Hydroxamic acids in cereal roots inhibit the growth of take-all

2,4-Dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) was the only hydroxamic acid (Hx) found in wheat (Triticum aestivum) roots, whereas both DIMBOA and 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA) were present in the roots of triticale (Triticosecale) and rye (Secale cereale). The Hx content of wheat, triticale and rye roots was highest in the apices. Growth of two isolates of the fungus Gaeumannomyces graminis var. tritici (Ggt), which causes the root disease take-all, was inhibited when extracts prepared from triticale and rye roots were incorporated into nutrient media. Similar extracts from two cultivars of wheat did not inhibit the growth of Ggt. When Hx were incorporated individually into nutrient media, DIBOA inhibited the growth of Ggt at concentrations as low as 0.5 mM, whereas 1 mM DIMBOA was required to inhibit fungal growth. The decomposition products of DIBOA and DIMBOA, 2(3)-benzoxazolinone (BOA) and 6-methoxybenzoxazolinone (MBOA), respectively, were less potent inhibitors of Ggt growth than the corresponding parent Hx. The effects of the Hx at concentrations up to 5 mM were only fungistatic, as growth of the colonies resumed when they were transferred to Hx-free media. The inhibition of Ggt growth by extracts of triticale and rye is attributed to the presence of DIBOA.