Veronica persica Poir. (also known as bird's-eye speedwell, common field-speedwell, Persian speedwell, large field speedwell, bird's-eye, or winter speedwell) is one of the widespread Veronica species in Eurasia and eastern Asia (Ono et al., 2010; Sharifi-Rad et al., 2018a). The genus Veronica belongs to the family Plantaginaceae of order Lamiales having 24 families and around 23,000 species (Choi et al., 2016). Veronica species are known as an effective traditional treatment with huge applications from wound healing to anti-cancer and anti-rheumatic activities (Sharifi-Rad et al., 2018b). The V. persica extract has been reported as medicinal plant for the treatment of Cutaneous leishmaniasis and has special anti-viral activities to suppress the growth of herpes simplex viral infections (Sharifi-Rad et al., 2018a; Sharifi-Rad et al., 2018c). Veronica species is rich in iridoids, flavones and phenolic contents (Fierascu et al., 2018) and has been reported for anti-inflammatory and antioxidant effects that functions for relief in lower abdomen and back pain (Park et al., 2018; Sharifi-Rad et al., 2018c). According to the naturalization survey of naturalized plants in South Korea V. persica Poir. is widely distributed with huge population (Lee et al., 2011). Despite the medicinal value the V. persica poir is reported as one of the dominant exotic weeds in South Korea (Park et al., 2011; Yang et al., 2012).
Exposure of exotic weeds across the different geo-physical area has a significant effect on the bio-diversity and ecological system (Clements and Ditommaso, 2011). Accidental introduction of exotic weed is the byproduct of human activities whereas natural introduction occurs through the movement of winds (Benvenuti, 2007). Invasion of these alien species may smother out the native species forcing them for extinction (Nasim and Shabbir, 2012). Moreover, massive industrialization has influenced the exposure of exotic plants through trade, on the other hand, anthropogenic human activities have adversely affected their eco-system that let them to get disappear (Adebayo and Uyi, 2010). Exotic weeds colonization in agriculture land have enhanced serious loss in grain production and have been reported for the global threat for food security (Orapa, 2001).
Exotic weeds might vary in their functionality such as Aquatic and terrestrial (Orapa, 2001), toxic and beneficial (Zhang et al., 2020). Toxic weeds can result in severe diseases when consumed by livestock in hay or pasture, hence noxious weeds need to be diagnosed to prevent the possible toxicity (Puschner, 2017). Nitrate accumulating plant such has Amaranthus retroreflexus and Chenopodium spp causes’ nitrite poisoning in ruminants resulting high mortalities, Pyroolizidine alkaloid containing plants such as Senecio vulgaris, Oleander (Nerium oleander), causes renal failure and develops cardiac signs, Irritating grasses like Bristlegrass (Setaria sp.) causes ulceration of the tongue, cheeks and gums (Puschner, 2017). However, Zhang et al. (2020) reported from an environmental perspective, colonization of toxic weeds might be more beneficial in degraded grassland by preventing the massive disturbance through livestock. Thus, the beneficiaries and toxicity need to be clearly classified according to the ecological effects.
Exotic plants may have minor effect or no effect but sometimes may become invasive and act as a pest. A case of Papua New Guinea where Salvinia, hydrilla, water letttuce and water hyacinth coverage in Sepik River around the area of 500 km2 deprived around 40,000 villagers from canoe access to the waterways to collect fish and sago due. The transportation was blocked and people were forced to feed with dried coconuts (Orapa, 2001). Likewise, (Rand and Louda, 2004) reported that the invasion of exotic thistles increased the susceptibility of native plants to weevil (Rhinocyllus conicus). Artemisia adamsii is reported for grassland destruction (Kinugasa et al., 2019), plant species like Crisium arvense and Solidage ssp. and Ambrosia artemisiifolia has huge invasion on swiss agriculture (Bohren, 2011). Exotic weeds like Senecio vulgaris dominance in Korean is now considered threat for eco-system and winter agriculture in Korea (Kim et al., 2018b). Approximately 321 taxa of exotic plant belonging to 40 families, 175 genera, 302 species, 15 varieties and 4 forms are reported in South Korea (Lee et al., 2011). The influx of exotic plant is rising rapidly in Korean peninsula, it has been reported that at least 158 annual weed species among which 100 species were inflowed within the last one decade. These inflows comprise 42% from Europe, 23% from North America, 9% from Eurasia and 8% from tropical America (Kim et al., 2000; Ko et al., 2019).
