Drought stress is a major factor in turfgrass management; however, the underlying mechanisms of turfgrass drought tolerance are not well understood. This greenhouse study was designed to investigate proline and hormone responses to drought stress in two tall fescue [Festuca arundinacea (Schreb.)] cultivars differing in drought tolerance. The two cultivars, Van Gogh (relatively drought-tolerant) and AST7002 (relatively drought-sensitive), were established and grown under either well-watered (maintaining 90% container capacity) or drought stress (≈26% container capacity) and then re-watered. Drought stress reduced turfgrass quality, relative leaf water content (LWC), leaf indole-3-acetic acid (IAA) and cytokinin zeatin riboside (ZR) content, and increased proline and abscisic acid (ABA) content. ‘Van Gogh’ had greater turfgrass quality rating, LWC, proline, ABA, and ZR content relative to ‘AST7002’ under drought stress conditions. At the end of drought stress, leaf proline, ZR, and ABA content were 32%, 43%, and 50% higher in ‘Van Gogh’ relative to ‘AST7002’, respectively. No cultivar difference was observed under well-watered conditions. The results of this study suggest that the proline, ABA, and ZR content are associated with drought tolerance. Selection and use of the cultivars with higher proline, ABA, and ZR content under drought stress may be a practical approach to improve tall fescue drought tolerance.
A genetic linkage map was constructed for watermelon using 117 recombinant inbred lines (RILs) (F2S7) descended from a cross between the high quality inbred line 97103 [Citrullus lanatus var. lanatus (Thunb.) Matsum. & Nakai] and the Fusarium wilt (races 0, 1, and 2) resistant U.S. Plant Introduction (PI) 296341 (C. lanatus var. citroides). The linkage map contains 87 randomly amplified polymorphic DNA (RAPD) markers, 13 inter simple sequence repeat (ISSR) markers, and four sequenced characterized amplified region (SCAR) markers. The map consists of 15 linkage groups. Among them are a large linkage group of 31 markers covering a mapping distance of 277.5 cM, six groups each with 4 to 12 markers covering a mapping distance of 51.7 to 172.2 cM, and eight small groups each with 2-5 markers covering a mapping distance of 7.9 to 46.4 cM. The map covers a total distance of 1027.5 cM with an average distance of 11.7 cM between two markers. The map is useful for the further development of quantitative trait loci (QTLs) affecting fruit qualities and for identification of genes conferring resistance to Fusarium wilt (races 0, 1 and 2). The present map can be used for further construction of a reference linkage map for watermelon based on an immortalized mapping population with progenies homozygous for most gene loci.
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.
Fruit oil content (FOC) is one of the most important commercial traits in oil palm; however, extensive study on related traits is still limited. The present study was conducted to analyze the relationship between FOC and fruit-related traits, as well as to predict the oil palm germplasm for potential improvement. In this study, a total of 11 traits, including fruit bunch number (FBN), average fruit weight (AFW), mesocarp-to-fruit ratio (M/F), kernel-to-fruit ratio (K/F), shell-to-fruit ratio (S/F), average fruit length (AFL), average fruit width (AFWD), average shell thickness (AST), mesocarp oil content (MOC), kernel oil content (KOC), and FOC were analyzed in 39 germplasms collected from seven different countries in Asia and Africa. Different statistical analyses were conducted to evaluate the relationship between FOC and fruit-related traits. Correlation analysis showed that FOC was positively and significantly correlated with M/F, MOC, and KOC, whereas negatively and significantly correlated with S/F and AST. Likewise, path analysis indicated that M/F and MOC have high positive direct effect on FOC, whereas S/F and AST have high negative direct and indirect effects on FOC. Furthermore, regression analysis showed significant correlation between predicted and observed FOC. In conclusion, FOC was mainly determined by M/F, MOC, S/F, and AST, and the FOC prediction in this study was reliable for germplasm evaluation. In addition, G39 (Tenera) and G2 (Parthenocarpy) have the highest FOC with 58.62% and 57.68%, respectively, indicating that they might be potential candidates for FOC improvement. These results could be applicable to oil palm breeding programs.
