Allelopathic Effect of Some Associated Weeds of Wheat on Germinability and Biomass Production of Wheat Seedlings

ABSTRACT: Weeds associated with crops may impose their phytotoxic effects on crop plants through the release of their allelochemicals and hence seriously reduce crop productivity. The present study was conducted to investigate the allelopathic effect of water soluble phenolics of weeds associated with wheat crop (Vicia sativa, Trigonella polycerata, Lathyrus aphaca, Medicago polymorpha, Melilotus indica) on germinability and biomass production of wheat seedlings by using their water extracts at 2.5% (w/v) and 5% (w/v) concentrations and residues of the same weeds with 0, 15 and 30 d decomposition periods at 2% (w/w) concentration. The results showed that the water extracts of M. indica and V. sativa at 5% concentration imposed the most inhibitory effect on energy of germination (81%) and prolonged time to 50% germination (226%), respectively; by contrast, T. polycerata and M. indica extracts at the same concentration inhibited shoot (8%) and root fresh biomass (64%). However, shoot dry biomass was exalted by the weed extracts at both concentrations with maximum increase (29%) caused by the M.indica extract at 2.5% concentration; however, root dry biomass (46%) and root/shoot ratio (51%) were decreased by M. polymorpha and M. indica extracts at 5% concentration, respectively. Residues of L. aphaca and M. polymorpha with a 30 d decomposition period proved the most toxic regarding energy of emergence (85%) and time to 50% emergence (138%), respectively; while, shoot fresh (41%) and dry biomass (26%) production were hindered mostly by M. indica and M. polymorpha residues with a 30 d decomposition period. There was the highest decrease in root fresh (64%) and dry biomass (64%), and root/shoot ratio (64%) when treatment was performed with V. sativa residues without decomposition. The results show that leachates and residues of weeds inhibit wheat germinability and biomass production through release of allelochemicals, and they are a threat to profitable crop production.

摘要：与作物伴生的杂草可通过释放化感物质（allelochemicals）对作物产生植物毒性效应，进而严重降低作物生产力。本研究旨在探究与小麦田伴生的5种杂草——大巢菜（Vicia sativa）、细果胡卢巴（Trigonella polycerata）、山黧豆（Lathyrus aphaca）、野苜蓿（Medicago polymorpha）、印度草木犀（Melilotus indica）——的水溶性酚类物质的化感作用。实验采用浓度为2.5%（w/v）与5%（w/v）的上述杂草水提液，以及浓度为2%（w/w）且腐解时长分别为0、15、30 d的同种杂草腐解残渣，分析其对小麦幼苗发芽能力与生物量积累的影响。结果显示：浓度为5%的印度草木犀与大巢菜水提液分别对发芽势（energy of germination）产生最强抑制效果，降幅达81%，并使50%发芽所需时长延长226%；与之相对，相同浓度下的细果胡卢巴与印度草木犀水提液分别抑制了小麦地上部鲜重（降幅8%）与根部鲜重（降幅64%）。不过，两种浓度的杂草水提液均可提升小麦地上部干重，其中2.5%浓度的印度草木犀水提液的提升效果最显著，增幅达29%；但浓度为5%的野苜蓿与印度草木犀水提液分别降低了小麦根部干重（降幅46%）与根冠比（降幅51%）。腐解30 d的山黧豆与野苜蓿残渣分别对出苗势（energy of emergence）与50%出苗所需时长表现出最强毒性，降幅分别达85%与138%；而腐解30 d的印度草木犀与野苜蓿残渣则分别显著抑制了小麦地上部鲜重与干重的积累，降幅分别为41%与26%。当使用未腐解的大巢菜残渣进行处理时，小麦根部鲜重、干重及根冠比的降幅均达最高，均为64%。研究结果表明，杂草淋溶物与腐解残渣可通过释放化感物质抑制小麦发芽能力与生物量积累，对作物的盈利性生产构成威胁。