**2.3** *Satsuma Dwarf virus* **or** *Citrus mosaic virus*

Both of them are shown in Japan the first and located in the *Secoviridae* family. The genome of the causal disease consists of two RNAs that are single-stranded, positive-sense. These viruses are transmitted by grafting infected budwood and mechanical with infected knives or scissors. The symptom of this agent is dwarfing because of short internodes, multiple sprouting and small leaves, and poor growth dues to the limitation of an extensive root system with a gradual decrease of yields. Sometimes, you can see various green patterns on the fruit rind of satsuma mandarin that cause a decline in commercial value which is called citrus mosaic. This virus does not make any symptoms on the trunk of infected trees. The symptom of leaves

#### **Figure 2.**

*Symptoms of* Citrus psorosis virus *on (a) the leaf (ring spots) and (b) bark (bark scaling), Mazandaran province, Iran. Source: Author.*

*Citrus Virus and Viroid Diseases DOI: http://dx.doi.org/10.5772/intechopen.108578*

are small, boat-and spoon-shaped leaves, and the infected fruits show small in size, with a thick rind and poor taste. If trees infect with the Citrus mosaic virus, fruits have rings, mosaic, and blotches patterns on their outer surfaces. During the growth of fruit, these patterns are changed to brown and dented, resulting in a rough fruit surface. In this disease, virus particles are found in leaf cells of satsuma because they fill Intercellular spaces and tubules [33].

#### **2.4** *Citrus variegation virus* **(CVV)**

This virus is another plant viral pathogenic that infects citrus cultivars. It belongs to the *Bromoviridae* family, *Ilarvirus* genus [37].

This virus is shown in the various kinds of citrus cultivars. Its symptom is variegated, mosaic, malformation on leaves, and dwarfing [2, 37]. The basis of the symptoms on citrus cultivars researchers introduced two strains: A strain can create chlorotic mottle with variable severity on the leaves and crinkles symptoms that are called infectious variegation strain. The other one is crinkly leaf strain causes distorted, puffed, or puckered leaf segments but without variegation. This agent like others transmitted by infected scion and mechanically [37].

#### **2.5** *Citrus leaf rugose virus*

This virus has a close relationship with the *Citrus variegation virus*. Both of them place in the same genus [2]. The genome of this virus is tripartite. It means it has three single-stranded RNAs [45].

This virus induces symptoms in some cultivars like lemons, Mexican lime, and grapefruit. The rest of the citrus cultivars do not show obvious symptoms. The symptom of sensitive hosts includes leaf flecking, puckering in leaves, and stunting [2].

#### **2.6** *Citrus leprosis Virus*

*Citrus leprosis* is an important disease in the North and South of the Americas and it caused millions of citrus trees to die. For the first time, it was reported from the USA. This disease damages the amount of citrus production annually in the USA. It is a very destructive disease on the Americas continent, especially on oranges and mandarins. This disease can be transmitted by the mites [13]. This disease is non-systemic. A casual disease is a heterogenic group of RNA viruses endemic to the North and South of the American continent. These viruses belong to three genera that include Cilevirus (bipartite positive sense (+) single-stranded [ss] RNA), higrevirus (tripartite (+) ssRNA), and dichorhavirus (bipartite negative sense (−) ssRNA, family Rhabdoviridae, order Mononegavirales). Cileviruses and higreviruses are active in the cytoplasm of infected plant cells but dichorhaviruses exist in the nucleus of infected plant cells. So this disease has two classifications that basis on the place of viroplasms in infected cells: CL-Cytoplasmic (CL-C) and CL-Nuclear (CL-N) [43].

The characteristic of Dichorhaviruses is short rod-like non-enveloped particles (40–50 × 100–110 nm) and encapsidate two ss (−) RNA molecules with 6 ORF. The type of virus in this genus is the orchid fleck virus (OFV). OFV has two types that include Citrus necrotic spot virus and Citrus leprosis virus Nuclear type (CL-N) [43]. The symptoms of this disease are necrotic or chlorotic spots in leaves, branches, and fruits, which progressively leads to the early drop of leaves and fruits, branch dieback, and occasionally to the death, predominantly, of the youngest citrus trees (**Figure 3**) [43].

