Impact of post‐flowering heat stress in winter wheat tracked through optical signals

Abstract

Increasing temperatures can severely affect wheat (Triticum aestivum L.) production, particularly when it coincides with the grain-filling period. Heat stress induces rapid senescence resulting in early maturity and shortened grain-filling period. In this study, the applicability of in vivo chlorophyll fluorescence (Chl-F) and chlorophyll index to track rate of senescence in flag leaves and spikes exposed to heat stress were investigated. Seven winter wheat varieties were exposed to post-flowering heat stress using growth chambers [35/15 • C (heat stress) and 25/15 • C (control) day/night] and unique field-based heat tents (imposed +6 • C higher than ambient). Effective quantum yield of photosystem II (PSII) (QY) was recorded temporally in flag leaves and spikes, and compared with in vitro chlorophyll-a (Chl-a) concentration and non-invasive estimation of chlorophyll and flavonoids index. Time point indicating the start of senescence (changepoint, CP) for QY was advanced by 0-8 and 0-6 d in flag leaves and spikes, respectively, under heat stress. In the chamber experiment, sustained heat stress induced accelerated decline of QY, particularly in wheat cultivars Larry and WB4458. Stronger positive relationship between days to senescence in spikes and thousand kernel weight indicated an extended period of assimilate supply from sink compared to the source tissue, during grain filling. Capturing heat stressinduced changes in photosynthetic pigments and QY at high temporal frequency presents an effective phenotyping approach for testing genetic diversity in largescale field experiments involving different crops.

High night temperature effects on wheat and rice: Current status and way forward

“…The high-resolution imaging and downstream colour changes were able to distinguish genotypes with different rates of panicle maturation/senescence in response to HNT stress and have the potential to be extended to large-scale phenotyping of populations. A similar approach is also likely to work for wheat spikes, as demonstrated recently using a hand-held fluorometer (Šebela, Bergkamp, Impa, Fritz, & Jagadish, 2020).…”

The potential of resilient carbon dynamics for stabilizing crop reproductive development and productivity during heat stress

“…Chlorophyll fluorescence is a somewhat underutilized approach for understanding photosynthesis in non‐foliar structures. Key exceptions here are the studies of Šebela, Bergkamp, Somayanda, Fritz, and Jagadish (2020) and Šebela, Quiñones, Olejníčková, and Jagadish (2015), where a chlorophyll fluorescence methodology was developed and utilized to determine temperature‐derived alterations to the optical properties of rice panicles and wheat spikes, respectively. Via this methodology, the authors were able to pinpoint the initiation of heat‐induced panicle senescence.…”

Safeners improve early‐stage chilling‐stress tolerance in sorghum

“…The maximal fluorescence yields () and actual fluorescence yields (Ft) of light‐adapted samples were measured by using saturating light [intensity approximately 3000 μmol (photons) m –2 s –1 ] and measuring light [intensity approximately 0.09 μmol (photons) m –2 s –1 ], respectively. The effective quantum yield (QY) of photosystem II (PS II) was calculated using Equation (Genty et al., 1989; Šebela et al., 2020). Total leaf area was measured using the leaf area meter (LI 3100 area meter, LI‐COR Biosciences, Lincoln, NE, USA) immediately after harvest.Where TSE is total seedlings emerged, n i is the number of seedlings that emerged on the i th day after planting (DAP i ).…”

“…Sorghum seedling emergence percentage and emergence indices were calculated using Equations 2 and 3, respectively, following methods described by Ostmeyer et al, 2020. The chlorophyll index using Equation 4 (Genty et al, 1989;Šebela et al, 2020). Total leaf area was measured using the leaf area meter (LI 3100 area meter, LI-COR Biosciences, Lincoln, NE, USA) immediately after harvest.…”