Variation in Bentgrass Susceptibility to Typhula incarnata and in Isolate Aggressiveness Under Controlled Environment Conditions

Abstract

Typhula incarnata, the causal agent of gray snow mold, is an important winter pathogen of turfgrasses in the northern United States. The relative susceptibility of cultivars of three bent-grass species (creeping, colonial, and velvet bentgrass) to Typhula incarnata and the aggressiveness of 15 T. incarnata isolates obtained from infected turfgrasses on golf courses in Michigan, Minnesota, and Wisconsin were evaluated under controlled conditions. A hypersensitive type of resistance response to T. incarnata was not observed in any cultivar. Disease severity increased with higher inoculum concentration of T. incarnata. Colonization by gray snow mold gradually decreased with increasing plant age from 11 weeks after seeding in most cultivars tested, suggesting that age-related resistance was expressed over time. There were significant differences in disease severity among the three bentgrass species, particularly between tetraploid (creeping and colonial) and diploid (velvet) species, and among cultivars within each species, indicating varying levels of susceptibility to T. incarnata. All 15 isolates were pathogenic on bentgrass and were significantly different in aggressiveness, but aggressiveness was not related to geographic origin. Therefore, turfgrass breeders should be able to use one or a few virulent representative isolates of the pathogen to screen for resistance.

Some Consequences of Using the Horsfall-Barratt Scale for Hypothesis Testing

“…The statistical analysis often aims at testing the null hypothesis (H 0 ) that the mean disease severities in the two treatments are equal. Rejecting the H 0 is then used as indication that the two treatments actually have different effects on the severity of disease or the development of the epidemic (6,8,24,32,33). A standard way to test for differences in mean disease severity on a continuous scale such as percent disease severity is by using a t test (37).…”

Screening St. Augustinegrass Genotypes for Brown Patch and Large Patch Disease Resistance

“…Previous research has shown influences of leaf blade thickness and canopy structure on BP development on tall fescue (Burpee, 1992; Giesler et al, 1996a, 1996b; Green et al, 1999; Yuen et al, 1994). Additional work with other host and pathogen systems also has shown ploidy level to play an important role in disease resistance in crops that include Musa spp., creeping bentgrass, and with SAG, possibly due to a dosage effect related to having more copies of resistance genes (Atilano and Busey, 1983; Chang et al, 2007; Craenen and Ortiz, 1996). The only significant effect of ploidy in this study was on Y and r L for LP inoculations with polyploid genotypes being more susceptible.…”