Factors affecting Fusarium head blight development and trichothecene accumulation in fusarium-infected wheat heads.

Abstract

Fusarium head blight (FHB), primarily caused by Fusarium graminearum Schwabe, is an economically important disease as it results in yield loss and quality losses of infected grain and the accumulation of mycotoxins produced by the invading fungus. Environmental factors, host genetics, and isolate aggressiveness impact FHB development and subsequently trichothecene production and accumulation. Though it is well established that moisture around anthesis promotes FHB development and trichothecene accumulation, the role of moisture, either in the form of rainfall or mist-irrigation during the period from anthesis to harvest has been largely overlooked. A three year field experiment was conducted in 2006, 2007 and 2008 to examine the influence of environmental factors, especially moisture, host resistance, and pathogen variation with respect to mycotoxin production capacity and pathogen aggressiveness, on infection, FHB development and mycotoxin production and accumulation in planta. In mature harvested grain FHB severity, visually scabby kernel (VSK) and mycotoxin concentration were significantly higher in Wheaton (FHB susceptible) than in the other two cultivars examined, Alsen and 2375. Although FHB severities were not significantly different in plots receiving different durations of mist-irrigation, VSK were significantly lower in the treatments receiving the least amount of mist-irrigation (14 DAI) than for treatments receiving mist-irrigation for longer periods, suggesting that extended periods of moisture promote disease development. DON concentration in harvested grain was, however, significantly lower in the treatment receiving the longest duration of mist-irrigation than those treatments receiving less water. In the whole head samples, which were collected 0, 7, 11, 14, 21, 28 and 41 days after inoculation, DON and other trichothecenes either declined with increased durations of mist-irrigation or remained low while water was being applied by the misting system. However, trichothecene accumulation was observed to increase after the cessation of mist-irrigation, with increases being most pronounced for the treatments with shorter mist-irrigation periods. The largest reduction in DON observed as a result of extended mist-irrigation periods was seen in the susceptible cultivar Wheaton.

The influence of host resistance and pathogen variation on infection, FHB infection, disease development and mycotoxin accumulation in planta was examined in the series of greenhouse experiments utilizing point and spray inoculations. The levels of FHB severity and mycotoxins were higher in spray inoculated experiment than point inoculation in all cultivars examined. Wheaton (FHB susceptible) had the highest FHB severity and levels of mycotoxins. Alsen (moderately resistant to FHB) had significantly lower FHB severities, DON, 15-ADON, 3-ADON and NIV than either 2375 or Wheaton. Though there were no significant differences in initial infection among cultivars examined, Alsen had reduced spread of FHB symptoms from initial infection presumably due to type II resistance. DON production did not peak in all treatments, but where evident, the peak was earlier in 2375 (11 dai) than Alsen and Wheaton (21 or 14 dai). Multiple peaks and declines in DON levels were also evident. The performance of isolates was highly variable, though generally isolates Butte86Ada-11 and B63A were the most aggressive isolates and 49-3 and B45A were the least.

The impact of free moisture, such as that from irrigation systems or rainfall, on mycotoxin accumulation was evaluated in greenhouse experiments. Despite the similar levels of FHB severity observed, the levels of mycotoxins were significantly less in the plants that received a single six hour wetting treatment compared to the respective control. The loss of DON and other mycotoxins was evident in all cultivars examined. Further, DON and 15-ADON were detected in run-off water.

The results of these studies suggest that the availability of free moisture such as from mist-irrigation or rainfall may increase FHB severity and VSK, although DON and other trichothecene concentrations may be concomitantly reduced. Leaching appears to contribute to reductions in DON following wetting events.