**4. Strawberry growth, yield, and quality improvement by probiotic bacteria**

Beneficial microorganisms especially bacteria that are associated with host plants either as rhizoplane, phylloplane, or endophyte and enhance growth of the host plants including yield are popularly known as plant probiotic bacteria (PPB). These PPB can also suppress plant diseases by various modes of action when applied proactively in adequate amounts [61]. PPB that are used as biofertilizers or biostimulants possess the ability to colonize the rhizosphere, plant roots, or both when applied to seeds or crops. Some of these microbes have shown potential to promote strawberry plant growth by the release of metabolites into the rhizosphere that may inhibit various pathogens as biocontrol agents [5–8]. However, Tomic et al. [9] found that the response to bacterial inoculation is cultivar-related in strawberries, which indicates that a specific microbial strain should be tested for efficacy against a specific strawberry variety before large scale use. Microbes belonging to this group are also known as plant growth promoting rhizobacteria (PGPR) and were reported to improve availability of plant nutrient and support plant development under natural or stressed conditions as well as increase yield and quality. Although beneficial microbes have not been widely researched or used for improving yield and quality of strawberry, a large body of evidence indicates that many available beneficial microbes were found to provide growth and yield enhancement to diverse crop commodities [10–12], which can be tested for similar efficacy on strawberry and thus may play a crucial role in sustainable strawberry production in the future. A significant body of literature suggests that these microbes can increase strawberry fruit quality in terms of taste and nutritional value and thereby have a positive impact on human health with associated reduction of healthcare costs [13, 14]. A few relevant examples of positive effects of antagonistic microbes on multiple crops include protection against *Verticillium dahliae* [62] and protection of tomato

*Strawberry - Pre- and Post-Harvest Management Techniques for Higher Fruit Quality*

from postharvest losses due to microbial infections [51, 54]. In addition, many investigators reported that chitosan use as a foliar spray increased vegetative growth,

yield, and biochemical contents in plants [55–58]. Improvement of yield and functional properties of strawberry fruit through application of chitosan should be considered a sustainable option. A recent study by Rahman et al. [58] showed that multiple application of low concentrations (ppm level) of chitosan on the canopy of field grown strawberry plants at the prebloom stage significantly improved growth and yield. Authors also reported concurrent increase in various antioxidant contents and total antioxidant activities in treated fruit compared to nontreated control. This is an interesting and significant finding as total antioxidants and pigments such as anthocyanins are determinants of health benefits of strawberry fruit. Rahman et al. [58] also determined the effect of different doses of chitosan biopolymer on growth, fruit yield, and human health benefiting antioxidant properties of strawberry and found that both yield and contents of antioxidants are increased in a dose-dependent manner to some extent compared to untreated control. These findings indicate that the biostimulant chitosan can be an attractive agent for production of high quality and human health benefiting strawberry [58]. Results also indicated that foliar application of varying doses of chitosan on strawberry canopy stimulated all aspects of vegetative growth (plant height and root length) that may have influenced fruit yield and fruit quality compared with untreated control (**Table 3**). These findings were also interesting as all doses of chitosan improved growth of strawberry plants to some extent and may be experimented in similar crops being grown in soils with varying physical, chemical, and biological characteristics. This study was one of the few of its kind that determined the effects of natural products such as chitosan application on field-grown strawberry plants influencing yield and contents of multiple antioxidants in fruit. Experimental protocol for this study can be found in

Among a few different chitosan concentrations tested in the study, 500 ppm provided the highest fruit yield (42% higher than untreated control) in "Strawberry Festival" compared with untreated control (**Table 3**). Similar to yield response and a few other antioxidants, chitosan spray application on the canopy of strawberry also significantly increased fruit anthocyanin contents in a dose-dependent manner that plateaued at 500 ppm with 184.3 mg cyanidin-3-*O*-glucoside/100 g fruit. This increase of anthocyanin contents was equivalent to 2.3-fold higher compared

