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Effects of microspore culture treatment with antimitotic agents colchicine, trifluralin and oryzalin on the frequency of embryo formation, embryo development, plant regeneration and diploidization rate in three F₁ hybrids of winter rapeseed cultivars were compared. The ploidy level analysis of 1709 flowering microspore-derived plants showed that in vitro applications of all antimitotic drugs increased the rate of doubled haploid (DH) plants significantly. The mean rate of DH plants from the trifluralin treatment was 85.7%, from colchicine 74.1% and 66.5% in the case of oryzalin, while only 42.3% in the untreated control variant whereas in vivo additional application of colchicine at the plantlet stage did not significantly increase the mean rate of DH plants (55.6%). Although there were no significant differences in diploidization efficiency between the in vitro applications of particular antimitotic agents, trifluralin showed to be the most suitable because of its positive effect on embryo development and conversion into whole plants. In addition, the diploidization rate was sufficient and stable in all genotypes tested. The results indicate that the trifluralin treatment of microspore cultures could provide efficient chromosome doubling for the production of doubled haploid lines from winter oilseed rape breeding materials.

The disease caused by Tomato spotted wilt virus (TSWV) belongs to the most destructive diseases of tomato all over the world. Therefore, tomato has been subjected to many breeding efforts, including the incorporation of resistance to the virus. Recently emerged approaches, ideas and technologies could affect the future direction of the virus resistance breeding. In particular molecular techniques have provided opportunities in the form of linked molecular markers to speed up and simplify the selection of host resistance genes. Transformation of an inbred tomato line with the TSWV nucleoprotein gene cassette resulted in high levels of resistance to TSWV that have been retained in the hybrids derived from the parental tomato line. These and other techniques offer great opportunities for improving the virus resistance and, therefore, it is time to reconsider the future direction of resistance breeding in tomato. The effort has been made to review available sources of resistance, conventional breeding methods, marker-assisted selection, pathogen-derived resistance and transgenic resistance approaches in this paper.

In order to study the genetic control of heat tolerance, four varieties/lines of Gossypium hirsutum L., namely MNH-554, Cocker-304, Delcerro and Albacala (71) 1190, were crossed in all possible combinations. Heat tolerance of 12 hybrids and their parents was measured at reproductive phase using an electrolyte leakage technique. The genetic analysis of the data showed significant effects of specific combining ability and reciprocals, but the effect of general combining ability appeared to be non-significant. Comparison of the parents for heat tolerance revealed that Delcerro and MNH-554 were the best general combiners for the character. The crosses Cocker-304 × Delcerro and Albacala (71) 1190 × MNH-554 were determined as the best combinations for heat tolerance and they involved one good general combiner as a parent. Significant effects due to specific combining ability indicated the importance of non-additive gene effects controlling heat tolerance. This information suggests that development of heat tolerance in the present plant material may be difficult; therefore it is necessary to design a specific breeding programme for efficient transfer of the trait.

In 2003-2005 faba bean accessions were evaluated in laboratory and field inoculation tests with a mixture of differently virulent isolates for susceptibility to anthracnose caused by the fungus Ascochyta fabae Speg. All tested commercial faba bean cultivars, both colour and white flowering, were found to be susceptible or highly susceptible. The highest level of resistance was found only in declared sources of resistance: 29H, L-8 and Petra. Segregation of F₂ plants derived from the cross of cultivar Merlin (susceptible, white flowering) with line Petra (resistant, colour flowering) was observed. The plants were moderately susceptible to highly susceptible. This finding indicates a multigenic character of resistance. Repeated selection cycles with the selection of resistant plants in F₂ and F₃ generations were performed. In the F4 generation, colour flowering lines with a high level of resistance, nearly at the same level as in line Petra, were obtained. In comparison with the parental cultivar Merlin an increase in the resistance of selected white flowering lines was proved. Resistance will be increased/stabilized in further repeated selection cycles.

The genetic diversity of 35 yellow-seeded Brassica napus L. accessions originating from China, Czech Republic and Poland was assessed by means of Amplified Fragment Length Polymorphism (AFLP) markers based on multiplex PCR using multi-colour fluorescent-labelled primers. Five brown-seeded accessions originating from China and France were selected as outliers. In total, 632 peaks were generated by AFLP reaction using 18 primer combinations. Only distinctly polymorphic markers among them were scored. In total, 242 polymorphic markers were detected with an average of 13.4 markers per primer combination. The AFLP analysis separated forty studied accessions into Chinese and European groups by UPGMA clustering and Principal Coordinates Analysis (PCA). The grouping of accessions based on the cluster analysis and PCA was generally consistent with known pedigree information and geographic origin. Notable geographical divergence was found between Chinese and European yellow-seeded accessions. This information is useful for yellow-seeded hybrid breeding and encouraging breeders to exchange their germplasm as to enlarge the genetic diversity of breeding accessions.

