Identification and Potential of Secondary Metabolism of Weeds as Bio Herbicides in Environmentally Friendly Citrus Cultivation

Production of oranges in Indonesia increased from 1.78 million tons to 2.16 million tons in 2014. In 2016, Indonesia imported 2,212 tons of oranges. Weed plants caused a decline in orange production, leading to a decrease in harvest yields by 61%. The research aimed to identify weed species and the potential secondary metabolism of dominant weeds on orange plants. The research method utilized weed vegetation analysis, focusing on the Summed Dominance Ratio (SDR). The treatments with kirinyuh extract (P0) were as follows: (Control); P1: 20%; P2: 40%; P3: 60%; P4: 80%. Observation parameters included phytotoxicity, wet weight, and dry weight. The research results revealed 10 families, 25 species, and 400 weed individuals. Weeds with the highest SDR value were of the Oldenlandia corymbose type, with a Summed Dominance Ratio (SDR) of 7.28%, and the second-highest SDR value was Euphorbia hirta weed with 7.22%. The lowest was the Richardia brasiliensis weed with an SDR value of 0.633%. Phytotoxicity on kirinyuh leaf plants was highest in P4 with a concentration of 80g/l at 47.33. Wet weight and dry weight influenced P4 concentration, with an 80g/l concentration most inhibiting the growth of kirinyuh leaves. Laboratory analysis of flavonoid, total phenolic, and tannin content showed that Euphorbia hirta weed had higher levels compared to Oldenlandia corymbose weed.


Introduction
Over the past five years, from 2014 to 2019, Citrus production in Indonesia has witnessed a notable increase, surging from 1.78 million tons to 2.16 million tons [1] [2].However, this growth has been accompanied by challenges, particularly in 2016, when Indonesia imported 2,212 tons of Citruss.The chief culprit behind the decline in Citrus production appears to be the prevalence of a botanical parasite, specifically weeds.Weeds are designated as plant parasites due to their capacity to impede the growth, development, and overall production of plants, necessitating the implementation of effective weed control methods [3,4].The reproductive versatility of weeds, enabling both vegetative and asexual propagation, further enhances their competitive abilities against agricultural crops [5].This occurrence poses a potential threat to agricultural crop yield, a concern underscored by previous studies [6].
Existing research has substantiated the adverse impact of plants in orchards, particularly when spaced at a proximity of 40 centimeters, resulting in a 27% reduction in agricultural output.Moreover, these undesirable plants have been identified as significant absorbers, extracting between 60 and 80 percent of the available nitrogen [7].Recent investigations emphasize that the presence of vegetation significantly diminishes agricultural productivity, leading to yield reductions of up to 61%.In the realm of rice fields, extensive studies in the published literature have examined the detrimental effects of weed 1338 (2024) 012013 IOP Publishing doi:10.1088/1755-1315/1338/1/012013 2 infestation on various facets of crop growth and yield, including decreased leaf count, diminished productive branches, reduced root dry weight, shortened leaf length, diminished flag leaf area, and an overall decline in crop yield.Earlier research posits that weeds can impede plant growth, reduce the number of fruitful shoots, lower grain production per ear or spike, diminish shoot dry weight, and reduce the weight of Citruss in orchards [8].A density of 10 weed plants per square meter has been found capable of producing 34,600 spores.The weed species mentioned earlier exhibit competitive traits, thriving in diverse climates and locations [9][10] [11].
Several environmental factors, such as plant spacing, plant age, soil quality, plant arrangement, and prevailing weather conditions, contribute to the proliferation of weeds in proximity to citrus trees [12].Analysis of interview data revealed that employing individuals for weed removal constitutes a substantial portion, ranging from 20% to 25%, of total production costs.A comprehensive investigation of this issue is imperative due to the varying risks of decreased crop yields associated with different weed types and their prevalence [13].The primary focus when exploring ecologically sustainable weed management strategies is the assessment of weed vegetation.
The coexistence of multiple vegetation species can have detrimental effects on agricultural productivity, resulting in a reduction in both the quantity and quality of crop yields.Study findings indicate that certain vegetation species possess allelopathic properties, exhibiting autotoxic or autopathic characteristics that harm neighboring plant species.Additionally, there are reports suggesting that specific weed varieties possess antifungal and antibacterial properties [14].This study aims to identify various weed types and assess their prevalence levels within the Tefa Citrus Orchard, serving as a research orchard for the Politeknik Negeri Jember.The primary objective is to evaluate the potential of utilizing weeds as a means to enhance Citrus crop productivity, considering both quantitative and qualitative variables.

