THE ROLE OF THE BARLEY TESTA LAYER AND ITS FLAVONOID CONTENT IN RESISTANCE TO FUSARIUM INFECTIONS

Developing testa layers of the barley proanthocyanidin-free mutants an t13-152, ant17-148, an118-159, ant19-109, ant22-1508, ant25-264, ant26 -485, ant27-489, ant28-484 and ant29-2110 and their mother varieties, were analysed for accumulation of proanthocyanidins and their flavonoi d precursors. In vitro infection of developing barley caryopses of wil d type and mutants with Fusarium poae, F. culmorum and F. graminearum revealed all mutants except ant 18-159 to be more sensitive to Fusariu m attack than wildtype. Mutant ant18-159 showed extreme resistance. Hi stological investigations of the infection process revealed that the h yphae were unable to penetrate the testa of this mutant. The testa lay er of ant18-159 accumulates small amounts of dihydroquercetin as a res ult of nonsense mutations in the structural gene for dihydroflavonol r eductase. Authentic dihydroquercetin and an autographic assay proves t his flavonoid to be a strong inhibitor of Fusarium growth and macrospo re formation. Mutant ant17-148, which accumulates the flavone chrysoer iol as a consequence of a mutation in the step catalysed by flavanone 3-hydroxylase, demonstrates that this flavone is not an inhibitor of F usarium growth in vivo. Comparison of flavonoid standards and monomers and polymers from other plants reveal monomeric flavonoids generally to be potent inhibitors of Fusarium.