Introduction of new species in cropland is influencing the change in ecosystem in which some of them poses adverse economic losses (Shabbir and Bajwa, 2006). It has been reported that united states alone invest approximately 40 billion $ to control invasion of new species among which 26.4 billion $ accounts for cropland weeds management (Clements et al., 2004). Considerable attention has been given in recent years for invasive species due to its ecological effects and global consequences (Bai, 2014). Due to the exotic weed contamination swiss farmers are provided with certain income through ecological compensation program (Bohren, 2011). A check efficacy and judicious selection of control measure is necessary to achieve complete control. Therefore, the current research is focused on studying the germinating characteristics of V. persica and its control measures through appropriate herbicides selection and application doses. The best herbicides selection and study of germination characteristics might be helpful in estimating the possible economic cost to control weed incidence and assessing its environmental impact in Korean agriculture and eco-system.
Materials and Methods
Bird’s Eye seeds used in this study were collected on March 20, 2020, from the apple orchard located in Yeongcheon-si, Gyeongsangbuk-do (N36°04'06" E128°53'24"). The seeds were stored at a low temperature (4℃) until germination study.
Germination characteristics of V. persica Poir under light and various temperature conditions
To investigate the characteristics of seed germination under different light conditions, 20 seeds were sowed on a disposable sterile petri-dish (60×15 mm) supplied with filter paper. The temperature of the incubator was maintained as 25℃ (NB-205Q, N-BIOTEK, Bucheon, Korea). 1 mL of distilled water was supplied at the first day and 0.5 mL of distilled water was supplied at intervals of 3 days to maintain the moisture. Dark-condition groups were fully covered by aluminum foil to block the light. The germination rates and plant heights were assessed 15 days after sowing (DAS). Germination was regarded as a seed having more than 2 mm radicle.
To investigate the characteristics of seed germination under different temperature, 20 seeds were sowed on a disposable sterile petri-dish (60×15 mm) supplied with filter paper. The temperature of the incubator was set as 5, 15, 25, and 35℃ (BF-50SIR, BioFREE, Bucheon, Korea). Moisture maintenance, germination rate and growth measurement were performed accordingly as mentioned above.
Germination characteristics of V. persica Poir in different sowing depths
To investigate the characteristics of seed germination in different seeding depths, 20 seeds were seeded in a pot (100 mm diameter×90 mm depth). Seeding depths were 0, 1, 2, 3, 4, 5, and 6 cm. Each pot was filled with horticultural soil (Han-aleum sangto®, Sinsung Mineral, Goesan, Korea), placed in a greenhouse which temperature was maintained 20±5℃. Growth condition and measurements were performed as described above.
To investigate the management of bird’s eye by herbicide treatments of the soil, 20 seeds were sowed in a pot (100 mm diameter×90 mm depth) and covered with soil about 2 cm. Three days after sowing, the pots were treated with alachlor, indaziflam, pedimethalin. with one-half, one and two-fold application rate of recommended rate (Table 1). After 21 days of herbicide treatment, fresh weight and dry weight were measured, and control values were calculated.
To investigate the management of V. persica by herbicide treatments of the foliage, 32 seeds were sowed in a plastic tray (32 holes). 30 days after sowing, 18 equal size of plants were selected and transplanted to pot (100 mm×90 mm). 10 days after transplantation, the pots were treated with a different herbicide with one-half, one and two-fold application rate of recommended rate through a sprayer (Table 1). After 21 days of herbicide treatment, fresh weight and dry weight were measured, and control values were calculated by following formula.
Control value (%)=(untreated group weight-treated group weight/untreated group weight)×100
The study was carried out in a complete randomized design in triplicate. Statistical analysis was performed with SAS 9.4 software (SAS Institute, Cary, NC, USA). The mean values among the treatments were separated using Duncan’s multiple range test.
Results and Discussion
Effect of light, temperature and sowing depth in germination rate and growth of V. persica Poir
The germination rate of V. Persica is around 98% under light condition whereas the germination rate was 90% under dark condition. Statistical analysis showed no significant changes in germination rate of plants when compared between light and dark conditions (Fig. 1). However, the temperature showed higher fluctuation in the germination rate of V. Persica Poir. The maximum germination rate (98%) was observed at 35℃ which gradually dropped with decrease in temperature. The germination rate was below 20% at 15℃ whereas, germination was completely ceased at 5℃ (Fig. 2). In addition, the sowing depth has significant effect on the germination rate of V. Persica Poir plant.
The germination rate was observed in between the sowing depth of 0, 1, 2, 3, 4, and 5 cm and maximum germination rate was observed at 2 cm. The germination rate of V. persica was significantly higher at 2 cm (98%) as compared to other sowing depths (Fig. 3).
Moreover, the results showed that the plant height was correlated according to the germination rate of V. persica according to temperature. Here, the plant height was significantly higher at 35℃ with average 3.8 cm and gradual decrease was observed with the fall in temperature. Since no germination was observed at 5℃ there is no any plant growth at 5℃ (Fig. 4).
Furthermore, our results showed that the plant height of V. persica plant was significantly higher when sown at 4 cm depth. Surface sowing showed the lowest plant height whereas considerable plant height was noticed at 1, 2, and 3 cm. Beyond 4 cm depth, the plant height started to decrease as showed by the considerable drop of plant height at 5 cm depth (Fig. 5).
