Electrolyte leakage and regrowth tests were used to estimate cold hardiness levels of field-grown ‘Midiron’ and ‘Tifgreen’ bermudagrass (Cynodon dactylon × C. transvaalensis crowns. The two procedures were in close agreement. ‘Midiron’ was hardier than ‘Tifgreen’ on all sampling dates. Greatest levels of freeze tolerance were –11°C for ‘Midiron’ and –7° for Tifgreen’ during December and January, ‘Midiron’ was killed at –5° in early June while ‘Tifgreen’ had lost all freeze tolerance by this date. Although the electrolyte leakage procedure was rapid and required no greenhouse space, it was relatively difficult to set up and evaluate.
Six African bermudagrass (Cynodon transvaalensis Burtt-Davy) genotypes, one common bermudagrass [C. dactylon (L.) Pers. var. dactylon] genotype, and ‘Tifway’ (C. dactylon × transvaalensis) hybrid bermudagrass were evaluated for shoot type, leaf angle, and shoot angle. Evaluations were conducted to determine if these measurements could be used to differentiate among upright, intermediate, and prostrate growth habits. Significant differences were found for all three techniques, but attempts to group plants together as having prostrate, intermediate, or upright growth habits was not possible. ‘Tifway’ was intermediate between the African bermudagrass genotypes and the common genotype for shoot type observations, but was more similar to upright-growing African bermudagrass for leaf angle and the more prostrate-growing common bermudagrass for shoot angle. Quantification of shoot type and leaf angle did not appear as useful as shoot angle measurements for screening germplasm to identify upright or prostrate growth habits in bermudagrass.
Cold acclimation (CA) of `Midiron' and `Tifgreen' turf bermudagrasses (Cynodon dactylon L. Pers. × C. transvaalensis Burtt-Davy) induced tolerance to lower freezing temperatures and altered protein synthesis in crowns. LT50 (lethal temperature for 50% of plants) values were lowered ≈5C after 4 weeks in controlled-environment chambers under CA [8/2C (day/night) cycles with a 10-hour photoperiod] vs. non-CA (28/24C) conditions. LT50 values for `Midiron' plants decreased from -6.5 to -11.3C after CA and from -3.6 to -8.5C for `Tifgreen'. Proteins synthesized by isolated crowns were radiolabeled in vivo for 16 hours with 35S-methionine and 35S-cysteine. Sodium dodecyl sulfate polyacrylamide gel electrophoresis and fluorography revealed increased synthesis of several cold-regulated (COR) proteins in CA crowns of both cultivars. Synthesis of intermediate molecular weight (MW) (32 to 37 kDa) and low-MW (20 to 26 kDa) COR proteins was greater in `Midiron' than `Tifgreen' crowns.