Silicon\u27s Role in Abiotic and Biotic Plant Stresses

Silicon (Si) plays a pivotal role in the nutritional status of a wide variety of monocot and dicot plant species and helps them, whether directly or indirectly, counteract abiotic and or biotic stresses. In general, plants with a high root or shoot Si concentration are less prone to pest attack and exhibit enhanced tolerance to abiotic stresses such as drought, low temperature, or metal toxicity. However, the most remarkable effect of Si is the reduction in the intensities of a number of seedborne, soilborne, and foliar diseases in many economically important crops that are caused by biotrophic, hemibiotrophic, and necrotrophic plant pathogens. The reduction in disease symptom expression is due to the effect of Si on some components of host resistance, including incubation period, lesion size, and lesion number. The mechanical barrier formed by the polymerization of Si beneath the cuticle and in the cell walls was the first proposed hypothesis to explain how this element reduced the severity of plant diseases. However, new insights have revealed that many plant species supplied with Si have the phenylpropanoid and terpenoid pathways potentiated and have a faster and stronger transcription of defense genes and higher activities of defense enzymes. Photosynthesis and the antioxidant system are also improved for Si-supplied plants. Although the current understanding of how this overlooked element improves plant reaction against pathogen infections, pest attacks, and abiotic stresses has advanced, the exact mechanism(s) by which it modulates plant physiology through the potentiation of host defense mechanisms still needs further investigation at the genomic, metabolomic, and proteomic levels

Effect of silicon rate and host resistance on blast, scald, and yield of upland price

Blast-resistant, partially resistant, and susceptible cultivars of rice were planted in soil amended with Si at 0, 500, or 1,000 kg/ha at two locations in eastern Colombia to assess differential responses to leaf blast, neck blast, and leaf scald, and to examine the quantity and quality of grains harvested. Leaf and neck blast on partially resistant and susceptible cultivars were reduced by Si as the rate of Si was increased. Depending on the location, the level of severity of leaf and neck blast on partially resistant cultivars, when fertilized with Si at 500 or 1,000 kg/ha, was lowered to that of resistant cultivars without Si. At both locations, yields were increased by as much as 42%, depending on the cultivar, by Si applied at 1,000 kg/ha. In general, high rates of Si reduced the number of broken grains harvested. Grain discoloration, regardless of cultivar or location, was reduced by as much as 70% at the high rate of Si. The application of Si to complement host resistance to blast and scald appears to be an effective strategy for disease management in rice and provides the added benefit of improving the quantity and quality of rice yields

Silicon enhances the accumulation of diterpenoid phytoalexins in rice: A potential mechanism for blast resistance

Although several reports underscore the importance of silicon (Si) in controlling Magnaporthe grisea on rice, no study has associated this beneficial effect with specific mechanisms of host defense responses against this fungal attack. In this study, however, we provide evidence that higher levels of momilactone phytoalexins were found in leaf extracts from plants inoculated with M. grisea and amended with silicon (Si+) than in leaf extracts from inoculated plants not amended with silicon (Si-) or noninoculated Si+ and Si- plants. On this basis, the more efficient stimulation of the terpenoid pathway in Si+ plants and, consequently, the increase in the levels of momilactones appears to be a factor contributing to enhanced rice resistance to blast. This may explain the lower level of blast severity observed on leaves of Si+ plants at 96 h after inoculation with M. grisea. The results of this study strongly suggest that Si plays an active role in the resistance of rice to blast rather than the formation of a physical barrier to penetration by M. grisea

Permanent genetic resources added to molecular ecology resources database 1 May 2009-31 July 2009

