Use of cool-season turfgrasses in transitional environments is limited, in part, by their heat tolerance. Development of a rapid heat tolerance screening technique would be of value in determining the potential of turf•grasses for use in warmer areas.

The heat tolerance of 22 Kentucky bluegrass (Poa pratensis L.) cultivars, Poa annua L., and four perennial ryegrass cultivars (Lolium perenne L.) was evaluated by exposing plants for 30 min to temperatures ranging from 41 to 49 C in single degree intervals. Ten-week-old plants, which had been grown under a low level of N fertilization and watered infrequently to maximize heat tolerance development, were sealed in plastic bags, placed in a constant temperature water bath for treatment, and then replanted. Recovery was evaluated by visually rating the plants 4 weeks after treatment or by harvesting and weighing plants 2 weeks after treatment and expressing the weight as a percentage of the weight of a non-stressed control (referred to as recovery weight). Cultivar comparisons were based on the average recovery weight over a given temperature range.

Initial injury occurred at 41 to 43 C with complete kill at 47 to 49 C. Kentucky bluegrass was more heat tolerant than Poa annua L. and perennial ryegrass. Heat tolerance of the latter two species was approximately equal. The Kentucky bluegrass cultivars tested were similar in heat tolerance. Among the ryegrasses, 'Loretta' was less heat tolerant than 'Diplomat', 'Pennfine', and 'Citation'. Of all the grasses, 'Sydsport' Kentucky bluegrass ranked the highest and Loretta perennial ryegrass the lowest in heat tolerance. The correlation between dilute acid extractable carbohydrate reserves and recovery weight for these five cultivars was not significant. There was a significant negative correlation between recovery weight and Fe and Al concentration.


Agronomy and Crop Sciences



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