Relationship of developmental traits and grain yield on durum wheat (Triticum durum Desf.) under terminal drought stress condition

The 154 durum wheat lines obtained from International Maize and Wheat Improvement Center (CIMMYT) were investigated under TDS conditions at Islamabad Agricultural Research Station across 2013-14. According to variation of days to heading, DHE, and days to maturity, DMA, 39 lines selected and investigated along with Saji cultivar as check under normal irrigation and TDS conditions in 2014-15. The experiments were conducted at Islamabad-e Gharb Agricultural Research Station, Kermanshah province, Iran. Transition trend of apex of main stem including: vegetative, double ridges, glum, spikelet, florets and terminal spikelet initiation was investigated and recorded by successive sampling and dissection sampled plants until the terminal spikelet formation. Each plot consisted of 2 rows, 2 m length with 32.5cm row spacing. Seed density was considered 450 seeds per m2. Sowing was done by hand. Irrigation cut was at booting stage (Z , 4.5) of crop. Statical analysis wrere done by MSTATC and SAS9.1. In most early lines, at least 475 and 691 growing degree days, GDD, equal to 105 and 132 days after planting ,DAP, needed to reach double ridge ,DR, and terminal spikelet stages, TS, respectively. Genotypes showed high variation for the duration of DR to TS and from 259 up to 339 GDD, equal to 35-57 days. Terminal drought reduced Stem elongation duration, SE, (from DR to anthesis) by 32 GDD, equal to 2 days. At least 96 mg/plant of dry matter was critical for stat of transition. Totally, genotypes showed high variation for duration of developmental stages. In optimum irrigation the duration of vegetative phase, VP, increased and led to increase of glum initiation, floret initiation, terminal spikelet formation, flag leaf stage, FL, anthesisi, ANTH ,STEL and GY. Increase of transition lenght, TL, resulted in decrease of STEL and showed negative correlation with GY. The life cycle duration , GY and GFR increased with increases of TL. Any increase in developmental stages up to FL increased growth cycle and improved GY. Extending the length of VP to DR led to reduction of GY under terminal drought stress condition. Any increase in duration of developmental stages led to reduction of STEL, FL and coincidence of filling period with terminal drought stress, and hence GY reduction. There was high variation among genotypes for response to terminal drought stress and GY reduction. Genotypes with shorter VP and high development rate headed early and benefited from adequate time for grain filling which contributed to higher GY.