| Summary: | Striga, a genus of obligate parasitic weeds in the family Orobanchaceae, has been
identified as the most important biological factor limiting agricultural productivity in sub-Saharan Africa. Germination of Striga seeds is triggered by strigolactone root exudates
from host plants. Strigolactones also induce hyphal branching in arbuscular mycorrhizal
(AM) fungi, which are important for plant uptake of phosphorus in low phosphorus soils.
Mechanisms of Striga resistance based on reduced strigolactone production may also
convey resistance to AM fungi which would require higher inputs of phosphorus fertilizer
to attain optimal crop growth. There is evidence for genetic differences in mycorrhizal
responsiveness in other grain crops; therefore it is beneficial for breeders to be aware of
these differences when developing Striga-resistant sorghum cultivars. This research aims
to determine phosphorus and mycorrhizal responsiveness of sorghum genotypes
important for or developed by breeders working on Striga resistance. Phosphorus
response curves were determined for twelve sorghum genotypes using pasteurized low
phosphorus soil amended to achieve four different phosphorus levels. Simple linear
regression was performed on root and shoot dry weight data. Results indicate variability
in phosphorus responsiveness within Striga resistant and susceptible genotypes. Seven of
these genotypes were selected for continued research, which analyzed responsiveness to
phosphorous and differences in mycorrhizal responsiveness in relation to reported
mechanisms of Striga resistance. Treatments included three levels of phosphorus
amendments and the addition of Funneliformis mosseae inoculum. All genotypes were
strongly responsive to P amendment when grown without AM fungi and showed a
decrease in responsiveness to P when inoculated with F. mosseae. Trends for all
genotypes indicate a greater uptake of P, Zn, and Mg by mycorrhizal plants as compared
to nonmycorrhizal plants. All seven genotypes were responsive to mycorrhizae, with a
significant increase in biomass for all genotypes, especially at the lowest phosphorus
level. The responsiveness to the mycorrhizal fungus does not appear to be directly related
to the susceptibility of genotypes to the parasitic weed Striga. === Graduation date: 2012
|
|---|
