Causal organism: Botrytis cinerea Pers. ex. Fr.
- The fungus produces grey growth on the surface of the fruit but in high humidity, the mycelial growth may be cottony and white.
- The conidiophores are long, slender, erect, hyaline, unbranched or seldom branched.
- The epical cells enlarged or rounded bearing clusters of conidia on short sterigmata.
- Conidia are hyaline, ovate or elliptical to almost globose, one celled conidia appear grey in mass. Black irregular sclerotia are frequently produced.
- Bunch rot, also known as grey mould rot or Botrytis rot and is prevalent throughout the world wherever the grapes are grown.
- The maximum damage due to of this disease is noticed in berries at the harvest time as well as during transport and storage.
Economic Importance
- Infection on flowers and berries is most important from economic point of view as it lowers both the quality and quantity of fruit, flowers provide an excellent source of nutrition to the fungus.
- The berries are resistant to infection during development stage until maturity, after which, these become increasingly susceptible.
- The famous noble rot represents a rare case of rotted food stuff becoming more valuable than healthy one. Under favourable dry conditions, following are heavy Botrytis attack, the mycelium of Botrytis fungi colonizes the berry skin and kills epidermal cells thereby allowing abundant evaporation of water through cuticle. After drying, a raisin-like shrunken fruit is picked up selectively.
- The famous, white Auslese- type wines, the most renowned originating from the Rhine Valley or Sauterne are made from such grapes ( Nelson,1951; Jarvis, 1980).
Symptoms
- The disease symptoms appear on all plant parts i.e. leaves, shoots, flowers and berries. Both young and relatively older leaves are infected by the pathogen.
- The fungus produces irregular, necrotic spots at the centre of the leaves. Under certain conditions, marginal necrosis also occurs.
- Infected flowers normally do not develop apparent symptoms but necrosis of stamens, the solitary ovary can often be seen covered with tufts of sporulating mycelia.
- The most prominent symptoms of the disease are found on the berries. Infected berries become dark coloured and show typical greyish, hairy mycelium all over their surface.
- Tufts of conidiophores and conidia protrude from stomata and peristomatal cracks on the skin of the berry. Under high disease pressure, all the berries in a bunch get affected.
Mode of spread and survival
- The fungus, Botrytis cinerea survives on the grapevines, rotted berries and stem clusters in the form of mycelium, conidia and sclerotia.
- The conidia of B. cinerea are dry and largely dispersed in air currents.
Epidemiology
- The optimum temperature for sclerotial germination after the infection is between 20 and 250C and relatively dry soil.
- Sclerotia are more likely to survive longer on canes and most important source of primary inoculum.
Management
- Maintaining the sanitation in the vineyard is the most important cultural practice to keep the disease under check.
- Diseased vines, leaves and fruits must be picked up and destroyed.
- Removal of grape mummies, the primary sources of infection, from vines at the time of pruning and burning them.
- Fungicide sprays of dicarboximide, procemidone, vinclozolin and iprodione are effective for disease control.
- Removal of leaves from vicinity of flower clusters and bunches helps in reducing the disease severity.
- Some of the promising new botrycides in grapes are triazole, folicur, sterol biosynthesis inhibitor (SBI)
|
Participants