Open Access Maydica 57-2012 Original Paper RECEIVED 11/15/2012 Behaviour of Quality Protein Maize (QPM) genotypes under well irrigated and water stress conditions in subtropical climate Ashok K Parihar 1 *, Shyam L Godawat 1 , Deepak Singh 2 , Chiter M Parihar 3 , Mangi L Jat 4 1 Department of Plant Breeding and Genetics, Rajasthan College of Agriculture, MPUA&T, Udaipur-313 001, Rajasthan, India 2 Indian Institute of Pulses Research, Kanpur-208024, Uttar Pradesh, India 3 Directorate of Maize Research, Pusa Campus, New Delhi-110012, India 4 Cropping System Agronomist, International Maize and wheat Improvement Center (CIMMYT), India *Corresponding author: E-mail: ashoka.parihar@gmail.com Keywords: QPM, water stress, tolerance indices, principal component analysis Drought or water stress is one of the prime problems affecting production of maize at global level. A major ob- jective of QPM breeding programs in semi arid tropics or subtropical climatic conditions is to increase genetic potential of QPM genotypes under water stress conditions. In order to identify drought tolerant single cross QPM hybrids an experiment with 85 genotypes was conducted under well irrigated and water stress conditions. Six drought tolerance indices viz, mean productivity (MP), geometric mean productivity (GMP), yield index (YI), toler- ance index (TOL), stress susceptibility index (SSI), and superiority measures (SM) were used on the basis of grain yield in water stress (Ys) and well irrigated (Yp) conditions. Highest significant positive correlations were observed among MP, GMP and YI indices. The hybrids 75, 38, 27, and 50 were more drought tolerant based on drought tol- erance indices. Three dimensional plot, bi-plot and cluster analysis confirmed these results. Principal component analysis reduced six indices down to two components with 90.71% proportional cumulative variance. Genotypes were grouped by two ways cluster analysis (using Ward’s method) based on Yp, Ys and drought tolerance indices. Also, the results of correlation, 3D graphs, bi-plot and cluster analysis reveals that the most suitable indices to screen QPM genotypes in drought stress conditions were MP, GMP and YI. These indices could be used in QPM breeding programs to introduce drought tolerance in single cross hybrids. Abstract Introduction Maize (Zea mays L) is an important food, feed and industrial crop after wheat and rice at global level. It is a versatile crop grown in diversified ecologies. Maize is the important source of protein (9-12%) (Bressani, 1991) and it supplies 15 % of global human protein requirements. However quality of protein like other cereals lacks sufficient quantities of lysine and tryp- tophan, which are essential amino acids in human nutrition. Its deficiency impedes utilization of other amino acids. These deficiencies have been corrected by the mutant opaque-2 (o2) gene, which raises the amount of lysine and tryptophan in the endosperm by two times over that of ordinary maize. The maize car- rying the o2 gene in homozygous condition, the hard modified endosperm with vitreous kernels is known as quality protein maize (QPM). An attempt has been made to develop and recognize superior inbred lines and single cross hybrids, which are sustainable for semi-arid rainfed and moisture stress environments in subtropical climate. Thus, the current effort on QPM is to increase its cultivation in the semi-arid rainfed and subtropical climatic region, experienc- ing problems of malnutrition and where normal maize is the staple food. In these regions, however, maize is frequently produced under environmental stress, among which drought is the most important. To identify drought resistance genotypes, some selection indices based on a mathematical equations between stress and optimum conditions has been proposed for selection of drought tolerant genotypes (Fischer and Maurere, 1978; Rosielle and Hamblin, 1981; Fernandez, 1992; Gavuzzi et al, 1997). Rosielle and Hamblin (1981) define tolerance index (TOL) as difference between crop yield in both stress and non stress conditions and mean productivity (MP) as the average grain yield in both conditions. High amount of TOL showed plant susceptibility to water stress and selection was based on low TOL. High MP also showed more tolerance to stress. Fernandez (1992) suggested geometric mean productivity (GMP) based on which maize hybrids identified with high yield in both stress and non-stress conditions (Khalili et al, 2004). The stress susceptibility index (SSI) is estimat- ed based on mean yield of plants under suitable and stress conditions (Drivand et al, 2012; Ahmadizadeh et al, 2012; Guttieri et al, 2001; Fischer and Maurere, 1978). If the value of SSI is more than one it indicates above average, susceptibility and SSI less than one indicate below average susceptibility to water stress.