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.
Figure 1. Stages of seeds, which use for the germination test (1 = Bloom, petals of ray flower wilting, 2 = All petals of ray flower dropped and partial wilting of disc flower, 3 = All petals of disc flower wilted but seeds still green, 4 = Seeds darken and drying up and 5 = Fully mature seeds)
120 Germination (%seed) stage 100 1 2 3 4 5 100 90 95
90 83 80 70
76 57 60 69
40 50 41
30 20
0 1234Time after cutting (days) Figure 2. Germination of the seeds of various stages
560 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.
Growth and other characters Seed germination in soil: About 65% of the seeds germinated within the first 10 days of the experiment, but the rate of germination increased gradually thereafter (Figure 3). 100 Germination (%) (4A) 90
73.9 73.9 80 72.1 73 73.4 73.8 74 69.6 70.6 71.3 65.1 68.2 70 72.1 73.4 73.7 73.8 73.9 73.9 60.4 69.2 69.9 70.8 71.3 60 52.3 65 65.3 50 56.7 45.9 40 30 20 10 0 5 6 7 8 9 1011121314151617181920212223242526272829303142 Days after broadcasting
Figure 3. Germination of seeds in 1 x 1 m2 plots
Growth and development: The plant height during the first 25 days averaged only 10 cm. At 36 days, plots of all planting densities produced plants of similar height. A difference in plant height was observed at 52 days, where the plots with 1 plant/m2 produced plants at a height of 48 cm while those in plots with a density of 58 plants/m2 resulted in an average height of 26 cm. No further gain in plant height was observed after 75 days (Figure 4). The plots with a single plant/ m2 recorded a height of 120 cm while those with 58 plants/m2, recorded a height of 95 cm. This is as expected due to severe competition for resources when the population density increases.
140Hiht ( ) plant number in 1 sq.m 120 1 100 4 58 80 First Appearing of blooming 60 flowering bud
40
20
0 17 22 27 31 36 41 45 52 57 62 66 71 76 80 85 90 94
Days after germination
Figure 4. Height of plants at varying density per m2
The number of branches per plant will influence the number of flowers as they are formed apically. Therefore, more branches would result in more seeds being produced. At 120 days, the plants still continued to branch, especially in the plots with a single plant/ m2, resulting in 246 branches. The plots with a density of 58 plants/m2 produced only 57 branches per plant (Figure 5) Number of leaves per plant showed a similar trend to that of plant height and number of branches. At 61 days after seeding, the plots with a single plant/ m2 had an average of 403 leaves while in the plot with 58 plants/ m2, it was 132 leaves per plant (Figure 6). It is worthy to note that after 35 days, apical floral buds were formed, followed by new branching of the central stem and then by the side stems. Seed production of this species is phenomenal, meeting the criteria that major weeds of the world are prolific seed producers. The number of flowers per plant was high, maturing with white petals of ray flowers that are clearly visible at 59 days after germination (Figure
561 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.
7). This is considered a complete flower and the plots with single plant/m2 produced about 89 blooms per day (Figure 6) while those with 58 plants/m2 produced only 1 new bloom per day. Flower production increased gradually as the plant become taller. Branches no. 300 plant number in 1 sq.m 250 1 4 200 58
150 First Appearing of blooming flowering bud 100
50
0 29 33 38 43 47 52 57 61 66 73 78 82 87 92 96 101 106
Days after germination
Figure 5. Number of branches per plant
Leaves no. 600 plant number in 1 sq.m 500 1 4 400 58
300 First Appearing of blooming 200 flowering bud
100
0 19 22 24 26 29 31 33 36 38 40 43 45 47 50 54 57 59 61 64 66 68
Days after germination
Figure 6. Number of leaves per plant
Flowering no. 60 plant number in 1 sq.m 50 1 4 40 58
30
20
10
0 59 61 64 66 68 71 73 75 78 80 82 85 87 89 92 94 96 99 101 103
Days after germination
Figure 7. Number of flowers in each plot size of varying density
The number of seeds per plant was highly variable, depending upon planting density/m2. The cumulative number of seeds formed on the 96th day after germination was 13,929 per plant for the treatment with a single plant/m2 while the lowest was in the plots with 58 plants/ m2 (761 seeds per plant). The estimated seed production for the plant densities of 1, 4 and 58 plants/ m2 is 13,929, 33619 and 44,142, respectively (Figure 8).
562 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.
