大花咸豐草化感作用對雜草防治效用及其於蔬菜栽培的應用研究

雜草管理是蔬菜生產體系相當重要的一環。一般農夫普遍採用的管理策略包括耕犁、刈草、覆蓋及施用除草劑等。其中又以除草劑的使用最為普遍。然而，研究指出過量使用除草劑及具除草劑抗性雜草的出現，已經造成許多環境及生態的問題。有鑑於此，部分科學家致力於從化感植物中找到新的天然植毒性物質，開發新型除草劑；或是致力於將化感植物或作物，作為覆蓋植物，導入輪作或間作的系統中。咸豐草(Bidens pilosa L.)是兼具傳統可食的野菜及中草藥的化感植物，具有導入蔬菜生產系統，提升雜草防治功效的潛力。在臺灣，咸豐草共計有白花鬼針(B. pilosa L. var. pilosa)、小白花鬼針(B. pilosa L. var. minor (Blume) Sherff)及大花咸豐草(B. pilosa L. var. radiata Sch. Bip.)等3個變種。其中以大花咸豐草入侵性最強，但針對此物種的發芽光需求、自毒作用、化感物質釋出途徑、化感作用識別以及在蔬菜生產系統中的雜草控制潛力的相關研究甚少。本研究首先進行實驗室、盆栽及田間試驗，用以評估不同pH、光環境及殘體植毒性對大花咸豐草的發芽影響，了解未來應用上如何防止該物種的衍生危害。其次，透過自田間蒐集大花咸豐草植群天然淋溶液、利用吸附劑吸收葉、莖及葉等不同部位揮發性化合物、搜集根部淋洗液及施用殘體或其水萃液試驗方法等，探討此物種之化感物質可能的釋出途徑、種類及其影響。為了評估大花咸豐草化感作用對其他植物的影響程度，以香附子(Cyperus rotundus L.)為測試植物，進行大花咸豐草殘體植毒性對香附子種間密度依賴(density-dependent)、兩物種種間競爭和大花咸豐草田間土壤與其殘體對香附子塊莖更新之影響等試驗。最後，本研究也以小白菜(Brassica rapa L. subsp. chinensis (L.) Makino)為材料，在盆栽中施用大花咸豐草殘體，探討其化感物質對小白菜生長期間的雜草防治效果，以及對小白菜生長是否會產生不良影響。試驗結果顯示，大花咸豐草種子最適發芽pH為5-7之間，其中以胚根生長對不同pH處理較為敏感，強酸性或偏鹼性環境對其幼苗之胚根發育有明顯負面影響。光照對大花咸豐草發芽影響隨環境而異，培養皿的試驗結果顯示，發芽並無光需求，但在以土壤為介質的盆栽則有明顯照光促進發芽的現象。遠紅光處理雖可抑制種子發芽，但預處理後於黑暗中培育仍可發芽的現象，顯示種子的發芽光反應應是極低光量反應(very low fluence response, VLFR)。試驗同時發現，大花咸豐草殘體與水萃液在控制(實驗室)、半自然(溫室或生長箱盆栽)及自然(田間)狀態下均可對其種子表現出植毒性。由遠紅光預處理後於黑暗中培育的發芽受抑現象推測，殘體或水萃液中所含的酚類化感物質可能會破壞Pfr光敏素，進而抑制種子的發芽率。在化感物質釋出途徑方面，試驗結果顯示大花咸豐草雖可透過淋溶、揮發、根分泌及殘體分解等途徑釋出植毒性物質，但以殘體分解為最重要的途徑。同時，由各途徑的化感物質分析得知，淋溶或殘體分解途徑的主要化感物質應為酚類，而揮發途徑則以-蒎烯(-pinene)、莰烯(camphene)、月桂油烯(myrcene)、檸烯(limonene)及石竹烯(caryophyllene)等萜類及苯基庚三炔(phenylheptatriyne)等多炔類(polyacetylene)化感物質為主。除此之外，植毒性-密度依賴試驗結果發現，施用大花咸豐草殘體可明顯改變香附子之單株乾重-栽培密度對數關係斜率。亦即殘體對香附子生長的抑制強度隨施用量遞增，但隨栽培密度增加而遞減，顯示殘體植毒性明顯存在低密度處理，但在高密度處理中則被稀釋了。而由大花咸豐草與香附子的種間競爭試驗進一步發現，相較於無施用處理，施用活性碳處理可提高香附子的生長，推測是因為大花咸豐草所釋出的植毒性物質經活性碳吸收，降低對香附子生長的影響，顯示化感作用在大花咸豐草與相鄰植物的競爭中扮演一定程度的影響。最後，在小白菜的栽培試驗中發現，大花咸豐草殘體可以顯著抑制雜草種子發芽達5週，並且即使在施用1週後播種小白菜，亦不會對小白菜的生長造成影響。大花咸豐草雖是高入侵性的外來植物，但在食用及醫藥方面極具發展潛力。本研究顯示，該植物殘體的化感作用具直接應用在田間防治雜草及導入蔬菜輪作生產系統的潛力。

