The genus Striga: a witch profile

Abstract

The genus Striga comprises about 30 obligate root-parasitic plants, commonly known as witchweeds. In particular, S. hermonthica, S. asiatica and S. gesnerioides cause immense losses to major stable crops in sub-Saharan Africa. Most Striga species parasitize grass species (Poaceae), but Striga gesnerioides has evolved to parasitize dicotyledonous plants. Aspects of phylogeny, economic impact, parasitic life style and molecular discoveries are briefly reviewed to profile one of the main biotic constraints to African agriculture.

Taxonomy: Striga Lour.; Kingdom Plant; Division Angiospermae; Clade Eudicots; Order Laminales; Family Orobanchaceae.

Important hosts: Sorghum Moench., maize (Zea mays L.), rice (Oryza L.), sugarcane (Saccharum L.), pearl millet [Pennisetum glaucum (L.) R. Br.], cowpea [Vigna unguiculata (L.) Walp.].

Disease symptoms: Stunted growth, drought-stressed-like appearance, in severe cases chlorosis and necrosis.

Economic importance: 1 billion $US per annum.

Disease control: Hand weeding, breeding, chemical control, intercropping with catch or trap crops.

Useful webpages: http://ppgp.huck.psu.edu; http://striga.psc.riken.jp.

Figure 1

(A) Global distribution of the economically most destructive Striga species and two major host plants, cowpea and sorghum, according to Mohamed and Musselman (2008) and Musselman (1980). The relative production of sorghum and cowpea in West Africa, East Africa and South‐East Asia is based on values published by the Food and Agriculture Organization of the United Nations (FAO, http://www.fao.org/corp/statistics/en) for 2011. (B) Striga asiatica (Sa) seed next to an Arabidopsis thaliana (At) seed. (C) Two‐week‐old S. asiatica (Sa) haustorium (arrow) on rice (Oryza sativa, Os). (D) Striga hermonthica‐infested sorghum field in Kismu (Kenya, December 2012). (B, C) Scale bars represent 200 μm.