Diverse landraces of wheat, collected from the semi-arid (150 to 250 mm of total annual rainfall) Northern Negev desert in Israel were considered as a potential genetic resource of drought resistance for wheat breeding . These materials were therefore evaluated for their reponses to drought stress in agronomical and physiological terms . Up to 68 landraces, comprising of Triticum durum, T aestivum, and T compactum were tested in two field drought environments, in one favourable field environment, under post-anthesis chemical plant desiccation which revealed the capacity for grain filling from mobilized stem reserves, under a controlled drought stress in a rainout shelter and in the growth chamber under polyethylene glycol (PEG)induced water stress . Biomass, grain yield and its components, harvest index, plant phenology, canopy temperatures, kernel weight loss by chemical plant desiccation, growth reduction by PEG-induced drought stress and osmotic adjustment were evaluated in the various experiments .
Landraces varied significantly for all parameters of drought response as measured in the different experiments, which was in accordance to their documented large morphological diversity . Variation in grain yield among landraces under an increasing drought stress after tillering was largely affected by spike number per unit area . Kernel weight contributed very little to yield variation among landraces under stress, probably because these tall (average of 131 cm) landraces generally excelled in their capacity to support kernel growth by stem reserve mobilization under stress . Yield under stress was reduced with a longer growth duration of landraces only under early planting but not under late planting . Landraces were generally late flowering but they were still considered well adapted phenologically to their native region where they were always planted late .
Landraces differed significantly in canopy temperature under drought stress . Canopy temperature under stress in the rainout shelter was negatively correlated across landraces with grain yield (r = 0 .67**) and biomass (r = 0 .64* *) under stress . Canopy temperature under stress in the rainout shelter was also positively correlated across landraces (r = 0 .50**) with canopy temperature in one stress field environment . Osmotic adjustment in PEG-stressed plants was negatively correlated (r = -0 .60**) with percent growth reduction by PEG-induced water stress . It was not correlated with yield under stress in any of the experiments .
In terms of yield under stress, canopy temperatures and stem reserve utilization for grain filling, the most drought resistant landrace was the 'Juljuli' population of T durum .