Wheat Yield Progress Associated with Higher Stomatal Conductance and Photosynthetic Rate, and Cooler Canopies

“Similar relationships have been reported in major crops, where enhancing g s has been associated with improved photosynthesis and yield [34–36].”

“This positive genotypic relationship between δ 13 C and yield contrasts with most field studies of bread and durum wheat under mild to moderate water stress, where δ 13 C is typically negatively correlated with yield, or ∆ 13 C is positively correlated with yield [19,63,64].”

“Stomata are typically located in the epidermis of plant leaves and serve as channels for the exchange of CO 2 and H 2 O between plants and the atmosphere, thereby influencing plant productivity and water use (Fischer et al. 1998; Stewart et al. 2011; Liao et al. 2022).”

“Most of the earlier workers have demonstrated a positive relationship between photosynthesis and crop yield when photosynthesis rates were performed on flag leaves at grain filling stage under open field conditions (Blum, 1990; Fischer et al., 1998; Reynolds et al., 2000; Furbank et al., 2013).”

“Consequently, increased stomatal conductance would be detrimental to productivity in dry environments, although it has been found to correlate with higher yields under good irrigation conditions [32].”

“CIMMYT began CTD measurements on different irrigated experiments in Northwest Mexico and it was found that phenotypic correlations of CTD with grain yield were occasionally positive (Reynolds et al., 1994; Fischer et al., 1998).”

“…with improvements in RUE, CO2 assimilation rate and stomatal conductance in the flag leaf (Shimshi and Ephrat, 1975; Reynolds et al., 1994; Watanabe et al., 1994; Fischer et al., 1998b; Gutierrez-Rodriguez et al., 2000; Reynolds et al., 2000; Shearman et al., 2005; Sadras and Lawson, 2011).”

“Genotypic variation in intrinsic stomatal conductance without stress has been reported for irrigated or well watered wheat (Condon et al., 1990; Morgan and LeCain, 1991; Fischer et al., 1998) and barley (e.”

“Single measurements are generally uncorrelated because they capture only an instant in time for a process that is constantly changing throughout the day, across seasons, and in relation to developmental stage (Zelitch 1982; Fischer et al. 1998; Reynolds et al. 2000; Driever et al. 2014).”

“This method, pioneered by Fischer et al. (1998), offers the unique advantage of detecting signatures of “cryptic” or indirect selection of breeders of physiological traits that likely contributed to yield increase (Baca Cabrera et al. 2025; Ding et al. 2025).”

“Mesophyll conductance was determined by dividing A N /C i 44,45 .”

“Stomatal conductance was measured on four randomly selected leaves per plot using a Decagon SC-1 portable porometer at 10:00–11:00 AM (Fischer et al. 1998).”

“For most of field trials that previously reported relationships between yield and photosynthesis, the strongest relationships were found at grain filling (Gent, 1995; Fischer et al., 1998; Reynolds et al., 2000; Zheng et al., 2011; Gaju et al., 2016), similarly to our results.”

“Water use efficiency (dividing photosynthesis by transpiration) and mesophyll conductive (dividing the amount of photosynthesis by the amount of substomatal CO 2 ) were obtained by methods presented by Fischer et al .”

“Protein content was analysed using a Kjeldahl machine (model V40) (28).”

“When wheat was under thermal stress, the CTD, flag leaf stomatal conductance, and photosynthetic rate were all positively correlated with yield (Fischer et al. 1998) [115] .”

“…the leaf and the loss of water from the leaf both occur through the stomata, creating a strong relationship between transpiration and productivity (de Wit, 1958; Fischer et al., 1998; Richards, 2000; Kemanian et al., 2005; Blum, 2009; Sperry et al., 2017; Sinclair, 2018; Xiong and Nadal, 2020).”

“As it is known, photosynthesis is the basic source of transformed natural power of sun and main factor of production process of plants [21], while the transpiration protects plants from overheat and dehydration in dry and hot weather by ensuring transportation of mineral substances absorbed from the soil up the plant…”

“This deficit must be compensated by irrigation which constitutes a possibility of reducing this stomatal regulation (Fischer et al., 1998).”

“Among endogenous factors, photosynthesis and leaf transpiration have a significant impact on this indicator, due to their significant physiological role in the production process and the plant's protective complex [1, 2, 3].”

“A high gs under steady-state conditions is associated with high 59 A and consequently improved growth (Fischer et al., 1998; Franks, 2006).”

“Higher stomatal conductance is associated with an increase in grain yield in wheat [26].”

“However, there are a few examples that have compared historical sequences of cultivars and observed correlations between leaf photosynthetic rate and wheat yield (Beche et al., 2014; Fischer et al., 1998; Gaju et al., 2016; Yao et al., 2019).”

“The Normalized Difference Vegetation Index (NDVI) is a ubiquitous example, which is frequently used to represent general vegetative health (Fischer et al., 1998).”

“The relative growth rate of plant was positively correlated with daily integrals of photosynthesis expressed in different species and environments, and 93% of the variation in relative growth rate can be explained by photosynthesis [4], when yield increased by 27%, maximum photosynthetic rate increased by 23% in wheat…”

“[7] recommended relative drought index (RDI) as a positive indicator for stress tolerance.”

“Golabadi et al. (2006) used MP, GMP, TOL, SSI and ST for discriminating F3 and F4 wheat lines.”

“for assimilates but also on the leaves stomatal conductance [15] and the key enzyme RuBisc [16], which requires this issue additional study in the culture.”