The normalized difference vegetation index (NDVI) is gaining popularity as a complementary selection tool, even though it requires an instrument not readily available in the developing world. We evaluated several parameters (originating from the analysis of digital photos using BreedPix software) as potential selection criteria in 23 winter wheat yield trials grown over 4 years at 2 sites. NDVI and digital photos were taken at key development stages from stem elongation to maturity. The correlations between digital photo parameters a and u and grain yield, as well as correlations between NDVI and grain yield within individual trials, varied depending on crop stage, moisture availability, and germplasm composition. NDVI, photo-a, and photo-u parameters had equal power in distinguishing high-and low-yielding genotypes in the trials and were significantly associated with yield in approximately 50% of all observations. The association of vegetative indices with grain yield can be improved by evaluating germplasm with a similar maturity range. An important challenge is in utilizing these tools in unreplicated small plots, including head rows where selection efficiency is low.

To evaluate the genetic diversity in 48 winter bread wheat genotypes originating from different countries, an experiment based on randomized complete block design with 4 replications was carried out in drip irrigation and rain-fed conditions at the field station of the Transitional Zone Agricultural Research Institute, Eskişehir, Turkey in 2011 and 2012. Based on grain yield under rain-fed and irrigated conditions, drought tolerance indices, i.e. stress susceptibility index (SSI), stress tolerance index (STI), tolerance index (TOL), mean productivity (MP), and geometric mean productivity (GMP), were calculated to identify genotypes with better yield and drought tolerance. Analysis of variance indicated that there were highly significant differences among the genotypes with regard to all the traits under the two experimental conditions. The correlation coefficients showed that STI, MP, and GMP were the most desirable selection criteria for high yielding and drought tolerant genotypes. Based on principle component analysis and biplot, genotypes numbered as 6, 11, 26, 41, 45, and 47 were susceptible genotypes. The genotypes numbered as 4, 12, 17, 24, 27, 28, 34, 35, 36, 38, and 42 were more stable under rain-fed conditions, while genotypes numbered as 9, 29, 31, and 44 were highly adapted to the irrigated conditions. Cluster analysis classified the genotypes into 3 groups: resistant, susceptible, and tolerant to drought conditions. In conclusion, this study showed that drought stress reduced the yield of some genotypes, while others were tolerant to drought, suggesting genetic variability of drought tolerance in this material. Therefore, breeders can select stress-resistant wheat genotypes based on the MP, GMP, and STI indices.