Cultivar and Environmental Effects on Freezing Tolerance of Narrow-Leaf Plantain

developed from populations that have evolved under more severe winter conditions before plantain could Improved cultivars of narrow leaf plantain (Plantago lanceolata become a viable forage for less temperate regions. NatuL.) have received increasing attention as possible pasture species for the northeastern USA because of their productivity during drought ralized populations of narrow-leaf plantain are found and high nutritive value. However, the cultivars currently available throughout the northeastern USA and could provide do not have sufficient freezing tolerance to survive northeastern U.S. parent material for cultivars with improved freezing tolwinters. This experiment examined the relationship between shoot erance. growth rate and root:shoot partitioning during cold-hardening and Plantain grows well under cool temperatures (Chatthe freezing tolerance of ‘Lancelot’ and ‘Tonic’ plantain compared terton et al., 1990) and is valued in New Zealand for its with ‘PG700’, an experimental line collected from the eastern USA. ability to remain green and leafy during winter (Stewart, I hypothesized that PG700 would exhibit reduced shoot structural 1996). However, in species such as alfalfa (Medicago growth and increased carbohydrate storage in roots during cold-hardsativa L.), fall dormancy is often closely associated with ening, resulting in increased freezing tolerance and survival. In growth winter survival (Schwab et al., 1996; Cunningham et al., chamber experiments, seedlings were cold hardened for 21 d and then frozen at 12 C for 3 h. Survival was evaluated after a 21-d recovery 2001), such that survival is reduced in cultivars that period. The experiment was conducted twice. Survival was greatest exhibit vigorous growth during the fall. However, others for PG700 (58%), followed by Lancelot (33%) and Tonic (18%) (P have shown that fall growth can be dissociated from 0.01). When combined across cultivars, survival was 59% in Trial 1 winter survival (Haagenson et al., 2003b). It remains compared with 11% in Trial 2 (P 0.01). None of the measured possible, however, that the poor winter survival of planparameters including overall root and shoot growth or relative partitain is directly related to its continued growth under tioning between roots and shoots were related to cultivar differences environmental conditions that induce fall dormancy in in freezing tolerance. Reduced survival in Trial 2 was accompanied more freezing tolerant species. Indeed, Lancelot, which by high nitrogen uptake and vigorous shoot relative to root growth had the greatest winter survival in a previous study during the cold-hardening period. Thus, reduced shoot growth was (Skinner and Gustine, 2002), is considered to be a winter accompanied by increased freezing tolerance when differences in survival were induced by environmental effects but was not related to dormant cultivar, while Tonic is considered to be more genetic differences in survival. winter active under New Zealand conditions (Stewart, 1996). Imposition of summer drought in the field increased plantain winter survival to 41% compared with less than I cultivars of narrow-leaf plantain have re10% survival under normal and excessive soil moisture ceived increasing attention as possible forage and treatments (Skinner and Gustine, 2002). They also found pasture species for the northeastern USA because of that plantain growth rates in the normal and wet treattheir reportedly high productivity during periods of ments were greater in September than they were during drought and high nutritive value (Stewart, 1996; RumJuly. However, growth rates were similar in September ball et al., 1997). However, the improved cultivars, and July in the dry treatment. It is possible that the Lancelot and Tonic, that are currently available were improved winter survival of drought-stressed plantain developed in New Zealand from germplasm originating was directly related to its reduced fall growth compared in northern Portugal and the North Island of New with well-watered plants. Zealand, respectively (Stewart, 1996), and do not appear The purpose of this experiment was to examine the to have sufficient freezing tolerance to survive northeffect that growth rate and root:shoot partitioning dureastern U.S. winters (Sanderson et al., 2001; Skinner ing the cold-hardening process has on the freezing tolerand Gustine, 2002). Sanderson et al. (2001) found that ance of Lancelot and Tonic plantain compared with plantain died out completely within 2 yr of planting in PG700, an experimental line developed from collections field trials. Skinner and Gustine (2002) concluded that made in several states in the eastern USA. The working Lancelot had slightly greater survival than Tonic, but hypothesis was that PG700 would exhibit reduced shoot neither cultivar had sufficient freezing tolerance to be structural growth and increased partitioning of nonrecommended for use in the northeastern USA. They structural carbohydrates and nitrogen compounds to further suggested that improved cultivars needed to be roots during cold-hardening, resulting in increased freezing tolerance and survival. USDA-ARS, Pasture Systems and Watershed Management Research Unit, Building 3702, Curtin Road, University Park, PA 16802. Received 12 Jan. 2005. *Corresponding author (howard.skinner@ars. MATERIALS AND METHODS usda.gov). The experimental line, PG700, was developed by Dr. A.V. Stewart at Pyne Gould Guiness, Ltd. in New Zealand from Published in Crop Sci. 45:2330–2336 (2005). Crop Physiology & Metabolism collections of erect plants made in Kansas, North Carolina, doi:10.2135/cropsci2005.0035 © Crop Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA Abbreviations: TNC, total nonstructural carbohydrates. 2330 Published online September 23, 2005