> **Total fruit weight/ plant (g)**

Control 19.5 ± 1.0b 19.25 ± 0.4c 246.6 ± 0.4d 81.11 ± 0.9d 310.4 ± 0.7c 250.9 ± 0.9c Ch 125 20.41 ± 0.9b 21.16 ± 0.2bc 317.5 ± 0.7c 83.1 ± 1.0cd 356.5 ± 1.0b 252.6 ± 1.0c Ch 250 21.75 ± 0.8b 22.66 ± 0.7ab 325.7 ± 0.5c 94.6 ± 0.5c 317.8 ± 0.5c 358.6 ± 1.0b Ch 500 25.1 ± 1.0a 24.33 ± 0.2a 351.25 ± 0.5a 184.3 ± 1.9a 363.2 ± 0.4ab 374.42 ± 1.0b Ch 1000 24.91 ± 1.5a 24.16 ± 0.6a 337.7 ± 0.4b 163.9 ± 0.6b 370.9 ± 0.4a 415.6 ± 0.5a *Five different concentrations, 0, 125, 250, 500, and 1000 ppm, of chitosan solution were prepared by dissolving the required amount in 0.1 N HCl and diluting with distilled water with pH adjusted at 6.5 by NaOH. Freshly prepared chitosan solutions were applied onto strawberry plants in each experimental unit prior to flowering and at 10% flowering stage by spraying up to run off at five different times with 10-d intervals. Cumulative fruit harvest from each plot was recorded. The required amounts of fruit tissues from first harvest were subjected to analyses for phenolics and other antioxidants mentioned in the table. Values are means ± standard errors of three independent replications (n = 3). Different superscripted letters within the column indicate statistically significant differences among the treatments according to Fisher's protected LSD (least significance difference) test at p* ≤ *0.05, adapted from [58].*

**Total anthocyanin content**

**Total phenolic content**

**Total antioxidant activity**

**86**

**Table 3.**

Rahman et al. [58].

**Treatment Plant** 

**height (cm)**

**Root length (cm)**

*Effect of chitosan application on yield and content of antioxidants in strawberry fruit.*

against *Alternaria solani* [63]. Some of these microbes were used in vitro and should be evaluated in vivo or in field conditions. For example, in vitro-beneficiallybacterized plantlets of grapevine not only grew faster than non-bacterized controls but also were sturdier, with a better developed root system and significantly greater capacity for withstanding gray mold fungus [64]. Similarly, banana plantlets treated with endophytes *Pseudomonas* and *Bacillus* species showed improved vegetative growth, physiological attributes, and strong defense against bunchy top diseases in the field [65, 66]. Seed treatment or augmenting beneficial microbial population in soil was also found to reduce seedling mortality from soil-borne diseases [67]. Biological agents such as *Trichoderma, Serratia,* and *Pseudomonas* and different plant extracts are some of the alternative strategies that have been explored to reduce the number of microsclerotia or wilt symptoms in multiple crops [65, 68–72]. A few studies also showed that application of beneficial bacteria significantly improved seed germination, seedling vigor, growth, yield, and early blight disease protection in tomato through multiple mechanisms including production of growth regulators and induced biosynthesis of antioxidant peroxidase and polyphenol oxidase [63]. Although many different strains of microbes belonging to multiple genera and species have been identified and tested for their efficacy, major genera of PPBs include *Bacillus*, *Paraburkholderia*, *Pseudomonas*, *Acinetobacter*, *Alcaligenes*, *Arthrobacter*, and *Serratia*. Major modes of action by which PPB provide beneficial effects to host plants include production of growth promoting hormones, antibiotics, and lytic enzymes that affect harmful microbes, nitrogen fixation from the atmosphere, nutrient solubilization from soil minerals for plant availability, and systemic resistance induction in the host or treated plants. Two PPB, *Bacillus amyloliquefaciens* and *Paraburkholderia fungorum* applied on strawberry by Rahman et al. [73] not only increased yield but also significantly improved contents of several antioxidants and total antioxidant activities of fruits. Treatments of strawberry plants with bacterial strains *B. amyloliquefaciens* and *P. fungorum* consistently produced higher antioxidants, carotenoids, flavonoids, phenolics, and total anthocyanins compared to nontreated control [73]. Flores-Félix [14] reported that application of a strain of genus *Phyllobacterium* on strawberry showed significant increase in vitamin C contents in fruits.

