Proceedings of the 21st Asian Pacific Weed Science Society Conference (Editors: B. Marambe, U.R. Sangakkara, W.A.J.M. De Costa, and A.S.K. Abeysekara), 2-6 October 2007, Colombo, Sri Lanka. SOME CHARACTERISTICS OF Bidens pilosa L. var. radiata Scheff., A NEW INVASIVE SPECIES IN THAILAND S. Zungsontiporn Weed Science Group, Plant Protection Research and Development Office, Department of Agriculture, Bangkok, Thailand [email protected] Abstract: Romerillo (Bidens pilosa L. var. radiata Schultz-Bip.), a native of Tropical America, was introduced to Thailand for apiculture around 1998-99 from Taiwan. The seeds were sown along road side in the Chiangmai province of northern Thailand. This species was detected 2 years after introduction. Seeds were collected and studied for weed potential such as seed germination, growth and seed production were studied in Bangkok. Other characteristics such as competitiveness including damage to crops were observed in the area of invasion in northern Thailand. It was found that the plant can survive in various habitats; on extreme dry land such as along cracks of concrete river banks, on flooded land and even in ditches. Each plant can produce about 41,000 seeds a year. The seeds harvested in Bangkok has about 72% germination rate, while the ones collected from the invasive area has 90-100% germination rate. The plant can complete its life cycle within 60 days. Propagation of this plant is both through reproductive and vegetative parts. The seed has small hooks and spines which assist in attaching to animal hairs, cloth or other materials aiding in dispersal far away. The plant has attractive flower heads with big ray flowers. Presently, this plant can be found in many locations such as in the north, northeast, south and central Thailand. Key words: Bidens pilosa, invasive plants, biology, Thailand Introduction Invasive weeds that cause serious economic damage to farmers and the country in general are introduced weeds. These include water hyacinth, giant sensitive plant, pennisetum and Shama millet. Their introductions could be intentional introduction for specific purposes such as for production of fodder, for soil improvement or for ornamental purposes. They could be legal or illegal introductions, while some introductions were ignorant introductions or unintentional introductions such as seed contamination of agricultural imports. Newly introduced species will adapt to the new environment. Establishment follows and if well established can become aggressive and turn into noxious weeds. Some species grow well together with native species, eventually become naturalized and no longer a problematic weed. Good examples of this instance are the water hyacinth (Eichhornia crassipes (Mart.) Solms) and Mexican fireplant (Euphorbia heterophylla (L.) Klotzsch & Garcke). The water hyacinth was introduced in 1901 for ornamental purpose and in 1913 the Water Hyacinth Control Act was promulgated. This law was ineffective as the weed continued to clog rivers, canals and waterways, impeding water traffic. However, a century after introduction, the water hyacinth is accepted as an naturalize plant. Romerillo (Bidens pilosa L. var. radiata Schultz-Bip.), a native of Tropical America, is a member of Asteraceae or Compositae Family with about 200 species in the Genus Bidens scattered in tropical and sub-tropical regions of the world. Only 4-5 species are reported in South-east Asia, Bidens pilosa being the most common but due to wide variations, the taxonomy of this species is not yet satisfied (Alonzo and Hidebrand, 1999). In Thailand, B. bipinnata L., B. pilosa L. and B. biternata (Lour.) Merr. & Sherff were reported (Forestry Botany Section, 2001) which only B. pilosa L. var pilosa, B. pilosa L. var minor and B. biternata (Lour.) Merr. & Sherff were used as medicinal herb (Wit, 1996) Seeds of Romerillo were brought to the Kingdom of Thailand around 1998 -1999 by a Taiwanese beekeeper as a food source as it flowers all year round, is a fast grower and needs 558 Proceedings of the 21st Asian Pacific Weed Science Society Conference (Editors: B. Marambe, U.R. Sangakkara, W.A.J.M. De Costa, and A.S.K. Abeysekara), 2-6 October 2007, Colombo, Sri Lanka. very little attention. Seeds have been scattered in many nearby areas and the species eventually became known as Chiang Rai daisy, for its daisy-like flower. Some call it Taiwanese cosmos, after the introducer. The plant is similar to B. pilosa L. var. minor, a common weed in Thailand but the flower is more attractive than that of B. pilosa L. var. minor. So the purpose of this study was to compare the different of this plant from other varieties of the same species and the invasiveness character of this plant in Thailand. Materials and Methods