Alternatives to ethoxyquin (Etq) are needed for controlling superficial scald of ‘Anjou’ european pears (Pyrus communis) during long-term storage. The current commercial standard storage conditions [Etq + −1 °C + controlled atmosphere (CA) with 1.5 kPa O2] reduced scald occurrence compared with control fruit (−1 °C + CA) during 6–8 months storage. At 1 °C in air, 1-methylcyclopropene (1-MCP) fumigation at 0.15 µL·L−1 at harvest was more efficient on reducing scald than Etq but did not prevent scald during 6–8 months storage. The 1-MCP-treated fruit at 1 °C in air developed their ripening capacity at 20 °C following 6–8 months storage but had deceased shipping ability (softening and yellowing of fruit). Although Etq inhibition of scald was associated with the inhibition of α-farnesene oxidation to conjugated trienols (CTols); 1-MCP reduced α-farnesene synthesis and thereby the availability of substrate to oxidize to CTols. CA storage at 1.5 kPa O2 totally prevented scald and retarded the loss of shipping ability without affecting the ripening capacity of 1-MCP-treated fruit at 1 °C through further decreases in the syntheses of ethylene, α-farnesene and CTols during 6–8 months storage. In addition, 1-MCP prevented a CA-induced disorder, pithy brown core (PBC), in ‘Anjou’ pears possibly through enhancing an oxidative/reductive metabolic balance during extended storage. In conclusion, the combinations of 1 °C + 1-MCP + CA is a potential commercial alternative to Etq for scald control while allowing the 1-MCP-treated ‘Anjou’ pears to recover ripening capacity during the shelf life period after 6–8 months storage.
Yan Xu and Bingru Huang
Summer decline in turf quality and growth of cool-season grass species is a major concern in turfgrass management. The objectives of this study were to investigate whether foliar application of trinexapac-ethyl (TE) and two biostimulants (TurfVigor and CPR) containing seaweed extracts would alleviate the decline in creeping bentgrass (Agrostis stolonifera L.) growth during summer months and to examine effects of TE and the biostimulants on leaf senescence and root growth. The study was performed on a ‘Penncross’ putting green built on a sandy loam soil at Hort Farm II, North Brunswick, NJ, in 2007 and 2008. Turf was foliar-sprayed with water (control), TE (0.05 kg a.i./ha), TurfVigor (47.75 L·ha−1), or CPR (19.10 L·ha−1) from late June to early September in a 2-week interval in both years. Turf quality, density, chlorophyll content, canopy photosynthetic rate (Pn), and root growth exhibited significant decline during July and August in both 2007 and 2008, to a greater extent in each parameter for the control treatment. Foliar application of TE resulted in significant improvement in turf quality, density, chlorophyll content, and Pn on certain sampling dates from July to September in both years compared with the control. Both TurfVigor and CPR significantly improved visual quality during July and August in both years by promoting both shoot and root growth. This study suggests that proper application of TE and selected biostimulants could be effective to improve summer performance of creeping bentgrass.
Yan Ma and Junyu Chen
From 1986 through 1993 wild rose species were investigated throughout China to catalog and to characterize the rose germplasm resources in mainland China. Many of the 94 rose species and 144 rose varieties in China have not been extensively utilized. The basic features of Chinese rose species are as follows. (1) There are many valuable and rare Rosa species in China. These species are sources of many unique and outstanding characters such as intense fragrance, white and yellow flower color, recurrent flowering and resistance to stress. More than 80% of the rose species in China are native to only China. (2) Although most Rosa species are still in the wild state, a few species cultivated from very early time have many forms available. (3) The number of rose species gradually increases from Northeast to Southwest China. The distribution centers of Rosa species in China are Sichuan and Yunnan Provinces. Chinese rose species can be introduced and used directly in gardens, or in breeding programs to develop new roses.
