Striga densiflora
(witchweed)

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Identity

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Preferred Scientific Name

• Striga densiflora (Benth.) Benth. (1863)

Preferred Common Name

• witchweed

Other Scientific Names

• Buchnera densiflora Benth. (1835)

EPPO code

• STRDE (Striga densiflora)

Taxonomic Tree

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• Domain: Eukaryota
•     Kingdom: Plantae
•         Phylum: Spermatophyta
•             Subphylum: Angiospermae
•                 Class: Dicotyledonae
•                     Order: Scrophulariales
•                         Family: Orobanchaceae
•                             Genus: Striga
•                                 Species: Striga densiflora

Notes on Taxonomy and Nomenclature

Top of page Having originally described the species under Buchnera densiflora in 1835, Bentham later made the combination Striga densiflora in 1863. No other names have been used.

Description

Top of page S. densiflora is very similar to S. asiatica but usually has a more congested appearance with more closely packed leaves and inflorescence. The plant is erect up to about 30 cm, little branched. The leaves are also often a little broader and with hooked hairs, and are characteristically down-curved. The flowers, always white, characteristically drying blue, are about 1 cm long, subtended by bracts which are leaf-like below but no longer than the calyx above. The anthers are bluish-black (brownish-yellow in S. asiatica). The calyx, up to 6 mm long, has just five ribs. The capsule is about 5 mm long, containing several hundred seeds c. 0.2 x 0.3 mm, which cannot be distinguished morphologically from those of S. asiatica (see Musselman and Parker, 1981). Chromosome number (2n) = 40.

Distribution

Top of page S. densiflora occurs mainly in South Asia, especially India, eastwards to Indonesia and China, but also in Oman, where it is assumed to have been introduced with sugar cane setts (Parker and Riches, 1993). There have been sporadic reports of occurrence in Africa, most recently by Reichmann et al. (1995), but none of these have been authoritatively confirmed.

Records for Nigeria, South Africa and Zimbabwe in EPPO (2003) require further confirmation.

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Risk of Introduction

Top of page All Striga species are listed as prohibited imports into Australia, Israel, Russia and the USA.

Habitat

Top of page Like S. asiatica and S. hermonthica, S. densiflora is a hemi-parasite associated with cereal crops and natural grass vegetation in semi-arid conditions, with low soil fertility and relatively dry conditions, rarely flourishing in wet soils.

Hosts/Species Affected

Top of page The host range of S. densiflora is comparable with that of S. asiatica, the most important economic hosts being sorghum, maize, sugarcane and finger millet, with rice and some other millets as less frequent hosts. Wild hosts are mostly members of the Poaceae but also include some Cyperaceae and dicots. Kumar and Solomon (1941) record 24 hosts species. Their 18 newly observed hosts included Andropogon, Digitaria, Dactyloctenium, Euchlaena, Lophopogon, Paspalum, Setaria, Tragus and Tripogon species as well as species of Commelina, Cyperus, Desmodium, Glossocardia, Indigofera and Iseilema.

References from before 1957, cited here and in other sections, are usefully available in the compilation by McGrath et al. (1957).

Host Plants and Other Plants Affected

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Growth Stages

Top of page Flowering stage, Fruiting stage, Vegetative growing stage

Symptoms

Top of page Symptoms caused by S. densiflora are comparable to those from S. hermonthica and include yellow blotching of foliage, dwarfing of stems and early senescence (Parker and Riches, 1993).

List of Symptoms/Signs

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Biology and Ecology

Top of page S. densiflora is a hemi-parasite, closely resembling S. asiatica and S. hermonthica in most aspects of its biology and ecology. Although it is stated in a number of older publications from India that it is 'not parasitic' there is no recent work to suggest that this could be true. Seeds are minute, not morphologically distinguishable from those of S. asiatica, making it an obligate parasite, dependent on stimulants exuded by host roots for germination, and on attachment to a host root within a few days of germination before further development can occur. Chowdhury and Ahmad (1993) studied penetration of haustoria into the roots of sugarcane and did not observe significant differences from the behaviour of S. asiatica. Limited studies suggest that it may differ to some degree from S. asiatica in its response to different germination stimulants. It is possibly less responsive to strigol and GR 24, but does respond to ethylene (Parker, 1983). Optimum temperatures for germination are over 30°C, as for S. asiatica. There is less tendency for development of secondary dormancy with prolonged conditioning in the absence of stimulant, as occurs in S. hermonthica (Reid and Parker, 1979). Once emerged, green leaves are produced and some photosynthesis presumably occurs, but no detailed physiological studies have been conducted on this species. Fertilization is autogamous (Musselman et al., 1991).

