The Relationship Between Flower Cultivation and Meteorological Conditions and an Analysis of Virus Disease Categories
1. Carnation Virus Diseases
(1) Carnation mottle virus (Car-MV)
Carnation mottle virus belongs to the genus Carmovirus. Infected carnations show leaf mottling and flower color breaking. The virus is transmitted through sap, and it occurs at all carnation cultivation bases in Yunnan Province, with an incidence rate as high as 60-70%.
(2) Carnation vein mottle virus (CVMV)
Carnation vein mottle virus belongs to the genus Potyvirus. On infected carnations, uneven mottling and necrosis appear on the veins of young leaves, and irregular chlorotic spots may also appear. Generally, necrotic spots of varying shades are produced on the leaves. The virus is transmitted non-persistently through sap and the green peach aphid. It occurs at all carnation cultivation bases in Yunnan Province, with an incidence rate of 20-30%.
(3) Carnation latent virus (CLV)
Carnation latent virus belongs to the genus Carlavirus. Infected carnations generally do not produce symptoms or show only mild mosaic. When co-infected with carnation mottle virus, it causes severe mosaic on carnation leaves. The virus is transmitted non-persistently through sap and the green peach aphid. It occurs at all carnation cultivation bases in Yunnan Province, often co-infecting with carnation vein mottle virus, with an incidence rate of 20-30%.
(4) Carnation etched ring virus (CERV)
Carnation etched ring virus belongs to the genus Caulimovirus. The symptoms of this viral disease are generally inconspicuous, but on large-flowered carnation varieties, it often causes ring-patterned, ring-shaped or broad stripe necrotic spots on the leaves, most obvious at the seedling stage. When the disease is severe, many grayish-white ring-patterned spots can merge into large lesions, causing the leaves to curl and become deformed. This disease becomes latent during hot seasons. The virus is transmitted non-persistently through sap and the green peach aphid. In poorly managed flower gardens, the incidence rate is 40-50%.
(5) Carnation necrotic fleck virus (CNFV)
Carnation necrotic fleck virus belongs to the genus Closterovirus. On infected carnation plants, the middle leaves show grayish-white to light yellow necrotic mottling or irregular streaks or dots, while the lower leaves show purplish-red spots and streaks. Subsequently, as the plant grows, the symptoms spread upward, causing the leaves to turn yellow and necrotic. The virus is transmitted non-persistently through sap and the green peach aphid. Under normal circumstances, it is difficult to inoculate with sap, but inoculation on Dianthus barbatus (sweet William) is easily successful, and it can serve as a diagnostic host for carnation necrotic fleck virus. In poorly managed flower gardens, the incidence rate reaches 50-60%.
2. Gladiolus Virus Diseases
Due to viral infection, gladiolus plants develop stem and leaf shrinkage, root rot, and flower deformation and abnormality, affecting or losing their ornamental value. At present, the degradation of gladiolus varieties in China is significantly influenced by viral diseases, which are one of the important factors. Streak disease symptoms include chlorotic spots on leaves, causing distortion and deformation, stunted plants, and abnormal, smaller flowers.
3. Chrysanthemum Virus Diseases
There are many types of viruses harmful to chrysanthemums, with more than 20 species reported. Seven species have been preliminarily identified in China. Different viruses cause different symptoms on chrysanthemums, and sometimes different chrysanthemum varieties infected with the same virus also show differing symptoms. During cultivation, chrysanthemums are often simultaneously infected by several viruses, worsening the symptoms and producing compound symptoms such as flowering leaf, mottling, ring spots, necrotic spots, deformity, dwarfing, and yellowing. Due to differences in variety, growth stage and cultivation environment, there may sometimes be latent symptoms, with symptoms sometimes appearing obvious and sometimes disappearing.
(1) Chrysanthemum B virus (CVB)
Chrysanthemum B virus is classified under the genus Carlavirus. On infected chrysanthemum leaves, it manifests as mild mosaic symptoms or shows no symptoms. On susceptible chrysanthemum varieties, it can form obvious mosaic symptoms or necrotic spots, and severely infected plants produce brown necrotic spots. Chrysanthemum B virus is transmitted by sap, cuttings, the green peach aphid and potatoes. It commonly occurs on ornamental chrysanthemums, with an incidence rate of 60-65%. Besides harming chrysanthemums, this virus also harms various plants such as wild chrysanthemum, Calendula, China aster, cineraria, annual chrysanthemum, pearl chrysanthemum, strawflower, zinnia, and petunia.