The Korean peninsula lies between Japanese and Chinese islands of East Asia (35°50′N, 127°00′W) which is influenced with Asian monsoon with an annual mean temperature of 6.6℃ (winter) to 16.6℃ (summer) (Nam et al., 2015). V. persica poir. emergence has been reported for spring, summer and autumn (Popay et al., 1995). Our results showed no growth of V. persica below 5℃, hence, it could barely affect the winter crops in Korea as the temperature falls below 5℃ during winter. However, the plant growth was observed ideal at 35℃, therefore, it could be predicted its distribution could be widely exposed during spring and summer season. Our results are in line with Song et al. (2019) who reported the average ideal growth temperature range of several Veronica species lies between 20℃ to 25℃. The emergence patterns are depended on the differences of rainfall and temperature which determines the nondormancy: dormancy of seed cycle in the soil.
Effect of herbicides on the growth and pre-emergence and post-emergence control of V. persica
In a post-emergence treatment, alachlor, indaziflam and pendimethalin was used. The application of alachlor and pendimethalin showed 100% control valueon post-emergence application. However, herbicide indaziflam showed 78% control valueat two-fold, 68% at single dose and 48% on one-half dose application Table 2.
The results showed that the highest control value was achieved with 2-fold application of glufosinate P with 94.7%. All the herbicides with half-dose application results the control valueto 85-92% except glyphosphate isopropylamine. Maximum control valueof 92.68% was achieved with one-half dose application of glufosinate P whereas single-fold application results to 93.63% control value. Moreover, the plant weight treated with different herbicides were measured and compared with control. The results showed that all the herbicides significantly dropped plant growth as compared to control. The maximum plant weight was observed in glyphosate isopropylamine treated plant whereas minimum plant weight was observed in glufosinate P treated plants Table 3.
Judicious selection of herbicides is crucial for sustainable agri-ecosystem. From the Table 3, it can be concluded that glufosinate P is the most efficient herbicides to control V. persica growth and glyphosate isopropylamine is considered to have low potential as compared to other herbicides for pre-emergence control.
Alachlor (2-chloro-2′,6′-diethyl-N-methoxymethylacetanilide) is considered as moderately mobile and pendimethalin [N-(1-ethylpropyl)-2,6-dinitro-3,4-xylidine] as non-mobile herbicides according to the adsorption/desorption study of pesticides leaching on rainfall and erosion (Kim et al., 2006). Since 100% control valuewas achieved with the application of alachlor and pendimethalin with one-half dose of recommended rate, it can be concluded that one-half dose application of either Alachlor or Pendimethalin is sufficient to achieve the absolute control of V. persica plant. Our results are in line with Ko et al. (2019) who showed the application of alachlor, pendimethalin and idanziflam application resulted 100% control of Oenothera biennis. However, there might be a severe threat of alachlor and pendimethalin as reported by Kim et al. (2018a) who strongly recommended the prohibition of alachlor and pendimethalin application, since, it has completely suppressed the growth of ballon flower (Platycodon grandiflorum). Therefore, the importance of studying the growth pattern and germination characteristics according to weed species seems crucial for the selection of herbicides for its control which is further justified by the results showed by Kim et al. (2018b) where, Linuron application has resulted 87% control of Senecio vulgaris whereas, alachlor and pendimethalin application limits the control valueto 81% and 28% respectively.
|Table 2. Effect of herbicides for pre-emergence control of V. persica.|
a-c: Different letters in the column after mean values represent the least significant differences at P ≤0.05.
Overall, both light and dark conditions are favorable for germination of the plants. The temperature of 35℃ and sowing depth of 2 cm are considered optimum for V. persica germination. For the control of V. persica invasion, glufosinate P effect was observed most efficient as post-emergence control. Whereas, one-half dose of alachlor and pendimethalin was found effective to completely control the V. persica incidence. Since half-dose of recommended rate of herbicides application has also showed a considerable control value of V. persica emergence and growth, the current findings may help to select efficient herbicides and formulate new recommended rate of application of different herbicides. We believe that our results would form a new baseline in terms of herbicides application to protect the environment and agricultural land from the possible hazards resulted from massive application of pesticides.
This study was supported by Agenda Program (Project No. PJ013216032020), Rural Development Administration, Republic of Korea.
Lee-Rang Kim, Division of Plant Biosciences, Kyungpook National University, Master student
Eun-Jung Park, Division of Plant Biosciences, Kyungpook National University, Researcher
Arjun Adhikari, Department of Applied Biosciences, Kyungpook National University, Doctor of Philosophy
Jin-Won Kim, Crop Protection Division, National Institute of Agricultural Sciences, RDA, Researcher
In-Jung Lee, 0000-0001-7154-4820