Distribution Since the plant was introduced without any record and it was first detected in year 2001, 2-3 years after introduction. So to clarify out the distribution and the habitat suitable of Romerillo, survey along roadside was done. Seed germination Matured seeds were collected from the northern region and from a net house in Bangkok in 2001. Seeds from each location were spread in a ∅90 mm Petri dish containing 1 piece of Whatman filter paper (No.4), at a rate of 50 seeds for each dish, with a total of 6 dishes per location. Five ml of distilled water was added to each Petri dish, and the Petri dishes were kept at room temperature to simulate the natural conditions in Bangkok. The numbers of germinated seed were recorded on the 7th day from the commencement of the experiment. Germination of seeds at different ages after development: Seeds of Romerillo were collected from flower head at (a) full bloom, petals of ray flower wilting, (b) all petals of ray flower dropped and partial wilting of disc flower, (c) all petals of disc flower wilted but seeds still green, (d) seeds darken and drying up, and (e) fully mature seeds. All the seeds were tested for germination at 1, 2, 3 and 4 day after removal. The seeds of each stage were spread in ∅ 90 mm Petri dish with 1 filter paper at a rate of 10 seeds per Petri dish, with 3 replicates. The number of germinated seed was record 7 days later. Growth and other character To study the growth habit and seed production of Romerillo, an experiment was set up in Bangkok, where 100 seeds of Romerillo were broadcasted in 1 x 1 m2 plot, with a total of 12 plots. The number of seedlings in each plot was recorded until 1 month, and then the seedlings uprooted in randomly selected plots. The plant height, branches, flowering number and number of matured seeds were recorded once in two days for 4 months. The growth characteristics of Romerillo were compared with those of B.s pilosa L. var. minor and B. biternata, which already exist in Thailand. Allelopathic potential of Romerillo Leaves of Romerillo, B. pilosa L. var. minor and B. pilosa L. var. pilosa were collected from the experimental plots and about 10 g of each were dried in oven at 50°C for 24 hrs. Then the dried leaves at 0 (control), 0.01, 0.05 and 0.1 g were laid between 2 layers of 10-10 ml of 0.5% agar at φ29 mm x 130 mm height. Six seeds of Mimosa pigra L. were placed on the top of the agar, sealed with transparent film. Another set was done following the same procedure, but using fresh leaves at the same weight. All the tubes were placed in a growth chamber at 30°C with 24 hrs light. Root length and plant height were recorded at 7 days later. 559 Proceedings of the 21st Asian Pacific Weed Science Society Conference (Editors: B. Marambe, U.R. Sangakkara, W.A.J.M. De Costa, and A.S.K. Abeysekara), 2-6 October 2007, Colombo, Sri Lanka. Results and Discussion Distribution Romerillo has its origins in tropical South America. There are reports that it is a serious weed in American Samoa (IPM Plans of Work – Alabama to Hawaii), very wide spread weed in Okinawa of Japan and similarly in Taiwan. In the USA, it is found in Alabama, Connecticut, Florida, Hawaii, Louisiana, Missouri and Pennsylvania. Surveyed areas in the northern Thailand include Chiang Mai, Chiangrai, Payao, Phrae, Nan, Lampang and Lampoon where the weed grows in all sorts of conditions. Along the road edge, along the rim of the canal, mid-road islands and even in cracks of hot and dry concrete banks along the Mekong River. It has spread into vegetable growing areas, citrus groves, mango and longan orchards as well as maize land. Farmers in the area indicated that they have applied herbicides in the maize plots to control Romerillo, however, the type of herbicide used could not be determined. Seed germination Germination of matured seeds collected from the northern region of Thailand showed high percentage of germination (94%). The seeds harvested from the net house in Bangkok gave a lower percentage of germination (72.3%). Various stages of seeds, which developed from flower, are shown in Figure 1 and their germination at each growth stage is shown in Figure 2. About 53-100% matured seeds germinated without dormancy. The seeds at stage 3-4 germinated at a rate of more than 50 % even when they are not completely matured at harvesting. The seeds, which were not well developed at the stage 1, did not geminate at any time of testing. However, the young seeds that were collected when the ray flowers were dropped (stage 2), germinated after keeping for 3 days, but the germinations rate was less than 50%. This implied that even the seeds are not completely mature at the time of cutting may develop further if left for few days, and geminate later.