Zahid Ata Cheema

The role of allelopathy in agricultural pest management

Allelopathy is a naturally occurring ecological phenomenon of interference among organisms that may be employed for managing weeds, insect pests and diseases in field crops. In field crops, allelopathy can be used following rotation, using cover crops, mulching and plant extracts for natural pest management. Application of allelopathic plant extracts can effectively control weeds and insect pests. However, mixtures of allelopathic water extracts are more effective than the application of single-plant extract in this regard. Combined application of allelopathic extract and reduced herbicide dose (up to half the standard dose) give as much weed control as the standard herbicide dose in several field crops. Lower doses of herbicides may help to reduce the development of herbicide resistance in weed ecotypes. Allelopathy thus offers an attractive environmentally friendly alternative to pesticides in agricultural pest management. In this review, application of allelopathy for natural pest management, particularly in small-farm intensive agricultural systems, is discussed.

Alternative control of wild oat and canary grass in wheat fields by allelopathic plant water extracts

The increasing concern about the toxicity of synthetic herbicides has boosted the search for eco-friendly and sustainable weed management practices. Allelopathic control of weeds has received great attention in recent years as a possible alternative for weed management. Here, a two-year field study was conducted to explore the herbicidal potential of sorghum water extract alone and in combination with water extracts of other allelopathic plants: eucalyptus, sesame, sunflower, tobacco and brassica, against wild oat (Avena fatua) and canary grass (Phalaris minor), two noxious weeds of wheat fields. Water extracts were applied twice 30 and 40 days after sowing. Our results show that application of sorghum and sunflower extracts at 12 L ha−1 each was more effective than other combinations. This treatment reduced wild oat dry matter by 42–62%, and canary grass by 36–55%. Application of sorghum and sunflower at 6 L ha−1 each increased the wheat grain yield by 89% during the first year, and by 35% during the second year. Application of the synthetic herbicide isoproturon at 1000 g active ingredient ha−1 was more effective for weed inhibition and yield increase than allelopathic water extracts. Nevertheless, application of sorghum and sunflower at 6 L ha−1 was economically more viable than the other treatments, with the highest marginal rate of return of 2824%.

Application of Allelopathy in Crop Production: Success Story from Pakistan

Allelopathy is an emerging field with its wider applications in agriculture and allied disciplines. In Pakistan, work on allelopathy was initiated in the early 1970s with screening of local flora for allelopathic potential in laboratory bioassays, while field studies were taken up during the early 1980s. Sorghum was found the most potent allelopathic plant in this regard, which was used as mulch material, intercrop, and plant water extracts for weed management. Application of sorghum plant water extracts proved more effective in controlling weeds than all other strategies. Several other plants including sunflower, canola, eucalyptus, rice, mulberry, etc. were also evaluated. Although each of the allelopathic sources provided some control, mixtures of allelopathic water extracts were more effective than the application of single plant extracts. To achieve effective weed control, allelopathic extracts were applied together with the lower herbicide dose. Mixed application of allelopathic extracts with one-third to half of the standard herbicide dose provided effective weed control as achieved from the standard herbicide dose in several field crops. Application of allelopathic mulches, soil incorporation of allelopathic residues, and intercropping with strong allelopathic crops also provided effective control of several weeds. In recent years, commercialization of allelopathic extracts for weed management is under way. Allelopathy has also been effective in controlling stored grain and field crop pests in addition to several pathogens which may also be controlled by allelopathy. Allelopathy is also being evaluated as growth promoter; foliar application of canola, sorghum, sunflower, and moringa extracts has been found effective in this regard. More recently, allelopathic extracts are being evaluated for their potential role in improving resistance against abiotic stresses in cereals.

