**6. Disease management**

The management of diseases caused by *P. capsici* may be very difficult and economically expensive, especially due to the excessive use of oomyceticides (formerly called fungicides). However, there are different alternatives which used in an integrated manner during the pre-sowing, production and post-harvest stages could reduce damage and losses in *Capsicum* crops. These alternatives are: the use of resistant cultivars, well-drained soils, crop rotation, soil treatments, tillage methods, irrigation control, improvement of irrigation water quality, and use of plastic mulches [12]. In any case, the infection of different plant organs of *Capsicum* (**Figure 2**) by

Phytophthora capsici *on* Capsicum *Plants: A Destructive Pathogen in Chili and Pepper Crops DOI: http://dx.doi.org/10.5772/intechopen.104726*

*P. caspici* makes the integrated implementation of measures by farmers, complex but worthwhile [16, 18].

### **6.1 Genetic control**

Obtaining resistant germplasm of *Capsicum* to *P. capsici* is a complex task, requiring different breeding techniques and germplasm screening including landraces as sources of resistance [9]. So far there are some resistant commercial cultivars such as Nathalie, Paladin, Ungara, Violeta, Ayesha, Violeta 1, Sempurna, and Ayesha Ungu, which are being used worldwide [3, 51]. Likewise, there are different resistant landraces such as CM-334, (*C. annuum*) ECU-12831 (*C. baccatum*), ECU-9129, (*C. chinense*) Code 5 (*C. frutescens*), ECU-1296 (*C. frutescens*), found in Ecuador and Mexico [3, 62] that could be used in breeding programs.

In one hand, *P. capsici* has developed different mechanisms to attack plants and to obtain its necessary nutrients, while on the other hand, plants have developed a complex defense system that prevents the entry or limits the advance of the oomycete in plant tissue, including physical, biochemical and molecular mechanisms [13, 14, 63]. One of the first barriers in pepper plants (*C. annuum*) limiting *P. capsici* infection is a thick cell wall and a high content of phenolics and flavonoids [16], such as the soluble phenols chlorogenic acid, luteolin glycoside, apiosil glucoside of luteolin, and aglycone apigenin [64, 65]. Other mechanisms include the synthesis of antimicrobial phytoalexins, the induction of hydrolytic enzymes such as chitinase and glucanase, and the production of proteins rich in hydroxyproline, reactive oxygen species (ROS), and capsidiol [66, 67]. Regarding the latter mechanism, this *Capsicum* phytoalexin could inhibit oomycete development [66, 67]. These and other mechanisms make *Capsicum* plants prevent or considerably delay the infection, colonization and reproduction of *P. capsici* in the different subterranean or aerial tissues.

### **6.2 Biological control**

The current need to consume healthy foods, free of synthetic-pesticide residues [68], has led to the promotion of alternatives such as the use of effective biological control agents i.e. *Bacillus* spp., *Trichoderma* spp., among others, which if used under suitable climatic conditions will contribute significantly and economically to the prevention and management of diseases caused by *P. capsici*, in addition to promoting the growth of *Capsicum* [69, 70].

The use of microorganisms such as *Bacillus* spp. and *Trichoderma* spp. are highly valuable alternatives for the management of diseases caused by *P. capsici*. Under laboratory and green house conditions, *Bacillus amyloliquefaciens* (strain PsL) can reduce the mycelial growth of *P. capsici* by up to 46%, in addition to the growth promotion of *P. capsici* pepper plants [70]. *Bacillus subtilis* (isolates R13 and R33) can reduce the incidence of foliar blight between 71 and 87% [23]. *In vitro* and *in vivo* experiments of native *Trichoderma* strains against *P. capsici* isolates in *C. pubescens* plants, showed that *T. harzianum* inhibits the radial growth of the phytopathogen by 43%, and reduces plant mortality by 10% at 20 DAI [71].

Endophytic microorganisms can also be used in biological control. Some of them such as *Nigrospora sphaerica*, *Enterobacter* sp. and *Dothideales* sp. have been used as biocontrollers of pathogens affecting *C. annuum*, such as *P. capsici* [72]. *Nigrospora sphaerica* (isolate A22F1) was used to control *P capsici* in susceptible seedlings of *C. annuum* (cvs. California Wonder, Numex spring and Pepper cayene), observing

a considerable reduction in root rot compared to control. Recently, a metagenomic study [73] found different fungal species that are used in the biological control of phytopathogens associated with the mycobiome of resistant and susceptible hypocotyls, infected or not with *P. capsici*.

### **6.3 Cultural control**

Cultural control is based on the use of measures that favor the development of the crop, and at the same time, affecting the phytopathogen, in order to reduce the intensity of the disease [74]. Strategies include limiting soil saturation, water accumulation in plots, and movement of infected plant debris or infested soil within a field [18]. Crop rotation is another very important aspect to consider because it affects the survival of the phytopathogen and the host range [26] e.g. crop rotation for 3 years can considerably reduce the propagules (mainly oospores) of *P. capsici*, which have the ability to remain in the soil for long periods of time [16, 22].

### **6.4 Chemical control**

The use of oomyceticides (previously called fungicides) is common in the management of diseases caused by *P. capsici* in *Capsicum* plants (Table 1), especially those that contain molecules with a direct mode of action on the phytopathogen [75]. The efficacy of these oomyceticides, of synthetic origin, has been demonstrated under laboratory and field conditions. For example, Mancozeb 64% + Metalaxyl 4% (7.5 g L-1) or Copper sulfate pentahydrate (2.5 mL L-1) applied to the soil, and Potassium phosphonate (5 mL L-1) applied to the leaf area, can totally reduce the incidence of root and crown rot [47]. Also, the use of Fosetil Aluminum (2.5 kg ha-1) applied to the soil (drench) can reduce up to 100% of wilting in pepper plants [76]. Other molecules such as ametoctradine + dimethomorph, cyazofamid, dimethomorph, famoxadon + cymoxanil, fluazinam, fluopicolide, mandipropamide, mefenoxam, phosphonates, and zoxamide + mancozeb, can also be used to control damping-off, leaf blight and fruit rot [26].

Despite the success achieved over the years with the use of chemical control, the inappropriate use of molecules has made some *P. capsici* isolates insensitive to commercial oomyceticides such as metalaxyl and mefenoxam [77, 78]. A solution to reduce these effects on the oomycete is the use of active ingredients such as mandipropamide and dimethomorph, considered molecules with low to medium risk of resistance [79, 80]. In order to reduce the selection pressure by the phytopathogen, the farmer must have a wide range of molecules applied in periodic and scheduled rotation during each crop cycle [81], and even use mixtures that have systemic and protective modes of action.

### **6.5 Integrated disease management**

Integrated disease management (IDM) aims to minimize the biological activity of the pathogen and increase crop productivity, involving the use of various techniques in favor of the environment by avoiding the excessive use of chemical molecules and reducing control costs of *P. capsici* [80]. To effectively manage diseases caused by *P. capsici* in *Capsicum,* different management strategies should be integrated in either agroecological, conventional or other production systems [81]. Usually a single strategy is ineffective for the management of *P. capsici* [80]; for this, IDM is based on

Phytophthora capsici *on* Capsicum *Plants: A Destructive Pathogen in Chili and Pepper Crops DOI: http://dx.doi.org/10.5772/intechopen.104726*

immunization, exclusion, eradication and crop protection mainly including soil and plant management through soil amendments, solarization, crop cover, water treatment, seed treatment (with a biofungicide to improve germination and reduce the incidence of damping-off), and others [82–84].