A recent study [73] explored an environment-friendly option for boosting strawberry plant growth, fruit yield, and functional properties of fruits through the application of two plant growth promoting probiotic bacteria and compared the results with that of nontreated control. Results showed significant improvement in plant growth, yield, various antioxidant contents, and total antioxidant activities of strawberry fruits by the application of both *B. amyloliquefaciens* BChi1 and *P. fungorum* BRRh-4 treatment compared to nontreated control. Inoculation of strawberry plants separately with two bacterial isolates significantly increased vegetative growth (plant height and root length) of the strawberry plants (**Table 4**). Generally, plant growth promoting rhizobacteria facilitate plant growth directly by either assisting in resource acquisition (nitrogen, phosphorus, and essential minerals) or modulating plant hormone levels, or indirectly by inhibiting various pathogens as biocontrol agents [11]. Early colonization of root system has the potential to preclude pathogen colonization and infection in addition to induction of disease resistance or a range of beneficial secondary metabolites. Plant height and root length also were positively influenced and varied significantly due to the plant probiotic bacterial applications. The highest plant height (20.50 cm) was observed in BRRh-4 treated plants (**Table 4**). Similar to plant height, root length also significantly (*p* < 0.05) varied among the treatments and was reflected by plant vigor (**Figure 1**). A hypothetical pathway of strawberry growth, yield, and fruit quality improvement is shown in **Figure 2**. Results from this study indicated that vegetative

**89**

**Figure 1.**

*Festival. Adapted from [58, 73].*

*Improving Yield and Antioxidant Properties of Strawberries by Utilizing Microbes and Natural…*

**Total fruit weight/plant (g)**

Control 18.6 ± 1.01a 19.3 ± 0.43b 316.6 ± 10.06b 81.1 ± 0.5b 317.1 ± 7.3b 250.9 ± 3.1b BChi1\* 119.3 ± 0.86a 22.7 ± 0.33a 453.0 ± 2.2a 187.5 ± 16.9a 377.8 ± 1.7a 382.0 ± 1.4a BRRh-4 20.5 ± 0.26a 23.5 ± 1.15a 467.8 ± 2.2a 223.0 ± 3.6a 380.5 ± 5.1a 385.5 ± 3.4a *Cumulative fruit harvest from each plot was recorded. The required amounts of fruit tissues from first harvest were subjected to analyses for phenolics and other antioxidants mentioned in the table. Values are means ± standard errors of three independent replications (n = 3). Different superscripted letters within the column indicate statistically significant differences among the treatments according to Fisher's protected LSD (least significance difference) test at* 

**Total anthocyanin content**

**Total phenolic content**

**Total antioxidant activity**

growth enhancement by probiotic bacteria may have also enhanced fruit yield and quality, enhancing secondary metabolites such as anthocyanins, phenolics, and total antioxidant activity (**Table 4**). Strawberry fruit from Paraburkholderia fungorum BRRh-4 and Bacillus amyloliquefaciens BChi1 treated plants had total phenolic content 380.5 and 377.72 μg gallic acid/g fruit, respectively compared with 317.08 μg gallic acid/g fruit in untreated control plants. Detailed experimental protocol can be

One of the interesting findings of this study is that both plant probiotic bacteria significantly improved growth and yield of strawberry almost at the same level with some minor differences although they belong to different bacterial genera. Probiotic bacterium, BRRh-4 provided the highest fruit yield increase (48%) in plants of "Strawberry Festival" compared to nontreated control (**Table 4**). Treatments of strawberry plants with bacterial strains BRRh-4 and BChi1 consistently produced higher antioxidants, carotenoids, flavonoids, phenolics, and total anthocyanins compared to nontreated control [73]. A previous study showed that the members of the genus *Phyllobacterium* were good plant probiotics with the capacity of increasing fruit yield as well as quality [14]. Application of plant probiotic bacteria significantly increased total anthocyanin content in strawberry

*Effect of different doses of chitosan and probiotic bacteria on vegetative and reproductive growth of cv. Strawberry* 

*DOI: http://dx.doi.org/10.5772/intechopen.84803*

**Root length (cm)**

*Effect of plant probiotic bacteria on yield and antioxidant content in strawberry fruit.*

**height (cm)**

**Treatment Plant** 

*p* ≤ *0.05, adapted from [73].*

**Table 4.**

found in a study by Rahman et al. [73].