Like S. asiatica and S. hermonthica, S. densiflora is a plant of semi-arid conditions, associated with low soil fertility and relatively dry conditions, rarely flourishing in wet soils or irrigated crops in the way S. aspera and S. angustifolia may do.

Natural enemies

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Notes on Natural Enemies

Top of page The range of insects associated with S. densiflora in India is the same as that affecting S. asiatica. See Greathead (1984) for a comprehensive summary.

Plant Trade

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Plant parts not known to carry the pest in trade/transport
Bark
Flowers/Inflorescences/Cones/Calyx
Leaves
Roots
Seedlings/Micropropagated plants
Stems (above ground)/Shoots/Trunks/Branches
Wood

Impact

Top of page Most cereal crops, and sugarcane, can be affected by S. densiflora. There are no estimates of crop loss, but in India it is regarded as no less a menace than S. asiatica (Parker and Riches, 1993). Parker (1984) showed that, although the individual plants of S. densiflora and S. asiatica were smaller and less damaging than those of S. hermonthica, the damage caused was apparently proportional to the total fresh weight of the emerged parasite in each of the three species.

Detection and Inspection

Top of page Infestation of a cereal crop by S. densiflora may be apparent before emergence from the soil, by the chlorotic blotches and/or wilting symptoms on the crop foliage. Uprooting may confirm the presence of the haustoria and young parasite seedlings on the root but the attachments are very fragile and washing the roots out of the soil will ensure a better chance of finding them. For detecting the seeds of Striga spp. in crop seeds, Berner et al. (1994) used a technique involving sampling from the bottom of sacks, elutriation of samples in turbulent flowing water and collection of seeds and other particles on a 90-µm mesh sieve. Striga seeds are then separated from heavier particles by suspension in a solution of potassium carbonate of specific gravity 1.4 in a separating column. Sound seeds collect at the interface and are transferred to a 60-µm mesh for counting. However, seeds of S. densiflora are not readily distinguishable from those of S. asiatica and S. hermonthica (see Musselman and Parker, 1981).

Similarities to Other Species/Conditions

Top of page S. densiflora is superficially very similar to other white-flowered species of Striga but is distinguished from S. asiatica and S. angustifolia by having only five calyx ribs. It is less distinct from the African species S. passargei which also has only five ribs. This usually has creamy white, yellow or pink flowers, drying black, not blue, and longer bracts. However, white-flowered forms of this species may be responsible for the occasional reports of S. densiflora in Africa. Seeds are minute, about 0.3 mm long, morphologically indistinguishable from those of S. asiatica (see Musselman and Parker, 1981).

Prevention and Control

Top of page S. densiflora is not known to differ from S. asiatica in its response to cultural control methods, and it can be presumed that rotation with non-host crops and improvement in soil fertility are likely to be helpful. Solomon (1952) notes less vigorous development under higher nutrient conditions. There is negligible evidence for the effectiveness of trap crops.

Although Upadhyay et al. (1977) reported unsatisfactory results with 2,4-D both pre- and post-emergence, other reports suggest it can be helpful at either stage (Kumar et al., 1949; Uppal, 1952).

Varieties of sorghum resistant to S. asiatica have generally been found to be resistant to S. densiflora as well. Although the African variety Boganhilo, resistant to S. asiatica was reported susceptible to S. densiflora in Anon. (1943), a later report (Jenkins, 1945) confirmed its resistance to S. densiflora and other reports suggest a generally comparable reaction of sorghum species and varieties to the two Striga species (Anon., 1942; Deodikar, 1951; Parker and Riches, 1993). The one exception in Deodikar's work was Sorghum conspicuum [S. bicolor] which proved susceptible to S. asiatica but resistant to S. densiflora.

There is a lack of information on the resistance of 'SAR' (Striga-asiatica-resistant) lines of sorghum to S. densiflora.

References

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Anon., 1942. Millets and pulses. Imperial College of Agricultural Research (India) Annual Report 1940, 41:11-12.

Anon., 1943. Millets and pulses. Imperial College of Agricultural Research (India) Annual Report 1941, 42:11.

Berner DK; Cardwell KF; Faturoti BO; Ikie FO; Williams OA, 1994. Relative roles of wind, crop seeds, and cattle in dispersal of Striga spp. Plant Disease, 78(4):402-406; 23 ref.

Chowdhury AM; Ahmad A, 1993. Histopathological studies of Striga spp. with sugarcane roots. Journal of Mycopathological Research, 31(1):1-4.

Cooke T, 1905. Striga. Bombay Flora, 2(2):302-304.

Deodikar GB, 1951. Sorghum versicolor, Anderss. - a species highly resistant to Striga. Current Science, India, 20:135-136.

