In recent years the importance of sustainable agriculture has risen to become one of the most important issues in agriculture. In addition, plant diseases continue to play a major limiting role in agricultural production. The control of plant diseases using classical pesticides raises serious concerns about food safety, environmental quality and pesticide resistance, which have dictated the need for alternative pest management techniques. In particular, nutrients could affect the disease tolerance or resistance of plants to pathogens. However, there are contradictory reports about the effect of nutrients on plant diseases and many factors that influence this response are not well understood. This review article summarizes the most recent information regarding the effect of nutrients, such as N, K, P, Mn, Zn, B, Cl and Si, on disease resistance and tolerance and their use in sustainable agriculture. There is a difference in the response of obligate parasites to N supply, as when there is a high N level there is an increase in severity of the infection. In contrast, in facultative parasites at high N supply there is a decrease in the severity of the infection. K decreases the susceptibility of host plants up to the optimal level for growth and beyond this point there is no further increase in resistance. In contrast to K, the role of P in resistance is variable and seemingly inconsistent. Among the micronutrients, Mn can control a number of diseases as Mn has an important role in lignin biosynthesis, phenol biosynthesis, photosynthesis and several other functions. Zn was found to have a number of different effects as in some cases it decreased, in others increased, and in others had no effect on plant susceptibility to disease. B was found to reduce the severity of many diseases because of the function that B has on cell wall structure, plant membranes and plant metabolism. Cl application can enhance host plants’ resistance to disease. Si has been shown to control a number of diseases and it is believed that Si creates a physical barrier which can restrict fungal hyphae penetration, or it may induce accumulation of antifungal compounds. Integrative plant nutrition is an essential component in sustainable agriculture, because in most cases it is more cost-effective and also environmentally friendly to control plant disease with the adequate amount of nutrients and with no pesticides. Nutrients can reduce disease to an acceptable level, or at least to a level at which further control by other cultural practices or conventional organic biocides are more successful and less expensive.

Role of nutrients in controlling plant diseases in sustainable agriculture.

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Role of Nutrients in Controlling Plant Diseases in Sustainable Agriculture: A Review

It is estimated that more than 95% of organic production is based on crop varieties that were bred for the conventional high-input sector. Recent studies have shown that such varieties lack important traits required under organic and low-input production conditions. This is primarily due to selection in conventional breeding programmes being carried out in the background of high inorganic fertilizer and crop protection inputs. Also, some of the traits (e.g., semi-dwarf genes) that were introduced to address problems like lodging in cereals in high-input systems were shown to have negative side-effects (reduced resistance to diseases such as Septoria, lower protein content and poorer nutrient-use efficiency) on the performance of varieties under organic and low-input agronomic conditions. This review paper, using wheat, tomato and broccoli as examples, describes (1) the main traits required under low-input conditions, (2) current breeding programmes for organic, low-input agriculture, (3) currently available breeding and/or selection approaches, and (4) the benefits and potential negative side-effects of different breeding methodologies and their relative acceptability under organic farming principles.

https://ir.library.oregonstate.edu/downloads/f7623d22v

The need to breed crop varieties suitable for organic farming, using wheat, tomato and broccoli as examples: A review

Although silicon (Si) is not recognized as an essential element for general higher plants, it has beneficial effects on the growth and production of a wide range of plant species. Si is known to effectively mitigate various environmental stresses and enhance plant resistance against both fungal and bacterial pathogens; however, the underlying mechanisms are largely unknown. In this review, the effects of Si on plant-pathogen interactions are discussedanalyzed, mainly from on physical, biochemical, and molecular aspects. In most cases, the Si-induced biochemical/molecular resistance during plant-pathogen interactions were dominated as joint resistance, involving activating defense-related enzymes activates, stimulating antimicrobial compound production, regulating the complex network of signal pathways, and activating of the expression of defense-related genes. The most previous studies described an independent process, however, the whole plant resistances were rarely considered, especially the interaction of different process in higher plants. Si can act as a modulator influencing plant defense responses and interacting with key components of plant stress signaling systems leading to induced resistance. Priming of plant defense responses, alterations in phytohormone homeostasis, and networking by defense signaling components are all potential mechanisms involved in Si-triggered resistance responses. This review summarizes the roles of Si in plant-microbe interactions, evaluates the potential for improving plant resistance by modifying Si fertilizer inputs, and highlights future research concerning the role of Si in agriculture.

