**3. Silicon and wheat yield**

Silicon fertilization in the soil resulted in positive effect on grain yield and its quality, mainly under stress. In China, a four-year field experiment in Calcareous Paddy soils indicated that Si fertilization increased the wheat yield by 4.1 to 9.3% under biotic stress [55], while other studies obtained increased in the grain yield due to silicate slag fertilization ranging from 5 to 12% [55, 56].

In New Jersey, in a three consecutive years of field experiment, calcium silicate (steel slag by-product) was added on a Quakertown Silt Loam soil increasing yield up to 10%, but only under biotic stress imposed by powdery mildew [57]. A two consecutive growing seasons experiment performed in Idaho evaluated the application of Si in the form of amorphous volcanic tuff in the Greenleaf-Owyhee Silt Loam soil indicated that there was no significant effect of Si on plant height, nutrient uptake, grain yield and grain protein content of winter wheat grown in non-stressed conditions [58]. A three site-years experiment was conducted on the Alluvial Floodplain soils in Louisiana to evaluated silicate slag applications on productivity of wheat under sufficient and high nitrogen application rates showed a numerical trends of grain yield increase increasing silicate slag rate, but significant increase was only observed in one site and year [59]. According authors, the inconsistencies observed in responses to Si treatments could be due to varying physicochemical properties of soils and more research is need to better understand the effect of silicate slag use in wheat production in Louisiana.

In Brazil, calcium silicate was used as a source of soluble Si in a three-years field experiment to control shoot diseases. The results showed that wheat plants grown in soil fertilized with calcium silicate that received one application of fungicide at the stem elongation stage showed a reduction on the biotic stress increasing grain yield by 1.0 t ha−1 (Pazdiora, P. C. – unpublished data). Grains from these experiments was used to determine the wheat technological quality through physicochemical and rheological analyses. The data indicated that calcium silicate showed little effect on the wheat technological quality under lower disease intensity, but under higher disease intensity, it ameliorated the damage caused, keeping the technological quality near the expected level of each cultivar (Dallagnol, L. J. – unpublished data). Pot experiment evaluating three soils (Rhodic Acrudox, Rhodic Hapludox and Arenic Hapludult) indicated that application of calcium/magnesium silicate in an acid clayey Rhodic Hapludox improves the development and yield of wheat, but the silicate application in soil with pH higher to 5.3 and high Si availability does not affect the agronomic characteristics and grain yield of wheat [60].

In Poland, a two-year field experiment evaluated different methods of application of powder (diatomaceous earth) and liquid (solution of monosilicic acid) forms of Si to soil, leaves and combined methods of application (to soil and leaves) on growth parameters and yielding [61]. Authors observed that the most efficient form of Si was a liquid formulation, while powder was less effective and only in combined application achieved similar effects such as liquid Si, increasing the number of seedling emergence, the height of plants and density of spikes and yield. Furthermore, according authors, soil and foliar Si application is more effective than soil or foliar application [61]. In Germany, an experiment performed in substrate showed that Si applied in the form of an engineered nanomaterial

(amorphous pyrogenic hydrophilic SiO2) was readily taken up by the wheat plants increasing the aboveground biomass production at low (1 g SiO2 pot−1) to medium (10 g SiO2 pot−1) supply levels of Si; and grain yield at medium Si supply, probably due to increased plant phosphorus availability and nutrition [34].

Foliar Si treatment also provided some effect on wheat growth and/or yield. In Canada, foliar application of potassium silicate increased the high of wheat plants, compared to control plants, but only under biotic stress and variable according Si-based product [62]. A study performed in Iran, under greenhouse, showed that wheat plant grown in pots that received foliar application of 6 mM sodium metasilicate significantly increased biomass and grain yield, being the highest positive effect of treatment observed with the application both at the tillering and anthesis stages, especially under drought stress [63]. Also, field experiment conducted in two seasons in Egypt to evaluate the effect of two nitrogen source combined with foliar spray of Si (diatomite) indicated that organic nitrogen (farm yard manure) combined to diatomite at rate of 0.4% produced the highest values of grain yield, weight of 100 grains and straw yield [64]. In Brazil, foliar application of Si (0.8% of soluble Si, as stabilized orthosilicic acid) increased mass of wheat seed without effect on its germination or vigor [65].

The fertilization results with Si sources on the yield and quality of wheat indicate that there is a trend of significant gains, especially under some kind of stress. However, the results among different studies are variable due to the differences in Si sources, the genetic variations of the wheat cultivars used and the stress levels imposed on the plant.

## **4. Wheat diseases affected by silicon**

The positive effect of Si fertilization on the control of diseases has been reported for pathosystems, mainly involving fungi as pathogens, around the world (**Figure 1**).

For blast (*Magnaporthe oryzae* pathotype Triticum), greenhouse experiments showed reduction of leaf blast severity up to 70% and up to 78% on the area under diseases progress curve (AUDPC) on plants grown in media containing 2 mM of Si compared to plants grown in media without addition of Si source [66, 67]. This effect of Si was associated to the increase in the incubation period by 28% and reduction up to 45% for the number of lesions per cm<sup>2</sup> of leaf [37]. The reduction on blast severity by Si was also associated to the restriction on the host cell colonization by the pathogen [68]. According to authors, in Si-supplied plants the fungal hyphae was restrict to the first-invaded epidermal cell compared to plants not amended with Si in which the fungal hyphae grew successfully and formed an extensive branched mycelium in the first-invaded epidermal cell and several neighboring cells. Leaf application of potassium silicate reduced blast severity, but the positive effect was variable among cultivars [51]. Another study evaluating leaf application of potassium silicate indicated blast severity reduction on the same proportion of fungicide treatment, but no additive or synergistic effect was observed mixing fungicide and potassium silicate [69]. Two-years field experiment showed that Si, applied in the soil as calcium and magnesium silicate in the furrow, and as potassium silicate applied on the leaves, reduced the incidence and severity of blast in the spike, but it effect was variable both with years and cultivars [70].

