How to prevent post-harvest diseases in grapevine crops

Phytosanitary problems in grape post-harvest generally begin in the field. However, the reduction in losses and the greater guarantee of product quality in pre- and post-harvest have been evidenced with the implementation of the Integrated Fruit Production (PIF) system, adopted since 2001 in vineyards in the Brazilian Northeast.

Post-harvest diseases in grapes cause quiescent infections (from the field). They are caused by fungi such as Alternaria, Colletotrichum, Lasiodiplodia e Botrytis, and acquired (generally in handling after harvest), in which the berries are generally affected by fungi such as Penicillium, Cladosporium, Aspergillus, Rhizopus and others that quickly manifest symptoms of rot. Furthermore, environmental factors contribute to the development of post-harvest diseases, as well as genetic ones, with compacted and thin-skinned berries being an undesirable characteristic, as they are more vulnerable to infections.

Alternaria rot

Alternaria rot is caused by the fungus A. alternata (Figure 1), whose spread occurs by wind. Preventive control is carried out through fumigation, mainly avoiding injuries to the curls. Many species of the genus Alternaria They are widely distributed in the soil, as a component of the microflora, and in the air. They naturally contaminate the aerial part of plants and are easily isolated from decomposing materials. This fungus, in addition to affecting grapes, also infects tomatoes, orchards (mainly stone fruits) such as persimmons, mangoes, as well as citrus, melon, pumpkin, peppers, carrots, beans and other vegetables and fruits.

Figure 1 - Conidia of alternaria alternata grape isolates

the fungus A. alternating is an important post-harvest pathogen of grapes, in which the infection generally begins in the peduncle. It is also a common pathogen in wine grapes. In 2003 it was detected in 80% of fruits collected in Argentina. This phytopathogen can infect plant tissue through wounds or natural openings. However, some researchers claim that this fungus is quite aggressive, not requiring wounds in the bark for penetration and maintaining constant development in a refrigerated environment. In persimmon fruits, it has been proven that A. alternata penetrates directly into the fruit. However, in work with table grapes, it was concluded that in uninjured berries there was no indication that A. alternata penetrate directly into the cells of the epidermis.

In export-type table grapes, A. alternata causes rot on the berries, characterized by firm lesions, dark brown to black in color and near the pedicel and stem, a grayish cottony tuft (Figure 2). It has already been found that in grapes, under conditions of high humidity, the fungus fructifications were present and the color of the tufts varied from grayish to olive green, evolving to black. The disease occurs in berries, pedicels and stems throughout the bunch development period, in addition to occurring in cold stored berries, however, its occurrence is sporadic in some shipments. This poses a serious challenge for long-term storage of table grapes at low temperatures. Stress factors during refrigeration can predispose table grape bunches to spoilage by this fungus.

Figure 2 - Progression of rot by alternaria alternata

Pathogenicity of alternaria alternata in grape

Due to the fungus A. alternata infecting different crops, an assay was carried out to verify the pathogenicity of isolates from other crops and from different parts of the vine (leaf and fruit) on grape berries of the Italy variety. 17 isolates were obtained (Table 1), some of which were pathogenic to the Itália variety. Isolates from grapes and tomatoes were more aggressive, presenting larger lesion sizes in a short period of time. Some isolates from the grape itself, mango, melon, cucumber and all tangerine isolates, in this trial, failed to cause disease in the Itália variety. But this does not mean that they are not pathogenic to other grape varieties.

Knowledge of this characteristic (presenting a wide variety of hosts for the fungus) is extremely important in post-harvest handling, preventing certain fruits/vegetables that have common pathogens from remaining in the same environment. If they are stored, transported or sold together, infection or reinfection may occur, as verified in the test with isolates of A. alternata of tomato and Chinese cabbage pathogenic to grapes (Figure 3). If preventive measures are not adopted, infection will probably occur and the loss will be more noticeable when it reaches the market and the final consumer, causing the product to depreciate.

Figure 3 - Injuries to isolates of alternaria alternata pathogenic to the Italy grape variety. A - isolated from Chinese cabbage and B - isolated from tomato

Future perspectives

In future trials, it will be interesting to evaluate whether grape isolates are pathogenic in other crops, to obtain answers about cross-infection and epidemiological factors that favor diseases, as well as alternative ways of controlling this pathosystem.

Table 1 - Origin, host and pathogenicity test of isolates alternaria alternata

Sizing	isolates	Host	Pathogenicity
1	LPPC*-Recife	fruit grape	-
2	LPPC-Recife	fruit grape	-
3	Petroline	fruit grape	+
4	Petroline	fruit grape	+
5	Petroline	fruit grape	+
6	Petroline	leaf grape	+
7	Petroline	leaf grape	-
8	Petroline	leaf grape	+
9	LPPC-Recife	manga	-
10	LPPC-Recife	manga	-
11	LPPC-Recife	melon	-
12	MMC**-878	Chinese cabbage	+
13	MMC-1160	tomato	+
14	MMC-879	cucumber	-
15	MMC-860	tangerine	-
16	MMC-861	tangerine	-
17	MMC-857	tangerine	-

Sizing

isolates

Host

Pathogenicity

1

LPPC*-Recife

fruit grape

-

2

LPPC-Recife

fruit grape

-

3

Petroline

fruit grape

+

4

Petroline

fruit grape

+

5

Petroline

fruit grape

+

6

Petroline

leaf grape

+

7

Petroline

leaf grape

-

8

Petroline

leaf grape

+

9

LPPC-Recife

manga

-

10

LPPC-Recife

manga

-

11

LPPC-Recife

melon

-

12

MMC**-878

Chinese cabbage

+

13

MMC-1160

tomato

+

14

MMC-879

cucumber

-

15

MMC-860

tangerine

-

16

MMC-861

tangerine

-

17

MMC-857

tangerine

-

- = non-pathogenic; + = pathogenic. *Post-Harvest Pathology Laboratory, **Maria Menezes Phytopathogenic Fungi Collection

Box 1 - economic importance

Brazil is the third largest fruit producer in the world, with grapes (Vitis vinifera) as one of the main representatives in the economic sphere of fruit exports. Grape cultivation basically takes place in the states of Rio Grande do Sul, Santa Catarina, Paraná, São Paulo, Minas Gerais, Bahia and Pernambuco. In the semi-arid region of Brazil (Bahia and Pernambuco), viticulture has been standing out on the national scene, due to the expansion of the cultivated area, production volume and, mainly, the high yields achieved and product quality.

Box 2 - Variety Italy

The Itália or Piróvano 65 variety was introduced in Brazil in the 20s and began to be commercially cultivated in the state of São Paulo in the 50s, spreading to the North of Paraná and other producing regions in the 60s. vigorous, long cycle, with average productivity of 30t/ha. The bunches have cylindrical-conical shapes, large (400g to 800g), somewhat elongated and naturally very compacted, requiring intense thinning. It is the main variety of fine table grapes produced in Brazil in the states of São Paulo, northern Paraná, Minas Gerais, Pernambuco and Bahia. In the semi-arid northeast of Brazil, this variety accounts for approximately 80% of the cultivated area. However, it has little resistance to diseases and pests.

Check out the article in issue 84 of Cultivar Hortaliças e Frutas magazine.