Tolerance to simulated ice encasement and Microdochium nivale in USA selections of greens-type Poa annua

Lack of winter hardiness is a limitation to the use of annual meadowgrass (Poa annua f. reptans) on golf course putting greens in northern climates. Our objectives were 1) to assess the tolerance of 13 selections of annual meadowgrass to simulated ice encasement (SIE) and pink snow mould (PSM, Microdochium nivale); 2) to determine if these tolerances were interrelated or related to plant concentrations of water soluble carbohydrates (WSC); and 3) to determine if tolerance to SIE can be associated with accumulation of toxic substances. Samples of the annual meadowgrass selections were taken from an experimental green at University Park, Pennsylvania, on four dates from 23 Nov. 2005 until 27 Mar. 2006. Samples of creeping bentgrass (Agrostis stolonifera L.) 'Penn A-4' were included for comparison in studies on SIE and WSC. Samples were vacuum-sealed in plastic bags at 1C for SIE and inoculated with three isolates of M. nivale for PSM tolerance. Small, but significant, differences were found among annual meadowgrass selections after 23 days of SIE, but all selections were dead after 33 days. Significant differences were detected in foliar blighting after inoculation with M. nivale, regrowth relative to uninoculated control being three times higher in the most tolerant than in the most susceptible selections. In late November, two annual meadowgrass selections contained significantly more WSC than did creeping bentgrass, but this was not correlated with tolerance to SIE or PSM, which were also not interrelated. A separate experiment with increasing duration of SIE to one of the annual meadowgrass selections and 'Penn A-4' showed that the critical exposure periods were 25-30 and 42-47 days, respectively. The concentrations of the phytotoxic compounds butan-l-ol and ethyl butyrate were two- to three-times higher in annual meadowgrass than in creeping bentgrass.