Effects of soil applied herbicides on leaf nitrate reductase and crude protein in the leaf and seed of two cowpea cultivars
A glass-house study was conducted to determine the effects of four commonly used herbicides (pendimethalin, metobromuron, metolachlor and prometryne) applied pre-emergence at rates of 0, 0.125, 0.625 and 1.25 kg ha−1, on leaf nitrate concentration (NO3−C), nitrate reductase activity (NRA), leaf crude protein and seed protein in two cowpea cultivars, 60 day (60D) and Ife brown (IB).
Control and treated plants of both cultivars showed separate peaks for NO3−C and NRA, 49 days after planting (DAP) and 35 DAP for 60D and IB respectively. Herbicide treatment generally enhanced NO3−C but tended to decrease NRA in both cultivars. Howver, metobromuron at 0.625 kg ha−1 increased NRA throughout the growth period with an optimum increase of 52.5%, over the control, at 35 DAP. Pendimethalin increased NO3−C NRA and leaf protein but did not influence seed protein appreciably. In contrast metobromuron increased NO3−C, decreased NRA, but increased seed protein by 29.6% over the control at 0.125 kg ha−1 in 60D. Metolachlor and prometryne were most inhibitory to seed protein development. In addition, metolachlor reversed the interdependence of NO3−C and NRA.
Key wordscowpea crude protein herbicides nitrate concentration nitrate reductase activity
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