Research Methods
This research was conducted at the Experimental Field of the Politeknik Negeri Jember, Sumbersari District, Jember Regency, at an altitude of approximately 89 meters above sea level.The research was conducted between July and September of 2023.The average temperature during the study period was between 24 and 33 degrees Celsius, and the average monthly precipitation was between 21 and 50 millimeters (dry season).The sweet Citrus cultivation area is approximately 3 years old, and the surrounding weeds were left undisturbed for about 4 months to allow them to grow and develop.
The research design falls under the category of quantitative descriptive research, which involved data collection, identification, and description of weed vegetation diversity.The sampling method used was quadrant sampling, with sample plots randomly arranged.Weeds with the highest dominance were analyzed in the laboratory to determine the content of their secondary metabolites.
The materials and tools used included plastic bags for collecting weed samples, square iron frames measuring 30 cm x 30 cm for creating quadrats, writing tools, and a camera.Sampling was done using the quadrant method.Observation quadrats for weed sampling were created as 30 cm x 30 cm squares, repeated 31 times.In each quadrat, the data collected included the name (weed species) and the number of each plant species to determine density, dominance, and frequency.Weed vegetation within each sample plot was harvested, placed in plastic bags, washed, drained, and identified to determine the weed species.Data analysis included vegetation analysis and biodiversity analysis.Vegetation analysis was performed to determine the Summed Dominance Ratio (SDR) of the weeds.The results of the laboratory analysis of secondary plant metabolism were used to assess the potential of the weeds around the Citrus trees as bioherbicides.

Weed Vegetation Analysis
In accordance with research findings, a comprehensive enumeration reveals the existence of 25 distinct weed species (Table 1).The collective count of individual weed specimens identified within the sampled plots amounted to 400.To gauge weed dominance, the Summed Dominance Ratio (SDR) was computed for each species.It is noteworthy that weed interference in citrus cultivation is akin to losses incurred from pests and diseases.The deleterious impact of weeds extends globally, with estimated rice crop losses of 10-15% on a global scale and a staggering 90-100% in arid regions, emphasizing the critical role of effective weed control measures.The consequential agricultural losses attributed to weeds primarily stem from their adeptness at competing with valuable commodities.These losses encompass not only the appropriation of water content, minerals, and biomass from the environment but also the suboptimal efficiency of harvesting, maintenance, and supervision processes due to vegetative encroachments in agricultural zones.being the most dominant species.Oldenlandia corymbosa, commonly referred to as pearl grass, is synonymous with Hedyotis corymbosa, and is recognized as a plant species thriving in roadside areas or unused land.Characterized as a herbaceous annual plant, it exhibits a slender, upright growth habit with a height ranging from 5 to 60 cm.The leaves are small, measuring 1 to 3 cm in length and 1.5 to 5 mm in width, arranged oppositely in a lanceolate shape with pointed tips and bases.The leaves are flatedged, with a grayish lower surface and a dark green upper surface containing cystoliths.The stem, which is rectangular and branches extensively, has a thickness of 1 mm and exhibits colors ranging from brownish green to grayish green.
Among the dominant weeds in Citrus gardens, besides Pearl grass, is patikan kebo (Euphorbia hirta).Euphorbia hirta L, commonly known as patikan kebo, is a wild weed frequently encountered in tropical regions, flourishing at elevations ranging from 1 to 1400 meters above sea level.This grounddwelling plant possesses brownish-green hair on its stem, with branches emerging near the stem's base and growing upright.It features oval-shaped leaves with serrated edges, covered in fine hairs on both upper and lower surfaces.The leaf blade measures up to 50 mm in length and 25 mm in width, exhibiting pinnate veins and an arrangement facing each other.The leaves display shades of green or purplishgreen.Patikan kebo reproduces through seeds and has a lifespan of approximately one year.
Oldenlandia corymbosa, another herbaceous plant growing densely in clusters with a height ranging from 7 to 65 cm, mirrors the characteristics of Pearl grass.It is an annual plant with slender, upright stems and small, single leaves arranged oppositely.The leaves are lanceolate, with pointed tips and bases, flat edges, and a grayish lower surface contrasted with a dark green upper surface containing cystoliths.The stem, rectangular in shape with a thickness of 1 mm, branches extensively, exhibiting colors ranging from brownish green to grayish green.Euphorbia hirta L shares similar features with Oldenlandia corymbosa, including its ground-dwelling propagation, brownish-green hair on the stem, and upright growth pattern with branches emerging from the stem's base.The leaves of both species are oval-shaped, tapering to obtuse, serrated, and hairy on both upper and lower surfaces.The patikan kebo plant (Euphorbia hirta L) has a one-year life span and reproduces through seeds.

Phytotoxicity
Phytotoxicity refers to the harm inflicted upon plants as a result of the application of chemicals.The manifestation of phytotoxic symptoms is contingent upon both the specific chemical employed and the particular type of plant it is administered to.Indications of phytotoxicity encompass the development of yellow or brown spots on the leaves, the emergence of black spots, the scorching of leaf tips, and the occurrence of yellowing (chlorosis) or browning (necrosis) along the leaf margins, ultimately leading to potential plant demise.The assessment of phytotoxicity involves a comparison between untreated portions of young shoots or plant leaves and their older counterparts that have been exposed to herbicides.Notably, symptoms of phytotoxicity exclusively manifest on mature, exposed leaves, while newly emerging leaves continue to exhibit vigorous growth [15].The application of botanical herbicides on the leaves of Oldenlandia corymbose and Euphorbia hirta induced a modification in the color of Kirinyuh leaves.Discrepancies in watering outcomes between the control group and the treatment group became notably apparent at an 80 g/l concentration.It is hypothesized that the metabolite compounds, such as alkaloids, saponins, and tannins, exhibit enhanced efficacy when administered at an extract concentration of 80 g/l.Administering leaf extracts from Oldenlandia corymbose and Euphorbia hirta at a concentration of 80 g/l is deemed effective in impeding the growth of Kirinyuh weed (Chromolaena odorata L).The alterations in leaf color impede the height and growth rate of Kirinyuh plants, as leaves serve as the site for photosynthesis, where food is converted into substances that serve as raw materials for plant growth and development.According to the observation table, the changes in Kirinyuh leaf color signify the impact of plant herbicides.