This article documents the addition of 512 microsatellite marker loci and nine pairs of Single Nucleotide Polymorphism (SNP) sequencing primers to the Molecular Ecology Resources Database. Loci were developed for the following species: Alcippe morrisonia morrisonia, Bashania fangiana, Bashania fargesii, Chaetodon vagabundus, Colletes floralis, Coluber constrictor flaviventris, Coptotermes gestroi, Crotophaga major, Cyprinella lutrensis, Danaus plexippus, Fagus grandifolia, Falco tinnunculus, Fletcherimyia fletcheri, Hydrilla verticillata, Laterallus jamaicensis coturniculus, Leavenworthia alabamica, Marmosops incanus, Miichthys miiuy, Nasua nasua, Noturus exilis, Odontesthes bonariensis, Quadrula fragosa, Pinctada maxima, Pseudaletia separata, Pseudoperonospora cubensis, Podocarpus elatus, Portunus trituberculatus, Rhagoletis cerasi, Rhinella schneideri, Sarracenia alata, Skeletonema marinoi, Sminthurus viridis, Syngnathus abaster, Uroteuthis (Photololigo) chinensis, Verticillium dahliae, Wasmannia auropunctata, and Zygochlamys patagonica. These loci were cross-tested on the following species: Chaetodon baronessa, Falco columbarius, Falco eleonorae, Falco naumanni, Falco peregrinus, Falco subbuteo, Didelphis aurita, Gracilinanus microtarsus, Marmosops paulensis, Monodelphis Americana, Odontesthes hatcheri, Podocarpus grayi, Podocarpus lawrencei, Podocarpus smithii, Portunus pelagicus, Syngnathus acus, Syngnathus typhle,Uroteuthis (Photololigo) edulis, Uroteuthis (Photololigo) duvauceli and Verticillium albo-atrum. This article also documents the addition of nine sequencing primer pairs and sixteen allele specific primers or probes for Oncorhynchus mykiss and Oncorhynchus tshawytscha; these primers and assays were cross-tested in both species. © 2009 Blackwell Publishing Ltd

Effects of surface application of calcium-magnesium silicate and gypsum on soil fertility and sugarcane yield

Lime application recommendations for amendment of soil acidity in sugarcane were developed with a burnt cane harvesting system in mind. Sugarcane is now harvested in most areas without burning, and lime application for amendment of soil acidity in this system in which the sugarcane crop residue remains on the ground has been carried out without a scientific basis. The aim of this study was to evaluate the changes in soil acidity and stalk and sugar yield with different rates of surface application of calcium, magnesium silicate, and gypsum in ratoon cane. The experiment was performed after the 3rd harvest of the variety SP 81-3250 in a commercial green sugarcane plantation of the Sao Luiz Sugar Mill (47 degrees 25'33 ''W; 21 degrees 59'46 ''S), located in Pirassununga, Sao Paulo, in southeast Brazil. A factorial arrangement of four Ca-Mg silicate rates (0, 850, 1700, and 3400 kg ha(-1)) and two gypsum rates (0 and 1700 kg ha(-1)) was used in the experiment. After 12 months, the experiment was harvested and technological measurements of stalk and sugar yield were made. After harvest, soil samples were taken at the depths of 0.00-0.05, 0.05-0.10, 0.10-0.20, 0.20-0.40, and 0.40-0.60 m in all plots, and the following determinations were made: soil pH in CaCl2, organic matter, P, S, K, Ca, Mg, H+ Al, Al, Si, and base saturation. The results show that the application of gypsum reduced the exchangeable Al3+ content and Al saturation below 0.05 m, and increased the Ca2+ concentration in the whole profile, the Mg2+ content below 0.10 m, K+ below 0.4 m, and base saturation below 0.20 m. This contributed to the effect of surface application of silicate on amendment of soil acidity reaching deeper layers. From the results of this study, it may be concluded that the silicate rate recommended may be too low, since the greater rates used in this experiment showed greater reduction in soil acidity, higher levels of nutrients at greater depths and an increase in stalk and sugar yield.As recomendações de corretivos de acidez em cana-de-açúcar foram desenvolvidas em sistema de colheita com cana queimada. Hoje, a maioria das áreas é colhida sem queima. Nesse novo sistema de colheita, em que o resíduo da colheita permanece na superfície do solo, a aplicação superficial de corretivos de acidez realiza-se sem embasamento científico. O objetivo deste estudo foi avaliar a alteração da acidez do solo e a produtividade de colmos e açúcar com a aplicação superficial de doses de silicato de cálcio-magnésio e gesso agrícola em cana-soca. O experimento foi realizado após a 3ª colheita da variedade SP 81-3250, em uma plantação comercial de cana crua da Usina São Luiz (47º 25' 33" W, 21º 59' 46" S), localizada em Pirassununga, Estado de São Paulo. O experimento foi montado em um arranjo fatorial com quatro doses de silicato de cálcio-magnésio (0, 850, 1.700 e 3.400 kg ha-1) e duas doses de gesso agrícola (0 e 1.700 kg ha-1). Após 12 meses, o experimento foi colhido e determinada a produtividade de colmos e açúcar. Após a colheita, amostras de solo foram retiradas nas profundidades de 0,00-0,05, 0,05-0,10, 0,10-0,20, 0,20-0,40 e 0,40-0,60 m em todas as parcelas, e realizadas as seguintes determinações: pH em CaCl2, matéria orgânica, P, S, K, Ca, Mg, H+Al, Al, Si e saturação por bases. A aplicação de gesso agrícola reduziu os teores de Al3+ e a saturação por Al abaixo de 0,05 m e aumentou o teor de Mg2+ abaixo de 0,10 m, a concentração de Ca2+ em todo o perfil, a concentração de K+ abaixo de 0,4 m e a saturação por bases abaixo dos 0,20 m. Isso contribuiu para que o efeito da aplicação superficial de silicato na alteração da acidez do solo atingisse camadas mais profundas. A partir dos resultados deste estudo, pode-se concluir que a dose de silicato recomendada pode ser insuficiente, já que as maiores doses utilizadas neste experimento propiciaram maior redução da acidez do solo, níveis mais elevados de nutrientes em profundidade e aumento na produtividade de colmos e açúcar.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Everglades Research and Education Center, University of Florida. 3200 E. Palm Beach Rd., Belle Glade, FL 33430.São Paulo Agency of Agribusiness Technology - APTA. Rod. Piracicaba, km 2, Guamium. Caixa Postal 28. CEP 13400-970 Piracicaba (SP), Brazil.College of Agricultural Sciences - FCA, São Paulo State University - UNESP. Rua José Barbosa de Barros, 1780. Caixa Postal 237. CEP 18610-307 Botucatu (SP), Brazil.Department of Crop Science, FCA, UNESP

