However, even under these conditions, the model was not successful in identifying triggering events. For example, there was a poor relationship between the powdery mildew index in a greenhouse near Monterey when the model was run with a temperature range of 65°F to 85°F . This relationship was improved somewhat by running the model for the same data using a temperature range of 65°F to 80°F . However, there were many times in the spring and early summer when the PMI indicated high disease risk but no disease was evident on the crop . We have no explanation for these persistent failures. Perhaps there was no inoculum in the greenhouse; perhaps we were not fully aware of all fungicide treatments; or perhaps greenhouse humidity is interacting in a way that confounds the model. Clearly a model that could predict the most opportune times for applying fungicide treatments to control powdery mildew on roses would be beneficial. We were encouraged by the fact that the model never indicated low risk when there was in fact significant disease , and that we sometimes saw a rise in mildew incidence after a rise in the index with an appropriate latent period lag . However, our research showed that the UC Davis powdery mildew risk assessment model for grapevines is not easily adapted to the challenge of powdery mildew on greenhouse roses. Additional research is needed to develop a more suitable modeling platform before it will be possible to effectively advise growers regarding risk periods.Effective IPM implementation was hindered at two sites by the citrus mealybug . This pest is generally not a problem for rose growers until IPM is implemented,flood table when the cessation of broad-spectrum pesticide applications can allow this pest to develop. It is generally a problem only at sites where roses are or were grown adjacent to other flower crops such as Stephanotis, an important citrus mealybug host plant. Unfortunately, natural enemies of the citrus mealybug are not regularly available at the commercial level, and the most effective mealybug pesticides are detrimental to spider mite predators.

We are working with the natural enemy suppliers to try to change this situation, and we continue to evaluate reduced-risk pesticides for efficacy against the citrus mealybug.Overall, we believe that the rose IPM program was successful. For example, most of the growers participating in the study wanted to abandon their conventional treatments in favor of using a biological control, predatory mites, to control two spotted spider mites; we allowed them to do so after we felt that enough data had been collected for a good comparison of the IPM and conventional treatments. Future work should concentrate on reducing the sampling effort while still collecting sufficient information to support good pest management decisions. In addition, more work is needed on refining the predictive powdery mildew model as well as on developing effective IPM techniques for secondary pests. This program represents the first and largest effort to demonstrate and implement an IPM strategy on floriculture crops in the United States. Drawing on the partnerships that are central to the Pest Management Alliance concept, we have shown that high-quality roses can be produced with substantially fewer pesticides and with the incorporation of biological control into mainstream floriculture. Effective partnering with the biological control industry has also been a hallmark of this program. This has led to the widespread use of predatory mites in commercial rose production in California, representing the largest use of biological control by the floriculture industry in the United States.Lignocellulosic biomass, a renewable source of organic carbon, will be a major feedstock for sustainable biorefineries producing bio-based fuels, chemicals, and materials. These biorefineries are required to address the twin global demands of increased energy availability and reduced emissions. Grasses, such as sorghum , Miscanthus × giganteus, and switch grass , are promising as dedicated bio-energy crops, due to their high photosynthetic efficiency and ability to grow in a range of environmental conditions. However, plant cell walls, which comprise most of lignocellulosic biomass, have evolved to provide many crucial functions to the plant, including structural support, and protection from herbivory and pathogens.

The resulting highly recalcitrant cell wall architecture is an impediment to the efficient deconstruction of plant cell walls into simple monomers. Improved understanding of the architecture of intact grass plant cell walls at a molecular level will provide key insights into this recalcitrance, and support the predictable design of both the biomass deconstruction process, as well as the development of engineered bio-energy crops. All plant cells are surrounded by a thin, extensible, primary cell wall. Thickened secondary cell walls are only deposited in certain cell types at the cessation of cell expansion, but form the majority of biomass. Secondary cell walls are composed of polysaccharides and a complex polyphenolic network of lignin. Cellulose makes up 35–45% of the dry weight of grass secondary cell walls. It consists of flat-ribbons of α-1,4-linked glucan chains which self-assemble into a crystalline fibrillar structure via hydrogen bonding. The resulting fibril has surfaces with distinct hydrophilicity that allow potential interactions with other cell wall components. However, cellulose crystallites are not perfect, and there is a significant fraction of cellulose that is less ordered, referred to as amorphous cellulose. Hence, two major domains of cellulose can be distinguished: a crystalline cellulose domain and an amorphous cellulose domain. Xylan is the major hemicellulose, which makes up 20–35% of the dry weight of grass secondary cell walls. Xylan has a α-1,4-linked xylosyl unit backbone. However, unlike in dicot plants, grass xylan is highly substituted by α-L-arabinofuranosyl units at the O-2 and O-3 positions on the xylosyl units of the backbone and comparatively low density of substitution with α-1,2-glucuronosyl or α-1,2–glucuronosyl units. This xylan structure is known as glucuronoarabinoxylan , though the exact substitution pattern is dependent on tissue and species. In addition, grass xylan is also substituted with acetyl groups on the backbone xylosyl units at the O-2 and O-3 positions, and some arabinosyl units can also carry acetyls at the O-2 position.Xylans are believed to be present in two major conformations, two-/ three-fold screw conformations, and the conformation is highly dependent on the pattern of substitution.

