Submitted to: Seed Technology Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2009
Publication Date: 2/3/2010
Citation: Nandula, V.K., Poston, D.H., Reddy, K.N. 2010. Seed Germination Differences Between Glyphosate-Resistant and -Susceptible Italian Ryegrass Populations. Seed Technology Journal. 31(2):123-133.
Interpretive Summary: Italian ryegrass tolerant to glyphosate is becoming a major weed problem in Mississippi Delta region. Scientists from the Mississippi State University Delta Research and Extension Center and the Agricultural Research Service Southern Weed Science Research Unit have studied germination differences in glyphosate-tolerant (T) and –susceptible (S) populations of Italian ryegrass. In general both the T and S Italian ryegrass have the ability to germinate under a broad range of environmental conditions. Between the two populations, the T Italian ryegrass germinated better than the S Italian ryegrass. These results indicate that under field conditions, the T Italian ryegrass population could germinate and establish in far greater numbers and gain a competitive advantage over the S Italian ryegrass population.
Technical Abstract: Italian ryegrass tolerant to glyphosate is becoming a major weed problem in glyphosate-resistant crops. The effects of temperature, light, pH, salt and osmotic stress, shikimic acid, and planting depth on germination of glyphosate-tolerant (T) and susceptible (S) Italian ryegrass populations were studied. Overall, germination of both Italian ryegrasses was highest at 13 C and decreased when temperature increased to 20 or 27 C under both light and dark conditions. In S Italian ryegrass population, light stimulated germination (57%) compared to darkness (41%) at 13 C, but light had no effect on germination at 20 and 27 C. In T Italian ryegrass population, light had no effect on germination at 13 C while light inhibited germination at 20 and 27 C. The T Italian ryegrass had higher germination (69 to 87%) compared to the S Italian ryegrass population (37 to 57%) at a pH 4 to 7 range. Seed germination decreased as NaCl concentration increased from 20 to 160 mM and osmotic potential increased from 0 (distilled water) to –0.8 MPa in both the T and S Italian ryegrass populations. Germination of T and S Italian ryegrass populations reduced from 76% to 25% and 67% to 12%, respectively, as shikimic acid concentration increased from 0 to 16 mM. Seedling emergence was highest from seed placed on the soil surface. Seedling emergence was less than 7% from seed planted at 0.5 cm depth and none emerged from seed planted below 2.5 cm depth in both populations. These results suggest that both the T and S Italian ryegrass have the ability to germinate under a broad range of environmental conditions. There were also some differences in germination response between the T and S Italian ryegrass populations. The T Italian ryegrass population germinated better than the S Italian ryegrass population across all the environmental factors studied.