Gummy stem blight incited by the fungus Didymella bryoniae is a major disease of melons worldwide. The objectives of the present study were to critically evaluate melon (Cucumis melo L.) germplasm for resistance to D. bryoniae and to characterize the genetics of resistance in the resistant accessions. Two hundred sources of germplasm (plant introduction accessions, cultivars, breeding lines, landraces, and wild relatives) were screened against a single highly virulent isolate (IS25) of D. bryoniae in a plastic tunnel. The genetics of resistance to D. bryoniae was studied in three crosses between plant introductions 157076, 420145, and 323498, resistant parents that were fairly adapted (flowering, fruiting, powdery mildew tolerance) to Nanjing conditions, and plant introductions 268227, 136170, and NSL 30032 susceptible parents, respectively. Six populations of each cross (susceptible parent, resistant parent, F1, F2, the two reciprocal backcrosses) were analyzed for their responses to D. bryoniae. Seedlings in both studies were inoculated with a spore suspension (5 × 105 spores/mL−1) of D. bryoniae at the four to six true-leaf stages and assessed for leaf and stem damage at 7, 14, and 21 d postinoculation. Results of germplasm screening indicated most germplasms reported as resistant elsewhere were confirmed resistant under our conditions. However, some plant introductions identified as highly resistant elsewhere were susceptible under our conditions, the most interesting being plant introduction 482399. This plant introduction that was considered resistant was highly susceptible in our study. We also identified other sources of resistance not reported previously, for example, JF1; a wild Cucumis from the highlands of Kenya was rated highly resistant. Analysis of segregation of F1, F2, and backcross generations of the three crosses indicated that each of the three plant introductions carry a single dominant gene for resistance to the D. bryoniae.
The objective of the present study was to consider the regulatory role of exogenous nitric oxide (NO) supplementation in response to chilling stress impose alterations on different physiological parameters in melon seedlings. Melon seedlings were treated with sodium nitroprusside (SNP, an NO donor), hemoglobin (a NO scavenger), NG-nitro-L-arginine methyl ester (an NO synthase inhibitor), and tungstate (a nitrite reductase inhibitor) under chilling stress conditions. The results showed that exogenous SNP improves the growth of melon seedlings under chilling stress conditions and ameliorates the harmful effects of chilling stress by increasing the levels of chlorophyll and soluble solutes, elevating the activity of sucrose phosphate synthase by enhancing the expression level of CmSPS. Moreover, exogenous NO significantly enhances the expression of genes and activities of antioxidant enzymes under chilling stress, resulting in lower reactive oxygen species accumulation. However, the protective effects of SNP are reversed by both NO scavenging and inhibition. Collectively, our results reveal that NO has the ability to ameliorate the harmful effects of chilling stress on melon seedlings by regulating carbohydrate metabolism and the antioxidant defense system.
