evaluation of defoliation on leaf water relations, chlorophyll content, and grain yield of triticale (x triticosecale wittmack) genotypes under water stress

Optimizing the source size and its utilization by the sink is one of the main factors enhancing the yield potential and decreasing water demand in crops when exposed to drought. to investigate the effect of defoliation on leaf water relations, chlorophyll content and yield components of five triticale genotypes including sanabad, juanillo, et-83-3, et-84-5 and et-84-8 under well-watered (100% fc) and water stress (50% fc) conditions, a controlled experiment was carried out at shiraz university in 2013. the results showed that et-84-8 and sanabad genotypes had higher chlorophyll content (ranged from 49.1 to 54.6 spad unit) under water stress. among the triticale cultivars, water stress caused 21 to 42% decline in the rate of water loss (rwl). in all genotypes except et-83-3 and juanillo, the excised leaf water retention (elwr) slowly decreased under water stress conditions. in all triticale genotypes except et-84-8, water stress declined main shoot yield 21-22%, while in et-84-8, it was only 9%. interestingly, in et-84-8, grain number per spike was not affected by moisture regimes. sanabad cultivar, with 2.57 g/g had the highest initial water content (iwc) at defoliation of all leaves except the flag leaf and penultimate leaf treatment under water stress. under defoliation and water stress, et-84-8 and sanabad genotypes showed a greater 100-grain weight ranged from 3.60 to 3.74 g. it was concluded that triticale cultivars were more sink-limited especially under water stress, and source restriction by defoliation which had less effects on main shoot yield could be used as a useful tool for lowering water consumption during grain filling.