P. Monneveux and M.P. Reynolds
CIMMYT
Wheat Program


Why focus on photosynthesis-related traits (PRTs)?

  • Progress in yield has shown to be strongly associated with harvest index (HI) (Calderini et al., 1995; Sayre et al., 1997), but HI is reaching its theoretical limit estimated at 60% (Austin et al., 1980)
  • Yield increase may be strongly related to progress in biomass production (Waddington et al., 1987)
  • Photosynthesis is the first process involved in biomass production


Methodologies to identify and study PRTs

  • Comparison of modern wheat to its wild progenitors
  • Evolution of PRTs in a historic set of varieties


Main PRTs associated with yield potential

Stomatal aperture traits (SATs)

  • Maximal photosynthetic rate (Am) and stomatal conductance (gS) (Fischer et al., 1998)
  • Canopy temperature depression (CTD), which is easier to measure than photosynthetic rate or stomatal conductance (Reynolds et al., 1994)
  • Carbon isotope discrimination of the grain (DG) (Fischer et al., 1998)
  • Oxygen isotope ratio of flag leaves (d18Ol) (Barbour et al., 2000)

Electron transfer efficiency

  • Electron transport rate per unit chlorophyll in isolated thylakoids is greater in diploid than in hexaploid wheats (Austin et al., 1987)
  • Quantum yield efficiency (FPSII) is generally higher in modern wheats (Fig. 1); comparison of net photosynthesis and FPSII values permits the evaluation of photorespiration

Leaf geometry and structure

  • Yield advantage of genotypes with erect leaves has been noted (Innes and Blackwell, 1983), probably because light is more evenly distributed in the canopy and senescence of lower leaves is slower (Austin, 1976)
  • Specific leaf dry weight (SLDW) negatively correlates with photosynthetic capacity (Dornhoff and Shibles, 1976), DG (Araus et al., 1997) and yield potential (Fig. 2)

 

Photosynthetic pigment composition

  • Diploid species have greater total chlorophyll and Chla/b ratio than hexaploids (Austin et al., 1987). Siddique et al. (1989) observed that total chlorophyll has been enhanced and Chla/b ratio gradually fallen in a series of Australian wheats. Similar trends are noted for CIMMYT germplasm (Fig. 3)
  • Decrease of Chla/b ratio in modern varieties indicates a decrease in the PSII reaction center complex relative to light-harvesting Chla/b protein complexes and suggests a loss of adaptation to high irradiance

 

References

Araus J.-L., Amaro T., Zuhair Y., Nachit M.M. 1997. Effect of leaf structure and water status on carbon isotope discrimination in field-grown durum wheat. Plant, Cell and Environment, 20, 1484-1494.

Austin R.B., Bingham J., Blackwell R.D., Evans L.T., Ford M.A., Morgan C.L., Taylor M. 1980. Genetic improvements in winter wheat yields since 1900 and associated physiological changes. J. Agric. Sci. Camb., 94, 675-689.

Austin R.B., Ford M.A., Miller T.E., Parry M.A.J. 1987. Progress in photosynthesis research, vol. IV, Marinius Niijhoff Publishers, Dordrecht, Netherlands, 361-368.

Austin R.B., Ford M.A., Edrich J.A., Hooper B.E., 1976. Some effects of leaf posture on photosynthesis and yield in wheat. Annals of Applied Biology, 83, 425-446.

Barbour M.M., Fischer R.A., Sayre K.D., Farquhar G.D. 2000. Oxygen isotope ratio of leaf and grain material correlates with stomatal conductance and grain yield in irrigated wheat. Aust. J. Plant Physiol., 27, 625-637.

Calderini D.F., Reynolds M.P., Slafer G.A. 1999. Genetic gains in wheat yield and main physiological changes associated with them during the 20th century. In: Satorre E.H., Slafer G.A., eds. Wheat: ecology and physiology of yield determination, New York, Food Products Press.

Dornhoff G.M., Shibles R.M., 1976. Leaf morphology and anatomy in relation to CO2 exchange rate of soybean leaves. Crop Sci., 16, 377-381.

Fischer R.A., Rees D., Sayre K.D., Lu Z.-M., Condon A.G., Larque Saavedra A. 1998. Wheat yield progress associated with higher stomatal conductance and photosynthetic rates, and cooler canopies. Crop Sci., 38, 1467-1475.

Innes P., Blackwell R.D. 1983. Some effects of leaf posture on the yield and water economy of winter wheat. J. of Agricultural Sci., 101, 367-376.

Reynolds M.P., Balota M., Delgado M.I.B., Amani I. Fischer R.A. 1994. Physiological and morphological traits associated with spring wheat yield under hot, irrigated conditions. Aust. J. Plant Physiol., 21, 717-730.

Sayre K.D., Rajaram S., Fischer R.A. 1997. Yield potential progress in short bread wheat in Northwest Mexico. Crop Sci., 37, 36-42.

Siddique K.H.M., Belford R.K., Perry M.W., Tennant D. 1989. Growth, development and light interception of old and modern wheat cultivars in a Mediterranean-type environment. Aust. J. of Agric. Res., 40, 473-487.

Waddington S.R., Osmanzai M., Yoshida M., Ransom J.K. 1987. The yield of durum wheats released in Mexico between 1960 and 1984. J. Agric. Sci. Camb., 108, 469-477.


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