Management of Infection by Parasitic Weeds: A Review

Abstract

Parasitic plants rely on neighboring host plants to complete their life cycle, forming vascular connections through which they withdraw needed nutritive resources. In natural ecosystems, parasitic plants form one component of the plant community and parasitism contributes to overall community balance. In contrast, when parasitic plants become established in low biodiversified agroecosystems, their persistence causes tremendous yield losses rendering agricultural lands uncultivable. The control of parasitic weeds is challenging because there are few sources of crop resistance and it is difficult to apply controlling methods selective enough to kill the weeds without damaging the crop to which they are physically and biochemically attached. The management of parasitic weeds is also hindered by their high fecundity, dispersal efficiency, persistent seedbank, and rapid responses to changes in agricultural practices, which allow them to adapt to new hosts and manifest increased aggressiveness against new resistant cultivars. New understanding of the physiological and molecular mechanisms behind the processes of germination and haustorium development, and behind the crop resistant response, in addition to the discovery of new targets for herbicides and bioherbicides will guide researchers on the design of modern agricultural strategies for more effective, durable, and health compatible parasitic weed control.

Keywords: Cuscuta; Orobanche; Phelipanche; Striga; bioherbicides; crop resistance; germination; haustorium; sustainable control; virulence.

Figure 1

Adaptation of parasitic plants to agricultural and urban ecosystems. Shown are representative photographs of parasitic plants in agricultural (A,B) and urban (C,D) locations. (A) Hemiparasitic shoot parasite Viscum sp. feeding on olive tree; (B) holoparasitic root parasite Orobanche sp. feeding on clover commercial field; (C) Viscum sp., in the city of Dijon, France; (D) Orobanche sp. parasitizing clover in a park in the city of Dijon, France.

Figure 2

Haustorial penetration of host plants and maturation of parasite. Shown are representative photographs of terminal (A–D,G–I) and lateral (E,F) haustorium penetration and maturation stages. (A) Young hemiparasitic weed Alectra vogelii infecting the root of cowpea; (B) young hemiparasitic weed Striga hermonthica infecting the root of sorghum; (C) young holoparasitic weed Phelipanche aegyptiaca infecting the root of Medicago; (D) young hemiparasitic weed Viscum cruciatum infecting an olive tree stem; (E) hemiparasitic weed Cuscuta campestris infecting a chickpea stem; (F) mature anchorage roots of Phelipanche aegyptiaca infecting the root of vetch; (G) underground shoot of Orobanche minor growing on clover roots towards soil surface; (H) emerged shoot of Orobanche minor; (I) emerged shoots of Conopholis americana feeding on oak roots.

Figure 3

Haustorial competent root cultures of obligated root parasitic weeds. Shown are representative photographs of (A) Striga hermonthica; (B) Phelipanche aegyptiaca.

Figure 4

Directional growth of five-day-old Cuscuta toward its host. Shown are representative photographs taken at 12-h intervals of the growth of Cuscuta and its host lentil. (A) Cuscuta seedlings rotate in a counterclockwise rotation; (B) Cuscuta seedling bending guided toward host stem; (C) Cuscuta coiling and adhesion; (D) formation of adhesive discs.

Figure 5

Haustorial hairs and papillae on root parasitic weeds. Shown are representative photographs of haustorial hairs (A,B) and papillae (C–E) formed in seedlings of root parasitic weeds. (A) Ramphicarpa fistulosa; (B) Striga hermonthica; (C,D) Phelipanche ramose; (E) Orobanche cumana.

Figure 6

Xylem to xylem junctures in sunflower root. (A) Longitudinal section of Orobanche cumana seedling connected to sunflower vascular system (shown in transversal section); (B) Longitudinal section of sunflower lateral root developed from main root sunflower root (shown in transversal section).

Figure 7

Hypersensitive-like response developed on host in response to parasite attack. Shown are representative photographs of host root responses to attempted penetration by parasite haustorium. (A) Phelipanche aegyptiaca on Vicia arthropurpurea and (B) Cuscuta campestris on Vicia sativa. Red arrows point at hypersensitive-like response at host-parasite interface both in Phelipanche and Cuscuta. White arrows point at V. sativa sites where Cuscuta haustorium was manually removed to make the resistance response more visible for explanatory reasons.