#### **Figure 3.**

*Symptom of citrus leprosis virus on (A and B) fruits, (C) twigs, (D) leaves in the United States. Source: Levy et al. [34].*

The casual of the disease is Citrus leprosis virus Cytoplasmic (CL-C) which is the type species of the genus Cilevirus, family Kitaviridae. The members of this family have bacilliform or spherical virions with positive-sense single-stranded RNA genomes [20]. The symptoms of this disease are shown on twigs, leaves, and fruits that are local chlorotic and/or necrotic lesions on the surface of the host's tissue [13, 20]. If mites feed the lesion, the agent of casual disease can transmit to the healthy plant. In addition, infected shoots induced the disease in healthy plants by grafting [13]. This virus do not move systematically in its host [13, 20].

There are many ways to control disease. First, the control of mite as a vector is important. After that, infestation gardening tools like knives and scissors. The last, remove the infected twigs and control weeds [13].

#### **2.7** *Indian citrus ringspot virus* **(ICRSV)**

ICRSV can infect mandarine and expand worldwide. This disease is reported by Wallace and Drake (1968) from California for the first time [46]. This virus has limitations on hosts. It attacks the mandarine. At the first, it is reported on "Kinnow" mandarin (*Citrus reticulata* cv. "Blanco," a hybrid between "King" and "Willow" mandarins) from India. This virus has a positive sense, flexuous RNA virus approximately 7.5 kb in size with six open reading frames (ORFs) belonging to the genus Mandarivirus in the Alphaflexiviridae family of order Tymovirales [42]. The shape of the virion looks like capilloviruses [47].

The symptom of this disease is bright yellow ring spots on mature leaves, followed by a rapid decline [42, 46, 54]. Several affected trees show dieback and decline type of symptoms and thus become less productive [46].

## **2.8** *Citrus leaf blotch virus*

This virus is placed in the Betaflexiviridae family and it is seed-borne [42]. This virus infects trifoliate rootstocks like Citrange and the symptom is bud union crease when propagated on Troyer citrange. Also sometimes it shows chlorotic blotching in young leaves. This disease detects in France for the first time. The virion of the virus is filamentous particles about 900 × 14 nm in size, with a single-stranded, positive sense, genomic RNA (gRNA) of 8747 nt, and a coat protein of about 41 kDa. The gRNA contains three open reading frames (ORFs) and untranslated regions of 73 and 541 nt at the 5′ and 3′ termini, respectively. Because this virus can be transmitted by grafting, sanitation, and quarantine of scions are very important [48].

## **2.9** *Bud-union crease of citrus trees*

The symptom of this disease is a dotted or continuous line of orange-yellow discoloration associated with projections or bark pegs on the inner bark surface and corresponding pits in the wood at the bud union [24, 15, 27, 49]. Sometimes, this disease causes the infected tree to decline and die or remain stunted. This disease is related to scion-rootstock combinations. Some sweet orange and lemon varieties on trifoliate orange and trifoliate orange hybrids are shown this disease. The basis on experiments, the casual of this disease is not a virus or other infection casual. It is guessed a physiological incompatibility causes this disease [49].

The infection tree shows a pale yellow color on the leaves. This symptom resembles suffering from a nutrient deficiency. Also, these trees have a poor flash that causes them to decline and die. The amount of production in infected trees is too low. In severe infection, a groove is made on the bark at the bud union. Gum-impregnated projections exist Underneath Bark strips [27].

