Yield, grain size, protein content and water use efficiency of null-LOX malt barley in a semiarid Mediterranean agroecosystem

The recent development of null-LOX barley (i.e. barley that is defective in the synthesis of two lipoxygenase enzymes, LOX-1 and LOX-2), which is oriented to produce a better quality beer, has increasingly drawn the attention of malt industry. However, the inhibition of LOX activity in such barley is raising concerns about the efficiency of its defense mechanisms to biotic and more specifically to abiotic stresses. A 2-year experiment was carried out in a typical Mediterranean environment of central southern Greece in order to: (i) explore the negative effect of drought on yield, yield components, grain size, grain protein content and water use efficiency in malt barley cultivars presenting a total loss of function of LOX-1 and LOX-2 activity, compared to a local malt barley cultivar having a full functional LOXs activity and (ii) introduce a new concept in water use efficiency, which focuses on the proportion of grains with acceptable size for malting, because according to malting industries one of the most limiting factors for the sustainable production of malt barley in the Mediterranean region is the inadequate grain size of malt barley, due to the frequent occurrence of terminal drought stress. The total loss of function of LOX-1 and LOX-2 activity did not cause any obvious advantage for the traditional malt barley cultivar over null-LOX cultivars, in terms of grain yield, yield components, grain size, grain protein content and water use efficiency. Increasing water availability with irrigation generally resulted in higher proportion of plump grains (>2.8mm) and lower proportion of thin grains (< 2.2mm), especially when water availability during the post-anthesis period was decreased and the temperature was increased. It was demonstrated that grain protein content of null-LOX cultivars was less responsive to soil water availability compared to grain size. Finally, it was shown that the new expressions of water use efficiency were able to discriminate the different adaptive responses of the studied barley cultivars to soil water availability.