Herbicide tolerance of Rabi sorghum varieties and germplasm

Sorghum (Sorghum bicolor (L.) Moench) is a staple cereal grown under moisture stress conditions with low inputs during rainy and post-rainy (Rabi)seasons. With the threat of climate change looming large on the crop productivity, sorghum being a drought hardy crop will play an important role in food, feed and fodder security in dry land economy. Weeds are a major deterrent in increasing the sorghum productivity as they compete with crop for soil moisture and nutrients, which are the major limiting factors in semi-arid areas. Therefore, efficient weed management becomes even more important under rainfed conditions. Atrazine (as preemergence) is the most widely used herbicide for weed control in grain sorghum. It has a low effectiveness on grasses (Dan et al. 2011) and its efficacy decreases under moisture stress conditions (Tapia et al.1997). Atrazine may also cause carry over effects in subsequent sensitive crops under some conditions, so alternative treatments are needed (Ishaya et al.2007, Keeling et al.2013). Sensitivity of grain sorghum to currently available postemergence herbicides is one of the major concerns to manage weeds that emerge after crop establishment (Archangelo et al.2002). Presently, 2,4-D is the only post-emergence herbicide used to control broadleaved weeds with varying degree of weed control and sensitivity in sorghum hybrids. Herbicide-tolerant crops make it possible to control weeds with nonselective herbicides. ALS-inhibitor herbicides viz.,nicosulfuron and nimsulfuron are widely used to control broad-leaf and grassy weeds in corn (Zea mays), but the sorghum is susceptible to these herbicides. However, by transferring a major resistance gene from wild sorghum relative, researchers at Kansas State University (KSU), USA developed a grain sorghum that is resistant to several ALS-inhibiting herbicides as Steadfast (nicosul-furon), Accent (nicosulfuron), Resolve (rimsulfuron) and Ally (metsulfuron) (Tuinstra and Al-Khatib 2007, Tuinstra et al.2009). Keeping these facts in view, the present experiment was conducted to evaluate the relative performance of Rabi sorghum germplasm and varieties to quizalofop ethyl, metsulfuron-methyl and carfentrazone-ethyl herbicides.