PSIS 111 11 Parasite plants

Parasitic Plants Overview

• Parasitic plants are flowering plants evolved to depend on other plants for nutrition.

• They are no longer autotrophs.

• Key examples include:

  • Mistletoes: Parasitize trees and woody plants.

  • Dodder: Infests ornamentals, some vegetables, and fruits.

  • Witchweed (Striga): Primarily affects agronomic grains.

Types of Parasitic Plants

Holoparasites

• Examples: Dodder and Dwarf Mistletoes.

• Characteristics:

  • Little to no chlorophyll.

  • Have tiny scales instead of leaves.

  • Lack true roots, relying entirely on host for food, water, and nutrients.

  • Parasitize both xylem and phloem of host plants.

Hemiparasites

• Example: True Mistletoes.

• Characteristics:

  • Contain chlorophyll.

  • Lack true roots but depend on the host for water and nutrients.

  • Primarily feed on xylem of the host.

Detailed Study on Dodder (Cuscuta sp)

• Impact on Agriculture:

  • Harms crops by sucking nutrients from host plants and shading them.

  • Member of the morning glory family and evolved as a parasite.

• Reproduction:

  • Reproduces through flowers and seeds, maintaining stems but lacking leaves and true roots.

Feeding Mechanism

• Dodder uses structures called haustoria to extract nutrients from the host's vascular system.

Transmission & Spread

• Dodder seeds can be harvested with host seeds, leading to spread during planting.

• Mulch made from dodder-infested hay can lead to local re-seeding.

Management Strategies for Dodder

Herbicidal Control

• Option 1: Use of non-selective post-emergence herbicides (e.g., Roundup) but will also kill the host.

• For perennial hosts, apply contact herbicides (e.g., Grammoxone) in fall, followed by pre-emergence herbicides to kill dodder seeds.

Alternative Control Methods

• Hand weeding can be a viable option.

Striga (Witchweed)

• Attaches to host roots and is a hemiparasite; can photosynthesize but needs a living host to reproduce.

• Affects crops like corn, sorghum, millet, and cowpea

• Symptoms:

  • Stunted growth of host plants.

  • Signs include yellow stems of the parasite at the base of the plant, leading to reduced yields.

Disease Cycle of Witchweed

• Seeds can remain viable in soil for up to 10 years.

• Root exudates stimulate germination of witchweed seeds.

• The germinated haustoria penetrate host roots, leading to the emergence of stems and production of flowers.

Mistletoes Overview

Dwarf Mistletoe

• Attacks coniferous trees.

• Classified as a true parasite; has leaves and typically affects young limbs.

True Mistletoe

• Attacks a range of hosts, including broadleaves and some conifers.

• Partial parasite with green leaves, relying on the host for water and some nutrients.

• Often considered a sacred plant in historical contexts.

• Signs include yellowing of host plants and impact on growth via excessive shoot production.

Dwarf Mistletoe Characteristics

• Generally leafless with flowers and dioecious (male and female plants).

• Seeds build water pressure in pods that can eject seeds up to 50 feet, leading to new infections.

Management of Dwarf Mistletoe

• Serious infestations must be managed through tree removal as this is the only effective control method.

Cultural and Historical Significance of Mistletoe

• Historically viewed as sacred by druids and associated with peace and reconciliation (e.g., kissing under mistletoe during Christmas).

True Mistletoe Features

• Hemi-parasites with green leaves that need their host for water and some nutrients.

• Produce seeds in berries that are spread by birds, aiding in dispersal.

• Can photosynthesize and manage light levels to some extent by cutting off light.