*Improving Yield and Antioxidant Properties of Strawberries by Utilizing Microbes and Natural… DOI: http://dx.doi.org/10.5772/intechopen.84803*


*Cumulative fruit harvest from each plot was recorded. The required amounts of fruit tissues from first harvest were subjected to analyses for phenolics and other antioxidants mentioned in the table. Values are means ± standard errors of three independent replications (n = 3). Different superscripted letters within the column indicate statistically significant differences among the treatments according to Fisher's protected LSD (least significance difference) test at p* ≤ *0.05, adapted from [73].*

#### **Table 4.**

*Strawberry - Pre- and Post-Harvest Management Techniques for Higher Fruit Quality*

produced higher antioxidants, carotenoids, flavonoids, phenolics, and total anthocyanins compared to nontreated control [73]. Flores-Félix [14] reported that application of a strain of genus *Phyllobacterium* on strawberry showed significant

A recent study [73] explored an environment-friendly option for boosting strawberry plant growth, fruit yield, and functional properties of fruits through the application of two plant growth promoting probiotic bacteria and compared the results with that of nontreated control. Results showed significant improvement in plant growth, yield, various antioxidant contents, and total antioxidant activities of strawberry fruits by the application of both *B. amyloliquefaciens* BChi1 and *P. fungorum* BRRh-4 treatment compared to nontreated control. Inoculation of strawberry plants separately with two bacterial isolates significantly increased vegetative growth (plant height and root length) of the strawberry plants (**Table 4**). Generally, plant growth promoting rhizobacteria facilitate plant growth directly by either assisting in resource acquisition (nitrogen, phosphorus, and essential minerals) or modulating plant hormone levels, or indirectly by inhibiting various pathogens as biocontrol agents [11]. Early colonization of root system has the potential to preclude pathogen colonization and infection in addition to induction of disease resistance or a range of beneficial secondary metabolites. Plant height and root length also were positively influenced and varied significantly due to the plant probiotic bacterial applications. The highest plant height (20.50 cm) was observed in BRRh-4 treated plants (**Table 4**). Similar to plant height, root length also significantly (*p* < 0.05) varied among the treatments and was reflected by plant vigor (**Figure 1**). A hypothetical pathway of strawberry growth, yield, and fruit quality improvement is shown in **Figure 2**. Results from this study indicated that vegetative

increase in vitamin C contents in fruits.

against *Alternaria solani* [63]. Some of these microbes were used in vitro and should be evaluated in vivo or in field conditions. For example, in vitro-beneficiallybacterized plantlets of grapevine not only grew faster than non-bacterized controls but also were sturdier, with a better developed root system and significantly greater capacity for withstanding gray mold fungus [64]. Similarly, banana plantlets treated with endophytes *Pseudomonas* and *Bacillus* species showed improved vegetative growth, physiological attributes, and strong defense against bunchy top diseases in the field [65, 66]. Seed treatment or augmenting beneficial microbial population in soil was also found to reduce seedling mortality from soil-borne diseases [67]. Biological agents such as *Trichoderma, Serratia,* and *Pseudomonas* and different plant extracts are some of the alternative strategies that have been explored to reduce the number of microsclerotia or wilt symptoms in multiple crops [65, 68–72]. A few studies also showed that application of beneficial bacteria significantly improved seed germination, seedling vigor, growth, yield, and early blight disease protection in tomato through multiple mechanisms including production of growth regulators and induced biosynthesis of antioxidant peroxidase and polyphenol oxidase [63]. Although many different strains of microbes belonging to multiple genera and species have been identified and tested for their efficacy, major genera of PPBs include *Bacillus*, *Paraburkholderia*, *Pseudomonas*, *Acinetobacter*, *Alcaligenes*, *Arthrobacter*, and *Serratia*. Major modes of action by which PPB provide beneficial effects to host plants include production of growth promoting hormones, antibiotics, and lytic enzymes that affect harmful microbes, nitrogen fixation from the atmosphere, nutrient solubilization from soil minerals for plant availability, and systemic resistance induction in the host or treated plants. Two PPB, *Bacillus amyloliquefaciens* and *Paraburkholderia fungorum* applied on strawberry by Rahman et al. [73] not only increased yield but also significantly improved contents of several antioxidants and total antioxidant activities of fruits. Treatments of strawberry plants with bacterial strains *B. amyloliquefaciens* and *P. fungorum* consistently

**88**

*Effect of plant probiotic bacteria on yield and antioxidant content in strawberry fruit.*

growth enhancement by probiotic bacteria may have also enhanced fruit yield and quality, enhancing secondary metabolites such as anthocyanins, phenolics, and total antioxidant activity (**Table 4**). Strawberry fruit from Paraburkholderia fungorum BRRh-4 and Bacillus amyloliquefaciens BChi1 treated plants had total phenolic content 380.5 and 377.72 μg gallic acid/g fruit, respectively compared with 317.08 μg gallic acid/g fruit in untreated control plants. Detailed experimental protocol can be found in a study by Rahman et al. [73].

