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FOCUS ON - Herbaceous crops in open fi elds

Despite the fact they belong to different species and orders, herbaceous crops in open fi elds show some common features in the plant disease management which are strictly linked to the geopedological and agro-meteorological knowledge and to the farming practices employed. The farming practices, in association with the agronomic, genetic, chemical and microbiological defense strategies, can guarantee quality production and environmental conservation. A few simple prophylactic measures are basic operating procedures and really effective against some pathogens infesting any kind of soil. They are the seed treatment, a wise choice of crop rotation, the rejection of sod-seeding and green manure (in the presence of strong infections), the removal and burning of infected residues. Such procedures apply independently of the phyto-pathological tests on the crop examined. According to the fi nal usage of the different produce, the extensive herbaceous crops are divided into plants grown for food and plants grown for industrial and processing purposes. Cereals belong to the fi rst group: crops which have always been staple food in the human diet and they still play a primary role in many peoples’ nutrition. Wheat, rice and maize are the most widely grown. Wheat is mainly widespread in Europe, rice in Asia and maize in America. Several adversities (viroses, pathogens, pests) have developed over time evolving with the crop little by little, while farming practices were turning increasingly intensive. Nowadays, risks, both for humans and animals, derived from the potential danger of food contamination caused by toxins of fungal derivation (ochratoxins, afl atoxins, fumonisins, ergosterols) can be avoided by employing suitable farming practices together with a rational use of agrochemicals. Industrial crops belong to different botanical species, but they are classifi ed according to their usage and industrial processing of the main product. Therefore we have oil producing plants (soyabean, sunfl ower, rape), sacchariferous plants (sugarbeet), textile fi bers plants (cotton, hemp, fl ax), biomass and fodder plants. The crops aiming at obtaining natural fi bers (not so widespread in Italy if not for research purposes) are meeting increasing interest among the no-food or not-onlyfood produce. Today, in Italy, tobacco, fodder and meadow plants on the one hand, aromatic and medicinal plants on the other, are increasingly relevant respectively for the invested land surface and for the specifi c properties. As far as pest management is concerned, pesticides are applied in open fi elds more frequently with “industrial crops”. Protection against adversities is basic and irreplaceable for these crops (e.g. the seed treatment) in order to preserve the quantitative and qualitative integrity of the produce (quantity: e.g. rhizomania for the beet; quality: fi ber integrity for the textile plants). Pesticides application with fodder plants may be considered an unusual practice. On the other hand, with medicinal plants the application of suitable farming practices (sometimes integrated by copper and sulphur treatments and insecticides spread on the soil) is usually enough to guarantee a good output.

1. Operative sheet - The seed treatment

The seed treatment is a process which is regarded today as a highly qualifi ed, rational and evolving procedure among the farming practices, being an alternative means to the use of phytochemicals to protect crops against pests in the open fi elds. In the past pesticides used to be spread over the whole crop in the fi elds; afterwards, with the advent of soil pesticides, phytochemicals were distributed over the ground along the seed rows. Finally, today the seed treatment further reduces the soil surface in contact with the chemical substance. This technique consists in an even, precise and localized application over the seed of specific products against fungal diseases and pests, with possible addition of nutritional elements suited to improve the plantlet germination and growth. The main advantages of seed treatment are:

• Protection of the crop in the early stages of development;

• Reduction of active substances spread over the ground;

• Targeted application of phytochemicals;

• Simpler operations in the fi elds compared to the treatments with micro-granulates or with additional spreading tools.

This allows to preserve the seed value to the advantage of the crop productivity and quality.

2. Operative sheet - Plant breeding: genetic improvement

The genetic improvement is a process carried out through techniques aiming at creating varieties or breeds able to meet farming production requirements both quantitatively and qualitatively. The fi rst step to obtain the genetic improvement is the selection by which to improve the intensity of trait of interest. All the individuals, showing that particularly marked trait, are crossed among each other and, among their offspring, the ones with those desirable traits are chosen and so on over many generations (inner breeding (or in-breeding). Finally, most individuals are homozygous for that desirable trait. Nowadays, most plant breeding techniques have two main purposes: crop increase and disease resistance. Resistance is a trait often found in the wild species similar to the domesticated one; therefore, crossbreeds between the species are carried out in order to create the resistance trait in the cultivated one. Repeated crossbreeds are necessary in order for the cultivated species to maintain the desirable traits and get the genes of resistance. In 1970, when a serious fungal disease, caused by Hemiltosporium, struck maize, destroying over half of the harvest in California, the worldwide damage was kept under control because disease resistant germplasms were searched and found in maize ecotypes of the Third World countries. On the one hand, however, genetic selection allows to obtain standard varieties which show the desirable traits, on the other hand it may give rise to the inbreeding depression (for example the case of consanguinity among human beings). Eukaryotes, being diploid, can be healthy carriers of many genetic diseases, without showing any symptoms because of heterozygosity. As a matter of fact, genetic abnormalities are usually carried by recessive genes, whose disorder is concealed by the normal gene. In the homozygous organism it is easy to fi nd in both genetic loci the same defective, less or not at all functioning allele, with consequent lower physiological performance of the homozygote. In order to avoid such problem, heterozygosity is re-established through an external breeding or outcrossing, through which the altered genes are replaced by necessarily different genes. The hybrids obtained will have different growth, size and reproductive capacity from the varieties they derive. This phenomenon is called heterosis or hybrid vigor. Maize is the crop which has taken great advantage from the realization of hybrids using this technique, registering a big increase in production over the last 50 years.

CHECKING SKILLS

Answer with T (True) or F (False)

1. Cereals may contain micotoxins which are poisonous to human health

2. Puccinia graminis only affects wheat (by causing stem, black cereals rusts)

3. Take-all is a bacteriosis affecting wheat

4. The pyralid Corn borer is a lepidopter affecting all cereals

5. Rice blast affects the leaves of rice

Complete text with the missing words

1. The following fungi cereals pests, Corn ........ and Tilletia caries, are classifi ed as .............................

2. The main pests affecting maize are the ........... European corn borer and Western corn rootworm.

3. The main fungal diseases affecting barley are Pyrenophora teres f. .............., ............................. secalis and Barley ................

4. Lissorhoptrus oryzophilus is an insect affecting .............

- pyralid

- rice

- smut

- maculata

- Basidiomycetes

- Rhynchosporium

- stripe

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