November 19, 2018

Botrytis cinerea - Epidemiology of the disease on the grapevine.

Botrytis cinerea infestation can be disastrous for many crops when conditions are favourable to the progression of the disease. Despite the fact that several plant protection products have been developed , the losses from botrytis are still significant.

At the same time, the ever-increasing sensitivity of consumers to the adverse effects of synthetic plant protection products on human health and the environment, together with zero tolerance for residues from many markets, leads to the restriction of their use.

Similarly, in the context of organic farming, which has been developing rapidly in recent decades, the use of chemical plant protection products is absent.

In order to maintain production at satisfactory levels under these plant protection conditions, an excellent knowledge of the epidemiology of the disease is required.

Conidia produced late in winter and early spring from overwintered mycelium or from sclerotia in host tissues or in the soil, are considered responsible for the primary infections caused by botrytis in spring. Many are the hosts of botrytis. Over 200 species have been found to be the source of primary botrytis infection ( Sutton et al.,1991).

It has been found that in areas characterized by the production of fruit and vegetables , the conidia of B. cinirea constitute a significant percentage of the microflora of the air (Bisiach et al., 1984).

In the spring , insects can also act as carriers of a primary infection for botrytis. There are also reports of warehouses in the vineyard, but these are rare.

It was found that the mycelium of B. Cinerea survived for 30 weeks in pruning of the vine, with its preservation being significantly influenced by applied weed destruction practices and prevailing temperatures (Thomas et al., 1983).

Epidemiological studies have shown that there is a significant link between the infestation of aged flowering tissues in spring and the progression of the disease during harvesting and storage. This makes flowering very important for the development and epidemiology of the disease.

Vine flowers, during their aging, are particularly susceptible to infection by botrytis (Jersch et al., 1989). The increased sensitivity to botrytis of vine blossoms may also be contributed by limited resveratrol synthesis (Keller et al., 2003).

In general, attacks during flowering cause latent infections in immature fruits (Williamson, 1994), but all infected fruits during harvest are not explained by bloom infections and latent infections.

The infestation of the pole and ovary by the conidia begins with the infection of the tissues of the pole which is followed by slow growth of mycelial hyphae inside the ovary, where eventually the botrytis falls into a latent phase. As the host’s defenses decrease, which usually coincides with ripening, botrytis completes its growth and causes rotting in the fruit.

On the vine, stigma infestation during the early stages of the vegetative period was considered the most common route for fruit contamination (McClellan and Hewitt, 1973, Nair and Parker, 1985, Nair and Hill, 1992).

In some wine-producing areas pole infections are considered less significant although fruit rots were found as a result of latent infections in the pole detachment zone (Pezet and Pont, 1986; Holz et al., 2003)

In other areas, these infections are considered important for the epidemiology of botrytis (Keller et al., 2003).

In favorable conditions, the reactivation of botrytis in the tissues of the pole leads to the production of conidia and therefore to the creation of additional sources of infection for the infestation of the remaining aged and necrotic pillars.

The role of the other floral organs beyond the pole was further investigated.

Infections from the stamens or petals and the growth of mycelial hyphae through the floral tissues to the calyx, cause latent infections that develop very aggressively during the ripening of the fruit.

In grapes, histological studies have shown that botrytis affects the stamens, progresses basipetally to infect the calyx and then develops systemically towards the peduncle and the duct tissue of the rails (Pezet and Pont, 1986).

Botrytis infections from the peduncles of the rails have been confirmed. The branches of the botry and to a lesser extent the back in the early stages of the development of the rails are also sensitive, but their resistance to infections increases over time (Holz, 2001).

The point of adhesion of the rail to the peduncle shows the highest percentage of botrytis infections. Stomata and occlusive cells are considered the entry point for botrytis infections in the peduncles and back (Holz et al., 2003).

A significant proportion (76 out of 90%) of rail infections started from the point of contact of the rail with the peduncle (Michailides et al., 2000b).

In grapes of the Red Globe table variety, it was found that the most important post-harvest infestations came from infections that occurred at the beginning of flowering and during full bloom (Michailides et al., 2000b, c).

Experimental data from vineyards around the world confirm the importance of flower infections in epidemiology and disease progression. For example, a single application with a botrydicide towards the end of flowering managed to reduce by 78 % the percentage of affected grapes during harvest (Viret and Keller, 2000).

Be that as it may, the possibilities of botrytis infection are many, and the infections caused by the conidia in the ripe fruits in the later vegetative stages are just as important as the latent infections of green tissues at the beginning of the vegetative period (Wilcox, 2002).

Floral residues that remain in the grape are attacked and colonized extensively by botrytis. There the fungus overcomes the summer conditions saprophytically, without causing obvious symptoms in the fruit, as during this period the natural defense of the rails is maintained at high levels. However, from percussion onwards the resistance mechanisms of the rails bend, and as the rails mature, the saprophytic mycelium is reactivated, providing sufficient contamination to cause severe lesions in the fruit (Keller et al., 2003).

Infected flower tissues remaining in the grape are a worthy source of mycelium. However, the evolution of this mycelium differs significantly between the cultivated varieties of the vine. Residues from stamens, flowers, rails, covers, propellers and pieces of leaves are often trapped in the grape. It was found that the contamination of these residues by botrytis ranged between 13 and 72%, demonstrating that, in direct contact with the developing rails, there is a significant contamination in the grape before it is “closed” (Seyb et al., 2000a).

As the plant’s defense mechanisms weaken, symptoms appear, new conidia are produced and dispersed in the environment, causing new infections. In vineyards all over the world, the maximum content of konidia in the air occurs during flowering, flowering and ripening (Vercesi and Bisiach, 1982).

Thus, when ripening begins there is plenty of infection to cause new infections in vegetation and fruits.