For instance, the even pattern of acetyls and glucuronosyl/4-O-methyl-glucuronosyl units on Arabidopsis thaliana allows these substitutions to lie on one side of the xylan backbone, where every two xylosyl units have a 360° turn forming a flatribbon shape. Without this even pattern, the xylan will have a 360° turn every three xylosyl units forming a helical shape due to steric hindrance. Additionally, another characteristic feature of grass secondary cell wall is the presence of hydroxycinnamic acids , which are esterified to the O-5 of the α-1,3-arabinosyl substitutions on grass xylan backbone and can be esterified and/or etherified to lignin. Ferulate units on grass xylan facilitate the covalent cross-link of xylan-xylan and xylan-lignin by formation of diferulates through dehydrodimerization and participation in lignification via radical coupling to bridge the lignin and polysaccharides, and stiffen the cell wall and maintain structural integrity. Although the chemical structures of individual cell wall components are relatively well defined, the interaction between the cell wall components that form the three-dimensional network remains poorly understood for grasses. Methods to access the molecular information of intact plant cell walls were limited by the need for additional chemical extraction and pre-treatments, until a groundbreaking effort by Hong and colleagues which employed multi-dimensional solid-state Nuclear Magnetic Resonance to reveal the architecture of native primary cell walls in Arabidopsis. More recently,rolling benches the architecture of secondary plant cell walls was also investigated via ssNMR. Simmons et al. found direct evidence for the presence of xylan in both two- and three-fold screw conformations in the dicot secondary cell wall. In a cross-polarizing experiment, which emphasizes the immobile components, the xylan-cellulose interaction was dominated by xylan in a two-fold screw conformation, with only a minor proportion of three-fold xylan detected. Terrett et al. reported similar xylan-cellulose interactions in the secondary plant cell walls of softwoods due to the even pattern of substitution of softwood GAX. Additionally, galactoglucomannan, the other major hemicellulose in softwoods, binds the same cellulose microfibrils. Both cellulose-bound xylan and galactoglucomannan are also associated with lignin. Kang et al. employed ssNMR to investigate the lignin-polysaccharide interactions in the secondary plant cell walls of maize . Results showed a conformation-dependent bridge behavior of xylan in the secondary plant cell walls, linking the cellulose fibrils and lignin, in which two-fold screw xylan coats the cellulose microfibril hydrophilic surface and the three-fold screw xylan connects the lignin nanodomain via electrostatic interactions. Using Arabidopsis with genetically engineered xylan structures, Grantham et al. determined that an even pattern of xylan substitution is critical for the formation of the two-fold screw conformation and its interaction with cellulose. Evenly patterned decorations on the xylan backbone allow the substitutions to orient along one side of the molecule, leaving the undecorated side of the resultant flat-ribbon shape free to hydrogen bond with the hydrophilic surface of the cellulose microfibril.

Although the substitution pattern of the xylan backbone in grasses is not known, the large amounts of arabinosyl units on grass xylan suggests that it may not follow the dicot and softwood pattern, which may in turn alter its interaction with cellulose. Here, to explore xylan-cellulose interactions in grasses, we perform multi-dimensional ssNMR analysis on sorghum to reveal the native architecture of its secondary cell wall. The results suggest a lack of two-fold screw xylan, with the majority of the xylan showing a three-fold screw conformation. However, this three-fold screw xylan shows relatively high rigidity as compared to Arabidopsis and softwood reported earlier, and close proximity with less ordered amorphous cellulose. We propose that sorghum xylan-cellulose interactions are dominated by xylan in the threefold screw conformation and amorphous cellulose, in contrast to the interactions between xylan in the two-fold screw conformation and crystalline cellulose in softwoods and dicot plants. We also show that the fraction of amorphous cellulose in the sorghum secondary cell wall is approximately three-fold higher than that in Arabidopsis, a model dicot plant. These findings provide molecular level understanding of the grass cell wall structure. Accurate cell wall models will enable a predictive understanding of biomass deconstruction by identifying the most recalcitrant aspects of the architecture. These models will also aid the identification of molecular targets for developing bioenergy crops with improved biomass properties.Sorghum plants were grown hydroponically in a 13CO2-containing atmosphere in our in-house 13C-growth chamber, as previously described. Upon harvest, all tissue was immediately frozen in liquid nitrogen, and sliced into 1–2 mm pieces to enable packing into the rotor, preventing them from thawing. No further processing of the tissue was performed, to allow us to investigate a cell wall architecture as close to native as possible. Stem internode tissue from the 3rd internode was divided into upper, middle, and lower . Leaf and root tissue was also retained and used for comparison.A sample of the harvested tissue was processed into alcohol insoluble residue , and used for compositional analysis. 13C enrichment was confirmed by following the procedure described in, and all tissue used in this study had a 13C incorporation rate of over 90% . Monosaccharide composition of the non-cellulosic fractions of the cell wall were determined by HPAEC-PAD analysis after mild acid hydrolysis, and were comparable to previously reported data .To characterize different parts of the same internode, quantitative direct polarization one-dimensional 13C NMR experiments, which detects all the 13C carbons present in the sample, were performed with a long recycle delay . No major difference was detected between the upper, middle, and lower sections of the same internode. From this point on, stem data were collected only on the lower part of the internode.To deconvolute the overlapping signals from the 1D spectra and obtain an overview of the chemical structure of native secondary cell wall components, the lower internode sample was investigated by two-dimensional double-quantum and single-quantum 13C-13C correlation experiments using the refocused INADEQUATE sequence with cross polarization. This measures the chemical shifts of directly bonded 13C nuclei from relatively immobile components of the cell wall . The DQ chemical shift represents the sum of the SQ chemical shifts of two directly bonded carbons. Chemical shifts were assigned with reference to previous reports.