Rice blast is a serious fungal disease of rice (Oryza sativa L.) that is threatening global food security. It has been extensively studied due to the importance of rice production and consumption, and because of its vast distribution and destructiveness across the world. Rice blast, caused by Pyricularia oryzae Cavara 1892 (A), can infect aboveground tissues of rice plants at any growth stage and cause total crop failure. The pathogen produces lesions on leaves (leaf blast), leaf collars (collar blast), culms, culm nodes, panicle neck nodes (neck rot), and panicles (panicle blast), which vary in color and shape depending on varietal resistance, environmental conditions, and age. Understanding how rice blast is affected by environmental conditions at the cellular and genetic level will provide critical insight into incidence of the disease in future climates for effective decision-making and management. Integrative strategies are required for successful control of rice blast, including chemical use, biocontrol, selection of advanced breeding lines and cultivars with resistance genes, investigating genetic diversity and virulence of the pathogen, forecasting and mapping distribution of the disease and pathogen races, and examining the role of wild rice and weeds in rice blast epidemics. These tactics should be integrated with agronomic practices including the removal of crop residues to decrease pathogen survival, crop and land rotations, avoiding broadcast planting and double cropping, water management, and removal of yield-limiting factors for rice production. Such an approach, where chemical use is based on crop injury and estimated yield and economic losses, is fundamental for the sustainable control of rice blast to improve rice production for global food security.

Rhodium-binap catalysts have been used with great success for asymmetric conjugate additions of aryl boron compounds to enones and other electron-deficient alkenes.[1] The approach, pioneered by Miyaura, Hayashi, and co-workers offers particular advantages over copper-based methods, [2] including high selectivities, ligand availability, water tolerance, and moderate temperatures. Limitations remain to be addressed, including expanding the scope to alkyl reagents, lowering the amount of borane needed for high reactivity, and identifying new ligands that can be modified readily to accommodate new substrates.[3] As a first step to address these issues and as part of an effort to identify new asymmetric catalysts, we report herein the synthesis and use of a novel class of chiral dicyclophane imidazolium, Nheterocyclic carbene (NHC) ligands. Conditions are reported for the highly selective conjugate addition of aryl borane reagents (1.5 equiv) to cyclic and acyclic enones at moderate temperature. These new C 2 -symmetric dicyclophane imidazolium ligands can be readily modified to allow substrateligand matching with this process and in applications to other asymmetric transformations.Complexes of N-heterocyclic carbenes (NHC) with transition metals [4] have been developed to catalyze Heck, [5] Suzuki-Miyaura, [6] Stille, and Kumada coupling reactions, [4] hydrogenation reactions, [7] and ruthenium metathesis reactions.[8] We recently reported base-free conditions with NHC-palladium catalysts for Heck and Suzuki coupling reactions and the use of novel, bulky NHC ligands for Sonogashira reactions.[9] Imidazolium carbene ligands provide higher stability and reactivity than phosphanes through strong s-bond donation to the metal, together with attenuated back-bonding through donation of the nitrogen lone pair of electrons.[10] This combination of electronic effects renders the metal more electron-rich, allowing a more favorable oxidative insertion step. Typical NHC complexes, formed by treatment of an imidazolium salt with base and a metal, are air-stable and can be purified by chromatography in some cases. Alternatively, the NHC-Pd complex can be formed in situ from the imidazolium precursor without added base. Although numerous recent reports of NHC ligands can be found, the area of asymmetric catalysis with chiral imidazolium ligands remains in its infancy. [11] Planar chiral [2.2]paracyclophane ligands previously have included diphosphanes, [12] oxazoline-phosphanes, [13] oxazoline-imidazolium, [7c] oxazoline-selenides, [14] oxazoline-alcohols, [15] and Schiff base phenols. These have been used for hydrogenation, allylic substitution, and organozinc addition reactions.[16] Dimeric chiral [2.2]paracyclophanes are rare and their use as catalysts has not been reported previously. [17] The synthesis of the new ligands began with the known compound S p -pseudo-ortho-bromoamino[2.2]paracyclophane (1; Scheme 1). This material can be readily accessed either from the resolved S p -dibromo[2.2]paracyclophane or from the amin...

No abstract

Dry matter reserved in vegetative tissues can be remobilized and contribute to crop yields. This study determined the magnitude of dry matter (DM) remobilization from various internodes in spring wheat (Triticum aestivum L.) under different water stresses. We hypothesized that the ability of DM remobilization differed between genotypes. The genotypes LC26 and LC27 were grown in a rain shelter facility under nonstress, moderate stress, and severe water stress during grain filling. Compared with the nonstress check, LC27 remobilized 22 mg plant−1 more preanthesis DM in its upper internodes under moderate stress and 32 mg plant−1 more under severe stress. Remobilization efficiency (percent maximum DM remobilized) increased by 110% in the stem, 137% in the lower internodes, and 33% in the upper internodes, under severe stress. Wheat grain yield was reduced by 21% under moderate stress and by 43% under severe stress compared with the nonstress check, but lost yields were partly compensated by DM remobilization. Remobilized DM from the stem of LC26 contributed 18% to the grain yield under nonstress, 27% under moderate stress, and 39% under severe stress. Dry matter reserved in the stem of LC27 contributed 13% to the grain yield under nonstress, 18% under moderate stress, and 37% under severe stress. The compensation from DM remobilization did not offset the lost yield, and thus, improved practices are required to manage soil water and to minimize yield losses caused by drought stress.

No abstract