Resistant Winter Wheats Compared at Differing Growth Stages and Leaf Positions for Tan Spot Severity

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Abstract
Resistance to tan spot, caused by Pyrenophora tritici-repentis, was ranked among 14 winter wheat genotypes previously determined to have some resistance. Resistance was compared among greenhouse-grown adult plants, vernalized seedlings, and unvernalized seedlings using ratings of lesion size recorded from each of the top three leaves. Regardless of growth stage, the oldest leaf was most severely spotted and the youngest leaf was the least severely spotted. Severity of spotting was lowest and separation of genotypes for level of resistance was best on adult-plant flag leaves in the greenhouse. The correlation of tan spot severity for greenhouse-grown plants with adult field plants was significant for adult greenhouse plants (r = 0.86) and high for vernalized seedlings (r = 0.64) and unvernalized seedlings (r = 0.79).