Acidovorax avenae subsp. avenae

Acidovorax avenae subsp. avenae It is a phytopathogenic bacterium known for causing diseases such as red streak in sugarcane; brown spot or watery streak in rice; and bacterial blight or watery spot in corn and sorghum.

In Brazil, it was first described in 1935, in the State of Rio de Janeiro.

Crops attacked

This bacteria affects several agricultural crops.

Among them:

• rice (Oryza sativa);

• sugar cane (Saccharum officinarum);

• corn (zea mays);

• sorghum (Bicolor sorghum).

Symptoms

Symptoms vary by culture.

In rice, brown streaks appear on the leaves.

In sugarcane, red streak (reddish streaks on the leaves) appears. These symptoms can extend to the apical meristem, causing top rot. Under favorable conditions, the rot appears in the stalk, creating cracks through which a foul-smelling liquid oozes.

In corn and sorghum, bacterial leaf blight occurs.

In forage grasses, the bacteria cause bacterial blight and decline, affecting turf quality.

Etiology and characteristics

Acidovorax avenae subsp. avenae is a gram-negative bacterium belonging to the Comamonadaceae family. It is aerobic and motile by polar flagella. Infection occurs mainly under conditions of high humidity and high temperature. It grows in medium containing asparagine as the sole source of carbon and nitrogen.

The bacteria can be transmitted by infected seeds, surviving between the glumes and pericarp or deeper in the seed.

It survives for long periods in seeds stored at low temperatures. Its survival in soil or crop residues is not common.

Taxonomic classification:

• Domain: Bacteria

• Phylum: Proteobacteria

• Class: Betaproteobacteria

• Order: Burkholderiales

• Family: Comamonadaceae

• Genre: Acidovorax

• Species: Acidovorax avenae

• Subspecies: Acidovorax avenae subsp. avenae

General features:

• Gram-negative, rod-shaped bacteria.

• Aerobic and mobile, with polar flagella.

• It survives in crop residues, soil and infected seeds.

• Spread occurs by water, wind, insects and agricultural practices.

Mechanisms of infection:

• Penetration: the bacteria penetrate the plant through wounds or natural openings, such as stomata or hydathodes.

• Multiplication: once inside the plant tissue, the bacteria multiply in the intercellular space, using nutrients from the plant.

• Production of enzymes and toxins: The bacteria produce enzymes (such as pectinases and cellulases) that degrade the plant cell wall, facilitating colonization. In addition, toxins can be released, causing tissue damage and visible symptoms.

• Systemic spread: In some cases, the bacteria can move through the plant's vascular system, causing systemic infections.

Control

The control of Acidovorax avenae subsp. avenae involves several practices.

It is recommended to use certified, pathogen-free seeds to avoid introducing bacteria into the crop.

Crop rotation with non-host species helps reduce inoculum in the field.

Elimination of volunteer plants and alternative hosts in the vicinity of the cultivated area is important to reduce sources of inoculum. The use of resistant cultivars, when available, is an effective strategy.

In specific cases, registered chemical products can be applied to the crop to control the bacteria (click here to find out which ones).

More information can be obtained in the Magazine Cultivating Great Crops 305 (click here).