Relationship between Cell Wall Components, Nitrogen Use Efficiency and Nitrate Reductase Activity in Dollar Spot Resistance among Agrostis Species and Genotypes.

Dollar spot (DS) caused by Sclerotinia homoeocarpa (F. T. Benn) is an important disease affecting golf greens. DS susceptibility varies among Agrostis species and genotypes, with velvet bentgrass (Agrostis canina L.) exhibiting superior resistance to DS than creeping bentgrass (Agrostis stolonifera L.). Leaf properties including cell wall components may affect the ability of the fungus to penetrate leaves and cause infection. Nitrogen use efficiency (NUE, productivity-to-plant N ratio) has been proposed in turfgrass maintained with less N, which is the current trend in the management of greens. NUE has been shown to be related to nitrate reductase activity (NRA) but its relationship to dollar spot has not been investigated. Our objectives were to evaluate DS severity among genotypes of creeping (CB) and velvet (VB) bentgrass and its relationships to cell wall components, NUE and NRA. In 2007, DS, total cell wall (TCW), ligno- and hemi-cellulose contents, shoot NUE and NRA measurements were be made in the field on seven VB and seven CB entries as part of the 2003 NTEP Greens Test. VB entries exhibited lower DS severity compared to CB. Shoot NRA and NUE were positively correlated. DS tolerant VB entries exhibited significantly lower NRA and NUE compared to DS susceptible CB. NRA was positively correlated with dollar spot severity accounting for at least 50% of the total variation in DS severity. DS tolerant CB cultivars such as Declaration exhibited greater hemicellulose content compared to intolerant cultivars such as Independence. Leaf hemicellulose content accounted for at least 30% of the variation in Agrostis DS severity. NUE was not correlated with DS severity. These measurements will be repeated in 2008. First year results suggest that lower shoot NRA and greater leaf hemicellulose content, especially in dollar spot susceptible creeping bentgrass cultivars, may lower DS incidence.