Occurrence and Seasonal Development of Plant Parasitic Algae Cephaleuros (Chlorophyta, Ulvophyceae) in Southern Thailand

The occurrence and seasonal development of three Cephaleuros species, namely C. karstenii, C. pilosa, and C. virescens, were assessed on Lansium domesticum, Garcinia mangostana, and Mangifera indica hosts, respectively, at study sites at Prince of Songkla University, southern Thailand. We compared the development of algal thalli, the number of thalli (lesions), and reproductive structures (gametangia and sporangia) between the rainy and summer seasons. Fresh algal thalli appeared on the leaves of the three plant hosts during the rainy season. The development of gametangia and sporangia on algal thalli varied between different Cephaleuros species. However, the release of gametes and zoospores occurred during the rainy season. The average numbers of thalli, gametangia, and sporangia of the three Cephaleuros species during the rainy season were significantly higher than during the summer. Pearson correlation analysis indicates that the occurrence of plant-parasitic algae is influenced by environmental factors such as humidity and rainfall patterns, with higher infection rates observed during the rainy season. Based on the results of this study, the number of algal thalli increased, and the maturation and release of gametes and zoospores predominantly occurred in the rainy season in tropical Thailand. This study highlights the need for increased awareness of plant-parasitic algae as a potential threat to crop production in southern Thailand. Further development of integrated management practices tailored to local climatic conditions should be explored.