Diversity and Characteristics of <i>Fusarium solani</i> Species Complex (FSSC) Isolates Causing Collar Rot and Fruit Rot of Passion Fruit in Taiwan

<i>Fusarium</i> <i>solani</i> species complex (FSSC) is a causal agent of collar rot and fruit rot in passion fruit worldwide. This study investigated the diversity and characteristics of FSSC isolates causing collar rot and fruit rot in Taiwanese passion fruit. Thirty-five FSSC isolates were harvested from collar rot and fruit rot samples of passion fruit from various cultivars and different geographical locations in Taiwan. The majority of these FSSC isolates caused collar rot and fruit rot disease of varying virulence in the stems and fruits of the purple and yellow cultivars of passion fruit. FSSC isolates were categorized into four groups: <i>F</i>. <i>solani</i>-<i>melongenae</i> (FSSC 21; <i>n</i> = 29), <i>F</i>. <i>solani</i> (FSSC 5; <i>n</i> = 1), <i>F</i>. <i>liriodendri</i> (FSSC 24; <i>n</i> = 1), and an unknown group (<i>n</i> = 4) based on the phylogenetic analysis of internal transcribed sequence (ITS), translation elongation factor 1 alpha (TEF-1α), and RNA polymerase II subunit 2 (RPB2) sequences. In Taiwan, <i>F</i>. <i>solani</i>-<i>melongenae</i> was the dominant species causing collar rot and fruit rot in passion fruit. <i>F</i>. <i>solani</i>-<i>melongenae</i> was a homothallic fungus that produced perithecia in diseased tissues. However, <i>F. solani</i> and <i>F</i>. <i>liriodendri</i> did not produce perithecia. The unknown FSSC group showed morphological characteristics similar to <i>F</i>. <i>solani</i>-<i>melongenae</i> and produced perithecia. Phylogenetic analysis based on the ITS and TEF-1α sequences demonstrated that the Taiwanese FSSC isolates were distinct from the Brazilian and Chinese FSSC isolates. In summary, FSSC isolates causing collar rot and fruit rot of Taiwanese passion fruit showed high diversity, potentially associated with the geographical locations.