Field Crops Research 123 (2011) 10–18 Contents lists available at ScienceDirect Field Crops Research journal homepage: www.elsevier.com/locate/fcr Characterization of sorghum genotypes for traits related to drought tolerance R.N. Mutava a , P.V.V. Prasad a,∗ , M.R. Tuinstra b , K.D. Kofoid c,1 , J. Yu a a Department of Agronomy, Kansas State University, Manhattan, KS 66506, USA b Department of Agronomy, Purdue University, West Lafayette, IN 47907, USA c Kansas State University, Agricultural Research Center, Hays, KS 67601, USA article info Article history: Received 11 December 2010 Received in revised form 6 April 2011 Accepted 6 April 2011 Keywords: Sorghum Water stress Leaf temperature Grain numbers Grain yield Harvest index abstract Grain sorghum (Sorghum bicolor L. Moench) is a genetically diverse cereal crop grown in many semiarid regions of the world. Improving drought tolerance in sorghum is of prime importance. An association panel of about 300 sorghum genotypes from different races, representative of sorghum globally, was assembled for genetic studies. The objectives of this research were to (i) quantify the performance of the association panel under field conditions in Kansas, (ii) characterize the association panel for phenological, physiological and yield traits that might be associated with tolerance to limited moisture (drought), and (iii) identify genotypes with higher yield potential and stability under different environments that may be used in the sorghum breeding program. Results show large diversity for physiological and yield traits such as chlorophyll content, leaf temperature, grain numbers and grain weight per panicle, harvest index and yield. Significant differences were found for plant height, grain weight and numbers per panicle, harvest index, and grain yield among and within races. The US elite lines had the highest number of grains and grain weight per panicle while the guinea and bicolor races recorded the lowest. Harvest index and yield was highest for the US elite lines and the caudatum genotypes. Overall, there was a negative correlation between plant height and grain weight, grain numbers and yield. Harvest index and grain numbers were negatively affected by moisture limitation for all the races. Among the races, the caudatum genotypes were more stable in grain yield across the different environments. Overall, there was a wide variability within the association panel for physiological and yield traits that may prove to be useful for improving drought tolerance in sorghum. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Sorghum (Sorghum bicolor (L.) Moench), a crop native to Sub- Saharan Africa, has been cultivated for centuries in Africa and Asia. It is an important grain crop and food source in many developing countries (Doggett, 1988). In the USA, sorghum is primarily grown as feed for livestock and is gaining attention as a bioenergy and specialty food crop. Abiotic stress factors remain a major constraint to the growth and productivity of crops. The single greatest abiotic stress fac- tor that limits crop growth worldwide is water availability (Araus et al., 2002). With mounting pressure on the existing limited water resources combined with climatic disruptions and increased house- hold water use, water threatens to become a progressively scarce resource for crop production. The impact of drought stress can be partly mitigated through genetic improvement for stress toler- ance. Genetic improvement for drought tolerance based on existing ∗ Corresponding author. Tel.: +1 785 532 3746; fax: +1 785 532 6094. E-mail address: vara@ksu.edu (P.V.V. Prasad). 1 Retired. genetic variability in a species is founded on the evaluation and selection of tolerant germplasm and understanding of the phys- iological and genetic responses to stress. Even though the world collections of sorghum contain over 35,000 accessions, the genetic base currently used in breeding programs is very small (about 3%). Even though use of exotic germplasm in the US has been on the increase since the first releases from the conversion program in 1969, most of the widely used parental lines are genetically sim- ilar (Rosenow and Dahlberg, 2000). Important genes that have impacted sorghum breeding are those affecting maturity, with greatest influences being photoperiod and temperature, and plant height. Genetic diversity in sorghum has been evaluated through molecular markers (Tao et al., 1993; Vierling et al., 1994; Taramino et al., 1997; Uptmoor et al., 2003) but these studies did not do a comprehensive sampling of existing germplasm. Another study by Ahnert et al. (1996) which used restriction fragment length poly- morphisms (RFLP) probes did not include germplasm from the world collection and therefore left out a significant portion of the germplasm pool utilized in breeding. Menz et al. (2004) evaluated genetic diversity in sorghum using amplifed fragment length poly- morphism (AFLP) and simple sequence repeat (SSR) markers but 0378-4290/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.fcr.2011.04.006