Wind tunnel tests were conducted in an NH-2-type wind tunnel to investigate the wind pressure coefficients and their distribution on the surfaces of a single-span plastic greenhouse and a solar greenhouse. Wind pressures at numerous points on the surfaces of the greenhouse models were simultaneously measured for various wind directions. The critical wind speeds, at which damage occurred on the surfaces of single-span plastic greenhouses and solar greenhouses, were derived. To clearly describe the wind pressure distribution on various surface zones of the greenhouses, the end surface and top surface of the plastic greenhouse and the transparent surface of the solar greenhouse were divided into nine zones, which were denoted as Zone I to Zone IX. The results were as follows: 1) At wind direction angles of 0° and 45°, the end surface of the single-span plastic greenhouse was on the windward side, and the maximum positive wind pressure coefficient was near 1. At wind direction angles of 90° and 180°, the entire end surface of the single-span plastic greenhouse was on the leeward side, and the maximum negative wind pressure coefficient was near −1. The maximum positive wind pressure on the end surface of the single-span plastic greenhouse appeared in Zone IV at a wind direction angle of 15°, whereas the maximum negative pressure appeared in Zone VIII at a wind direction angle of 105°. 2) Most of the wind pressure coefficients on the top surface of the plastic greenhouse were negative. The maximum positive and negative wind pressure coefficient on the top surface of the plastic greenhouse occurred in Zones I and II, respectively, at a wind direction angle of 60°. 3) At a wind direction angle of 0°, the distribution of wind pressure coefficient contours was steady in the middle and lower zones of the transparent surface of the solar greenhouse, and the wind pressure coefficients were positive. At a wind direction angle of 90°, the wind pressure coefficients were negative on the transparent surface of the solar greenhouse. A maximum positive wind pressure coefficient was attained at a wind direction angle of 30° in Zone IX, whereas the maximum suction force occurred in Zone VII at a wind direction angle of 135°. 4) The minimum critical wind speeds required to impair the single-span plastic greenhouse and solar greenhouse were 14.5 and 18.9 m·s−1, respectively.
Powdery mildew of cucurbits, incited by Podosphaera xanthii (Castagne) Braun & Shishkoff (syn. Sphaerotheca fuliginea auct. p.p.), is an economically important foliar disease. which is now common in watermelon [Citrullus lanatus (Thunb.) Mastum. & Nakai]. This disease occurs in all watermelon-growing areas and can reduce yields by up to 30%. Finding and breeding for resistance to this disease is important to reduce dependence on fungicides and to use in combination with fungicides to limit the spread of fungicide-resistant P. xanthii. This is the first English report that race 2WF of P. xanthii can infect watermelon. It is the prevalent race of watermelon powdery mildew in Beijing.
Because of the growing threat of global warming, drought stress could severely affect the normal growth and development of crop plants. To alleviate such an adverse effect, there is a need to screen watermelon germplasm collections to identify genetic sources for potential drought tolerance. In the present study, 820 accessions of USDA's Citrullus PIs and 246 watermelon breeding lines were evaluated for their drought tolerance at the seedling stage under extreme water stress conditions in a greenhouse. Significant variations in drought tolerance were observed in the Citrullus germplasm collections. Using fast clustering analysis, the tested watermelon materials could be assigned into four groups, including tolerant, intermediate tolerant, moderately sensitive, and sensitive, respectively. The most drought-tolerant Citrullus germplasm, including 13 Citrullus lanatus var. lanatus and 12 C. lanatus var. citroides accessions, were originated from Africa. These genetic materials could be used for rootstock breeding or for developing drought-tolerant watermelon cultivars.
Application of sugar alcohol zinc (SA-Zn) spray to apple trees at certain developmental stages can improve fruit quality. Increasing the Zn concentration of fruit can improve nutritional content and promote human health. We conducted foliar application of SA-Zn to 13-year-old ‘Fuji’ apple trees at different developmental stages. The effects of SA-Zn application on Zn concentration, reducing sugar content, and carbohydrate metabolism-related enzyme activity in fruit were investigated. The foliar treatment increased Zn and reducing sugar concentrations significantly in mature fruit. Sorbitol dehydrogenase activity was higher in the fruit of trees treated before budbreak and 3 weeks after flowering compared with the control at the early fruit stage and was higher during fruit expansion in plants treated after termination of spring shoot growth. Mature fruit of trees treated during the fruit expansion stage showed higher sorbitol dehydrogenase activity than the control. Foliar SA-Zn treatment did not have a significant effect on sorbitol oxidase activity in apple fruit. Treatment before budbreak and at 3 weeks after flowering led to a significant increase in the activity of sucrose synthase and acid invertase at the early fruit stage. Treatment during the fruit expansion stage significantly increased the activity of acid invertase at maturity but had no effect on the activity of neutral invertase. Our results indicate that foliar SA-Zn application resulted in biofortification of Zn in apples, which led to higher activity of carbohydrate metabolism-related enzymes and accumulation of sugars.