The tolerance of PSII to high temperatures in durum wheat (T-turgidum conv. durum): genetic variation and relationship with yield under heat stress

The yield performance of three hundred and twenty durum wheat genotypes has been evaluated under late-planting conditions at Aleppo, Syria. Chlorophyl l fluorometry was used to determine the in vivo tolerance of photosynthetic membranes to high temperatures in leaves of a subset of seventeen lines wh ich covered a wide range of yield. An important variation was noted for Tc, the threshold temperature for photosystem-II denaturation and for Tp, the peak temperature corresponding to maximal Fo fluorescence. A strong correla tion was noted between the two traits (r = 0.69**). A significant correlati on (r = 0.53*) was registered between Tc and yield under late-planting cond itions. Earliness was also found to strongly correlate with yield (r = 0.75 ***). Various durum wheat varieties and several lines derived from a cross between the heat susceptible durum variety Korifla and the heat tolerant ac cession T. dicoccoides 600808 were screened for the tolerance of photosynth etic membranes to high temperatures. The potential interest of the accessio n T. dicoccoides 600808 as source of heat tolerance has been confirmed.