Glyphosate tolerance in maize (Zea mays L.). 1. Differential response among inbred lines

Abstract

Variation in susceptibility to the safe broad-spectrum herbicide glyphosate was investigated in maize . Eleven inbred lines, grown in a growth chamber, were evaluated for their tolerance to the herbicide at 2 .4 mM (0 .2 kg a .i . in 400 1 ha ' of water) . Following treatment with glyphosate at the three-leaf stage, significant variation in damage, expressed as visual injury ratings scored 7, 14 and 21 days after the application of the herbicide, was found . Effects on dry weight and shoot height were consistent with visual scores and the carbon-exchange rate was found to be a sensitive index of differential injury .Biochemical characterization of 5-enol-pyruvyl-shikimate-3-phosphate (EPSP) synthase, the main target of the herbicide, ruled out the possibility that this differential susceptibility was due to variations in the sensitivity of the enzyme. On the contrary, a positive correlation was found between in vivo tolerance and EPSP synthase levels, measured at different stages during seedling growth . This result suggests that a naturally occurring difference in EPSP synthase levels in the tissues may contribute to the differential response observed in vivo in maize inbreds .Abbreviations : CER -carbon-exchange rate, EPSP -5-enol-pyruvyl-shikimate-3-phosphate, ID50 -concentration causing 50% inhibition

Glyphosate tolerance in maize (Zea mays L.). 2. Selection and characterization of a tolerant somaclone

“…Families displayed a continuum of responses to glyphosate, ranging from susceptible to tolerant, thus suggesting a complex genetic control of the trait . Moreover, contrary to the results obtained as to the natural variability of maize inbreds for the sensitivity to glyphosate (Forlani & Racchi, 1995), the percent reduction in dry weight was poorly correlated with the relative tolerance assessed as visual rating (r = 0 .196 NS , n= 11) .…”

“…Though so far a direct action of glyphosate on photosynthesis has not been demonstrated (Cole, 1985), data obtained on maize inbreds clearly showed the carbon-exchange rate as an early and sensitive index of glyphosate injury, and indicated that differences in response for CER fit the differences in the overall sensitivity to the herbicide (Forlani & Racchi, 1995) . Also in this case the most tolerant family exhibits a capacity to maintain a high level of CER, contrary to what occurs Table 3.…”

“…The selection was performed on R2 families of regenerated plants of different genetic backgrounds . The choice of starting materials was influenced by the ease with which these lines give rise to embryogenic, highly regenerative cultures, although the same lines had shown differential sensitivities to glyphosate, ranging from medium to low levels of tolerance (Forlani & Racchi, 1995) .…”

“…A natural difference in EPSP synthase levels in seedling tissues was found as one of the factors accounting for the differential susceptibility (Forlani & Racchi, 1995) . Here we report the result of a screening for glyphosate tolerance of a hundred maize somaclones .…”

The Effects of Glyphosate on the Growth of Birdsfoot Trefoil (Lotus corniculatus) and Its Interaction with Different Phosphorus Contents in Soil

“…The effects of glyphosate on the EPSPS enzyme are known, but this inhibition affects other biochemical and physiological processes (Baylis, 2000), with differences among species such as Convolvulus arvensis (DeGennaro and Weller, 1984), Zea mays L. (Forlani & Racchi, 1995), Lolium rigidum Gaudin (Lorraine-Colwill et al, 2001), and Capsicum anuum (Ronco et al, 2008).…”