Semi-parasitic plants

R. Brown and coworkers observed that seeds of Striga, known as witchweed, a semi-parasitic plant of grasses and corn, germinated only in the presence of root exudates from the living host. They isolated the sirupy exudate, [VJ > + 20° (water), resembling a pentose, but did not specifically identify the active substance. A study of many carbohydrates, mostly pentoses, showed that only D-ihreo-pentulose, C 3) — 32° (water), had the required activity L-[Pg.416]

MISTLETOE, Viscum album L., family Viscaceae, is a semi-parasite, growing on leafy trees. There are other subspecies that grow on coniferous trees. The mistletoe takes water and salts from the host plant, but it has its own photosynthesis and its secondary metabolites are totally different from those of the host plant. Five main groups are said to be characteristic of mistletoe ... 

A decrease in the percentage of linolenic acid is observed in all polar lipids of chloroplasts from semi-arid tropics. Phospholipids of all hemiparasitic plants contain oleic acid in large amounts and glycolipids to a lesser degree. The specific fra/i.y-A3-hexadecenoic acid is present in phosphatidylglycerol of all parasitic plants in normal proportion. 

Allelopathy found hopeful utilization in plant protection against parasite weeds. The main world parasitic species are the witchweeds (Striga spp.), broomrapes (Orobanche spp.), and eventually dodder (Cuscuta spp.). Witchweeds and broom-rapes attack many economically important crops especially throughout the semi-arid regions. Early detection of parasitic weed infestation and protection is difficult because of the growth habit of a root parasite and huge production of dust-like seeds viable up to 20 years (Kebreab and Murdoch 1999). 

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