Cultivar Differences in Rough Bluegrass Germination Occur with Increased Salinity

 

James J. Camberato, S. Bruce Martin, and Amy V. Turner

Clemson University, Pee Dee Research and Education Center

 

            Rough bluegrass (Poa trivialis) is frequently used to overseed golf course greens in coastal areas of the Carolinas where irrigation water can be saline (high in salts). Salinity slows the germination of bentgrass, ryegrass, and tall fescue as well as other grasses. Within a type of grass there are also cultivar differences in sensitivity to salinity--the germination of some cultivars is minimally affected by salinity, whereas that of others is seriously reduced. Our previous work with rough bluegrass, in the absence of salinity, established substantial differences in germination among cultivars, as well as among seed lots of the same cultivar (Carolinas Green, May-June 1999). In view of this earlier research we wanted to determine the effects of salinity on rough bluegrass and the extent of cultivar/seed lot variation in salinity sensitivity. To obtain this information, we exposed 14 cultivars/seed lots of rough bluegrass to different levels of salinity (0, 1.8, 3.4, and 5.0 dS/m or mmhos/cm) under controlled conditions and quantified germination.

 

Materials and Methods

 

            Seed from ten rough bluegrass cultivars/seed lots was collected in October and November, 1999 from golf course superintendents who had purchased commercially available seed. Seed from four cultivars (#3, #5, #9, and #13) was collected from commercially available seed the previous year. Cultivar/seed lot information is listed in Table 1.

            Fifty seed of each cultivar were placed on pre-moistened germination paper in petri dishes and then sealed with parafilm. Moistening solutions differed in salinity— 0, 1.8, 3.4, and 5.0 dS/m  or mmhos/cm established with NaCl at 0.88, 1.75, and 2.63 g L^-1. These levels of salinity correspond to 0, 1150, 2175, and 3200 ppm or mg/L. Petri dishes were placed in growth chambers with 12 h of light at 68 ^oF and 12 h of darkness at 50 ^oF. These conditions are ideal for rough bluegrass germination.

            Salinity effects and cultivar differences in rapidity of germination were assessed by determining germination 6 days after seeding (DAS). Total germination was determined at 17 DAS. Earlier studies showed that germination of rough bluegrass at this temperature regime was essentially complete at 17 DAS. Seed was considered germinated if both a shoot and root were visible to the eye with a magnifying lens.

            Experimental design was split block with salinity level as the main block and cultivar randomized within salinity level. There were nine replications of each treatment. Analysis of variance was used to identify treatment differences.

     

 

Results

 

            There were substantial differences in early germination among the cultivars and seed lots (Fig. 1). The most rapid cultivar/seed lot examined was Laser (#4, #5). Germination was 65-70% at 6 days after seeding (DAS) for the two seed lots of this cultivar at a salinity level of 0 dS/m. The slowest cultivar/seed lot in this study was a seed lot of Winterplay (#13) that had 18% germination at this same time. However, differences in early germination among seed lots of the same cultivar were just as great as between cultivars. For example, the other Winterplay seed lot (#12) had twice the  germination at 6 DAS, as the slowest germinating Winterplay seed lot (#13).  Similarly, the three seed lots of Cypress (#1-3), ranged in germination at 6 DAS from 34 to 60% in the no salinity treatment.

            Salinity reduced early germination of all cultivars, and each level of salinity slowed germination (Fig. 1). The salinity levels used in this study, 1.8, 3.4, or 5.0 dS/m, were chosen to simulate the use of poor quality irrigation water with salinity levels in the 0.8 to 2 dS/m range. With evaporation of water at the soil surface, salinity levels of the moisture surrounding the seed is likely to be two to three times that in the irrigation water.