Many golf courses and turfgrass managers use recycled water, which contains high salts, as part or a sole irrigation source to lower costs and comply with governmental restrictions on water use. High salinity negatively affects turfgrass performance. Using salt-tolerant species or cultivars is one the most effective methods to address salinity problems. Twenty-six commercially available creeping bentgrass (Agrostis stolonifera) cultivars were evaluated for salt tolerance during in vitro germination on 1% agar media supplemented with NaCl at 0, 5, 10, 15, or 20 g·L−1 at 25/15 °C (day/night) under fluorescent light (36 μmol·s−1·m−2) with an 8- to16-h photoperiod. Significant variations in salinity tolerance were observed among the cultivars. Final germination rate (FGR, %) and daily germination rate (DGR, %/d) decreased linearly or quadratically as salinity levels increased. ‘Declaration’, ‘Seaside II’, ‘T-1’, and ‘Bengal’ were the most salt-tolerant, requiring salt levels at or greater than 16.0 and 10.0 g·L−1, respectively, to reduce FGR and DGR by 50%. In contrast, ‘Tyee’, ‘Kingpin’, and ‘SR1150’ required average salinity levels of 11.6 and 6.5 g·L−1 to cause 50% reduction in FGR and DGR, respectively, showing that they were the least salt-tolerant cultivars. The largest difference between FGR (1.9%) and DGR (26.2%) reduction under saline conditions was observed at 5 g·L−1, indicating that DGR was more sensitive to salinity changes than FGR. Therefore, DGR might be a more reliable method to be used for salt selection.
Sheng Wang and Qi Zhang
Sheng Wang, Qi Zhang and Eric Watkins
Prairie junegrass (Koeleria macrantha) is a perennial, cool-season, native grass that has shown potential for use as a turfgrass species in the northern Great Plains; however, limited information is available on its salt tolerance. In this study, salinity tolerance of four junegrass populations from North America (Colorado, Minnesota, Nebraska, and North Dakota) and two improved turf-type cultivars from Europe (‘Barleria’ and ‘Barkoel’) was evaluated and compared with kentucky bluegrass (Poa pratensis), perennial ryegrass (Lolium perenne), sheep fescue (Festuca ovina), hard fescue (F. brevipila), and tall fescue (F. arundinacea). Salinity tolerance was determined based on the predicted salinity level causing 50% reduction of final germination rate (PSLF) and daily germination rate (PSLD) as well as electrolyte leakage (EL), tissue dry weight (DW), and visual quality (VQ) of mature plants. All populations of prairie junegrass showed similar salt tolerance with an average of PSLF and PSLD being 7.1 and 5.3 g·L−1 NaCl, respectively, comparable to kentucky bluegrass and hard and sheep fescue but lower than tall fescue and perennial ryegrass. Larger variations were observed in VQ in the junegrasses compared with EL and DW, in which ‘Barleria’ from the European population showed the highest VQ, following two salt-tolerant grasses, tall fescue and sheep fescue. Nebraska population was the least salt-tolerant within the species but still exhibited similar or higher tolerance than kentucky bluegrass and perennial ryegrass cv. Arctic Green. Overall, junegrass was more salt-sensitive during germination but more tolerant to salinity when mature. Salinity tolerance of junegrass may be further improved through turfgrass breeding because salinity tolerance varied in different populations.
Qi Zhang, Sheng Wang and Kevin Rue
Salinity tolerance of 12 turfgrasses in four groups, creeping bentgrass (Agrostis stolonifera L.), fescues (Festuca spp.), kentucky bluegrass (Poa pratesis L.), and alkaligrass [Puccinellia distans (Jacq.) Parl.], was evaluated using three germination methods. Seeds were germinated on 1% agar medium, on germination paper, or in a hydroponic system under salinity levels of 0, 5, 10, 15, or 20 g·L−1 NaCl. Germination rate and seedling growth of each grass were determined. Salinity reduced the final germination rate (FGR), daily germination rate (DGR), and seedling leaf area (LA) in all tests. On agar medium, no significant difference in salinity tolerance was observed among the four turf groups; however, ‘Turf Blue’ kentucky bluegrass with a corn starch-based coating (coated ‘Turf Blue’) showed a significant higher salinity tolerance than the uncoated one. Using germination paper, creeping bentgrass required the highest salinity level to cause 50% reduction in FGR followed by alkaligrass, fescues, and kentucky bluegrass. Kentucky bluegrass required the lowest salinity level (9.5 g·L−1) to reduce DGR by 50%. With the hydroponic system, alkaligrass required a salinity level of 26.3 g·L−1 to reduce FGR by 50%, the highest among the four groups. Alkaligrass showed again the highest salinity tolerance with an average of 12.7 g·L−1 needed to reduce LA by 50%. Among the grasses, coated ‘Turf Blue’ kentucky bluegrass, ‘Declaration’ creeping bentgrass, and ‘Fults’ alkaligrass showed the highest salinity tolerance when evaluated on agar medium, on germination paper, or in the hydroponic system, respectively. The present study determined the salinity tolerance of 12 turfgrasses at seed germination and early seedling growth stages and showed that the germination method was a factor affecting the evaluation result and it should be considered in a seed germination test of turfgrass for salinity tolerance.
