Title page for ETD etd-31098-10830

Type of Document Dissertation
Author Nandula, Vijay K. II
Author's Email Address nandula@badlands.nodak.edu
URN etd-31098-10830
Degree PhD
Department Plant Pathology, Physiology, and Weed Science
Advisory Committee
Advisor Name Title
Foy, Chester L. Committee Chair
Hatzios, Kriton K. Committee Member
Hess, John L. Committee Member
Hilu, Khidir W. Committee Member
Orcutt, David M. Committee Member
  • Glyphosate
  • Orobanche aegyptiaca
  • Egyptian broomrape
  • Amino acid
Date of Defense 1998-02-05
Availability unrestricted

Broomrapes are achlorophyllous holoparasites of many economically important

dicotyledonous crops. As weeds, they cause reductions in crop yield, adversely affect crop

quality, and result in loss of cultivated land due to reduced crop alternatives. Few effective

control measures exist for broomrapes. One of the most promising approaches is the use of

low rates of glyphosate in hosts with tolerance to the herbicide. Recently, availability of

glyphosate-resistant crops has provided an alternative in broomrape infested areas.

Knowledge about the nitrogen status of broomrapes is essential for developing new control

strategies. Broomrapes have two potential sources of amino acids. First, the haustorium aids

in the translocation of amino acids from the host plant to the parasites. Second, broomrapes

may be able to synthesize some amino acids themselves and obtain the rest from the host.

However, the relative importance of these two modes of acquiring amino acids by broomrapes

is not clear. Osmotic stress has been implicated as a possible reason for inhibition of

broomrape germination by nitrogen. To date, there has been no attempt to correlate osmotic

potential with nitrogen induced inhibition of broomrape germination. Optimum temperatures

for conditioning and germination are different among broomrape species. Although

temperature is known to influence germination in broomrape, its effect on subsequent

development of the parasitic seedling has not been studied. Studies were conducted to

determine the use of glyphosate in controlling broomrape in common vetch that is tolerant to

low rates of glyphosate, and to compare this response with broomrape control in oilseed rape

that has been genetically engineered for glyphosate resistance. Glyphosate dose response

studies using a commercial formulation and patterns of absorption, translocation, and

metabolism, using 14 C-glyphosate, were determined for both host crops. Glyphosate

significantly reduced the growth of broomrape at 0.18 and 0.36 kg ae ha

-1 in common vetch and 0.25 to 0.75 kg ha -1 in oilseed rape. More than 25% of translocated 14 C-glyphosate in both host crops accumulated in broomrape tubercles. Broomrape parasitism caused a

redistribution of translocated 14 C-glyphosate in the roots of both host crops. Glyphosate was

metabolized up to 25% in common vetch, but remained intact in oilseed rape. Studies were

conducted to analyze amino acid composition of both nonparasitized and broomrape-parasitized

hosts and associated broomrape after hydrolysis and phenylisothiocyanate

derivatization of amino acids. Results indicated that amino acid concentrations of leaves of

parasitized carrot plants were lower than those of the leaves of nonparasitized carrot plants.

Broomrape tubercles had equal or higher amino acid concentrations compared to those of the

leaves of nonparasitized carrot plants. Levels of free alanine and arginine concentrations of

broomrape callus were higher than those of any other tissue of either carrot or broomrape.

The effect of glyphosate on the host-broomrape interaction regarding amino acid metabolism

was examined. Glyphosate generally increased the amino acid concentrations in common

vetch and oilseed rape plants, and broomrape attachments. The aromatic amino acids,

phenylalanine and tyrosine, did not differ from this pattern. Concentrations of certain amino

acids in broomrape were similar to those of parasitized common vetch and parasitized oilseed

rape, whereas levels of several others, were higher in broomrape attachments compared to the

host plants. In vitro studies were conducted to determine the influence of osmotic potential

and temperature on broomrape germination. Osmotic potential significantly affected

germination and radicle elongation of broomrapes. No correlation was found between

osmotic potential and ammonium-induced inhibition of germination of broomrapes.

Temperature significantly influenced germination and radicle elongation of all broomrape

species tested.

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