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Allelopathy in parasitic weeds management: Role of catch and trap crops

B.M. Chittapur*, C.S. Hunshal and H. Shenoy
Department of Agronomy University of Agricultural Sciences,Dharwad -580 005, Karnataka, India
Phone (Office): +390881741632, FAX (Office): +390881741632, Phone (Home): +390881686273, Mobile Number, E. Mail: ............................

(Received in revised form: December 22, 2000)

• CONTENTS

• INTRODUCTION
• CATCH AND TRAP CROPS
  • 2.1 Catch crop
  • 2.2 Trap crop
  • 2.3 Identification of catch and trap crops
• BIOLOGY AND HOST PARASITE RELATIONS
  • 3.1 Striga sp.
  • 3.2 Orobanche spp
• WEED MANAGEMENT
  • 4.1 Striga spp. management
  • 4.2 Orobanche spp. management
  • 4.3 Catch and trap cropping for other parasitic weeds
• FUTURE LINES OF WORK
• REFERENCES

ABSTRACT

Integrated weed management systems involving catch crops and trap crops are needed to reduce the herbicides use in agriculture. The catch or trap cropping is done to induce the germination of parasitic weeds seed but do not allowing it to produce seed. The effective catch crops viz., fodder millet (Panicum miliaceum L.), sorghum (Sorghum bicolor Moench.), corn (Zea mays L.), sudangrass(Sorghum sudanense Stapf.) have been identified for the management of Striga asiatica [(L.) O.Kuntze) and the cowpea (Vigna catjang Walp.) for S. gesnerioides [(Wild.) Vatke]. Cotton (Gossypium spp.), soybean (Glycine max L. Merr.) and peanut(Arachis hypogaea L.) are the important trap crops. Intercropping of soybean or peanut with sorghum effectively controls the S. hermonthica [(Del.) Benth).

Keywords: Catch crop, Cuscuta sp, host parasite relation, Orobanche sp, Striga sp .trap crop.
Please arrange in Alphabetical Order.

* Correspondence Author. Foot Note, Author please add at end of Page 1 of Ms?

1. INTRODUCTION

Weeds cause appreciable losses in grain production and depletes the nutrients in arable land. As the growth of parasitic weeds depend on the host, hence, they cause substantial damage to agricultural crops. There are about 1800 species of parasitic weeds world-wide, of these Striga, Orobanche andCuscuta are most harmful to crops (30). Striga and Orobanche threaten crop production in 5% of the world's arable land, in the drier and warmer regions of Africa and Asia. Total crop losses in some areas have resulted in migration of villages (31). Orobanche is also equally devastating in the Mediterranean region. Though, post-emergence herbicides are effective, but these weeds cause considerable damage to crops in the pre-emergence stage.

2. TRAP AND CATCH CROPS

Parasitic weeds produce large number of seeds with prolonged longevity in the soil. A chemical stimulant is required to break their seed dormancy and initiate seed germination. This chemical is synthesized and released as root exudates by the host of the parasitic weed or other plants, which can serve as catch crops or as trap crops. The primary consideration in parasitic weed management, is the reduction of the parasitic weed seed bank in soil.

3. BIOLOGY AND HOST-PARASITE RELATIONS

• 3.1. Striga
  Striga is an important genus in family Scrophulariacae associated with grasslands in tropics and sub-tropics. Its 36 species and subspecies are mostly distributed in African savannas and 4 important species in Asia [S.asiatica (=S. lutea), S. hermonthica, S.gesneriodies and S. euphrasoides (=S. angustifolia). All the species, except S. gesneriodiesparasitise the roots of grasses. S. hermonthica seed germinates in response to germination stimulants exuded by cereal roots (28). A. striga plant produces several thousand seeds, which remain viable in the soil for upto 20 years (11).

• 3.2. Orobanche
  The family Orobanchaceae has 17 genera and 150 species. The genus Orobanchecontains 60 species, except O. cernua all are unbranched and parasitic. All species are devoid of chlorophyll and variable in colour. The parasite lives entirely on the host through attachment of strong haustoria to their roots. Each plant produces between 40,000 to 1,20,000 small seeds which remain viable in the soil for more than a decade. When grazed, seeds pass through alimentary tracts of animals unharmed. Under the influence of chemical in root exudate, seeds germinate up to a distance of 10 mm, but only seeds within 2 to 3 mm of the root surface infect the host plant.

• 4. WEED MANAGEMENT
  1. In Indian agriculture, crop mixtures and crop rotations are common, these stopped the build up of host specific pests including parasitic weeds. Therefore, problem of parasitic weed is not as severe as in Africa or Mediterrenean countries. However, with the introduction of hybrid sorghum, CSH-I, the problem of Striga has increased (as one of the hybrid parents is fromAfrica). The rotation of cotton with sorghum kept the Striga under control. Now soybean production has become popular, hence, Striga may remain under control in the near future. In tobacco areas, sunnhemp green manure is becoming popular which will keep these parasitic weeds under control.

• 5. FUTURE LINES OF WORK
  I. Identify the new and potential plant species With allelopathic effects on the highly evolved parasitic weeds. For example, stray studies with Cymopsis tetragonaloba indicated stunted growth, premature cessation and degeneration of flowers in Cuscuta chinensis, an obligate stem parasite and stimulation of seed germination and failure of establishment in Alectra vogelii, a root parasite. Therefore, extensive study on this crop for its allelopathic uses areessential. 2. Sunflower is major host for some Orobanche spp. Hence, its potential as trap crop may be studied. 3. Studies are needed to develop new integrated weed management systems involving trap/catch crops in view of environmental concerns associated with herbicides. Moreover, such systems are compatible with the existing farming conditions in semi-arid tropics. . 4. Identification and isolation of allelochemicals from the root exudates needs emphasis so that synthetic stimulants with longer persistence in soil can be formulated for control of parasitic weeds.

6. REFERENCES

(Please add, Recent References of last 10-years [Arranged in Alphabetical Order] are preferred)
Please critically follow the Style/Pattern of References as under:

• Abu-Irmaileh, B.E. (1984). Effects of planting flax on the subsequent infestation of tomato by Orobanche ramosa. In: Proceedings of 3rd International. Symposium on Parasitic Weeds, (Eds., C. Parker, L.J. Musselman, R.M. Polnill and A.K. Wilson) pp 250-255. ICARDA/International Parasitic Weeds Research, Aleppo, Syria.
• Anonymous. (1993). Final Report-ICAR Ad-hoc Pproject on Management of Parasitic Weeds. Division of Agronomy, University of Agricultural Sciences, Dharwad, India.
• Bebawi, F.F. (1987). Cultural practices in witch weed management. In: Parasitic Weeds in Agriculture Volume I: Striga (Ed., L.J. Musselman) pp. 159 -172. CRC Press Inc, Florida,USA.
• Bebawi, F.F. and Mutwali, E.M. (1991). Witch weed management by sorghum-sudangrass. Seed size and stage of harvest. Agronomy Journal 83 : 781- 786.
• Bell-Ielong, D., Butler, L.G., Ejeta, G. and Hess, D. (1994.) Do phenolics from the parasitic weed Striga inhibit host growth? Acta Horticulturae 381 : 683-686.

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