Qi Zhang, Kevin Rue and Sheng Wang
Salinity tolerance of five buffalograss [Buchloe dactyloides (Nutt.) Englem.] cultivars (Texoka, Cody, Bison, Sharp's Improved II, and Bowie) and three blue grama [Bouteloua gracilis (Willd. ex Kunth) Lag. ex Griffiths] ecotypes (‘Lovington’, ‘Hachita’, and ‘Bad River’) was determined during in vitro seed germination and vegetative growth in a hydroponic system. Seeds were germinated on 0.6% agar medium supplemented with NaCl at 0, 5, 10, 15, and 20 g·L−1. Salinity reduced the final germination rate (FGR) and daily germination rate (DGR). Similarly, shoot dry weight (SDW), longest root length (LRL), and percentage of green tissue (PGT) of mature grasses declined with increasing salinity levels (NaCl = 0, 2.5, 5, 7.5, and 10 g·L−1). However, root dry weight (RDW) was not significantly affected by salinity. Blue grama exhibited a lower reduction in FGR and DGR than buffalograss at salinity levels lower than 10 g·L−1. Germination of all buffalograss cultivars and ‘Hachita’ blue grama was inhibited at salinity levels of 15 and 20 g·L−1 NaCl. However, buffalograss was more salt-tolerant than blue grama at the vegetative growth stage. Variations of salinity tolerance were observed within buffalograss cultivars and blue grama ecotypes, especially during the seed germination stage. Overall, buffalograss appeared to be salt-sensitive during germination but moderately salt-tolerant at the mature stage. However, blue grama was more salt-tolerant at the germination stage than the mature stage. Noticeable differences in salinity tolerance were observed between different germplasms. Therefore, salt tolerance of buffalograss and blue grama may be improved through turfgrass breeding efforts.
Lili Dong, Qi Wang, Feng Xiong, Na Liu and ShuiMing Zhang
More axillary buds 1 (MAX1), initially identified in arabidopsis (Arabidopsis thaliana), is a key regulatory gene in strigolactone synthesis. CmMAX1, an ortholog of MAX1 was cloned from chrysanthemum (Chrysanthemum morifolium cv. Jinba). It had an open reading frame of 1611 bp and encoded 536 amino acid of P450 protein, with a conserved heme-binding motif of PFG × GPR × C × G, as well as PERF and KExxR motifs. The predicted amino acid sequence of CmMAX1 was most closely related to the MAX1 ortholog identified in lotus (Nelumbo nucifera), NnMAX1, with 55.33% amino acid sequence similarity. Expression analysis revealed there was no significant difference of CmMAX1 expression among various tissues. Phosphorus (P) deficiency significantly improved the expression levels of CmMAX1. Strigolactone, auxin, and cytokinin negatively regulated the expression of CmMAX1. Overexpression of CmMAX1 reduced the branch numbers of arabidopsis max1-1. These results suggest that CmMAX1 may be a candidate gene for reducing the shoot branching of chrysanthemum.
Jia-yi Wang, Jian-shuang Shen, Mengmeng Gu, Jia Wang, Tang-ren Cheng, Hui-tang Pan and Qi-xiang Zhang
Yellow-leafed cultivars usually do not grow as vigorous as their green-leafed counterparts, which affect their use in landscapes. To breed Forsythia cultivars with both yellow leaves and vigorous growth, crosses between F. ‘Courtaneur’ (♀) and Forsythia koreana ‘Suwon Gold’ (♂) were conducted, and 52 F1 hybrid progenies with different leaf colors (green, chartreuse, and yellow) were obtained. The progenies were categorized into three groups [Yellow Group (YG), Chartreuse Group (CG), and Green Group (GG)] based on leaf colors. The growth index (GI) and the number of branches and leaves of YG progenies were significantly lower at 2%, 35%, and 34% of GG progenies. As the leaves changed from green to chartreuse and to yellow, chlorophyll content, leaf thickness, and chlorophyll fluorescence parameters decreased and the chloroplast structures were disintegrated gradually, which influenced the leaf photosynthetic activity and led to weak growth. Compared with yellow-leafed progenies, the leaf chlorophyll content and leaf thickness of chartreuse-leafed progenies were significantly higher at 71% and 9%. The chloroplast structure of stroma lamella of chartreuse-leafed progenies was relatively intact. Carboxylation efficiency (CE), photochemical efficiency of PS II (F v/F m), and the number of branches and leaves of GG progenies were significantly higher than YG progenies; however, they have no significant difference with CG progenies. The results were promising for breeding new forsythia cultivars from moderate growth and chartreuse leaves.
