We detected tobacco mosaic virus (TMV), a member of the genus Tobamovirus and one of the most significant plant-infecting viruses, for the first time in a chrysanthemum in Thailand using reverse-transcription polymerase chain reaction (RT–PCR). The TMV-infected chrysanthemum leaves exhibited mosaic symptoms. We conducted a sequence analysis of the coat protein (CP) gene and found that the TMV detected in the chrysanthemum had 98% identity with other TMV isolates in GenBank. We carried out bioassays and showed that TMV induced mosaic and stunting symptoms in inoculated chrysanthemums. We observed the rigid rod structure of TMV under a transmission electron microscope (TEM). To enhance the speed and sensitivity of detection, we developed a colorimetric RT loop-mediated isothermal amplification (LAMP) technique. We achieved LAMP detection after 30 min incubation in isothermal conditions at 65 °C, and distinguished the positive results according to the color change from pink to yellow. The sensitivity of the LAMP technique was 1000-fold greater than that of RT–PCR, and we found no cross-reactivity with other viruses or viroids. This is the first reported case of a TMV-infected chrysanthemum in Thailand, and our colorimetric RT–LAMP TMV detection method is the first of its kind.

Chrysanthemum chlorotic mottle viroid (CChMVd) is a serious pathogen infecting chrysanthemum worldwide. To improve and enhance the detection procedure, the colorimetric loop-mediated isothermal amplifi cation (LAMP) technique was developed. Six LAMP primers were newly designed and tested the optimal conditions using a recombinant plasmid of CChMVd as a DNA template. The optimal conditions for colorimetric LAMP were incubation at 65°C for 60 min. At these conditions, the ladder-liked pattern LAMP products were detected along with the change of color from pink to yellow in the positive reactions. The sensitivity of colorimetric LAMP was up to 2.18 × 103 copies of recombinant plasmid concentration which was 104-fold greater than that of polymerase chain reaction (PCR). The developed colorimetric LAMP was not cross reacted to other viruse s and viroid. Effi ciency of colorimetric reverse transcription (RT)-LAMP for detecting CChMVd in chrysanthemum plantlets obtained from meristem tip culture was evaluated to verify and ensure CChMVd-free plantlets production. The results showed that 18 chrysanthemum plantlets were free of CChMVd contamination. Therefore, the colorimetric RT-LAMP can be used to detect CChMVd routinely due to its accuracy, rapidness and sensitivity.

Athelia rolfsii is one of the most destructive and aggressive fungal pathogens worldwide and causes southern blight disease of lettuce. A nonthermal atmospheric-pressure dielectric barrier discharge (DBD) plasma has attracted interest as an alternative control method to chemical usage because of its antimicrobial activity. Exposure of A. rolfsii to DBD plasma for 5, 10, 15, and 20 min resulted in in vitro fungal inhibition of mycelial discs and sclerotia. The results showed that DBD plasma exposure for 10 min completely inhibited fungal growth of mycelial discs, whereas exposure for over 20 min was required to inhibit the hyphal growth of sclerotia. Scanning electron microscopy (SEM) observations of mycelia and sclerotia abnormalities revealed laceration and damage of both mycelia and sclerotia. In addition, disease incidence and severity were reduced in mycelial and sclerotia inoculation following DBD plasma exposure for 15 and 20 min, respectively, compared with the positive control. In conclusion, the DBD plasma demonstrates antifungal activity against A. rolfsii via inhibition of fungal growth and reduction in disease incidence and severity. Therefore, DBD plasma has the potential to be applied in controlling southern blight disease of lettuce.

Melon yellow spot virus (MYSV) was previously reported from wax gourd in Thailand. A survey of cantaloupe, cucumber, melon, pumpkin and watermelon plants was carried out to determine if MYSV occurred more widely in cucurbit species. The survey revealed melon was mostly infected with MYSV. In addition, MYSV was detected for the first time in pumpkin in Thailand.

Chrysanthemum (Chrysanthemum x morifolium) belongs to the family Asteraceae, and it is one of the most popular ornamental plants in the world for its wide range of flower colour and structure (Hadizadeh et al., 2021). Chrysanthemum plants are infected by two viroids, the smallest and simplest plant pathogens, consisting of chrysanthemum chlorotic mottle viroid (CChMVd) and chrysanthemum stunt viroid (CSVd) (Cho et al., 2013). Viroids are small (250-400 nt), circular, highly structured RNAs that do not encode proteins and are replicated by nuclear or chloroplastic DNA-dependent RNA polymerases that accept RNA templates of the host plants (Ding & Itaya, 2007). Recently, more than 30 viroids have been identified and classified into two families based on biological, structural, biochemical features and especially, the present of CCR and hammerhead ribozymes that are uniquely