Wet weight and dry weight
Dry weight and wet weight of kirinyuh leaves are indicators of the growth of kirinyuh weed.The greater the dry weight value, the better the growth and this will result in higher competitiveness with the main crop.

Figure 1. Wet weight and dry weight of kirinyuh plants
The research results showed that the P4 concentration of 80g/l most inhibited the growth of kirinyuh leaves.Dry weight still has an influence.The effect can be seen from the wet weight value and the dry weight value being directly proportional.The wet weight and dry weight of kirinyuh leaves without treatment (control) produced greater values than treated kirinyuh leaves.Dry weight reflects the pattern of plants accumulating products from the photosynthesis process and is an integration with other environmental factors [16].

Secondary Metabolite Test
Based on the results of the vegetation analysis, the two weeds that had the highest SDR values were tested in the laboratory using the Photometry test method.This is to determine the potential of the two weeds as bioherbicides.The following are the results of the analysis.The content of chemical compounds contained in the pearl grass plant (Oldenlandia corymbosa) in the form of liquid extract was tested for phytochemistry and the results showed that it contained secondary metabolite compounds in the form of flavonoids, total phenolics and tannins that were lower than Euphorbia hirta L (Table 2).Another study [17], [18], also tested that methanol extract which was tested for phytochemistry showed that Oldenlandia corymbose contained secondary metabolite compounds in the alkaloid, steroid, tannin and saponin groups.The concentrated ethanol extract from O. corymbosa which was tested for phytochemistry had positive results containing alkaloids, flavonoids, saponins, steroids and tannins.Meanwhile, patikan kebo (Euphorbia hirta L) has the highest average secondary metabolism content so it has the potential to be developed into a bioherbicide.Based on research [19], [20], the ability of patikan kebo (Euphorbia hirta L) in treating various diseases involves chemical compounds in it which can be antiseptic, anti-inflammatory, antifungal and antibacterial, such as the content of tannins, flavonoids (especially quarcitrin and myricitrin) and tannins.Related to the research that will be carried out are 3 compounds contained in patikan kebo (Euphorbia hirta L) which help in healing wounds, namely flavonoids, tannins and saponins.
Phenolic compounds found in weeds have the ability to inhibit the metabolism of the breakdown of food reserves.Germination begins after the entry of water which will stimulate the activity of germination hormones and enzymes.The entry of phenolic compounds such as tannins will damage the catalytic power of germination enzymes, especially those related to the breakdown of carbohydrates.Tannins can inhibit the activity of germination enzymes such as cellulase, polygalacturonase, proteinase, dehydrogenase and decarboxylase.Germination barriers can also be caused by interference with phenolic compounds during the mitotic process in the embryo [21].According to research results [22].the use of weed extracts that are dominant in an area of land is effective in inhibiting weed germination.
The use of weeds as bioherbicides has the potential to be developed.This is due to the abundance of resources and applicability in implementing environmentally friendly agriculture.Apart from that, plant-based weed control can also increase the activity of plant roots in absorbing water and nutrients so that plant production increases.The allelopathic potential of weeds which can absorb nitrogen and phosphorus up to two times, and potassium up to three times the absorption capacity can be minimized.So that in the future studies on the use of weeds need to be carried out.

Conclusion
Research results show 10 families, 25 species and 400 individual weeds.The weed that has the highest SDR value is the Pearl grass type weed (Oldenlandia corymbose) with a Summed Dominance Ratio (SDR) value of 7.28% and the second highest SDR value is the patikan kebo weed (Euphorbia hirta) (7.22%).The lowest was the weed plant Richardia brasiliensis with an SDR value of 0.633%.Phytotoxicity in kirinyuh leaf plants is P4 with a concentration of 80g/l of 47.33.Wet weight and dry weight affect the P4 concentration with 80g/l most inhibiting the growth of kirinyuh leaves.Patikan kebo weed (Euphorbia hirta L) has the highest content of flavonoid compounds, total phenolics and tannins so it has the potential to be developed into a bioherbicide.

Acknowledgement
This research was funded by Politeknik Negeri Jember.

Table 1 .
Analysis of weed vegetation in Citrus groves at the State Politeknik Negeri Jember Based on the data presented in Table 1, the Summed Dominance Ratio (SDR) for weeds affecting Citrus plants in the Polije garden is recorded as 7.28, with Pearl grass (Oldenlandia corymbosa)

Table 3 .
Content of secondary metabolic compounds in weeds with the highest SDR valuesNo.