Effects of Sub-Optimal Temperatures on Seed Germination of Three Warm-Season Turfgrasses with Perspectives of Cultivation in Transition Zone

Warm-season turfgrass species prevail in tropical and subtropical areas, but can also be grown in the transition zone. In this case, cold tolerance is a key aspect for germination and successful turfgrass establishment. The germination response to sub-optimal temperatures was investigated for <i>Cynodon dactylon</i> (cvs Jackpot, La Paloma, Transcontinental, Yukon, Riviera), <i>Buchloe dactyloides</i> (cv SWI 2000) and <i>Paspalum vaginatum</i> (cv Pure Dynasty). Four temperature regimes were applied, i.e., 20/30 &#176;C, 15/25 &#176;C, 10/20 &#176;C and 5/15 &#176;C, with a 12:12 h (light:dark) photoperiod. Germination assays were performed twice, with six replicates (Petri dishes) per treatment in each experiment, fifty seeds per dish. The final germinated percentages at last inspection time (FGP) were obtained for each Petri dish and processed by using a generalized linear mixed model (binomial error and logit link). Germination curves were fitted to each Petri dish by using time-to-event methods and germination rates (GR) for the 10th, 20th and 30th percentiles were derived and used to fit a linear thermal-time model. For all cultivars, FGP decreased with decreasing mean daily temperatures. Base temperatures (Tb) ranged between 11.4 &#176;C and 17.0 &#176;C, while the thermal time to obtain 30% germination ranged from 51.3 &#176;C day for SWI 2000 to 144.0 &#176;C day for Pure Dynasty. The estimated parameters were used to predict germination time in the field, considering the observed soil temperatures in Legnaro. The estimated date for the beginning of germination in the field would range from early April for SWI 2000 and Transcontinental to mid-May for Riviera. These results might be used as a practical support for planning spring sowing, which is crucial for successful turfgrass establishment, especially without irrigation.