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Vol 7No 12001

The goal of plant breeders is to improve the resistance of crops against virus, bacterium and fungus pathogens was easiest to achieve by selection for phenotypes displaying the hypersensitive reaction. The resistant plant of that type keeps its health by preventing or delaying the systemization of the pathogen by destruction of cells a...nd tissues of variable size or amputation of the contaminated organs. The faster the reaction of the host plant is the more efficient and economical is the defense, since the extent of tissue destruction decreases proportionally with the speed of reaction.

During a breeding program for resistance carried out on several plant species, mainly vegetables over thirty years, also an alternative defense reaction has been experienced, which fundamentally differs from the hypersensitive reaction. In that reaction the cells and tissues of the host plant being exposed to the pathogen do not die, on the contrary they hinder systemization of the pathogen by tissue thickening. An additional significant difference is that on the contrary to hypersensitive reaction this reaction is less host- or pathogen-specific and works excellently even at high temperature (over 40 °C).

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Vol 9No 22003

The objective of this study was to examine the reaction of 44 Capsicum genotypes to common strain of Tobacco mosaic virus (TMV-C/U1), Obuda pepper virus (ObPV), NTN strain of Potato virus Y (PVYNTN) and legume strain of Cucumber mosaic virus (CMV­U/246). Reaction (extreme resistance, hype...rsensitive reaction, latent susceptibility, susceptibility) of the tested Capsicum species/hybrids and breeding lines seemed to be greatly depending on hosts and viruses. Out of the breeding materials 4/99 F2 and IX-8 in to CMV-U/246, while 32.Bogyisz. type, VI-57 ii. 57/83 and V-12=19/98 to TMV-C/Ui showed extreme resistance. Two lines (V-25 F1=32/98 F1 and V-27 in F4=35/98 F4) showed hypersensitive reaction to ObPV. Latent susceptibility to PVYNTN was observed in case of all eleven tested Capsicum genotypes and in case of several lines to TMV-C/U1, ObPV and CMV-U/246. Other breeding materials proved susceptible to the mentioned viruses. Pepper genotypes showing extreme resistance and hypersensitivity could be used for resistance breeding to viruses.

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Vol 8No 3-42002

Our observations regarding the symptoms not fitting into, significantly differing from the hypersensitive defense system, which we noticed during the judgment of several plant species, symptoms provoked on several million plants have constituted a unified entity. They have provided evidence for the existence of a different plant defense system.... We called this so far unknown basic response of plants to biotic effects as general defense system. This system defends them from the attack of numerous microbe species in the environment.

The evolutionary intermediate phase between the general and the specific, the two defense systems is the susceptible host—pathogen relation. The vertical resistance system of plants escaping from the susceptible host—pathogen relation, based on specific hypersensitive reaction also suggested the existence of a more original, general defense system and the susceptible host—pathogen relation developed as a result of the collapse of that system.

The evolutionary relation of the two defense systems is proved by the only recessive inheritance of the older general defense system and in the majority of cases dominant hereditary course of the specific defense system. In our experiences, the modifying genes of the recessive general defense system, in most cases, are behind the specific defense systems, which are known to have monogenic dominant hereditary course and react with hypersensitive tissue destruction. This seemingly striking genetic fact is explained by the following: the general defense system less dependent on environmental effects regulates much faster pathophysiological reaction than the specific resistance genes strongly dependant on environmental effects coding dominant hypersensitive reaction.

The general and specific defense reactions, the processes excluding the microbes attacking plants with compacting of cell growth and tissue destruction, which mean two opposite strategies, building on and regulating each other constitute the entity of resistance to plant disease.

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Vol 7No 3-42001

In addition to successes achieved in certain varieties in resistance breeding based on a defense reaction of host plants involving hypersensitive tissue destruction, resistant varieties putting a very strong selection pressure on pathogens have selected more and more aggressive types of pathogens. The never-ending race between plant and pathoge...n resulting from this can only be controlled by a defense system characterised by a different strategy. In each of the plant species that we bred a defence system was found, which contrary to hypersensitive reaction strives to keep the tissues at all costs and is not pathogen specific. This is implied in the term general defense system.


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Vol 6No 42000

The aim of our study was to examine susceptibility or resistance of 18 pepper varieties to four viruses [tobacco mosaic

tobamovirus (TMV), sowbane mosaic sobemovirus (SoMV), NTN strain of potato Y potyvirus  (PVYNTN) and cucumber mosaic cucumovirus (CMV). Out of the 18 varieties, 13 were resistant to CMV infection. Thirteen were susceptible to TMV, while five ones (Dabora Fl, Brill Fl, Feherozon Synthetic, Ciklon Fl, Cecil Fl) showed only local hypersensitive reaction. All of the tested pepper varieties showed resistance to SoMV. Eight varieties (Tuba, Fehérözön Synthetic, Boni, Alba Regia, Korona, Édesalma, Cecil Fl, Star) were found to be resistant to PVYNTN. Out of the examined varieties five (Boni, Alba Regia, Korona, Édesalma, Star) were resistant to three viruses (SoMV, CMV and PVYNTN). Only one (Cecil F1) displayed complex, extreme resistance to SoMV, PVYNTN, CMV and hypersensitive reaction to TMV, therefore this hybrid is very important in pepper breeding and growing for virus resistance.

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Vol 20No 1-22014

Among diseases that affect walnut, bacterial blight is considered the most important one in all walnut growing areas both from Hungary and Romania. For the determination of susceptibility/resistance of walnut cultivars in our posterior work planned, 61 bacterial isolates were collected from walnuts showing symptoms of blight, with the purpose o...f isolating Xanthomonas arboricola pv. juglandis (Xaj). The characteristic Xaj colonies, frequently present as saprophytes in the infected plant tissues, were separated from other bacteria according to their morphology, yellow colour, hydrolysis of starch, and oxidation of glucose. All isolates were tested for pathogenicity by hypersensitive reaction on tobacco leaves (Nicotiana tabacum L.), bean pods (Phaseolus vulgaris L) and unripe nuts (Juglans regia L.). Determination of taxonomy of the selected isolates denotes a possible subdivision (races, biotypes) of Xaj occurring in different geographical areas, API 20NE and API 50CH kits were used. Hungarian and Romanian strains showed a high degree of similarity of carbohydrate utilization but slightly differed from the type strain. All were Cu-sensitive.

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