**5. Disease cycle of** *Phytophthora capsici*

Every disease begins with the survival of the phytopathogen (source of primary inoculum); in the case of *P. capsici* (**Figure 4**) the mycelium can survive in the soil and cultural debris, or in the weeds that serve as facultative hosts. Besides, the oospores

### **Figure 4.**

*Biological cycle of* Phytophthora capsici *causing root, crown and fruit rot, and foliar blight in* Capsicum *plants. This figure was developed with the help of the BioRender platform. Source: Unpublished photographs from the authors.*

can persist for long periods in the soil [16, 53, 54]. From these structures, sporangia are formed, which spread towards the tissues of the host located in near or distant crops, mainly through water (rainfall or irrigation) [18]. Under conditions of high relative humidity and between 27 and 32°C, the sporangia release motile biflagellate zoospores that swim through the irrigation water until they reach plant tissues [12, 55]. Although it is mentioned that the wind is also a disseminating factor of the pathogen [56], this is not fully accepted yet.

Sporangia can germinate directly on the plant surface, forming a germ tube that penetrates the anticlinal walls of rhizodermal cells [12]. Likewise, they can do it indirectly through zoospores released from the interior of sporangia that encyst on the surface of root, crown and leaf tissues, subsequently producing a germ tube, and finally an appressorium used to penetrate epidermal cells [55–57]. *Phytophthora capsici* is a hemibiotrophic phytopathogen, which initially presents a biotrophic lifestyle, followed by a necrotrophic phase [58]. In fact, once the penetrating hyphae of the oomycete enter plant tissues intercellularly, these structures form haustoria to remove nutrients from the cells [57, 58]. Subsequently, vegetative hyphae and haustoria are formed in the form of lateral branches that colonize intracellularly and epicuticularly [27]. Finally*, P. capsici* intensely colonizes epidermal, vascular (phloem, xylem) and parenchymal cells [16]. Both the infection and colonization processes (latent period) can last between four and seven days [3].

The last phase of the primary cycle of the disease is completed with the reproduction of the pathogen, which occurs on the external surface of the host. *Phytophthora capsici* is a heterothallic species that has one of two mating types called A1 and A2, producing a male gametangium (antheridium) and a female gametangium (oogonium), resulting in sexual spores called oospores, with thick walls adapted to survive winter and unfavorable weather conditions [30, 55, 59]. These reproductive structures go through a rest period and serve for the survival of the phytopathogen [53]. There is also asexual reproduction that is characterized by the formation of sporangia from branched sporangiophores [30, 55]. The production of sporangia occurs between 25 and 30°C, under conditions of high relative humidity, and ≈90 hours after infection, which will produce zoospores by cytoplasmic cleavage [24, 55].

Although root and crown rot are monocyclic diseases, others such as leaf blight and fruit rot would be polycyclic. Thus, the sporangia of *P. capsici* would function as a secondary inoculum [53, 57]. These structures or propagules would reach the aerial tissues through water splashes, initiating a new infectious cycle [53, 60, 61], repeating the previously mentioned phases of infection, colonization and reproduction. The ability of the phytopathogen to reach practically all plant tissues makes its management complex.