5000 Nftdd/d 4500 no. of plant in 1x1sq.m. 4000 1 4 58 3500 3000 2500 2000 1500 1000 500 0 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95
Days after germination
Figure 8. Number of Romerillo seeds produced m² under varying planting densities
Allelopathic potential of Romerillo In comparison with B. pilosa L. var. pilosa and B. pilosa L. var. minor, leaves of all three species at 0.1 and 0.5 g were able to inhibit growth of young Mimosa pigra, with Romerillo demonstrating the highest ipact (Figure 9). Hence, in its natural habitat, it is usually seen growing in pure stands.
Figure 9. Growth of Mimosa pigra in fresh and dried leaves of 3 varieties of Bidens pilosa L.; var radiata (R), var. minor (M), and var. pilosa (P)
In Thailand the B. pilosa var. minor and var. pilosa are common weeds, especially in the northern region. The var. minor has ray flowers with petals while the var. pilosa does not. Moreover, the field surveys also indicated that cuttings of mature stems sealed in polyethylene bags for 7 days with adequate moisture were still with green leaves, and many adventitious roots forming from the base up to top 4-5 leaves. When these cuttings were planted in the soil, they established well and continued to grow and compete against other species. The large white-ray flowers are attractive when compared to other plants. As they grow well without much attention, people harvest seeds and plant them on vacant land, helping the spread of the species. The seeds have 2 – 6 hooks at one end, which help the get attached to clothing, animal hairs, etc. supporting their dispersal. This study revealed that the seeds of Romerillo have no dormancy, with 80 – 90% germination rate in the laboratory and
563 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.
72% in the field. Among the newly emerged plants, 81% produced seeds after 35 – 40 days and completed the full cycle within 57 – 70 days. In Thailand, the climatic conditions enable Romerillo to go through 5 – 6 cycles per year, with the original plant still reproducing. Estimation done based on these figures resulted in a minimum of 31 million plants after 2 years of growth from one single plant (Table 1), which is worse than B. pilosa Linn. that has already established in Thailand. A single plant of B. pilosa Linn. can produce about 3,000 - 6,000 mature seeds, which are ready to germinate. Bidens pilosa Linn completes about 3 – 4 cycles in a given year with 95% germination rate, and even after 3 – 5 years of storage, the seeds still have about 80% germination rate. The Romerillo’s capabilities surpass this species. In its natural habitat in the north, Romerillo does not grow in mixed stand, most likely due to its stronger alleopathic effects than B. pilosa.. The summarized properties of the species when compared to the characteristics of an ideal weed Muenscher (1981) are shown in Table 2.
Table 1. Number of seeds produced
Year No. of Seeds Available 72% Germination 80% Survived No. of seeds produced 1 1 41,787 2 41,7 87 30,0 87 24,069 54,950,23 9 3 54,950,23 9 39,564,17 2 31,651,33 8 72,260,004,276 4 72,260,004,276 52,027,203,079 41,621,762,463 95,022,483,703,177
Table 2. Important properties of weeds as summarized by Muenscher (1981)
Some Important Properties of Weeds Characteristics of Romerillo Growth Grow well under unsuitable conditions and suitable G row well in moist and drought conditions, even in conditions similar to that required by the crop. concrete cracks and in the shade. Contain undesirable odor or unpalatable taste, Contain allelochemicals inhibiting growth of other plants. covered with hairs, thorns or slime, enabling it to Leaves release odor when crushed. Leaves not damaged survive attacks by insects and animals. by insects and no known natural enemies in Thailand. Seed Production Able to produce many seeds per year. 1, 4 and 58 plants/m2 produce 41,787, 25,215 and 2,283 seeds/year, respectively Seed viability is long, able to germinate even if in Seeds known to survive up to 6 years the soil for many years Seeds able to develop into maturity, even if Seeds mature 10-15 days after bloom and can germinate removed from plant early, some species seeds at only 6-7 days later. And it can germinate even not mature at flowering stage mature. Seeds usually difficult to separate from seeds of crop as usually of similar size and shape Fruit or seeds usually have dispersal aids 2 – 6 hooks found at one end of seeds and along the seed length there are small thorns, which aid in seeds attaching to animal hairs or human clothing Propagation Able to propagate with stem and roots Cut stem can form roots and grow given adequate moisture
Literature cited
Alonzo, D.S., Hidebrand, J.W. 1999. Bidens L.. In: de Padua, L.S., Bunyapraphatsara, N. and Lemmens, R.H.MJ. (Editors): Plant Resources of South-East Asia Vol.12 (1) Medicinal and poisonous plants 1. Backhuy Publishers, Leiden, the Netherlands. pp 150-155. Forestry Botany Section, 2001. “Plants of Thailand” Tem Smitan, Revised edition. p 74. Muenscher, W.C. 1981. Weeds 2nd ed. Cornell University Press. USA. 586p. Wit, T. 1996. Encyclopedia of Thai Medicinal Plant. Prachumthongkarnpim. p 2.
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