Freezing tolerance of selected Pennisetum species

Poor winter survival often limits the successful persistence of perennial Pennisetum species to the warmest areas of the southern United States. To investigate winter survival in Pennisetum, conductance measurements were used to evaluate changes in electrolyte leakage as an indicator of freezing tolerance of selected species using field-grown plants, growth chamber-grown seedlings, and callus tissue. A buffelgrass (Pennisetum ciliare [L.] Link syn Cenchrus ciliaris L.) x birdwoodgrass (C. setigerus L.) hybrid (BxBW) with poor winter survival at College Station, Texas, a moderately winter-hardy buffelgrass genotype (PI 409704), and a winter-hardy species (P. orientale L. C. Rich. cv. Cowboy) were tested in the field in 1989-1990. Tiller bases were collected in December, January, March, and April, with the freezing tolerance estimated by the electrolyte leakage method. The freeze tolerance of PI 409704 in December was similar to Cowboy and significantly greater than BxBW, however, only Cowboy survived the 1989-1990 winter in the field. Seedlings of two winter-hardy species, Cowboy and P. flaccidum Griseb. cv. Carostan, two moderately winter-hardy species P. mezianum Leeke, PI 214061 and PI 409704, and a buffelgrass cultivar with poor winter hardiness (Common) were grown at either 20⚬/15⚬C or 10⚬/5⚬C with photoperiods of 9 h or 15 h. The freezing tolerance was estimated by the electrolyte leakage method. Photoperiod had no effect on the freezing tolerance of any genotype tested. All species had greater freezing tolerance when grown at 10⚬/5⚬C with Carostan having the greatest freezing tolerance (-8.3⚬C) and Common the least (-4.0⚬C). Callus tissues from the same genotypes were grown at either 17⚬C or 7⚬C, and the freezing tolerance determined. Carostan calli had greater freezing tolerance at 7⚬C (-3.6⚬C) than at 17⚬(-1 1⚬C). The other genotypes exhibited no detectable freezing tolerance at either temperature. These results indicate that freezing tolerance in Carostan and Cowboy may be an important factor in their winter survival.