One of the interesting findings of this study is that both plant probiotic bacteria significantly improved growth and yield of strawberry almost at the same level with some minor differences although they belong to different bacterial genera. Probiotic bacterium, BRRh-4 provided the highest fruit yield increase (48%) in plants of "Strawberry Festival" compared to nontreated control (**Table 4**). Treatments of strawberry plants with bacterial strains BRRh-4 and BChi1 consistently produced higher antioxidants, carotenoids, flavonoids, phenolics, and total anthocyanins compared to nontreated control [73]. A previous study showed that the members of the genus *Phyllobacterium* were good plant probiotics with the capacity of increasing fruit yield as well as quality [14]. Application of plant probiotic bacteria significantly increased total anthocyanin content in strawberry

#### **Figure 1.**

*Effect of different doses of chitosan and probiotic bacteria on vegetative and reproductive growth of cv. Strawberry Festival. Adapted from [58, 73].*

#### **Figure 2.**

*A hypothetical pathway of stimulation of fruit yield and accumulation of antioxidants in strawberry fruit due to the root colonization by probiotic bacteria.*

fruits compared to nontreated control. The highest anthocyanin content (222.0 mg cyanidin-3-*O*-glucoside/100 g fruit) in strawberry fruits was recorded in plants treated with BRRh-4 followed by BChi1 (187.47 mg cyanidin-3-*O*-glucoside/100 g fruit). To evaluate whether plant probiotic bacteria had any effect on antioxidant activities of strawberry fruits obtained from both probiotic bacteria and nontreated control plants, we estimated total antioxidant activities of fresh strawberry fruits by DPPH assay. The results of the DPPH assay for total antioxidant activity were expressed as butylated hydroxytoluene (BHT) equivalents per gram of strawberry fruit. As expected, the total antioxidant activity of fresh strawberry fruits was the highest in BRRh-4 (385.47 μg BHT/g fruit) followed by BChi1 treatment (382.00 μg BHT/g fruit) (**Table 4**) [73].

#### **4.1 Bio-rational/natural product-based approach for strawberry root disease management for boosting yield**

The strawberry black root rot complex (BRRC) and crown rot are increasing problems in perennial strawberry plantings worldwide and have been identified as limiting factors of sustainable strawberry production [74, 75]. Yield loss from black root rot alone can range from 20 to 50% [76], which can dramatically increase if crown rot occurs concurrently. Because several factors are involved in BRRC of strawberry, including a range of infectious agents (nematodes and root infecting fungi) and various abiotic factors such as poor soil characteristics [77], the disease control is complicated, and no general control measure is completely effective. On the other hand, crown rot disease of strawberry caused primarily by the fungal species *Colletotrichum gloeosporioides* and *Phytophthora cactorum* [78] can sometimes also incur significant yield loss in strawberry production in the US and other strawberry growing countries [78]. Although inoculum sources for crown rot in fruiting fields may be diverse, infected planting stock is the

**91**

activity [102].

for maximum ITC release.

*Improving Yield and Antioxidant Properties of Strawberries by Utilizing Microbes and Natural…*

