Growth‐Chamber and Field Reaction of Three Smooth Bromegrass Strains to Pyrenophora bromi (Died.) Drechsl1

Abstract

Improved screening procedures would aid in selection for resistance to brown leaf spot caused by Pyrenophora bromi (Died.) Drechsl. (Helminthosporium bromi Died.) in smooth bromegrass (Bromus inermis Leyss.). The objectives of this research were to use a growthchamber inoculation procedure to study variation in brown leaf spot reaction among and within three smooth bromegrass strains and to compare the results with field disease ratings. Reaction to brown leaf spot in the growth chamber was determined as the percentage diseased leaf area on the four youngest leaves on one tiller per plant. Average percentage diseased leaf area increased with an increase in leaf age. The wide range of variation in percentage diseased leaf area among plants within the three strains indicates that the growth‐chamber inoculation procedure would be useful for screening plants for brown leaf spot resistance. The association between repeated determinations on the same set of plants suggests that preliminary selection of resistant genotypes on the basis of rank performance in a single growth‐chamber trial would be reasonably effective. SB‐5, a fiveclone synthetic selected for brown leaf spot resistance in the field, was more resistant to infection in the growth chamber and field than SB‐C3, the population from which parent clones of SB‐5 were selected, and ‘Lincoln’, a susceptible cultivar. SB‐C3 and Lincoln were not significantly different in disease reaction in the growth chamber, but SB‐C3 was more resistant than Lincoln in the field.