Dugje IY; Kamara AY; Omoigui LO, 2006. Infestation of crop fields by Striga species in the savanna zones of northeast Nigeria. Agriculture, Ecosystems & Environment, 116(3/4):251-254. http://www.sciencedirect.com/science/journal/01678809

EPPO, 2014. PQR database. Paris, France: European and Mediterranean Plant Protection Organization. http://www.eppo.int/DATABASES/pqr/pqr.htm

Greathead DJ, 1984. The natural enemies of Striga spp. and the prospects for their utilisation as biological control agents. In: Ayensu ES, Doggett H, Keynes RD, Marton-Lefevre J, Musselman LJ, Parker C, Pickering A, ed. Striga. Biology and control Paris, ICSU Press France, 133-160

Jain AK; Tripathi SK, 2002. Occurrence of Striga and its influence on yield of Kodo millet. Crop Research (Hisar), 23(3):532-535.

Jenkins WJ, 1945. Research work. Crop Protection. Bombay Department of Agriculture Annual Report 1943, 44:14-17.

Kumar LSS, 1939. Crop protection from parasitic plants - phanerogamic parasities. India Bd. Agriculture and Animal Husbandry Crop and Soils Wing Proceedings, 2(1937):341-342.

Kumar LSS; Solomon S, 1941. A list of hosts of some phanerogamic root-parasites attacking economic crops in India. Indian Academy of Science Proceedings, Section B, 13:151-156.

Kumar LSS; Solomon S; Rao MVV, 1949. Preliminary studies in the use of synthetic hormones as weedkillers in the Bombay Province. Indian Academy of Sciences Proceedings Section B, 30:243-248.

Luthra JC, 1939. Parasitic plants occurring in the Punjab. India Board Agriculture and Animal Husbandry Crop and Soils Wing Proceedings, 2:343.

MBG, 2000. Missouri Botanical Garden: Flora of China Checklist. World Wide Web page at http://mobot.mobot.org/.

McGrath H; Shaw WC; Jansen LL; Lipscomb BR; Miller PR; Ennis WB, 1957. Witchweed (Striga asiatica) - a new parasitic plant in the United States. Plant Disease Epidemics and Identification Section, Agricultural Research Service, United States Department of Agriculture Special Publication, 10.

Musselman LJ; Bhrathalakshmi; Safa SB; Knepper DA; Mohamed KI; White CL, 1991. Recent research on the biology of Striga asiatica, S. gesnerioides and S. hermonthica. Combating striga in Africa: proceedings of the international workshop held in Ibadan, Nigeria, 22-24 August 1988 [edited by Kim, S. K.] Ibadan, Nigeria; International Institute of Tropical Agriculture, 31-41

Musselman LJ; Parker C, 1981. Surface features of Striga seeds (Scrophulariaceae). Adansonia, 20(4):431-438

Parker C, 1983. Factors influencing Striga seed germination and host-parasite specificity. Proceedings of the 2nd International Workshop on Striga. ICRISAT Patancheru India, 31-35

Parker C, 1984. The influence of Striga species on sorghum under varying nitrogen fertilization. Proceedings of the Third International Symposium on Parasitic Weeds. International Center for Agricultural Research in the Dry Areas Aleppo Syria, 90-98

Parker C; Riches CR, 1993. Parasitic Weeds of the World: Biology and Control. Wallingford, UK: CAB International.

Reichmann S; Kroschel J; Sauerborn J, 1995. Distribution and infestation of Striga species in Shinyanga region of Tanzania and evaluation of control methods. Brighton crop protection conference: weeds. Proceedings of an international conference, Brighton, UK, 20-23 November 1995., Vol. 1:151-156; 15 ref.

Reid DC; Parker C, 1979. Germination requirements of Striga spp. Proceedings, Second International Symposium on Parasitic Weeds, North Carolina, 1979., 202-210

Solomon S, 1952. Studies in the physiology of phanerogamic parasitism with special reference to Striga lutea Lour. and S. densiflora Benth. on Andropogon sorghum Hack. I. The osmotic pressure of the host and parasite in relation to the nutrition of the host. Indian Academy of Science Proceedings Section B, 35:122-131.

Srinavasan AR, 1947. Some new hosts for Striga. Current Science (India), 16:320-321.

Upadhyay UC; Khan QA; Nandwate HD, Studies on weed control in sorghum. Program and Abstracts of Papers, Weed Science Conference and Workshop in India, 1977., Paper No. 41:24

Uppal BN, 1952. Research work. Crop protection. Bombay Department of Agriculture Annual Report 1947, 48:28-31.

Zuberi MI; Ahmad A; Biswas MAR; Ghosh GP; Choudhury ANMA; Roy PC, 1987. Striga densiflora Benth., an angiospermic root parasite of rice in Bangladesh. International Rice Research Newsletter, 12(6):32-33

Distribution Maps

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