(2) Chrysanthemum stunt viroid (CSVD)
Chrysanthemum stunt viroid is classified under the genus Pospiviroid. Infected chrysanthemums show smaller, deformed cotyledons and dwarfed plants. Some varieties develop color-breaking flowers. It is transmitted by sap, by grafting knives, and by dodder, with a few capable of seed transmission. It commonly occurs at all chrysanthemum cultivation bases and on ornamental chrysanthemums in parks in Yunnan Province, with an incidence rate of 20-30%.
(3) Vein mottle disease
Yellow vein-patterned mottling appears on chrysanthemum leaves, causing the leaves to lose their proper vitality and appear listless, with small flowers that sometimes fail to open. The pathogen is chrysanthemum vein mottle virus. This virus is mainly transmitted through sap, grafting, and the chrysanthemum aphid (Macrosiphoniella sanborni). Besides harming chrysanthemums, it also harms wild chrysanthemum and Cleveland tobacco.
4. Lily Virus Diseases
The virus mainly overwinters in the bulbs, becoming the primary infection source for the following year; secondary infection in the field is mainly caused by aphid transmission. When there are many diseased bulbs, dry weather, and high aphid populations, this disease occurs severely.
Lily symptomless virus (LSV)
Lily symptomless virus is classified under the genus Carlavirus. Generally, no special lesions appear on the leaves, but the entire plant takes on a yellow color, internodes shorten, plants dwarf, and leaves yellow and shrink. It is transmitted by sap, the green peach aphid and the lily aphid. It often co-infects with cucumber mosaic virus. It commonly occurs at all lily cultivation bases in Yunnan Province, with an incidence rate of 40-50%.
5. Gerbera Virus Diseases
Yellow-green mosaic symptoms form on the leaves. The virus can be transmitted by sap and various aphids. Mosaic forms on diseased leaves. It occasionally occurs at lily cultivation bases in Yunnan Province, with an incidence rate of 1-10%.
6. Salvia Virus Diseases
Salvia virus disease, also known as salvia mosaic disease, is the most common disease of salvia and occurs throughout the country. After the plant is infected, the leaves mainly show dark and light green mosaic, yellow-green mosaic, and in severe cases the leaf surface becomes uneven, even showing fern-leaf symptoms, the number of flowers decreases sharply, and the plant dwarfs. The pathogens are wild cucumber mosaic virus (CMV), tobacco mosaic virus (TMV), Salvia virus 1, beet curly top virus, and broad bean wilt virus.
7. Peony Virus Diseases
(1) Peony ring spot virus (PRV)
The virus particles are spherical, 27 nanometers. It is difficult to transmit by sap rubbing or grafting, but can be transmitted by aphids. Peony ring spot virus (PRV) produces concentric ring-patterned round spots of alternating green and light green on the leaves, along with small necrotic spots, and the plant is small and dwarfed.
(2) Tobacco rattle virus (TRV)
There are two types of virus particles, the long ones being 190 nanometers and the short ones 45-115 nanometers. TRV produces ring spots or concentric rings of varying sizes, sometimes irregular in shape; it can be inoculated by sap, and nematodes, dodder and peony seeds can all transmit the virus.
(3) Peony leaf curl virus (PLCV)
Transmitted by grafting. PLCV causes obvious dwarfing of the plant, with the lower branches thin and twisted, and leaves yellowing and curling. PRV and PLCV harm peony and tree peony; TRV, besides peony and tree peony, also harms flowers such as hyacinth, narcissus and tulip.
8. Orchid Virus Diseases
This is an important category of diseases in orchid cultivation. Orchid plants suffering from viral diseases will remain diseased for life; even newly emerged young leaves and young shoots carry the virus, bringing huge losses to orchid production. Orchid virus diseases mainly include cymbidium mosaic disease, odontoglossum ringspot disease, and cattleya orchid color-breaking disease.
(1) Cymbidium mosaic disease (Cymbidium Mosaic Virus, CyMV)
Cymbidium mosaic disease is also called orchid black streak disease and cattleya orchid leaf necrosis disease. It is generally distributed in orchid-producing areas, with moderate damage. Infected plants develop chlorotic spots and necrotic spots on the leaves, and local necrosis forms on inoculated cattleya leaves. This disease causes mosaic in Cymbidium plants, and the pathogen is Cymbidium Mosaic Virus (CyMV). This virus is generally transmitted by sap, mechanical contact, and aphids. After infection, most plants form necrotic spots or mosaic on the leaves. Tests have shown that pouring water that has flowed through virus-carrying orchids into virus-free orchid pots can also cause the virus-free orchids to carry the virus. Therefore, precious orchid varieties should be cultivated in isolation.
