*2.2.1.11 Symptoms of shoot wilt in areca nut*

The crown leaves wilt suddenly, the color of the leaves becomes dull, the tips of the leaves turn brown, and the leaf midrib hangs and finally falls.

#### *2.2.1.12 Symptoms disease of bacterial leaf stripe in areca nut*

The fungus *Xanthomonas campestris* Areca is known to be present in areca nut infections. Symptoms of the disease arise in the form of yellowish or dark green spots on the leaf blade, the underside of the leaf surface is covered by bacterial colonies, and yellowish leaf twigs, in the end, the leaf arrangement grows irregularly and is grayish white. The crown of the tree resembles a rose.

#### *2.2.1.13 Symptoms disease of stem bleeding in areca nut*

Symptoms of this disease can be observed in stems that change color to dark red, stem tissue secretes dark brown fluid, yellowish spots on leaf blades, roots turn yellowish brown and rot is not uncommon. Another symptom of the fruit shows a change in color

#### **Figure 7.**

*Symptoms of leaf blight on areca nut: (A) symptoms of brown spot on leaves, (B) colony morphology of*  Pestalotia palmarum *Cooke., (C) conidia of* P. palmarum *[11].*

to dark green. This disease is known to be caused by the fungus *Thielaviopsis paradoxa*. Von Hohn (*Ceralostomelia paradox*).

#### *2.2.1.14 Symptoms disease of nut splitting in areca nut*

Symptoms of the disease that can be observed from this condition include yellowish spots on the leaf blade, yellowish fruit color in the half-ripe fruit phase, and the apical end of the fruit showing signs of falling fruit.

#### *2.2.1.15 Symptoms disease of Antracnose in areca nut*

Symptoms that can be observed from this disease are brown circular spots with yellow circles surrounding the spots. The leaf veins turn yellow from the tip to the base of the leaf (**Figure 10**).

#### *2.2.1.16 Symptoms disease of leaf sheath rot*

Symptoms that can be observed in midrib rot disease are yellowish white and brown sclerotia on the leaves and covered with white mycelia on the surface. There are first reports of the attack of this disease by the fungus *Athelia rolfsii* in India [14].

#### **Figure 8.**

*Symptoms of red rust disease on areca nut: (A-B) symptoms of rust spots red on leaves, (C) sign of hyphae growth on leaves, (D) microscopic morphology of* Cephaleuros *sp. [11].*

#### **3. Pathogen infection cycle and chain**

The disease cycle is inseparable from a pathogenesis [15]. An infection cycle can occur over and over again during a plant's growth period. If this condition continues repeatedly, it is referred to as a chain of infection, so that the pathogen spreads to fill the planting area. The sequence of disease occurrence and disease distribution includes the stages of spore germination, penetration, colonization, infection, sporulation, and disease dispersion. Biochemical processes begin to take place as long as the spores germinate. If the spores are active, if they get the right conditions (host plants and a supportive physical and chemical environment), infection will likely occur. Spores are referred to as dispersion units. Spores germinate morphologically visible germination tube, swelling of the germination tube is known as appressorium, and hyphae to attach when penetration occurs in the host plant tissue. This development becomes the unit of infection. Units of infection can cause disease symptoms [16]. In the areca nut itself, disease symptoms can occur in the vegetative organs and generative organs. Symptoms of the disease can be recognized locally or systemically. If the symptoms occur locally, they only occur in one organ, for example in the leaves. However, if the symptoms are systemic, some organs change, for example, stem bleeding is found in the cross-section of blackish brown fluid, yellowish spots on the leaves, and root rot due to a manifestation of systemic infection.

#### **Figure 9.**

*Symptoms of root rot disease on areca nut; (A) infection of the base of the stem, (B) systemic symptoms on the tree, (C) fruiting bodies of* Ganoderma lucidum*, and (D) spores of* G. lucidum *[11].*

The chain of infection can be divided into homogeneous chains if the dispersion unit consists of only one type. For example, the dispersion unit is only conidia. However, in the case of an infection chain consisting of several dispersion units such as ascospores and conidiospores, it is said to be a heterogeneous infection chain. Very often this heterogeneous chain of infection occurs in different seasons in perennial plants [16].

#### **4. Plant defense response**

The defense response of plant cells against pathogenic microbial infections are divided into two mechanisms, including mechanisms related to 1) the structure of the plant body itself including the presence of a waxy layer on the surface of plant organs. On the other hand, hard and thick epidermal cells narrow the chance of pathogen penetration. In addition, plant defenses against pathogens are also found in the various structures of stomata and guard cells as natural access that plants have to pathogens. For many plant varieties with narrow entrance variations and tall and wide guard cells reduce the chances of pathogens penetrating; 2) production of antimicrobial secondary metabolites. This is a limiting factor for the continued penetration of pathogenic microbes [16].

When pathogens attack plant cells, plant enzymes catalyze oxidative reactions to produce reactive oxygen species that can damage pathogenic microbial cells.

#### **Figure 10.**

*Antracnose; (A-B) symptoms of brown spots on leaves with a yellow halo around them, (C) morphology of the fungus* Colletotrichum gloeosporioides*, (D) conidia of fungi* C. gloeosporioides *[11].*

This reactive oxygen also serves to strengthen cell walls as well as signal intermediaries to neighboring cells that foreign cell attacks are taking place. In addition, plant cells respond by synthesizing and storing some callose (polysaccharide polymer) which is located between the cell wall and the plant cell membrane. Callose blocks the penetration of pathogenic cells at the site of infection [16].
