Different tolerance in bread wheat, Durum wheat and barley to Fusarium crown rot disease caused by Fusarium pseudograminearum

Fusarium crown rot (FCR) is a major disease of wheat and barley, and stem-base browning has been routinely used to measure resistance. Compared with barley (Hordeum vulgare L.), bread wheat (Triticum aestivum L.) shows less severe FCR stem-base browning symptoms (indicative of greater resistance or tolerance) but suffers higher yield loss (indicative of greater susceptibility), whereas durum wheat (T. durum Desf.) shows similar FCR severity but suffers much worse yield loss. To understand these differences, fungal biomass in bread and durum wheats and barley was estimated by realtime quantitative PCR at different stages of FCR disease development. Similar to a previous report on bread wheat infection by Fusarium graminearum, FCR infection caused by Fusarium pseudograminearum also showed three distinct phases in each of the three crop species analysed. During all stages of FCR disease development,barley varieties invariably displayed earlier and faster fungal accumulation compared with either bread or durum wheat. Although suffering much greater yield loss than barley, durum wheat appears to accumulate significantly lower levels of F. pseodugraminearum during infection. These results demonstrate that bread wheat varieties are more resistant to FCR infection and pathogen accumulation than barley varieties, and the less yield loss of the latter is likely due to its better tolerance to this disease. If also existing among different sources of resistance within a given species, these different features of disease resistance and tolerance could be exploited to minimize yield loss of new varieties.