Effects of genotype, harvest year and genotype-by-harvest year interactions on arabinoxylan, endoxylanase activity and endoxylanase inhibitor levels in wheat kernels

The effects of genotype, harvest year and their interaction on the levels of arabinoxylans (AX), endoxylanases and endoxylanase inhibitors in wheat were studied using 14 varieties grown in three successive growing periods with diverse climatological conditions. Relations with more commonly evaluated wheat characteristics such as yield, thousand kernel weight, specific weight, protein level, Hagberg falling number (HFN) and α-amylase activity level were examined. Water extractable arabinoxylan (WE-AX) levels in wheat varied much more than total arabinoxylan (TOT-AX) levels. This variability was mainly genetically determined, but harvest year also had an important effect. Total endoxylanase activity levels varied more than a factor of 20 between the different wheat samples. Endogenous endoxylanases typically accounted for only 10–15% of this activity, while wheat-associated microbial endoxylanases accounted for the remaining 85–90%. However, when preharvest sprouting occurred, the contribution of endogenous endoxylanases could sometimes amount to over 40% of this total activity. Endogenous endoxylanase activity levels were mainly determined by the interaction of genotype and harvest year, while wheat-associated microbial endoxylanase activity levels were predominantly determined by genotype alone. Endogenous and microbial endoxylanase activity levels were strongly correlated, suggesting that wheat varieties which are susceptible to preharvest sprouting are often also susceptible to microbial contamination. The TAXI and XIP-type endoxylanase inhibitor levels varied by a factor of 8 and 1.8, respectively. They were mainly determined by genotype and were rather similar in the different growing periods.