FREEZING TOLERANCE OF SELECTED PENNISETUM SPECIES

Poor winter survival often limits the successful persistence of perenn ial Pennisetum species to the warmest areas of the southern United Sta tes. To investigate winter survival in Pennisetum, conductance measure ments were used to evaluate changes in electrolyte leakage as an indic ator of freezing tolerance of selected species using field-grown plant s, growth chamber-grown seedlings, and callus tissue. A buffelgrass (P ennisetum ciliare [L.] Link syn Cenchrus ciliaris L.) x birdwoodgrass (C. setigerus L.) hybrid (B x BW) with poor winter survival at College Station, Texas, a moderately winter-hardy buffelgrass genotype (PI 40 9704), and a winter-hardy species (P. orientale L. C. Rich. cv. Cowboy ) were tested in the field in 1989-1990. Tiller bases were collected i n December, January, March, and April, with the freezing tolerance est imated by the electrolyte leakage method. The freeze tolerance of PI 4 09704 in December was similar to Cowboy and significantly greater than B x BW, however, only Cowboy survived the 1989-1990 winter in the fie ld. Seedlings of two winter-hardy species, Cowboy and P. flaccidum Gri seb. cv. Carostan, two moderately winter-hardy species P. mezianum Lee ke, PI 214061 and PI 409704, and a buffelgrass cultivar with poor wint er hardiness (Common) were grown at either 20 degrees/15 degrees C or 10 degrees/5 degrees 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 s pecies had greater freezing tolerance when grown at 10 degrees/5 degre es C with Carostan having the greatest freezing tolerance (-8.3 degree s C) and Common the least (-4.0 degrees C). Callus tissues from the sa me genotypes were grown at either 17 degrees C or 7 degrees C, and the freezing tolerance determined. Carostan calli had greater freezing to lerance at 7 degrees C (-3.6 degrees C) than at 17 degrees (-1.1 degre es 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 surv ival.