Allelopathic Activity of Crop Residue Incorporation Alone or Mixed Against Rice and its Associated Grass Weed Jungle Rice (Echinochloa colona [L.] Link)

La represion de malezas es uno de los beneficios logrados por la incorporacion de residuos de cosecha al suelo y se cree que es de naturaleza alelopatica. Se evaluo el potencial alelopatico de diversos residuos de cultivos: sorgo (Sorghum bicolor [L.] Moench), girasol (Helianthus annuus L.) y coles (Brassica Compestris L.) en arroz (Oryza sativa L.) y pasto arroz o pasto Shama (Echinochloa colona [L.] Link). Los residuos de cosecha picados se incorporaron solos y en mezcla a 6 g kg-1 de suelo (12 t ha-1) y se compararon con un testigo sin residuos. La incorporacion de los residuos al suelo retraso sustancialmente la germinacion del pasto arroz o pasto Shama. El tiempo para empezar la germinacion, el tiempo a 50% de emergencia, el tiempo medio de emergencia, el indice de emergencia, y el porcentaje de germinacion final fueron influidos negativamente por la incorporacion de residuos. La germinacion final del arroz y del pasto arroz o pasto Shama se redujo en 11 a 15% y 11 a 27% con el uso exclusivo de residuos, y en 18 a 22% y 8 a 34% con la combinacion de los residuos de cultivos, respectivamente. Los residuos de cultivos ejercieron una marcada influencia negativa en la longitud de brotes (25-100% y 14-44%) y la longitud de raices (22-100% y 10-43%) de arroz y de pasto arroz o pasto Shama, respectivamente. Peso seco de brotes y raices de arroz y pasto del arroz o pasto Shama tambien decrecieron significativamente. Una apreciable cantidad de fenoles fue registrada en el suelo enmendado con residuos de sorgo+girasol+coles. Desde que los residuos alelopaticos de cultivos se incorporaron al suelo tambien fueron perjudiciales para la germinacion y crecimiento de las plantulas de arroz, asi se sugiere que el momento de la aplicacion de los residuos para la supresion de arroz de la selva y el tiempo de la siembra del arroz deben ser ajustados para reducir al minimo el dano del cultivo de arroz.

A 75% reduction in herbicide use through integration with sorghum + sunflower extracts for weed management in wheat.

BACKGROUND To reduce herbicide use by 75%, integrated use of sorghum and sunflower extracts each at 18 L ha(-1) combined with 1/4(th) (75% less) of label rates of four herbicides (mesosulfuron + idosulfuron, metribuzin, phenoxaprop-p-ethyl and isoproturon) were investigated for the management of wild oat and canary grass, the two pernicious weeds in wheat fields worldwide. RESULTS The results revealed that sorghum + sunflower extracts combined with 1/4(th) (75% less) of label rates of herbicides inhibited dry matter production of wild oat by up to 89% and canary grass by up to 92%. The wild oat and canary grass persistence index in sorghum + sunflower extracts combined with 1/4(th) (75% less) of label rates of herbicides was either lower or equal to respective label rates of herbicides, except sorghum + sunflower extract + 1/4(th) phenoxaprop-p-ethyl. Lower herbicide rates + water extracts also produced wheat grain yield statistically equal with label rates of respective herbicides. Two treatments having water extracts + lower herbicides rates were economical and sorghum + sunflower + 1/4(th) mesosulfuron + idosulfuron produced the highest (4404%) marginal rate of return. CONCLUSION Herbicides use can be reduced by 75% through integration with sorghum + sunflower extracts without compromising yield and net benefits for cost-effective and eco-friendly management of wild oat and canary grass in wheat.

Allelopathy and Abiotic Stress Interaction in Crop Plants

Global climate models predict the increase in daily mean temperature, changed patterns of precipitation, increase in episodes of drought, and floods in future, the abiotic stresses, all posing threats to crop production and food security. Plants have evolved several mechanisms to cope with abiotic stresses. Ecological interaction of production and release of secondary metabolites among organisms in ecosystems, the allelopathy, has been associated with the tolerance mechanism against abiotic stresses. Endogenous levels of secondary metabolites, defined as allelochemicals, have been taken as indices of abiotic stress resistance. Exogenous application of allelochemicals has been found to increase their endogenous level with simultaneous increase in growth and resistance against abiotic stresses. Identification of genes responsible for allelochemicals production, and development of transgenic crops with these genes is becoming an attractive option for improving resistance against abiotic stresses. In this chapter, the production of allelochemicals under abiotic stresses in plants, strategies to enhance their production, and role in improving resistance against abiotic stresses is discussed.

