We tested two genes together in hybrid poplars (genus Populus), CP4 and GOX, for imparting tolerance to glyphosate (the active ingredient in Roundup® herbicide). Using Agrobacterium-based transformation, 80 independent transgenic lines (i.e., products of asexual gene transfer) were produced in a variety of hybrid poplar clones (40 lines in Populus trichocarpa Torr. & Gray × Populus deltoides Bartr., 35 lines in Populus tremula L. × Populus alba L., and five lines in P. tremula × Populus tremuloides Michx.). We evaluated glyphosate tolerance over 2 years in field studies conducted in eastern and western Oregon. Ten percent of our transgenic lines showed no foliar damage or reduced growth after being sprayed with Roundup® at concentrations above normal commercial rates. Lack of damage was associated with expression of the CP4 gene but not of the GOX gene. It was suspected that GOX caused undesirable side effects, so we produced 12 lines into which only the CP4 gene was inserted. The performance of these newly regenerated lines was compared with an identical number of lines, produced in the same genotype, that had previously been engineered to contain both CP4 and GOX. Growth of the lines transformed with just CP4 was significantly better than those containing both genes and exhibited less damage in response to glyphosate treatment. This is the first report of transgenic poplars exhibiting high levels of glyphosate tolerance when grown under field conditions. With a modest transformation effort, it is possible to produce lines with commercially useful levels of glyphosate tolerance and little apparent collateral genetic damage.
Tiller development of sweet corn (Zea mays L.) was slowed or terminated following clipping of early leaves. Clipping reduced the size or mass of tillers more than it reduced tiller number. Increasing stand density and early clipping both reduced tillering. Planting date had little effect on tiller production, with or without clipping.
Increases in the harvest index of sweet corn (Zea mays L.) following clipping of early leaves were found to be the result of a reduction in plant stover, and not an increase in ear fresh weight. All stover components were reduced, but tillers were most affected. Early clipping reduced leaf area, but had no effect on percent stalk-stored soluble solids. Examination of stem apices following clipping suggested that the greater reduction in stover compared to ears was due to a longer interruption in vegetative growth than in reproductive development.
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