#### **2.10** *Citrus yellow vein clearing virus*

This disease is showed in Pakistan for the first time in 1988 on sour orange (*Citrus aurantium* L.) and lemon (*C. limon* Burm. f.) [35, 36, 50]. The symptom of this disease is strong yellow vein clearing, leaf distortion, and occasionally, ring spots and veinal necrosis [35, 36]. The symptoms of mild or moderate vein clearing or chlorosis have been observed only in young leaves during spring flushes [35]. This virus after inoculation on chenopodium showed local lesions while phaseolus Vulgaris showed systemic chlorosis, severe mosaic, blotching, and necrosis. The casual disease is the *Citrus yellow vein clearing virus* (CYVCV). The virion of the virus is the flexuous filamentous virion particle is sized between 13 and 14 nm in diameter with a modal length of 685 nm [35]. The place of virions of virus in infected plants is in the phloem [35]. This virus is a single-strand positive-sense RNA virus comprised of 7529 nucleotides (nt) [35, 44, 50] and the genome of the virus has 6 open reading frames (ORF). *Citrus yellow vein clearing virus* (CYVCV) belongs to Genus (Mandarivirus), family (Alphaflexiviridae) [50].

In China, upon becoming infected with CVYCV, the leaves of young spring or autumn shoots in lemon or sour orange trees display a water-soaked appearance and yellow, clearing veins on their ventral side. The leaves also represent chlorotic with significant crinkling and warping [23, 35].

In India, the symptoms are different and it may be shown, with mosaic and irregular ring spot-like symptoms. In drastic infection, fruits are imperfect and trees die and which changes the amount of production. This virus on herbaceous plants appears different symptoms like mosaic-like patterns, chlorosis, and necrosis on leaves. The infection in weeds is asymptomatic. Also, this virus can infect a wild grapevine and causes different symptoms that include short internodes, reduced leaf size, chlorosis, and necrosis [23].

The symptoms of the disease disappear in summer. The many possibilities are for this reaction. One of them is the high temperature causes the limitation of replication of the virus. Another reason is related to the movement of viruses. The high temperature in summer may inhibit the virus' movement in the plant, or cause the virus to transfer to other tissues in the asymptomatic tree [35].

This virus can be transmitted by grafting, knife, and scissors gardening, and insects like aphids and white flies [23, 35]. The genus of aphids can infect contain *Aphis spiraecola* Patch, *Aphis craccivora* Koch, *Aphis gossypii* Glover, and citrus whitefly *Dialeurodes citri* (Ashmead) [23, 35].

Now, this virus is expanded in many citrus-growing areas in Asia like China, Iran, and Turkey [50].

#### **2.11** *Leaf variegation with ring spots*

The symptom of this disease is yellowish variegation on both the upper and lower surfaces of the leaves, although the yellow color is lighter on the lower surface. The shape and size of yellow areas are different but most of them are small and more or less circular in outline they have a green center and they are more similar to ring spots. Yellow spots can expand on the twigs with variegated leaves. Sometimes leaves that have yellow spots midribs are colored with gum. Fruit on branches with variegated leaves develops slight depressions or furrows, yellow in color.

The rate of transmission of this disease to healthy plants is very low. It is transmitted by grafting infected shoots. It is guessed the casual of this disease is a virus [41].

#### **2.12** *Citrus variegation virus*

The symptom of this disease consists of leaf flecking, mosaic, malformation, and dwarfing. The casual of this disease is the *Citrus variegation virus* (CVV) which is a member of subgroup 2 of the genus *Ilarvirus* (Bromoviridae). This disease is expanding in the Mediterranean regions and the Americas continent. The symptom of disease on Citrons and lemons is more severe than on oranges and mandarine. It includes a reduction in yield and fruit malformation. This virus has two strains: infectious variegation strain, and crinkly leaf strain. The first strain can cause chlorotic mottle with variable severity on the leaves and sometimes can show crinkle symptoms on infected trees. The second strain induces distorted, puffed, or puckered leaf segments but without variegation. This disease can be transmitted by grafting and mechanical [37].

#### **2.13 Management of citrus viral diseases**

The first step for controlling viral diseases is the exclusion of the disease and forbidden to enter the infected propagation scion. The major transmission among citrus viral diseases is grafting infected buds. So, for the propagation of citrus cultivars, it is better to use certificated budwood. If viral diseases exist in a specific area, it is better to use tolerant or resistant cultivars for rootstocks. Other ways to control

include cross-protection and cultural practices [2]. Furthermore, Sanitation is very important. After working with scissors and/or knives, they wash with a disinfectant solution.