Powdery mildew (*Blumeria graminis* f. sp. *tritici*) was the first wheat disease reported to be affected by Si [71]. In a three-years experiment evaluating the straw incorporated in the soil conferred the reduction of several wheat disease including

*Silicon Use in the Integrated Disease Management of Wheat: Current Knowledge DOI: http://dx.doi.org/10.5772/intechopen.95285*


#### **Figure 1.**

*Examples of the effect of silicon (Si) on wheat diseases through root or foliar application (Si supply) in experiments conducted under greenhouse or field environments (Environ.) in different regions (Country) through evaluating disease incidence (Inc.), disease severity (Sev.) or area under disease progress curve (AUDPC) and the percentage of control obtained by silicon treatment. Credits of blast photos to Amanda Baseggio.*

powdery mildew [72]. Authors attributed this effect to the increase in the Si availability in the soil conferred by the straw incorporated, being this effect of Si increased in the soil confirmed under greenhouse experiment [72, 73]. Bélanger et al. [74] reported that on wheat plants not supplied with Si the first signs of *B. graminis* f. sp. *tritici* infection were observed at five days after inoculation developing rapidly thereafter reaching to disease severity of up to 40% after five weeks, while plants supplied with Si, colonies of *B. graminis* f. sp. *tritici* were reduced even after five weeks with severity lesser than 5%, indicating very limited fungal colonization on leaf tissue. Later, another study reported reduction on powdery mildew severity up to 80% when Si was supplied via the roots, but leaf spray was less effective reducing the disease severity up to 40% [62]. Field experiment during three consecutive years indicated that calcium silicate (steel slag by-product) reduced powdery mildew severity, in all season that disease occurred, up to 44% [57]. Wheat plants grown in

nutrient solution containing different doses of soluble sodium metasilicate showed that the increase of Si concentration in plant showed inverse proportionality to pathogen index indicating an effective action of Si against *B. graminis* f. sp. *tritici* infection in the foliar surface [75].

For spot blotch (*Bipolaris sorokiniana*) the AUDPC was reduced by 59% due soil fertilization with calcium silicate (wollastonite) [76]. The effect of Si on the AUDPC of spot blotch was associated to an increase in the incubation period and decrease in the number of lesions per cm<sup>2</sup> of leaf area and disease severity [77, 78]. This effect of Si on the infectious process of *B. sorokiniana* indicated a limited fungal growth in tissue of Si-supplied plants because authors detected only a sparse network of hypha colonizing the cells as well as a reduced number of epidermal cells showing browning [79].

For tan spot (*Pyrenophora tritici-repentis*), greenhouse experiment using calcium and magnesium silicate (steel slag by-product) incorporated in the soil increased leaf Si concentration which was correlated to longer incubation period and reduced infection efficiency, final number of lesions per cm2 , rate of lesion expansion, lesion size, disease severity and AUDPC [80–82].

For fusarium head blight (*Fusarium graminearum* specie complex), greenhouse experiment indicated that calcium and magnesium silicate incorporated in the soil increased the incubation period in 15% and reduced up to 32% de disease severity and up to 53% de concentration of deoxynivaleonol (a harmful mycotoxin produced by *Fusarium* species) [83]. As the chemical control of fusarium head blight is closely linked to the timing of fungicide application at spike and not all tillers start anthesis at the same time, Si showed a potential to increase the time of fungicide application and still providing a good control of the disease due a longer incubation period and lower rate of colonization (Pazdiora, P. C. Unpublished data).

Field experiment during three years indicated that calcium and magnesium silicate fertilization increased the Si concentration in the soil and wheat leaf and spike tissues, which was associated to the reduction in the severity of both tan spot and fusarium head blight. The reduction of disease severity conferred by Si was greater for tan spot than to fusarium head blight. The greatest control of tan spot and fusarium head blight was obtained with the moderately resistant cultivar treated with two fungicide sprayings. On the other hand, wheat plants grown in soil fertilized with calcium and magnesium silicate that received one application of fungicide at the stem elongation stage showed a reduction up to 50% on tan spot severity and an increase of grain yield by 1 t ha−1 compared to the same fungicide treatment on plants grown on soil that received limestone (Pazdiora, P. C. – unpublished data).

Another wheat disease that was affected by Si are leaf blotch (*Parastagnospora nodorum*) under both field and greenhouse trials [72, 73], septoria leaf blotch (*Zymoseptoria tritici*) and eyespot (*Oculimacula yallundae*). However, the efficiency of Si in reducing these diseases was variable and attributed to the type of growing substrate used in the experiments [73]. Furthermore, for bacterial leaf streak (*Xanthomonas translucens* pv. *undulosa*), the Si treatment in the soil not affected the incubation period, latent period, necrotic leaf area, and severity, but reduced up to 50% the chlorotic leaf area [84].
