POLLEN ALLELOPATHY FOR BIOLOGICAL CONTROL OF WEEDS

摘要

Crops are being grown since ancient times without damage to the environment, but the use of herbicides during the short span of last 50 years have raised serious doubts about their continuous use. Indiscriminate use of herbicides for weed control hasresulted in serious ecological and environmental problems as under : (A) Increasing incidence of resistance in weeds to important herbicides such as S-triazines and dinitroanilines. (B) Shifts in weed population (a) to species that are more closely related to the crops that they infest e.g. wild oat (Avena fatua L.) in oat, shattercane (Sorghum biocolor L. Mocnch) in sorghum (S. vulgare Pers.), wild okra (Abelmoschits esculentus L. Mocnch) in cotton (Gossypium hirsutum L.) and red rice in rice both Oryza sativa L. and (b) minor weeds have become dominant. In crop fields many major weeds suppress Cyperus rotundus and keep its population under control, but after their chemical control, the competitors of C. rotundus have minimised and thereby it has become a dominant weed. (C) Greater environmental pollution and health hazard (a) particularly from surface and groundwater contamination which is used for human and livestock consumption, for example in USA, the ground water contains sizeable quantity of alachlor and atrazine widely used herbicides and (b) from their inhalation during handling and application. (D) Toxic residues of herbicides pollute the environment and may prove hazardous to even future generations. (E) Some agricultural commodities may contain minute quantities of herbicide residues, with long term adverse effects on human and livestock health. Because of these reasons, serious ecological questions about the reliance on herbicides for weed control have been raised. Now theagronomists arc searching the alternative of weed control to minimize the herbicide use. Pollen allelopathy is a new field of research and most of the research has been done in the last 25 years. It is mediated by heterospccific pollen transfer (HPT). Unlike other forms of HPT, pollen allelopathy describes the deleterious effects of chemicals in the pollen of certain plant species on (a) pollen germination, (b) pollen tube growth, (c) stigma and/or style receptivity, (d) ovule development, (e) sporophytic respiration, (f) seed germination, (g) growth, (h) leaf chlorophyll content and (i) seed set in other plant species. Pollen allclochemicals may also kill non-specialist floral visitors. If the crops are pollcn-allelopalhic and if that pollen reaches other weed plants, then weeds may be suppressed.