關鍵字

化感作用；化感物質；大花咸豐草；香附子；蔬菜生產；雜草管理

並列摘要

Weed management is important for vegetable production. The often-used management strategies include plowing, mowing, mulching, and herbicide, and so many; among these strategies, herbicide utilization is the most widely used method. However, research indicated that the increased herbicide utilization and the occurrence of weeds with herbicide resistance have caused many environmental and ecological problems. Due to this reason, some researchers devoted themselves to exploring new/effective natural phytotoxic compounds from allelopathic plants while some aimed to introduce allelopathic plants/crops as the cover crop in the rotation or intercropping system. Bidens pilosa L. has been identified as an edible and medicinal herb with allelopathy, possessing the potential to enhance weed control in the vegetable production system. Three varieties, i.e. B. pilosa var. pilosa, B. pilosa var. minor, and B. pilosa var. radiata (BPr), were found in Taiwan. Among them, BPr was known as the most invasive one but few studies were conducted on its germination light requirement, autotoxicity, allelopathy, and the weed control potential in the vegetable production system. In this study, experiments at the scales of laboratory, pot, and field were conducted to evaluate the effects of pH, light conditions, and residue phytotoxicity on BPr germination. To evaluate the possible allelopathic pathways of BPr, natural leachates, volatile compounds, root exudates, and residues of this species were collected and examined in the laboratory, pot, and field according. In addition, to understand the effects of BPr allelopathy on the neighbor plants, Cyperus rotundus L. (CR) was selected as the target plant for the density-dependent experiments, interspecies competition experiments, and several field residue/mulch application experiments. Finally, the effects of BPr residue on the weed control and growth of Chinese mustard (Brassica campestris L. ssp. chinensis (L.) Makino) were also evaluated. The results showed that the suitable pH for BPr germination was 5 - 7, and the radicle growth was more sensitive to pH than germination. A strong acid or alkali environment had significant inhibition on radicle growth. The influence of light on BPr germination varied in different conditions, i.e., no light requirement was observed when incubated in the Petri dishes while germination was stimulated under the light when incubated in pots. Besides, although far-red light almost completely inhibited BPr germination, seeds germinated when incubated in the darkness after far-red light pretreatment. This phenomenon indicated that the light response of BPr seed germination might be a very low fluence response (VLFR). The results also demonstrated that the BPr residues and their water extracts exhibited phytotoxicity to its seeds in the experiments of controlled (laboratory), semi-natural (pots in the greenhouse or growth chamber), and natural (field) conditions. Since the germination inhibition was found in the dark incubation after far-red light pretreatment, it was suggested that the phenolics contained in the residues or water extracts might destroy the Pfr phytochrome and further inhibited the seed germination. For the research of allelochemical releasing pathways, the results illustrated that BPr could release phytotoxic substances through leaching, volatilization, root exudation, and residue decomposition; however, residue decomposition was supposed the most important pathway. According to the results of compound analysis, the main allelochemicals in leaching and residue decomposition pathways were phenolics while the terpenoids such as -pinene, camphene, myrcene, limonene, and caryophyllene, and the polyacetylene, such as phenylheptatriyne, were the main allelochemicals in volatilization pathway. In addition, the results from the density-dependent phytotoxicity experiments showed that BPr residue could alter the slope of the logarithmic relationship between dry weight per plant and the density of CR. In other words, the inhibition of the residue phytotoxicity on CR growth increased with application rate but decreased with increasing CR density. The phytotoxicity was exhibited in the low-density treatments but diluted in the high-density treatments. In the interspecies competition between BPr and CR, it was found that CR had greater growth when applied with activated carbon than that without activated carbon. It was presumed that the phytotoxins released from BPr were adsorbed by the activated carbon, and hence reduced the inhibition on the CR. Lastly, in the Chinese mustard growth experiments, it was demonstrated that the BPr residue could significantly inhibit the weed germination for five weeks while no growth reduction was found in the Chinese mustard even sowed one week after residue application. Although BPr is a highly invasive species, it exhibits great development potential in edible and herbal medicinal purposes. In this study, it was found that the BPr residues were capable of being used for controlling weeds in the field and being introduced to the vegetable rotation systems.