In ornamental gardening, Spiraea × vanhouttei is a frequently planted spirea species in the Czech Republic. In 2003, there arose a suspicion of possible occurrence of fire blight caused by Erwinia amylovora on spirea shrubs in Prague and its environs. This suspicion was disproved for a certainty. The absence of the fire blight pathogen in symptomatic spirea plants stimulates a further effort to tackle the problem of a cause of conspicuous fire blight-like symptoms or inflorescence blast occurring on some spirea shrubs. The subject of this paper is: (i) to describe symptoms, incidence and severity of inflorescence blast, bud and flower abnormalities occurring in Spiraea × vanhouttei shrubs; (ii) to find out differences in the occurrence of blasted inflorescences between Spiraea species and cultivars with the intention of verifying the hypothesis that the blast inflorescence and sterility of some spirea species are associated with hybrid species. Symptoms of inflorescence blast are every growing season. No seed is produced by blasted inflorescences. Besides inflorescence blast, aborted floral buds appeared sporadically on a small scale. Spirea species were split into four categories according to the incidence of blasted inflorescences. Out of 52 species evaluated, 10% showed no or scarce incidence, 52% medium incidence, 27% high incidence and 11% very high incidence. The scarce incidence of blasted inflorescences was connected with the high seed production. And vice versa, very high incidence of blighted inflorescences was closely connected with no or low seed production or with high incidence of sterility. Fifteen out of the evaluated spirea species are the result of hybridization. These hybrids occur in each of the four categories of spirea species distinguished by the incidence of blasted inflorescence. However, it is remarkable that the highest incidence of hybrid spireas occurs in the category with the highest incidence of blasted inflorescence (83.33%). In the remaining three categories of spirea species, the proportion of hybrids ranged from 18 to 21%. It might indicate some connection of spirea hybrids with sterility.

An improved protocol for Brassica protoplast culture and plant regeneration was developed. Isolated protoplasts from four-weeks-old in vitro shoot tip culture of Brassica oleracea var. botrytis cv. Siria F1 and Brassica napus doubled haploid of breeding line OP-1 were cultured at a density of 9.8-11.2 × 10⁴ protoplasts/ml in darkness at 25°C in a modified medium containing 2% glucose, 0.25 mg/l 2,4-D, 1 mg/l BAP and 1 mg/l NAA. The first divisions of protoplasts were observed on the third day of culture in B. oleracea and on the fourth day in B. napus. The protoplast cultures were diluted with low osmotic medium on 7^th and 11^th day. The frequency of dividing cells was about 80% in B. oleracea and 50% in B. napus. After one month, the microcalli of approximately 0.5-1 mm in size were transferred into an induction medium with various combinations of growth regulators. Minimum duration of enzyme treatment time and extended dark period in the initial phase of culture increased the survival rate of protoplasts. Organogenesis started when the calli enlarged in size on an induction medium (1 mg/l NAA, 0.02 mg/l GA₃, 1 mg/l 2iP) with 2% sucrose and 0.8% agar. Regeneration frequency of calli was found to be 69-75% in B. oleracea and 2-3% in B. napus. Well-developed shoots were transferred for rooting to a half-strength MS medium without growth regulators. More than 100 B. oleracea regenerants were transferred into soil, and they produced normal heads and set seeds. This very simple procedure is efficient and suitable mainly for B. oleracea var. botrytis and represents a background for fusion experiments.

In 2001-2004 virulence of the wheat leaf rust population in the Czech Republic was studied on Thatcher near-isogenic lines with Lr1, Lr2a, Lr2b, Lr2c, Lr3a, Lr9, Lr10, Lr11, Lr15, Lr17, Lr19, Lr21, Lr23, Lr24, Lr26 and Lr28. Samples of leaf rust (180 in total) were obtained from different parts of the Czech Republic. Resistance genes Lr9 and Lr19 were effective to all tested isolates like in the previous years. Unlike the previous years virulence on Lr24 and Lr28 was observed. Relatively effective were also Lr1, Lr2a, Lr24, Lr28 and Lr2b. Other Lr genes were defeated by the majority of the tested samples. Our results transformed to the numbers of physiologic races indicate that race 61SaBa prevailed like in the previous years, followed by races 61, 2, 12SaBa, 2SaBa, 14, 77SaBa, 12, 57, 6, 53, 53SaBa, 77, and 14SaBa. Twenty-one winter wheat cultivars registered in 2001-2004 were tested with 8 leaf rust isolates. Out of them 15 showed resistance at least to one rust isolate. High resistance recorded in field trials for cvs Batis and Ilias, which were susceptible to all tested rust isolates at the seedling stage, demonstrates the importance of field (partial) resistance.

Progression of deoxynivalenol (DON) concentrations in spikes and kernels was studied in relation to Fusarium head blight (FHB) symptoms in five winter wheat cultivars, differing in resistance to FHB, after single floret inoculation with an aggressive isolate of Fusarium culmorum. After inoculation in field conditions the spikes were detached from the plant and kept in the greenhouse under controlled conditions. High concentrations of DON were detected in susceptible cultivars at an early stage of pathogenesis (7 days after inoculation). Over the whole examined 21-day period and also at maturity spikes contained more DON than kernels. While differences between cultivars in the accumulation of DON were highly expressed already 7 days after inoculation, differences in symptomatic reactions were not clear until day 21. Owing to the reported crucial role of DON at early stages of pathogenesis, the importance of appropriate timing of fungicide application is highly stressed.