Comparison of Greenhouse and Field Testing to Identify Wheat Resistant to Tan Spot.

Incorporation of tan spot resistance into adapted wheat (Triticum aestivum) lines requires screening procedures in the greenhouse and field that correctly identify reaction to tan spot. This study compares greenhouse (seedling) and field (adult plants) testing of wheat lines for reaction to tan spot following inoculation with conidia by Pyrenophora tritici-repentis. Mistirrigation was used to provide adequate moisture for infection by P. tritici-repentis in the greenhouse and in the field. Reaction of seedlings to tan spot in the greenhouse was measured by lesion length. Area under the disease progress curve (AUDPC) was used to determine reaction in the field. The effect of tan spot on grain yield and kernel weight was determined by comparing inoculated with fungicide-sprayed split-plot values. In greenhouse tests, lesion length ranged from 1.2 to 4.1 mm. Lesions were 1.2 mm long on Red Chief, a tan spot-resistant check. Lesions were 3.6 mm long on TAM 105, a tan spot-susceptible check. Four breeder lines had levels of seedling (greenhouse) resistance nearly equal to that of Red Chief. Ranks of lesion length and field assessments of the AUDPC were significantly correlated (r = 0.75 to 0.93, P ≤0.05). Thus, greenhouse assessment was useful for screening large numbers of wheat genotypes for reaction to tan spot and identifying selected entries for further screening in the field. Mean grain yield from P. tritici-repentis inoculated plots was approximately 15% less than yield from fungicide-sprayed plots. Kernel weight was reduced an average of 7 and 13% at two field locations.