Barley mildew, fungicidal resistance

It is of special interest that the type of encapsulation seen in barley varieties with high resistance against powdery mildew is the same as that seen in the azole fungicide treated plants. This suggests that the fungicide induces some kind of resistance reaction in the host plant. 

The next figure (Figure 10) demonstrates that the intercellular mycelium in the treated tissue advanced to the mesophyll cells where it elicited a hypersensitive response within colonized, as well as in adjacent cells. The fungicide treatment induced in the susceptible wheat variety a reaction (hypersensitivity) which resembled that of a highly resistant host plant after rust attack, as described earlier for powdery mildew and barley. 

One of our most trladlmenol resistant barley powdery mildew strains has a normal sterol composition in the conldia collected from fungicide treated plants (36), although in sensitive strains this, and lower doses of trladlmenol, cause the appearance of 24-methylene dihydrolanosterol. Since uptake of trladlmenol by this resistant strain was apparently normal, and it did not appear to metabolise the fungicide in any way, this suggests that the 14DM may be altered, so that normal sterol biosynthesis can continue. 

Besides the intrinsic properties of each resistance mechanism, the economic impact of Qol resistance on the Qol market is also governed by the availability of alternative fungicidal modes of action for disease control and resistance management in each crop. For example, the early and rapid development of resistance of cereal powdery mildew (Blumeria graminis) in European wheat and barley production from 1998 on had a remarkably low impact on Qol consumption. The broad disease spectrum controlled by Qols and the availability of several other modes of action for the control of powdery mildews in cereals such as DMIs, amines, cyprodinil, quinoxyfen, and metrafenone resulted in a nearly unchanged use frequency of Qols in European cereal production. 

Mildew and crown mst are the major diseases of oats. Oat mosaic vims is not coimnonly seen the cmrent winter varieties are resistant. Winter oats may require a fungicide at GS 31 against mildew and at GS 39 against crown rast and mildew. Oats are not so susceptible as wheat and barley to Fusarium sp. in the ear. Mycotoxin levels are usually very low in the grain. 

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