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Drought stress during the reproductive period of cereal crops leads to significant yield reductions, therefore, exploring effective methods to improve tolerance to post-anthesis drought is necessary. Pot experiment was carried out to investigate the effects of pre-drought priming on physiological characteristics and grain yield with drought stress at post-anthesis. Moderate water deficits (60–65% of the field capacity) were imposed to prime wheat plants during either the tillering or jointing stages, while severe drought stress (40–45% of the field capacity) was applied during the grain filling stage. The priming treatments significantly improved grain yield resulting in higher biomass. Compared to the control, the grain yield and biomass of the non-priming, tillering priming, and jointing priming treatments were reduced by 15.7, 9.1, and 9.3% and by 11.1, 6.1, and 10.5%, respectively. The primed plants exhibited higher adaptability to subsequent severe drought stress during grain filling, showing...

Wheat crop endures a considerable penalty of yield reduction to escape the drought events during post-anthesis period. Drought priming under a pre-drought stress can enhance the crop potential to tolerate the subsequent drought stress by triggering a faster and stronger defense mechanism. Towards these understandings, a set of controlled moderate drought stress at 55-60% field capacity (FC) was developed to prime the plants of two wheat cultivars namely Luhan-7 (drought tolerant) and Yangmai-16 (drought sensitive) during tillering (Feekes 2 stage) and jointing (Feekes 6 stage), respectively. The comparative response of primed and non-primed plants, cultivars and priming stages was evaluated by applying a subsequent severe drought stress at 7 days after anthesis. The results showed that primed plants of both cultivars showed higher potential to tolerate the post-anthesis drought stress through improved leaf water potential, more chlorophyll, and ribulose-1, 5-bisphosphate carboxylase/oxygenase contents, enhanced photosynthesis, better photoprotection and efficient enzymatic antioxidant system leading to less yield reductions. The primed plants of Luhan-7 showed higher capability to adapt the drought stress events than Yangmai-16. The positive effects of drought priming to sustain higher grain yield were pronounced in plants primed at tillering than those primed at jointing. In consequence, upregulated functioning of photosynthetic apparatus and efficient enzymatic antioxidant activities in primed plants indicated their superior potential to alleviate a subsequently occurring drought stress, which contributed to lower yield reductions than non-primed plants. However, genotypic and priming stages differences in response to drought stress also contributed to affect the capability of primed plants to tolerate the post-anthesis drought stress conditions in wheat.

Elucidating the growth responses of roots to water status will reveal physiological mechanisms underlying drought tolerance and water conservation in plants. Hydroponic experiments were conducted using two winter wheat cultivars, Wangshuibai (drought-sensitive) and Luohan 7 (drought-tolerant), and a water deficit was induced using a 20 % (m/v) aqueous solution of polyethylene glycol 6000 (−0.6 MPa). The lack of water significantly reduced the plant dry weight, leaf area, total root length (TRL) and surface area in seminal (SRs) and nodal roots (NRs), but the effects were less pronounced in Luohan 7 than in Wangshuibai. After re-watering, leaf area, TRL and surface area of Luohan 7 increased significantly, as compared to the controls, due to rapid compensatory growth of SRs, while those of Wangshuibai were still significantly reduced. Under water-deficit conditions, the concentrations of indole-3-acetic acid (IAA) and cytokinin (CTK) and their ratio (IAA/CTK) in SRs and NRs of both cultivars were significantly lower than those of controls, but increased after re-watering. However, Luohan 7 showed significantly increases in IAA/CTK of SRs as compared to the control. Net photosynthetic rate was much lower during water deficit in both cultivars, but it was enhanced significantly after re-watering, especially for Luohan 7. Moreover, sucrose content was significantly increased in leaves while reduced in roots under water-deficit conditions. After re-watering, sucrose content in leaves of both cultivars and in roots of Wangshuibai was severely reduced, while the values in roots of Luohan 7 were significantly increased as compared to the control. These results indicate that the drought-tolerant cultivar has a greater ability to maintain plant growth under water deficit and greater compensatory growth in SRs associated with higher IAA/CTK and photosynthetic products supply after re-watering.

Efficient nitrogen (N) nutrition has the potential to alleviate drought stress in crops by maintaining metabolic activities even at low tissue water potential. This study was aimed to understand the potential of N to minimize the effects of drought stress applied/occur during tillering (Feekes stage 2) and jointing (Feekes stage 6) growth stages of wheat by observing the regulations and limitations of physiological activities, crop growth rate during drought periods as well as final grain yields at maturity. In present study, pot cultured plants of a wheat cultivar Yangmai-16 were exposed to three water levels [severe stress at 35–40% field capacity (FC), moderate stress at 55–60% FC and well-watered at 75–80% FC] under two N rates (0.24 g and 0.16 g/kg soil). The results showed that the plants under severe drought stress accompanied by low N exhibited highly downregulated photosynthesis, and chlorophyll (Chl) fluorescence during the drought stress periods, and showed an accelerated grain filling rate with shortened grain filling duration (GFD) at post-anthesis, and reduced grain yields. Severe drought-stressed plants especially at jointing, exhibited lower Chl and Rubisco contents, lower efficiency of photosystem II and greater grain yield reductions. In contrast, drought-stressed plants under higher N showed tolerance to drought stress by maintaining higher leaf water potential, Chl and Rubisco content; lower lipid peroxidation associated with higher superoxide dismutase and ascorbate peroxidase activities during drought periods. The plants under higher N showed delayed senescence, increased GFD and lower grain yield reductions. The results of the study suggested that higher N nutrition contributed to drought tolerance in wheat by maintaining higher photosynthetic activities and antioxidative defense system during vegetative growth periods.

Determining the effect of water deficit during vegetative growth periods on grain yield will provide reasonable strategy for water-saving management of winter wheat (Triticum aestivum L.). Pot experiment was conducted using winter wheat cultivar (Yangmai16) to investigate the effects of water deficit during vegetative periods on post-anthesis photosynthetic capacity and the relationship with grain yield formation during the growing season of 2013–2014. Water deficit consisted of moderate (leaf water potential of −1.20 to −1.40 MPa) and severe (leaf water potential of −1.80 to −2.20 MPa) levels during tillering and jointing growth stages, respectively. Moderate water deficit during tillering significantly increased grain yield through an enhanced yield capacity per stem and moderate water deficit during jointing resulted in similar grain yields as compared to control, while severe water deficit during both periods significantly reduced grain yield due to strong reduction in number of spikes as compared to control. Moderate or severe water deficit during tillering had no effect on flag leaf area but reduced it significantly when it occurred during jointing. Water deficit treatments during jointing and tillering increased net photosynthetic rate (P n) of flag leaves, the treatment during jointing being the most stimulatory. The maximum photochemical efficiency of Photosystem II, actual photochemical efficiency, the maximum carboxylation rate and photosynthetic electron transport rate increased in ways similar to P n in response to water deficit but non-photochemical quenching decreased. We conclude that improved photosynthetic capacity by moderate water deficit during vegetative growth period highly contributes to grain yield, especially during tillering period, while grain yield decreased by the limitation of leaf area and spikes under severe water deficit.