Fruit rot of cucurbits caused by several pathogenic fungi has become an important postharvest disease worldwide. In 2022, fruit rot on watermelon (Citrullus lanatus) and muskmelon (Cucumis melo) was observed during the postharvest storage phase in the Chiang Mai and Phitsanulok Provinces of northern Thailand. These diseases can lead to significant economic losses. This present study was conducted to isolate the causal agent of fungi in lesions of fruit rot. A total of four fungal isolates were obtained, of which two isolates (SDBR-CMU422 and SDBR-CMU423) were obtained from rot lesions of watermelons, while the remaining isolates (SDBR-CMU424 and SDBR-CMU425) were obtained from rot lesions of muskmelons. All fungal isolates were identified using both morphological characteristics and molecular analyses. Morphologically, all isolated fungal isolates were classified into the genus Fusarium. Multi-gene phylogenetic analyses of a combination of the translation elongation factor 1-alpha (tef-1), calmodulin (cam), and RNA polymerase second largest subunit (rpb2) genes reveled that four fungal isolates belonged to the Fusarium incarnatum–equiseti species complex and were distinct from all other known species. Thus, we have described them as two new species, namely F. citrullicola (SDBR-CMU422 and SDBR-CMU423) and F. melonis (SDBR-CMU424 and SDBR-CMU425). A full description, illustrations, and a phylogenetic tree indicating the position of both new species have been provided. Moreover, pathogenicity tests were subsequently performed and the results showed that F. citrullicola and F. melonis caused symptoms of fruit rot on inoculated watermelon and muskmelon fruits, respectively. Notably, this outcome was indicative of the symptoms that appeared during the postharvest storage phase. To our knowledge, two new pathogenic fungi, F. citrullicola and F. melonis, are new causal agents of watermelon and muskmelon fruit rot, respectively. Importantly, these findings provide valuable information for the development of effective strategies for the monitoring and prevention of these diseases.

Fruit rot caused by phytopathogenic fungi is one of the major diseases affecting watermelons (Citrullus lanatus) around the world, which can result in unmarketable fruits and significant economic losses. Fruit rot was observed on watermelons throughout the postharvest storage periods in Phayao Province, northern Thailand in 2022. For the present study, a total of ten fungal isolates were isolated from the rot lesions of watermelons. All obtained fungal isolates were then characterized in terms of their pathogenicity. The results indicated that only four fungal isolates caused rot disease with similar symptoms during the postharvest storage period. Based on their morphological characteristics, these four fungal isolates were identified as belonging to the genus Fusarium. Using multi-gene phylogenetic analyses with a combination of the translation elongation factor 1-alpha (tef-1), calmodulin (cam), and RNA polymerase second largest subunit (rpb2) genes, the fungal isolates were subsequently identified as Fusarium compactum and F. paranaense. Taken together, the results of this study indicate that F. compactum and F. paranaense cause fruit rot disease in watermelons. To the best of our knowledge, this is the first study to report F. compactum and F. paranaense as novel pathogens of watermelon fruit rot both in Thailand and elsewhere in the world.

Cantaloupe (Cucumis melo var. cantalupo) has become an economically important crop in Thailand and the fruit is popular among consumers. In June 2016, gummy stem blight, an important disease of cucurbits, was found on cantaloupe in Phayao Province, Thailand. The causal fungus was isolated from lesions and identified as Stagonosporopsis cucurbitacearum based on morphological characteristics and phylogenetic analysis of combined sequences of the internal transcribed spacer and large subunit regions of ribosomal DNA, and β-tubulin genes. The isolated fungus caused symptoms of gummy stem blight on inoculated cantaloupe, which were similar to the natural symptoms observed in the field. This is the first report in Thailand of gummy stem blight disease on cantaloupe caused by S. cucurbitacearum.

A new endophytic ascomycete, described herein as Fusarium endophyticum, was isolated from leaves of Camellia sinensis var. assamica collected from Nan Province, northern Thailand. This species is described using morphological characteristics and molecular multi-gene analyses. Multi-gene phylogenetic analyses of a combination of internal transcribed spacer region of the rDNA (ITS), translation-elongation factor 1 alpha (tef-1), RNA polymerase II second largest subunit (rpb2), and RNA polymerase II largest subunit (rpb1) genes revealed that F. endophyticum belonged to the Fusarium lateritium species complex (FLSC) and was distinct from all other known species. A full description, illustrations and a phylogenetic tree showing the position of F. endophyticum are provided.

Culinary melon (Cucumis melo subsp. agrestis var. conomon) is widely cultivated throughout Thailand and represents an important agricultural crop. During 2023–2024, anthracnose, charcoal rot, and fruit rot caused by fungi were observed on postharvest culinary melon fruits in northern Thailand. This study aimed to isolate and identify fungal pathogens associated with these postharvest diseases in culinary melons, as well as to assess their pathogenicity. Eight fungal strains were isolated and identified through morphological characterization and multi-gene phylogenetic analysis. Colletotrichum chlorophyti and C. siamense were identified as the causal agents of anthracnose, Fusarium sulawesiense caused fruit rot, and Macrophomina phaseolina was responsible for charcoal rot. Pathogenicity tests were conducted, and the fungi were successfully re-isolated from the symptomatic lesions. Moreover, sensitivity tests for fungicides revealed that C. siamense was completely inhibited by copper oxychloride and copper hydroxide. Colletotrichum chlorophyti was inhibited by benalaxyl-M + mancozeb, copper hydroxide, and mancozeb. In the case of M. phaseolina, complete inhibition was observed with the use of benalaxyl-M + mancozeb, mancozeb, and propineb. Copper hydroxide successfully inhibited F. sulawesiense completely. To our knowledge, this study is the first to report C. siamense and C. chlorophyti as causes of anthracnose, F. sulawesiense as a cause of fruit rot, and M. phaseolina as a cause of charcoal rot in postharvest culinary melon fruits in Thailand. It also marks the first global report of C. siamense, M. phaseolina, and F. sulawesiense as causal agents of these respective diseases in culinary melon. Furthermore, the results of the fungicide sensitivity tests provide valuable information for developing effective management strategies to control these postharvest diseases in the future.