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Hrvoje Rukavina* and Harrison Hughes

Efforts are ongoing at Colorado State Univ. to develop cultivars of saltgrass for turf use. Crossing among genotypes have been limited because of the species' short flowering period that generally occurs in late May or early June. Therefore, this study was made to establish a floral induction procedure for saltgrass to facilitate winter crosses in the greenhouse. The effects of vernalization/photoperiod, nitrogen and burning on the flowering induction of three saltgrass genotypes were investigated in the Colorado State Univ. greenhouse. Genotypes 49 and C66 from South Dakota and Nevada, respectively did not respond to flowering induction treatments. Only genotype A54 from the Colorado Front Range gave adequate response to flowering induction treatments. Saltgrass genotype (origin of clone) is a major factor relative to floral induction with the treatments used. All three treatment factors significantly influenced the number of spikes or flowering in saltgrass clone A54. There was a highly significant effect of vernalization/photoperiod (P < 0.01) and burning treatment (P < 0.01), with a smaller but significant interaction (P <0.05) among these two factors. There was also a significant effect of nitrogen (P <0.05). Burning had a significant influence on flowering only in treatments without vernalization/photoperiod effect. Vernalization/photoperiod levels significantly influenced flowering regardless of the burning treatment. Since flowering induction requirements differ among saltgrass genotypes originating in different areas, further studies will evaluate more Colorado genotypes as well as different lengths of vernalization/photoperiod on efficiency of flower induction.

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Hrvoje Rukavina and Harrison G. Hughes

Saltgrass (Distichlis spicata) has received increased attention as a result of its low input needs. A good understanding of the factors that influence greater flower production in saltgrass clones would facilitate seed production management and hybridization in the breeding program. Therefore, the influence of sampling time from the field, nitrogen (N) fertilization, and burning on flowering spike production of five saltgrass clones from three cold-hardiness zones were evaluated over 2 years. Clones were sampled from the field at two times (August and November) in the first and at three times (August, November, and January) in the second experimental year. After field sampling, clones were transferred to the greenhouse and received N and burning treatments. N fertilization increased number of spikes (flowering) for all saltgrass clones by ≈30% in both experimental years. In the second experimental year, the number of spikes was increased to a greater extent when N was applied in combination with burning treatment as compared with N without burning. The burning treatment had a greater effect on the number of spikes in plants sampled in August as compared with those sampled in November and January. Sampling in November increased flowering in three clones as compared with August sampling, but with the greatest effect in clone A1540. Sampling in January further increased the number of spikes in clones 1490 and A1610 but with no significant effect on the number of spikes in clone A1540. Environmental adaptation associated with origin of saltgrass clones is a major factor that influences flowering spike production.

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Hrvoje Rukavina, Harrison Hughes and Randy Johnson

Development of a new turfgrass cultivar requires an evaluation of numerous traits as well as an understanding of environmental factors influencing those traits. Growth or ability to fill in gaps and time of fall dormancy (fall color retention) that indicates cold hardiness are important traits for turfgrasses. This study was initiated to characterize variation in saltgrass [Distichlis spicata L. (Greene)] growth and time of fall dormancy related to climatic and geographical factors at the source location (geographical location of clone origin). Growth traits and time of fall dormancy were measured on 52 saltgrass clones collected from 41 locations and established at one location (common garden) in Fort Collins, CO. Principal component analysis on the morphological traits extracted the first principal component that explained 78% of the variability. The first principal component and time of fall dormancy were related to climatic and geographical factors at the source locations. Variation in growth traits was related to seasonal climatic variables of summer drying and fall cooling that explained ≈50% of variability in morphological traits. Variation in time of fall dormancy was related to longitude of clone origin and minimum winter temperature. These two variables explained ≈60% of the total variability in time of fall dormancy. Information obtained in this study may help breeders identify the best environments for specific traits and suggests that cold tolerance could be a problem for some clones from western sources if established too far east.

