relative humidity, and 16 hours of light. Out of the 90 garlic cloves investigated, 18 showed signs of decay, characterized by a brown color and rot, with the surface covered in blue and white mold layers. Six symptomatic cloves were collected for isolating the pathogen using the method described in a previous study (Wu et al. 2021). After 2 d of incubation, individual spores were harvested from the fungal colonies and recultured. Single-spore cultures growing on PDA medium appeared white and flocculent when viewed from the top, and yellowish-brown when viewed from the bottom. After 5 d of cultivation, the colonies had a diameter of approximately 5.8 cm and microscopic examination revealed that the mycelium had a diameter of about 9-13 µm (Fig. S1a, b and c). Isolate As1 produced three types of spores: oval-shaped chlamydospores with a diameter of approximately 6 µm, while spindle-shaped microconidia and sickle-shaped macroconidia measuring approximately 6-7 × 20-30 µm and 8 × 50 µm, respectively (Fig. S1d and e). The mycelial characteristics and reproductive structures of the isolates fit the morphological description of Fusarium solani (Xie et al. 2022). To confirm the identification, TEF1, RPB1 and RPB2 regions of the genome were amplified from three separate isolates (As1, As2, and As3) using EF1/EF2, RPB1-Fa/G2R, RPB2-5F2/7cR, and RPB2-7cF/11aR primer pairs (O'Donnell et al. 2022). The results indicated that the sequences of the three isolates were completely identical. Furthermore, the BLASTn comparison results of the TEF1 (OR916018, 710bp, 100%), RPB1 (OR916019, 1797bp, 99.8%), and RPB2 (OR916020, 1874bp, 100%) sequences in the FUSARIUM-ID v.3.0 database revealed that As1 was identified as F. solani species complex 5 (O'Donnell et al. 2022). To assess the pathogenicity of As1, the surface of healthy garlic cloves (n = 30) was spread with 106 microconidia/mL As1 suspension, while a control group (n = 30) was inoculated with sterile water. All inoculated cloves were placed in an artificial climate chamber under same conditions described above. After 10 d, all inoculated cloves exhibited rot symptoms consistent with those of the initially infected cloves identified in September 2023, while the control plant cloves remained asymptomatic (Fig. S2). Based on morphological and molecular characters (TEF1, RPB1, and RPB2), the reisolated pathogen from diseased plants was identical to the As1 isolate used for inoculation, and the disease assays were repeated twice. Fusarium spp. has been reported as the causal agent of garlic rot disease in several countries such as Mexico, America, and Russia (Gálvez and Palmero 2022). Tai (1979) previously published a report on the presence of F. solani in garlic; however, the content in the book is rather basic, lacking detailed information on the isolation, identification, and the potential for causing garlic diseases, whether postharvest or during growth. Our research can be considered a supplement and improvement to the study by Tai (1979) and lays the groundwork for future studies on management strategies to combat plant diseases caused by F. solani.