Yan Xu and Bingru Huang
Leaf senescence can be induced by many environmental stresses, including supraoptimal temperatures. The objectives of this study were to evaluate leaf senescence induced by heat stress for two Agrostis species contrasting in heat tolerance and to examine whether heat-induced leaf senescence in both species was associated with changes in three major senescence-related hormones: ethylene, abscisic acid (ABA), and cytokinins. Plants of heat-tolerant rough bentgrass (Agrostis scabra Willd.) and heat-sensitive creeping bentgrass (Agrostis stolonifera L.) were exposed to 35/30 °C (day/night) (high temperature) or 20/15 °C (control) for 35 d in growth chambers. Turf quality, photochemical efficiency (Fv/Fm), and the contents of two pigments (chlorophyll and carotenoid) for both species decreased under high temperature; however, heat-tolerant A. scabra exhibited delayed and less severe decline in all parameters compared with heat-sensitive A. stolonifera. Ethylene production rate increased in both species at 35 °C, but the increase was observed 21 days later in A. scabra compared with that in A. stolonifera. ABA content increased at the initiation of heat stress and then declined in both species after prolonged heat stress. However, the timing of the increase was delayed for 7 days and the highest level of ABA content was less in A. scabra (4.0 times that of the control) than that in A. stolonifera (5.9 times that of the control). Decreases in both forms of cytokinins (transzeatin/zeatin riboside and isopentenyl adenosine) were also delayed for 14 days and less pronounced in A. scabra. Correlation analysis revealed that leaf senescence induced by heat stress was negatively correlated to ethylene and ABA accumulation and positively correlated to cytokinin production. Delayed leaf senescence in A. scabra under heat stress could be related to slower and less magnitude of changes in ethylene, ABA, and cytokinins.
Yan Hong and SiLan Dai
The light-dependent coloration of the vital organs of horticultural crops affects multiple parts of production and sales. The simplicity of the metabolic pathways of anthocyanins and the characteristics of light-dependent coloration make chrysanthemum (Chrysanthemum ×morifolium) an ideal subject for studying the mechanism of light-regulated anthocyanin biosynthesis. In this study, real-time quantitative reverse transcription–polymerase chain reaction (PCR) was used in the analysis of the expression levels of anthocyanin biosynthesis genes in C. ×morifolium ‘Reagan’. The reference genes selected were those assumed to remain at constant levels in three flower color lines at five floral developmental stages and at two light conditions. Using digital gene expression technology, we selected nine reference genes with moderate expression in the chrysanthemum ray florets at various floral developmental stages under illuminated and dark conditions as the candidate reference genes for further study. After comprehensively analyzing the stability of gene expression with three distinct statistical algorithms, geNorm, NormFinder, and qBase plus, we found that F-box and PP2A were the most stable genes in all of the samples. In addition, we analyzed the relative expression level of the CmF3H gene in different samples to verify the reference genes that we selected. This study provides a consensus list of validated reference genes that will benefit future studies of the expression of chrysanthemum genes involved in anthocyanin biosynthesis and floral development under various light conditions. Moreover, this information will also promote the molecular breeding of horticultural crops for their color modification.
Yan Xu and Yuejin Wang
Expressed sequence tags (ESTs) constitute a rapid and informative strategy for studying gene-expression profiles of specific stages of annual and perennial plant species. Compared with annual plants, the NCBI database has very little sequence information from perennial plant species. To date, only ∼145 ESTs of Vitis pseudoreticulata W.T. Wang have been deposited in databases. This is insufficient to understand the biology and development of this species. In this report, a cDNA library constructed from young leaf inoculated with powdery mildew pathogen [Uncinula necator (Schw.) Burr.] of Chinese wild Vitis pseudoreticulata. Leaf was harvested at various times after inoculation for total RNA extraction, which was used to generate ESTs. In our study, 107 cDNA clones were sequenced either from 5' or 3' end of the cDNAs. Among them, 60 unigenes (56%) were functionally characterized by the BLASTX matches to known function proteins, and 20 unigenes (18.6 %) matched significantly with those having unknown function in the public databases. The remaining 27 unigenes (25.2%) failed to show significant homology to any proteins in the public databases, suggesting that they represent novel sequences. Some functional genes identified from the cDNA library to be potentially associated with plant defence-related responses are discussed.
