Brown spot disease (of Rocha pear)

This disease was confirmed for the first time in Portugal in 1996 in the Rocha and Passe Crassan pear varieties, currently assuming an epidemic situation in the so-called Oeste region of the country. Its effects are so devastating that, for example, between 2014 and 2016, it caused losses of approximately 30 million euros in the Rocha pear industry, according to data presented in 2017 by INIAV, at the Technical Days about Fruit Crops.

Caused by the fungus Stemphylium versicarium, the brown spot disease of the pear tree attacks the leaves and fruits, and the symptoms vary according to the variety of the pear tree. The spots tend to invade the entire leaf, along the central vein, causing it to dry out and fall; in fruits, they appear on the faces most exposed to the sun and spread to the whole fruit if the climatic conditions are favorable to the proliferation of the disease.

Also present in the orchard at the time of flowering, infections by the fungus Stemphylium vesicarium can occur in flowers, namely in anthers and sepals. And when there are favorable conditions of temperature and humidity, the fungus develops and infections increase, sometimes leading to the fall of the fruits.

The incidence of the disease depends on the varieties of pear and the level of ripeness of the fruits, and seems also to be linked to the alteration of treatment schemes for scab (one of the most important diseases of pome trees in the world, such as pear and apple trees), in particular the use of active substances that only control the scab and have no effect on brown spot disease.

Rice blast

Caused by the fungus Magnaporthe oryzae, rice blast is one of the most common diseases in rice worldwide and also in Portugal, affecting all producing basins, from Mondego to Tagus, Sorraia and Sado.

Magnaporthe oryzae's attack may result in losses in production of around 50%, as happened to rice farmers in Tejo-Sorraia in 2018. However, losses in production are more or less considerable depending on the variety of rice and climatic factors, like humidity and temperature. In cultivation sites where a relative humidity of 95% prevails with an average temperature of 26 °C/ 27 °C, the risk of infection and spore spreading is high.

The presence of rice blast is visible by the appearance of circular or elliptical spots, presenting a grayish center surrounded by reddish-brown edges, and can manifest itself in all aerial parts of the plant and at any time of its development process, from the early stages to the milky grain phase.

Yellow rust

The fungus Puccinia striiformis f. sp. sp. tritici is responsible for the wheat yellow rust, whose name is due to the yellow color and the distribution of the fungus' uredinia in the leaves, arranged in long linear striations parallel to the direction of the leaf veins. The symptoms of the disease can manifest at any stage of crop development, but the yellowish color of the leaves is the most characteristic.

There are few studies on the occurrence, epidemiology, damage and control of yellow rust, but the few data released reveal that the disease causes losses in wheat crops that can vary between 5 and 50%.

With a simple propagation capacity, wheat yellow rust spores spread through the wind, easily crossing borders and reaching other countries. New aggressive strains of the yellow rust fungus have emerged since the turn of the century, reaching some countries, including Portugal in 2013 and 2014. According to data released by INIAV in 2015, the new yellow rust strain (called Warrior) that affected the wheat crops in Portugal in these years “combines a broad spectrum of virulence that allows it to attack both common wheat and durum wheat, and triticale”, a hybrid cereal resulting from the crossing of wheat with rye.

The introduction of resistant genes in plants, the reduction of primary sources of dissemination and the spraying with specific fungicides are the disease control measures currently available on the market, but they have proved to be ineffective.

It should be noted that wheat is the second largest cereal crop in the world (after maize) and a staple food, used to make flour and bread, used as animal feed and as an ingredient in beer production.