(2) Odontoglossum ringspot disease (Odontoglossum Ringspot Virus, ORV)
Odontoglossum ringspot disease is also called cymbidium ringspot disease. It is distributed at bases in Fuzhou, Chengdu and Shanghai in China. The pathogen causing odontoglossum ringspot disease is Odontoglossum Ringspot Virus (ORV). After this virus infects plants, it produces mosaic on Cymbidium, necrotic spots on cattleya, and ring spots on Oncidium. The main routes of transmission of this virus are sap, horticultural operations and tools.
(3) Cattleya orchid color-breaking disease (Orchid strain tobacco mosaic virus)
When this virus infects plants, it first forms round or oval necrotic spots on the leaves. Subsequently, the small lesions merge into large lesions, causing the leaves to turn yellow and withered. In severe cases, the flowers become smaller, discolored, and sometimes deformed. The pathogen causing this disease is the orchid strain of tobacco mosaic virus (Orchid strain tobacco mosaic virus). This virus is transmitted through sap and horticultural tools. The seed transmission rate is relatively low.
(4) Cymbidium hybridum virus disease
It is the most widespread orchid virus in the world. The most common manifestation is grayish-green leaves and flowers with yellow mottling, which finally become brown sunken lesions, causing the plant leaves to become mosaic, with poor development or abnormal flowering, generally occurring on plants grown from meristem seedlings of old stems. Its transmission routes are often through tools, division, and contact transmission by piercing-sucking insects.
9. Tulip Virus Diseases
(1) Color-breaking disease
Color-breaking disease, also known as tulip white streak disease, is a worldwide disease that occurs in all tulip-producing areas. Most tulips planted in Shanghai are imported from the Netherlands; some varieties have an incidence rate of color-breaking disease as high as over 90%, and some varieties around 90%. Tulip color-breaking disease is one of the important causes of tulip bulb degradation. Tulip leaves develop light green or grayish-white streaks, sometimes forming mosaic. On red or purple varieties, color-breaking flowers are produced, with light-colored spots or streaks of varying sizes forming on the petals. On varieties with light-colored or white flowers, the petal color-breaking symptoms are not obvious; this is due to the lack of anthocyanin in the petals themselves. In severe cases, the plants grow poorly. When tulip color-breaking virus harms Lilium longiflorum, it produces mosaic or symptomless infection. Tulip color-breaking virus is transmitted non-persistently by sap or aphids. This virus can harm various tulips and lilies. Lilium formosanum and Lilium longiflorum are often more susceptible to tulips than single-petaled tulips.
(2) Mosaic disease
Mosaic disease, also known as tulip soft rot disease, is like tulip color-breaking disease in being widely distributed, and sometimes produces compound infection together with tulip color-breaking virus, forming severe mosaic. Yellow stripes or fine granular spots form on tulip leaves, and dark spots form on the petals; in severe cases the leaves rot. Tulip mosaic virus can be transmitted through diseased sap. Aphids are also vector insects of tulip mosaic virus.
10. Ornamental pepper vein mottle disease
Ornamental pepper, also known as cluster pepper and ornamental pepper, is a plant grown for its ornamental fruit. Vein mottle disease occurs commonly in places such as Shanghai, Nanjing and Hangzhou, hindering the normal development of the plant and affecting the ornamental effect. On infected plants, the leaf veins first turn yellow, after which the leaves gradually become mosaic or mottled; when the disease is severe, the leaves become deformed, even fern-like, and the peppers produced are few, small and deformed, or no peppers are produced. It is transmitted by two aphids, the green peach aphid and the cotton aphid. Besides ornamental pepper, it also systematically infects plants such as globe amaranth, petunia, henbane, wild tobacco, Nicotiana glutinosa, and chili pepper. When inoculated onto the diagnostic hosts common tobacco, Datura, and Chenopodium amaranticolor, it produces local necrotic spots on all of them.
11. Cycas necrotic stunt virus (CNSV)
CNSV can only infect Aizoaceae, Amaranthaceae, Chenopodiaceae and Cycadaceae. Naturally infected cycads show plant dwarfing, young leaves curling, and mature leaves with chlorosis or necrotic spots; cycad seedlings inoculated by sap rubbing show chlorotic symptoms on the leaves. The seed transmission characteristics of cycads themselves remain unclear.