Zong-zhe Wan, Ya-nan Li, Xin-yu Qi, Dan Wang and Ling Wang
Ming Cai, Ke Wang, Le Luo, Hui-tang Pan, Qi-xiang Zhang and Yu-yong Yang
Hydrangea macrophylla is the most popular species in the genus Hydrangea because of its large and brightly colored inflorescences. Since the early 1900s, numerous cultivars with showy flowers have been selected. Although many H. macrophylla cultivars have been developed, cold hardiness is still the major limitation to their outdoor use. Hydrangea arborescens is a small attractive shrub or subshrub native to northeastern parts of the United States, which is valued for its hardiness. Interspecific breeding of H. arborescens and H. macrophylla has been tried, but putative hybrid seedlings either died at an early stage or were not verified. We made successful hybridizations between H. macrophylla ‘Blue Diamond’ and H. arborescens ‘Annabelle’ and used in vitro ovary culture to produce viable plants. Hybrids were intermediate in appearance between parents, but variable in leaves, inflorescences, and flower color. The success of this hybridization was confirmed by six simple sequence repeat (SSR) genetic markers. The maternal chromosome number was 36, and the paternal number was 38. Chromosome counts of hybrids indicated that nearly half of them were aneuploids. Male fertility of progeny was evaluated by fluorescein diacetate staining of pollen. Twelve out of 14 hybrids (85.7%) had male fertility. We documented the first flowering progeny of H. macrophylla and H. arborescens, suggesting an effective beginning to a cold hardiness breeding program.
Qi Wang, Rui Zhao, Qihang Chen, Jaime A. Teixeira da Silva, Liqi Chen and Xiaonan Yu
Herbaceous peony is a perennial flowering plant with strong environmental adaptability and may be a good candidate for culture in arid areas. In this study, the physiological and biochemical responses of two herbaceous peony cultivars to different soil moisture gradients in pots were assessed by analyzing changes in 13 stress-related indices. The drought damage index (DDI) and the contents of malondialdehyde (MDA), soluble sugar, proline, and abscisic acid (ABA) generally increased as drought stress intensified, whereas leaf relative water content (LRWC) decreased, and the contents of soluble protein, indole-3-acetic acid (IAA), the ratio of IAA and ABA, and the activities of four antioxidant enzymes fluctuated. For the leaves, a positive correlation was found between DDI and superoxide dismutase (SOD), MDA, soluble sugar, proline, ascorbate peroxidase (APX), and ABA, but it was negatively correlated with LRWC, peroxidase (POD), and catalase (CAT). In fibrous roots, DDI was positively correlated with MDA, soluble sugar, proline, soluble protein, and ABA but was negatively correlated with SOD, CAT, APX, and IAA/ABA. Principal component analysis and subordinate functions were used to evaluate drought resistance of the two cultivars, with ‘Karl Rosenfield’ showing greater resistance to drought than ‘Da Fu Gui’.
Lanqing Wang, Yinfeng Li, Dehai Liu, Chaohui Zhang, Yuancheng Qi, Yuqian Gao, Jinwen Shen and Liyou Qiu
We investigated a practical method for immobilizing liquid spawn of oyster mushroom (Pleurotus ostreatus) to prolong the storage time and provide convenient transportation of liquid spawn of edible mushrooms. The method was based on the mycelial pellets of liquid spawn adsorbed in carriers. Selected carriers were similar to cultivation substrates, and the best carrier was a mixture of cottonseed hull, corn core, and wheat bran with a ratio of 4.5:4.5:1 by weight. Immobilized spawn were prepared by mixing the pellets from liquid spawn with carriers using a ratio of 1:8 by weight. Within the first 15 days of storage at 20–25 °C, the immobilized spawn grew strongly, respiration intensity and cellulase activities rose rapidly, and the count and brightness of the isozyme bands of esterase, peroxidase, and polyphenol oxidase increased remarkably as well. From days 30 to 60, the cellulase activities fell and the brightness of the peroxidase and polyphenol oxidase bands gradually decreased, whereas the respiration intensity and the band count of esterase and peroxidase remained constant. After 60 days, the cultivated characteristics of the immobilized spawn were same as the fresh conventional solid cottonseed hull spawn. The results showed that immobilized spawn on the basis of the mycelial pellets of liquid spawn adsorbed in carrier can be used to extend the storage time and simplify transportation of liquid spawn of edible mushroom.