|Abstract or Summary
- Growth of individual goosegrass (Eleusine indica (L) Gaertn.) plants of
three dinitroaniline-herbicide resistant (R) and three susceptible (S) biotypes from
North Carolina, South Carolina, and Mississippi was analyzed in greenhouse
experiments. Leaf area and biomass measurements, including root, shoot,
above-ground, and total dry weights were similar among the biotypes studied.
However, S-biotypes produced between 15% and 30% more reproductive biomass
than R-biotypes. Slight differences in instantaneous leaf area ratio, net
assimilation rate, and relative growth rate among biotypes were inconsistent and
unrelated to dinitroaniline-herbicide sensitivity. Results confirmed that S-biotypes
allocate more resources towards reproduction than R-biotypes, but overall growth
is similar among biotypes.
Responses of a R- and a S-biotype to competition were determined by
planting both biotypes at various monoculture and mixture densities and proportions.
In monoculture, reproductive output per plant decreased more with increasing
density in the R-biotype than in the S-biotype, although no differences in
above-ground biomass per plant were observed. Thus, the two biotypes differed
in their partitioning of resources to seed production. In mixture, the R-biotype
was more detrimentally affected by competition with the S-biotype than with itself.
On the other hand, the S-biotype was more affected by intra-biotype competition
than by competition with the R-biotype. Inter-biotype competition resulted in
reduced tiller and inflorescence numbers, above-ground biomass, and, especially,
reproductive output in the R-biotype. Results indicated that the R-biotype is
less fit than the S-biotype.
Several goosegrass populations from various counties from North Carolina
and South Carolina were also tested for trifluralin sensitivity. Most populations
were susceptible to the herbicide with GR₅₀ (herbicide rate required to reduce
above-ground dry weight by 50%) values ranging from 0.33 to 1.82 ppm. Populations
from Calhoun county (SC) had intermediate resistance to trifluralin (GR₅₀=
2.50-4.86 ppm). R-biotypes were not affected by the herbicide at the highest rate
tested (4.86 ppm). Foliar isozyme patterns of selected populations were determined.
The populations were homogeneous in isozyme activities, especially for
malate dehydrogenase, peroxidase, and superoxide dismutase. Some variability
in esterase was detected among populations but was unrelated to herbicide
Cytological studies were conducted with five R- and three S-biotypes not
exposed to dinitroaniline herbicides before examination with the electron microscope.
Cell-wall malformations were found in some cells from two of the R-biotypes
and in one of the S-biotypes. Malformations consisted of partially deposited
cell walls and the inclusion of cell-wall material in the cytoplasm. Some of the
affected cells also had abnormal, lobed nuclei and malformed mitochondria. Sgoosegrass
treated with trifluralin [2,6- dinitro- N,N- dipropyl -4- (trifluoromethyl)
benzenamide] exhibited typical cellular abnormalities, including binucleated cells.