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I created 12 populations crossing four varieties of spring barley Jersey, Diplom, Saloon, Prestige. Varieties with greater root system size (RSS) better use soil water and nutrients in dry environment than varieties with smaller RSS. I studied effect of selection in 12 populations developed by mutual crossing of 4 parents in F3 generation as response on selection in preceding generation F2 for great (A) and small (B) . Six plants with the greatest (A) and six with the smallest (B) RSS from 24 plants were selected in each population. In F2 generation had the A-plants RSS greater by 39.7% and B plants smaller by 43.1% in comparison with the average of the four parents. In progeny (F3 generation) the difference amounted +3.9% and -2.3% for RSS and +8.1% and -5.1% for grain yield respectively. The selection differences in F2 generation were inherited into F3 by 9.8% in A- and by 5.3% in B-selection. Varieties Saloon and Diplom increased and other two varieties decreased the RSS in their progenies. Combinations Diplom x Saloon and Diplom x Prestige showed the greatest RSS (6.48 and 6.22 nF, respectively), the smallest RSS had a combination with only 1.81 nF. It can be concluded that recombination of some varieties showed greater RSS in progenies than was that of the parents, inheritance was comparable with grain yield and selection for the trait was effective. Selection differences were reflected about two times more in grain yield.

The dissertation is focused on the effect of three antivirals (acyclovir, rimanatadine or zidovudine) for their potencial use in the process of chemotherapy in the combination of meristem culture method as a possible method for Onion yellow stripe virus, Leek yellow stripe virus, Garlic common laten virus and Shallot latent virus eradication in in vitro conditions. Antivirals were always applied separately into cultivation media and two amounts of antivirals (25 or 50 mg.l-1) were used. The treatment time was two weeks. Meristem culture only was a control method. Murashige and Skood medium was used for all variants. During the first year, young plants of the variety D Alsace Freres cultivated in vitro were treated with chemotherapy. These plants had been treated with the meristem culture only in the past but the treatment had not been successful. The virus presence was detected with the ELISA method. Rimantadine variant in the amount of 50 mg.l-1 was the most effective variant for the monitored virus elimination. More sensitive method reverse transcription polymerase chain reaction (RT-PCR) was optimized for monitored viruses in the next parts of this work. Garlic common latent virus (GCLV) primers were designed as well. During the second year, the chemotherapy was applied on explants with the size 0.8 mm during meristem culture. Explants of the varieties Blanin, Sukoradský and Japo, however, did not regenerate and the chemotherapy could not be evaluated. In the next two years of the work, the chemotherapy was applied on individual cloves of the Unikát variety. Whilst detecting the presence of viruses in plants prior the treatment, it was established that only one plant was free from all the monitored viruses. After treatment, acyclovir variant in amount of 25 mg.l-1 was evaluated as the most effective variant for the virus complex elimination, and also from the economical point of view. Real-Time PCR method for virus detection has been started in the dissertation. The detection of GCLV was optimized from the start. Isolates which had been negative for the GCLV presence after RT-PCR were tested with Real-Time PCR. A higher percentage of GCLV positive plants were detected with Real-Time PCR. Real-Time PCR optimization for other viruses will be the objective of futur experiments.