Difesa delle colture

Difesa: colture erbacee in pieno campo 83 parte 1 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 first 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 find 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) T F T F 3. Take-all is a bacteriosis affecting wheat T 4. The pyralid Corn borer is a lepidopter affecting all cereals T 5. Rice blast affects the leaves of rice T F F F Complete text with the missing words 1. The following fungi cereals pests, Corn ........ and Tilletia caries, are classified as ............................. 2. The main pests affecting maize are the ........... European corn borer and Western corn rootworm. - pyralid - rice - smut - maculata - Basidiomycetes - Rhynchosporium - stripe 3. The main fungal diseases affecting barley are Pyrenophora teres f. .............., ................................ secalis and Barley ................ 4. Lissorhoptrus oryzophilus is an insect affecting ............. DIGITAL BOOK ITALIAN VERSION

Difesa delle colture
Difesa delle colture
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