Effects of silicon on the penetration and reproduction events of Meloidogyne exigua on coffee roots

Considering that the root-knot nematode Meloidogyne exigua has caused great yield losses to coffee production in Brazil, this study aimed to determine whether the penetration and the reproduction events of this nematode on the roots of plants from two coffee cultivars with different levels of basal resistance to this nematode could be affected by silicon (Si). Coffee plants from the cultivars Catuaí and IAPAR 59, which are susceptible and resistant, respectively, to M. exigua, were grown in pots containing Si-deficient soil that was amended with either calcium silicate (+Si) or calcium carbonate (–Si). The Si concentration on the root tissue significantly increased by 159 and 97% for the +Si plants from the cultivars Catuaí and IAPAR 59, respectively, compared to the –Si plants of these cultivars. The population of M. exigua, the number of galls and the number of eggs were significantly reduced on the roots of the +Si plants of the cultivars Catuaí and IAPAR 59 compared to the –Si plants of these cultivars. It was concluded that the development and reproduction events of M. exigua were negatively impacted on the roots of coffee plants supplied with Si

Desenvolvimento da aveia branca e disponibilidade de fósforo em razão da aplicação de silicato de potássio

A aplicação de silicato de potássio pode aumentar a disponibilidade de fósforo no solo, além de influenciar no crescimento da aveia branca. Objetivou-se neste trabalho avaliar o efeito da aplicação de doses de silicato de potássio no solo no desenvolvimento da aveia branca e na disponibilidade de fósforo. O delineamento experimental foi inteiramente ao acaso, em esquema fatorial 2 x 4, com seis repetições. Os tratamentos foram 20 e 200 mg dm-3 de P2O5 combinados com 0, 150, 300 e 450 mg dm-3 de Si, aplicados por ocasião da semeadura. Após a colheita, determinaram-se a matéria seca de folhas + colmos, das panículas e o total da parte aérea. A palha das panículas foi separada para avaliação dos teores de P e Si nas folhas + colmos, grãos e palha das panículas. As concentrações de Si e P no solo foram avaliadas após colheita das plantas. A aplicação de silicato aumenta os teores de Si no solo e influencia na maior disponibilidade de fósforo. A matéria seca de folhas + colmos é incrementada pelo silicato quando os teores iniciais de P são baixos. Mesmo com a dose elevada de P, a aplicação de silicato aumenta a disponibilidade de P no solo e a absorção pelas plantas. Os teores de Si na palha das panículas, folhas + colmos e grãos são influenciados pela maior disponibilidade do elemento no solo