Heat stress symptoms and evaluations

In many areas, the flowering to maturity period in wheat coincides with the beginning of hot, dry weather. If desiccating winds occur along with high temperatures, major reductions in yield may be experienced. Early heat stress has reduced tillering whereas during flower affects grains / spike whereas late-maturity reduce grain weight.

Effects:
The effects of high temperatures often are associated with the effects of moisture stress, and the symptoms are difficult to separate. Moderately high temperatures increase the rate of plant development and reduce its rate of growth. The number and formation of spikelets and florets, as well as grain filling, are reduced, resulting in lower yields. The late-boot and seed-set stages are especially vulnerable and, in many areas, high temperatures are more likely to occur during these later stages of plant development. Very high temperatures will kill plants by denaturing proteins.

Evaluation:
Direct evaluation of effect of heat stress include measurement of yield and yield components (grain yield, thousand kernel weight, grains / spike or number of effective tiller / meter square etc.) under heat stressed and non-stressed conditions. Generally plants remain grain longer (stay green) has been considered as important indivator for heat stress tolerance. Indirect criteria may be Canopy temperature depression, chlorophyll fluorescence and chlrophyll content, which indirectly measures photosynthetic efficiency under heat stress, have been considered as useful screening criterion for high temperature tolerance in wheat.

Heat shock proteins
Plants respond to high temperature stress by the synthesis of an assortment of heat shock proteins that have been correlated with an acquired thermal tolerance to otherwise lethal temperatures.

References

Physiological approaches in wheat breeding
http://www.fao.org/DOCREP/006/Y4011E/y4011e0a.htm


Wheat doctor
http://wheatdoctor.cimmyt.org/index.php?option=com_easygallery&Itemid=33

Physiological and Molecular breeding

http://en.wikipedia.org/wiki/Physiological_and_molecular_wheat_breeding