Popcorn breeding for water-stress tolerance or for agronomic water-use efficiency?

Soil water limitations can cause high losses in agricultural yields. In order to investigate how popcorn varieties are affected by reduced water availability, we evaluated grain yield (GY) and popping expansion (PE) of 20 popcorn lines under water stress (WS) and well-watered conditions (WW), to propose discrimination with regard to the level of water-stress tolerance (T) and agronomic water-use efficiency (WUE), as well as to identify crosses for the breeding of superior hybrid combinations and for inheritance studies. A randomized complete block design with three replications was used. Irrigation was applied at pre-anthesis. The germplasm was discriminated based on the Stress tolerance index (STI), Stress susceptibility index (SSI), Stability index (SIN), Drought resistance index (DRI), and Agronomic water-use efficiency (WUE). Genetic diversity was measured by 15 EST-SSR markers. The reduction in GY under water stress was 55.29% and PE was reduced 29.19%. For the identification of genotypes with higher phenotypic means, STI and WUE were similarly efficient, whereas SSI and SIN identified genotypes with a lower proportional performance loss in the WS compared to the WW environment. For both GY and PE, there was a lack of relationship between WUE (more productive) and T (more stable). To explore the allelic complementarity for WUE, for T and for both, respectively, the combinations L59 x P7, L55 x P1 and L71 x P6 had the best performances. The lines L61, L63 and L65 phenotypically contrasted to those with high WUE and T and could be used for inheritance studies. Genotypes with higher WUE are considered the most appropriate option for breeding programs under WS.