most important source of C*. gloeosporioides* [79–83] whereas *P. cactorum* is mostly soil-borne and builds up in a strawberry field over time. Occurrence of crown rot caused by *Fusarium oxysporum* f.sp. *fragariae* is also on the rise. Mass [84] observed that in many cases where crop rotation was not an option, fumigation of soil was necessary to control soil-borne diseases. Methyl bromide (MeBr) was previously used as a preplant broad-spectrum soil fumigant to control soil-borne diseases, nematodes, insects, and weeds in high value crop such as strawberry [85]. However, with the disappearance of this highly effective soil fumigant MeBr, and restrictions on the allowed use of other alternative synthetic fumigants, the interest in the development of safe, sustainable, and economically viable fumigation strategies have increased to manage soil-borne fungi and nematodes [85]. More importantly, the demands from organic growers and small growers who cannot use synthetic fumigants have increased tremendously [86]. Alternative strategies are also required especially for strawberries as disease-resistant cultivars are unavailable [87]. Among multiple alternatives of soil fumigation with synthetic chemicals, glucosinolate-containing Brassica spp. is known to release volatile isothiocyanates (ITCs), which are toxic to different pathogens [88]. The chemistry involved in the biofumigation can be attributed to the action of myrosinase enzyme on the glucosinolates (GLS) to release ITCs, thiocyanates, nitriles, oxazolidine, dimethyl sulfide, and methanethiol, among other compounds [88, 89]. Several lines of evidence suggest that biofumigation with ITC-producing plants have shown promising results against soil-borne fungal pathogens, for example, *Rhizoctonia*, *Verticillium*, *Fusarium, Pythium,* and *Phytophthora* spp. [90–92]. However, the concentration of ITCs produced is influenced by mustard variety [93], soil texture, moisture, temperature, microbial community, and pH [94, 95], resulting in variable soil-borne disease control efficacy. From a NE-SARE funded project in the U.S., Balzano [93] found the highest glucosinolate content and biomass in "Caliente-199." While these observations indicate a need for selecting the right variety, site-specific testing, optimization of the method such as selection of the best growth stage (highest content of glucosinolate), optimum tissue disruption, and quick soil incorporation may also play a significant role. This is crucial for the success of this approach as laboratory experiments indicated that the efficacy of the conversion to ITCs was only 5% of the potential when using tissue disruption methods (cutting and chopping) similar to those frequently used under field conditions [95, 96]. Matthiessen et al. [97] were able to increase soil ITC levels by 20-fold (100 nmol per g soil) using a tractor-drawn tissue pulverizing implement compared to when using a cutting and chopping implement. In addition, they showed that adding excess water to the pulverized tissue was necessary

Another promising nonchemical soil-borne disease control alternative is anaerobic soil disinfestation (ASD), which was adapted from the previously described methods of biological soil disinfestation (BSD) and soil reductive sterilization [98, 99] to create a treatment suitable for strawberry [100]. A wide range of soil-borne plant pathogens and plant parasitic nematodes have been controlled in a variety of crops using ASD [100]. Implementation of ASD is done in three different steps. First, a labile carbon source is added to the soil followed by the generation of anaerobic conditions through application of water to fill soil pore space. In the third step, the soil is covered with plastic mulch to prevent oxygen exchange. The exact mechanisms that lead to disease suppression with ASD are not clearly understood but may involve production of organic acids and other biologically active volatiles [101] and amplification of specific microbes with biocontrol

*DOI: http://dx.doi.org/10.5772/intechopen.84803*

#### *Improving Yield and Antioxidant Properties of Strawberries by Utilizing Microbes and Natural… DOI: http://dx.doi.org/10.5772/intechopen.84803*