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Hrvoje Rukavina, Harrison G. Hughes and Yaling Qian

Freezing is the major abiotic stress that limits geographic distribution of warm season turfgrasses. Prior studies have indicated variation in freezing tolerance in saltgrass clones. Therefore, this study examined freezing tolerance of 27 saltgrass clones as related to collection sites in three zones of cold hardiness. Furthermore, these clones were evaluated for time of leaf browning in the fall with the intent to determine if there was a correlation between this trait and freezing tolerance. Rhizomes were sampled during 2004 and 2005 midwinters from clones established in Fort Collins, Colo., and then subjected to a freezing test in a programmable freezer. Saltgrass freezing tolerance was highly influenced by the climatic zone of clone origin in both years of the experiment. Clones with greater freezing tolerance turned brown earlier in fall in both seasons. Ranking of zones for the average LT50 (lethal temperature at which 50% of rhizomes died) was: zone 4, most northern (−17.2 °C) < zone 5 (−14.4 °C), < zone 6, most southern (−11.1 °C) in 2004, and zone 4 (−18.3 °C), < zone 5 (−15.7 °C) < zone 6 (−13.1 °C) in 2005. Clones from northern areas tolerated lower freezing temperatures overall. This likely indicates that freezing tolerance is inherited. Large intraspecific variation in freezing tolerance may be effectively used in developing cold hardy cultivars.

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Hrvoje Rukavina, Harrison Hughes and Yaling Qian

Efforts are ongoing at Colorado State University to develop turf-type saltgrass cultivars. Prior freezing studies have indicated variation in freezing tolerance in saltgrass lines. Therefore, this study was made to examine relative freezing tolerance of 27 saltgrass clones as related to collection sites in three zones of cold hardiness. Furthermore, these lines were evaluated for fall color retention with the intent to determine if there is a correlation with fall color and freezing tolerance. Saltgrass rhizomes were sampled in mid-winter 2004 from lines established in Fort Collins, Colo., and then subjected to a laboratory-freezing test. Saltgrass freezing tolerance was highly influenced by climate zones of clones' origin (P < 0.01) and genotypes within zones (P < 0.01). There was a high negative correlation between color retention in the fall and freezing tolerance (P < 0.01). Average freezing tolerance of saltgrass clones within zones of origin significantly differed among zones. Ranking of zones for least square mean LT50 (OC) was: zone 4 (–17.2) < zone 5 (-14.4) < zone 6 (–11.1). LT50 values in zone 4 ranged from –17.8 (accession 72) to –17.0 (accession 87). Clones in zone 5 showed LT50 values from –17.8 (accession A29) to –11.9 (accession A137). Zone 6 clones had LT50 values that ranged from –9.5 (accession C92) to –12.6 (accession C12). Large intraspecific variation in freezing tolerance may be effectively used in new cold hardy cultivar development. Environmental adaptation inherited by origin of clone is useful in defining clones' adaptation range and may along with fall color retention serve as a selection criterion in saltgrass cold hardiness improvement.

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Hrvoje Rukavina, Harrison Hughes and Yaling Qian

Freezing is the major abiotic stress that limits geographical distribution of warm-season turfgrasses. Prior studies have indicated variation in freezing tolerance in saltgrass clones. Therefore, this 2-year study examined the freezing tolerance of 27 saltgrass clones as related to collection sites in three zones of cold hardiness. Furthermore, these clones were evaluated for time of leaf browning in the fall with the intent to determine if there was a correlation between this trait and freezing tolerance. Rhizomes were sampled during 2004 and 2005 midwinters from clones established in Fort Collins, Colo., and then subjected to a freezing test. Saltgrass freezing tolerance was highly influenced by the climatic zone of clone origin in both years of the experiment. Clones with greater freezing tolerance turned brown earlier in fall in both seasons. Ranking of zones for the average LT50 was: zone 4 (–17.2 °C) < zone 5 (–14.4 °C) < zone 6 (–11.1 °C) in 2004 and zone 4 (–18.3 °C) < zone 5 (–15.7 °C) < zone 6 (–13.1 °C) in 2005. Clones from northern areas tolerated lower freezing temperatures better overall. This confirmed that freezing tolerance is inherited. Large intraspecific variation in freezing tolerance may be effectively used in developing cold-hardy cultivars.