ROLE OF BORON IN LEAF ELONGATION AND TILLERING DYNAMICS IN FINE-GRAIN AROMATIC RICE

This study was conducted to explore the role of boron (B) in seedling emergence, leaf elongation, and tillering dynamics. Boron was applied as seed priming. For priming seeds of two rice cultivars (Super Basmati and Shaheen Basmati) were soaked in B solutions having 0.001, 0.01, 0.1 and 0.5% concentrations. Substantial improvement in seedling emergence was observed from hydropriming and seed priming in 0.001 and 0.01% solutions; beyond this B concentration, emergence potential was suppressed. Seeds primed in 0.5% B solution even did not emerge. A linear increase in plant height was recorded up to 30 days from seeds primed in 0.001% solution. Similarly rate of leaf emergence and elongation and rate of tiller appearance were substantially improved in seedlings raised from seeds primed in 0.001% B solution. Overall B plays a significant role in leaf appearance, elongation and tillering dynamics of rice when used in very low concentration.

Sorghum Allelopathy for Weed Management in Wheat

Weeds cause substantial decline in agricultural production. To overcome weed infestation modern agricultural practices adopted heavy use of a large variety of herbicides. With rising human health and ecological concerns about the adverse effects of indiscriminate use of farm chemicals research on alternative weed management methods is underway worldwide. Exploitation of allelopathic potential of different crop/plant species for weed management under field conditions is one such approach. Sorghum has been reported to contain several allelochemicals in its aerial as well as underground parts. It offers a great promise as a tool for weed management. We conducted a series of field experiments to test allelopathic effects of this crop on weed control and yield of wheat. We found that 10% w/v water leachate of aerial parts of sorghum (also called sorgaab) applied at 30 and 60 days after sowing can reduce weed biomass by as much as 49% with concomitant increase of wheat yield over 20% compared to control. Furthermore, use of sorgaab in combination of herbicides can significantly reduce the amount of herbicide use (by 50%) and get comparable grain yield of wheat as obtained by using the recommended dose of the herbicides. We concluded that sorgaab used alone or in combination with herbicide has a great promise in increasing weed control and grain yield of wheat. Application of this method of weed management has enormous economic and environmental benefits in wheat cultivation.

Maize–sorghum intercropping systems for purple nutsedge management

Intercropping is a viable option for weed management. Six maize–sorghum intercropping systems were compared in a two-year field study for the management of purple nutsedge. The intercropping systems included maize planting in 70-cm spaced rows intercropped with one row of dwarf or tall sorghum and maize in 105-cm spaced double-row strips intercropped with one or two rows of dwarf or tall sorghum; sole maize planted in 70-cm spaced single rows was used as a control. Two intercropping systems as maize in 70-cm spaced rows + one row of tall sorghum and maize in 105-cm spaced double-row strips + two rows of tall sorghum controlled purple nutsedge by 48 and 52% compared with the sole crop of maize, respectively. However, all the maize–sorghum intercropping systems decreased the maize grain yield compared with control. Maize planted in 105-cm spaced double-row strips + one row of dwarf sorghum was the best option because it reduced the maize yield by only 6%. However, the decrease in maize yield was compensated for by sorghum yield. Intercropping maize in 105-cm spaced double-row strips + one row of dwarf sorghum may be used for management of purple nutsedge in maize.

Role of Allelopathy in Weed Management

Weeds are a severe threat to sustainable crop production as yield losses caused by weeds exceed the losses from all other biotic and abiotic stresses. Although chemical herbicides provide effective weed control in field crops, environmental and health concerns are pressing the researchers to explore alternate means of weed control. Allelopathy, a naturally occurring ecological phenomenon of interference among organisms, offers a pragmatic, economical, effective and environmental friendly approach for weed management in field crops. The phenomenon of allelopathy may be used in weed management as mix cropping/intercropping, use of surface mulchs, soil incorporation of plant residues, application of allelopathic aqueous extracts alone, and/or combined with lower herbicide doses and crop rotation. Use of biotechnology and conventional breeding may be helpful in developing genotypes with strong allelopathic potential. In this chapter, experiences and perspectives of using allelopathy for weed management are discussed.