Expl Agric.: page 1 of 21 C  Cambridge University Press 2015 doi:10.1017/S0014479715000034 RESPONSES OF WHEAT PLANTS UNDER POST-ANTHESIS STRESS INDUCED BY DEFOLIATION: I. CONTRIBUTION OF AGRO-PHYSIOLOGICAL TRAITS TO GRAIN YIELD By DEJAN DODIG†‡, JASNA SAVI ´ C§, VESNA KANDI ´ C†, MIROSLAV ZORI ´ C¶, BILJANA VUCELI ´ C RADOVI ´ C§, ALEKSANDRA POPOVI ´ C†† and STEVE QUARRIE‡‡ †Maize Research Institute Zemun Polje, 1 Slobodana Baji´ ca Street, 11185 Zemun-Belgrade, Serbia,§Faculty of Agriculture, University of Belgrade, 6 Nemanjina Street, 11080 Zemun-Belgrade, Serbia, ¶Institute of Field and Vegetable Crops, 30 Maksima Gorkog Street, 21000 Novi Sad, Serbia, ††Faculty of Agriculture, University of Novi Sad, Trg Dositeja Obradovi´ ca 8, 21000 Novi Sad, Serbia and ‡‡Faculty of Biology, University of Belgrade, Studentski trg 1, 11000 Belgrade, Serbia (Accepted 14 January 2015) SUMMARY When water stress develops post-anthesis, wheat (Triticum aestivum L.) plants have to rely increasingly on remobilization of previously stored assimilates to maintain grain filling. In two-year field trials, we studied more than 20 agronomic and developmental traits in 61 wheat genotypes (27 F4:5 families, 17 parents used for the crosses and 17 standards), comparing plants that were defoliated (DP) by cutting off all leaf blades 10 days after anthesis with intact control plants (CP). Estimated contributions of stem and sheath assimilate reserves to grain weight/spike were from 10–54% and from 24–84% in CP and DP plants, respectively. Stem-related traits were among key traits determining stem reserve contribution (SRC). The most important genetic variables in differentiating genotypes for stress tolerance were biomass/stem, stem reserves mobilization efficiency and grain filling rate (GFR). Balance among traits related to yield maintenance in DP were more important than their high values. In general F4:5 families (FAM), that had been crossed to combine typical breeding traits such as biomass and yield components, showed better tolerance under moderate stress than standards and parents. INTRODUCTION In semi-arid areas of the world with a Mediterranean-type climate, high temperature and drought stress are among the two most important environmental factors influencing yield processes when wheat enters the grain-filling period. In south-east Europe, which is subject to Mediterranean weather patterns, there is a tendency of rising air temperature in the critical winter wheat growing period (April–June) to be combined with decreases in precipitation (Morgounov et al., 2013). Other authors have also indicated that the prevalence and intensity of drought and heat stress during reproductive processes (e.g. pollination and fertilization) and grain filling are expected to increase and will be limiting factors in crop production under future ‡Corresponding author. Email: ddodig@mrizp.rs