Yan Zhang, Cuiyue Liang, Yan Xu, Thomas Gianfagna and Bingru Huang
The objective of the study was to determine whether the expression of a cytokinin (CK) biosynthesis gene encoding adenine isopentenyl transferase (ipt) would delay or suppress leaf senescence induced by nitrogen (N) or phosphorus (P) deficiency in a C3 grass species, creeping bentgrass (Agrostis stolonifera). The ipt gene was ligated to a senescence-associated promoter, SAG12, and was transferred into creeping bentgrass using an agrobacterium (Agrobacterium tumefaciens)-mediated transformation technique. Plants from an SAG12-ipt transgenic line (S41) and a null transformant (NT) control line were grown in nutrient solutions with all essential elements or without N (−N) or P (−P) for 21 days. Significant declines in leaf photochemical efficiency (Fv/Fm) and chlorophyll content of mature leaves were detected in NT and SAG12-ipt plants exposed to N or P deficiency. Compared to the NT control line, SAG12-ipt plants had higher levels of Fv/Fm, chlorophyll, and CK contents in leaves, and these differences between the NT control and SAG12-ipt line became more pronounced with treatment duration. The ipt expression was detected in the −P-treated and the −N-treated plants after 21 days, although the level of expression decreased under N or P deficiency. Under −P treatment, root acid phosphatase activity was greater in SAG12-ipt line than in the NT control line. No significant differences in nitrate reductase activity were detected in leaves or roots between the SAG12-ipt and the NT control lines. Our results demonstrated that SAG12-ipt expression suppressed leaf senescence induced by N or P deficiency in a perennial grass species. The suppressing effects on leaf senescence under P deficiency may be related to CK regulation of more efficient use of P in roots of the SAG12-ipt plants.
Stanley J. Kays and Yan Wang
Using the sweetpotato as a model, we identified precursors of critical flavor volatiles by fractionating, based upon solubility, raw roots into major groups of constituents. Volatile thermophyllic products from the individual fractions were analyized and compared to those from non-extracted root material. Volatile components were seperated and identified using GC-MS and quantified using internal standard methodology. Mechanisms of synthesis of flavor volatiles via thermophyllic reactions will be discussed, as will postharvest treatments that can modulate eventual aromatic properties of cooked plant products.
Yan Wang and Stanley J. Kays
The sweetpotato weevil is the single most critical insect pest of the sweetpotato worldwide. While male weevils can be lured to traps using a synthetic female pheromone, crop losses are not adequately reduced since damage is caused by the larvae arrising from eggs laid by female weevils in the storage roots. Identification of a female attractant could greatly enhance the control of the insect. The leaves and storage roots are known to emit volatiles that attract the female and in the following tests, we demonstrate that feeding by female weevils stimulates the synthesis of a volatile attractant which attracts additional females to the root. Undamaged, artificially damaged, and female weevil feeding damaged periderm were tested in dual-choice and no-choice olfactometers. Volatiles from feeding damaged roots were significantly more attractive than undamaged and artificially damaged roots. To test whether the volatile attractant was of weevil or root origin, volatiles were collected in MeCl2 after removal of the weevils and fractionated on a megabore DB-1 capillary column using a GC fitted with a TC detector. Fractions were collected from the exit port and their activity index (AI) determined using dual choice and no choice olfactometry. The active fraction was ascertained and active components identified via GC-MS.
Yan Shi and C.R. Rom
Fifty apple cultivars and 30 Malus species were evaluated for resistance to four isolates of bitter rot pathogens, Colletotrichum gloeosporioides and C. acutatum, in controlled conditions. Fruit were wound-inoculated by placing 0.1 ml of inoculum (106 conidia/ml) into puncture wounds (2 mm in diameter), and intact fruit were inoculated by spraying with inoculum. Inoculated fruit were incubated at 25 to 28C for 2 weeks. `Golden Delicious' (susceptible) and `Red Delicious' (resistant) were used as controls. Diseases were quantified by measuring lesion diameter, and disease severity was objectively rated. Relative lesion diameter and severity rating were calculated as [X × 100/RD – 100] and (X – RD) × 100/7 (X = parameter of given cultivar or species, RD = parameter of `Red Delicious') to determine relative resistance. Conclusions were as follows: 1) different levels of resistance were identified in apple cultivars and Malus species and also were detected within `Golden Delicious' and `Red Delicious' types; 2) `Jonagold', `Oregon Spur II', `Spartan', `Melrose', `Red Cort', `Jonafree', `VPI-9', and `Red Delicious showed good relative resistant; 3) M. halliana, angustifolia, prunifolia, sylvestris, and fusca were more resistant than `Delicious'; 4) M. angustifolia was immune to two isolates of C. acutatum.