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Role of silicon on plant-pathogen interactions.

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Recent Advances in the Diagnosis and Management of Plant Diseases

Nonfungicide alternatives for control of brown patch (caused by Rhizoctonia solani Kuhn) and dollar spot (caused by Sclerotinia homoeocarpa F.T. Bennett) diseases are needed. Calcium silicate (CaSiO 3 ) was applied as a topdressing (2440 or 4880 kg ha -1 ) to evaluate brown patch suppression in 'Bonsai 2000' and 'Tar Heel' tall fescue (Festuca arundinacea Schreb.) and 'L-93' creeping bentgrass (Agrostis palustris Huds.) in the field, or amended into soil at 7325 or 14650 kg ha -1 to evaluate dollar spot on 'Penncross' creeping bentgrass in a growth chamber. The Chase silty clay loam (fine, mont-morillonitic, mesic Aquic Argiudoll) under tall fescue had a pH of 6.4, a high initial Si content (173 mg kg -1 ), and Si accumulation in leaves was minimal (one of five observations). Calcium silicate applied at 2440 kg ha -1 increased the area under disease progress curves (AUDPC) for brown patch by 26% in 2002 and 30% (both rates) in 2003. Tall fescue leaf P and K concentrations were reduced by CaSiO 3 and were negatively correlated (r = -0.41 for P; -0.44 for K; P < 0.02) with brown patch. Calcium silicate topdressing increased Si in creeping bentgrass leaf tissue as well as the sand root zone, which initially contained <12 mg kg Si. A positive correlation (r = 0.81; P < 0.001) occurred between creeping bentgrass leaf Si concentration and brown patch severity in one of three years, which may have resulted from reduced leaf P and K after CaSiO 3 application. The silty clay loam (170 mg kg -1 Si) amended with CaSiO 3 before planting creeping bentgrass had no effect on leaf Si concentrations or dollar spot incidence. Thus, CaSiO 3 application to soil containing adequate Si should not be recommended for control of brown patch on tall fescue, nor should CaSiO 3 be recommended to control brown patch on creeping bentgrass grown on low Si soil or dollar spot on high Si soil. In fact, CaSiO 3 application may exacerbate brown patch disease incidence possibly because of nutrient imbalances, particularly in tall fescue.

http://www.nutricaodeplantas.agr.br/site/downloads/unesp_jaboticabal/si_doenca20.pdf

Evaluation of Calcium Silicate for Brown Patch and Dollar Spot Suppression on Turfgrasses

Some researchers report that one potential tool for reducing fungicide requirements on turfgrasses may be the use of silicon (Si) fertilizers. Silicon has been reported to suppress diseases on various crops in the last decade (Raid et al., 1992; Cherif et al., 1994; Deren et al, 1994; Seebold et al, 2000; Seebold et al., 2001). Researchers in North Carolina found that brown patch and dollar spot on creeping bentgrass were reduced approximately 20 percent and 30 percent, respectively, when soluble potassium silicate (21 percent SiOz) at 0.5 pounds per 1,000 square feet was applied (Uriarte et al., 2004). However, in that study measurable increases in potassium but not Si occurred in creeping bentgrass leaves. Gray leaf spot on St. Augustinegrass was reduced 9 percent to 28 percent by Si alone (100 pounds per 1,000 square feet) and 59 percent to 68 percent with the comContinued on page 60 IN THIS ISSUE

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Kathy Lowe

Papers

Evaluation of Calcium Silicate for Brown Patch and Dollar Spot Suppression on Turfgrasses

CaSi Doesn't Strengthen Creeping Bent, Tall Fescue against Foliar Disease