most important source of C*. gloeosporioides* [79–83] whereas *P. cactorum* is mostly soil-borne and builds up in a strawberry field over time. Occurrence of crown rot caused by *Fusarium oxysporum* f.sp. *fragariae* is also on the rise. Mass [84] observed that in many cases where crop rotation was not an option, fumigation of soil was necessary to control soil-borne diseases. Methyl bromide (MeBr) was previously used as a preplant broad-spectrum soil fumigant to control soil-borne diseases, nematodes, insects, and weeds in high value crop such as strawberry [85]. However, with the disappearance of this highly effective soil fumigant MeBr, and restrictions on the allowed use of other alternative synthetic fumigants, the interest in the development of safe, sustainable, and economically viable fumigation strategies have increased to manage soil-borne fungi and nematodes [85]. More importantly, the demands from organic growers and small growers who cannot use synthetic fumigants have increased tremendously [86]. Alternative strategies are also required especially for strawberries as disease-resistant cultivars are unavailable [87]. Among multiple alternatives of soil fumigation with synthetic chemicals, glucosinolate-containing Brassica spp. is known to release volatile isothiocyanates (ITCs), which are toxic to different pathogens [88]. The chemistry involved in the biofumigation can be attributed to the action of myrosinase enzyme on the glucosinolates (GLS) to release ITCs, thiocyanates, nitriles, oxazolidine, dimethyl sulfide, and methanethiol, among other compounds [88, 89]. Several lines of evidence suggest that biofumigation with ITC-producing plants have shown promising results against soil-borne fungal pathogens, for example, *Rhizoctonia*, *Verticillium*, *Fusarium, Pythium,* and *Phytophthora* spp. [90–92]. However, the concentration of ITCs produced is influenced by mustard variety [93], soil texture, moisture, temperature, microbial community, and pH [94, 95], resulting in variable soil-borne disease control efficacy. From a NE-SARE funded project in the U.S., Balzano [93] found the highest glucosinolate content and biomass in "Caliente-199." While these observations indicate a need for selecting the right variety, site-specific testing, optimization of the method such as selection of the best growth stage (highest content of glucosinolate), optimum tissue disruption, and quick soil incorporation may also play a significant role. This is crucial for the success of this approach as laboratory experiments indicated that the efficacy of the conversion to ITCs was only 5% of the potential when using tissue disruption methods (cutting and chopping) similar to those frequently used under field conditions [95, 96]. Matthiessen et al. [97] were able to increase soil ITC levels by 20-fold (100 nmol per g soil) using a tractor-drawn tissue pulverizing implement compared to when using a cutting and chopping implement. In addition, they showed that adding excess water to the pulverized tissue was necessary for maximum ITC release.

Another promising nonchemical soil-borne disease control alternative is anaerobic soil disinfestation (ASD), which was adapted from the previously described methods of biological soil disinfestation (BSD) and soil reductive sterilization [98, 99] to create a treatment suitable for strawberry [100]. A wide range of soil-borne plant pathogens and plant parasitic nematodes have been controlled in a variety of crops using ASD [100]. Implementation of ASD is done in three different steps. First, a labile carbon source is added to the soil followed by the generation of anaerobic conditions through application of water to fill soil pore space. In the third step, the soil is covered with plastic mulch to prevent oxygen exchange. The exact mechanisms that lead to disease suppression with ASD are not clearly understood but may involve production of organic acids and other biologically active volatiles [101] and amplification of specific microbes with biocontrol activity [102].

*Strawberry - Pre- and Post-Harvest Management Techniques for Higher Fruit Quality*

fruits compared to nontreated control. The highest anthocyanin content (222.0 mg cyanidin-3-*O*-glucoside/100 g fruit) in strawberry fruits was recorded in plants treated with BRRh-4 followed by BChi1 (187.47 mg cyanidin-3-*O*-glucoside/100 g fruit). To evaluate whether plant probiotic bacteria had any effect on antioxidant activities of strawberry fruits obtained from both probiotic bacteria and nontreated control plants, we estimated total antioxidant activities of fresh strawberry fruits by DPPH assay. The results of the DPPH assay for total antioxidant activity were expressed as butylated hydroxytoluene (BHT) equivalents per gram of strawberry fruit. As expected, the total antioxidant activity of fresh strawberry fruits was the highest in BRRh-4 (385.47 μg BHT/g fruit) followed by BChi1 treatment (382.00 μg

*A hypothetical pathway of stimulation of fruit yield and accumulation of antioxidants in strawberry fruit due* 

**4.1 Bio-rational/natural product-based approach for strawberry root disease** 

The strawberry black root rot complex (BRRC) and crown rot are increasing problems in perennial strawberry plantings worldwide and have been identified as limiting factors of sustainable strawberry production [74, 75]. Yield loss from black root rot alone can range from 20 to 50% [76], which can dramatically increase if crown rot occurs concurrently. Because several factors are involved in BRRC of strawberry, including a range of infectious agents (nematodes and root infecting fungi) and various abiotic factors such as poor soil characteristics [77], the disease control is complicated, and no general control measure is completely effective. On the other hand, crown rot disease of strawberry caused primarily by the fungal species *Colletotrichum gloeosporioides* and *Phytophthora cactorum* [78] can sometimes also incur significant yield loss in strawberry production in the US and other strawberry growing countries [78]. Although inoculum sources for crown rot in fruiting fields may be diverse, infected planting stock is the

**90**

BHT/g fruit) (**Table 4**) [73].

*to the root colonization by probiotic bacteria.*

**Figure 2.**

**management for boosting yield**
