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V nasadih jablan sort Idared in Elstar smo tri leta preučevali vpliv aplikacije rastnega regulatorja proheksadion-Ca na količino in kakovost pridelka jabolk. Proheksadion-Ca smo nanesli dvakrat v rastni dobi v odmerku 75 g/ha pri sorti Idared in 150 g/ha pri sorti Elstar. Prvi nanos je bil izvršen, ko so poganjki dosegli dolžino 5–8 cm, in drugi tri tedne pozneje. Izvedli smo primerjave med učinki uporabe regulatorja proheksadion pri različnih sortah in zdravimi jablanovimi drevesi in drevesi, ki so bila okužena s fitoplazmo, povzročiteljico bolezni metličavost jablan (AP – Apple proliferation – Candidatus phytoplasma mali). Delo je bilo usmerjeno predvsem v preučevanje učinka rastnega regulatorja na potek patogeneze in jakost izražanja bolezenskih znakov pri drevesih okuženih z AP-fitoplazmo. Uporaba proheksadion-Ca je značilno povečala kakovost in količino pridelka jabolk tako pri zdravih kot pri okuženih drevesih. Pridelek jabolk okuženih dreves se je pri sorti Idared povečal za 18 % in pri sorti Elstar za 15 %. Na podlagi primerjave med okuženimi drevesi, ki niso bila ali pa so bila tretirana z regulatorjem proheksadion-Ca, smo prišli glede učinkov uporabe proheksadion-Ca do naslednjih ugotovitev: delež plodov prvega razreda se je pri sorti Idared povečal iz 17 % na 36 % in pri sorti Elstar iz 18 % na 30 %, povprečna vsebnost sladkorja se je pri plodovih sorte Idared povečala iz 9.8 °Brix na 10.9 °Brix in iz 11.6 °Brix na 12.5 °Brix pri sorti Elstar, trdota plodov in vsebnost skupnih kislin se je nekoliko zmanjšala pri plodovih obeh sort. Uporaba proheksadion-Ca je značilno zmanjšala izražanje bolezenskih znamenj, to je pojavljanje izrazitih metlastih poganjkov. Predstavljeni so tudi nekateri vidiki ekonomike uporabe rastnega regulatorja. Nanos regulatorja proheksadion-Ca pri jablanah, okuženih z AP-fitoplazmo, značilno omili posledice bolezni in izboljša kakovost pridelka. The influence of the application of Prohexadion-Ca (Regalis) plant growth regulator on apple yield quantity and quality was studied in plantations of Idared and Elstar apples for the period of three years. Prohesadion-Ca (75 g/ha for Idared and 150 g/ha for Elstar) was applied twice each season. First it was applied when apple shoots reached length between 5 and 8 cm and once again three weeks later. We compared the Prohexadion-Ca effects on studied yield quantity and quality parameters of two cultivars and of healthy and AP (apple prolifaretion – Canidatus Phytoplasma mali) diseased apple trees. The research was focused on effects in AP diseased trees to found out if this growth regulator influences the AP pathogenesis and disease severity. The use of Prohexadion-Ca resulted in significantly increased quality and quantity of yield in both, healthy and diseased trees. The yield increase in AP diseased trees of Idared and Elstar reached 18% and 15% respectively. The comparison of Proheksadion-Ca non-treated and treated trees showed that the application of Prohexadion-Ca on diseased trees resulted also in the following effects: the percentage of first class fruits increased from 17% to 36% in case of Idared, and from 18% to 30% in Elstar trees the average sugar content of fruits increased from 9.8 °Brix to 10.9 °Brix in Idared fruits and from 11.6 °Brix to 12.5 °Brix in Elstar fruits, while the hardness of fruits and total acid content of fruits were decreased slightly at both studied cultivars. The application of Prohexadion-Ca also significantly reduced the expression of AP disease symptoms and a significant reduction of formation of typical proliferated broom-shaped sprouts was observed. The economic aspects of the use of Prohexadin-Ca were also studied. It was found that the application of Proheksadion-Ca to AP diseased apple trees of studied cultivars can extenuate significantly the AP disease severity and improve the yield quality.

Die Bedeutung phenolischer Inhaltsstoffe, ihre Rolle als Resistenzfaktoren und die Beeinflussung ihrer Biosynthese durch verschiedenste exogene und endogene Faktoren wurden im Rahmen der vorliegenden Arbeit an Birnenpflanzen untersucht. Dabei zeigte sich, dass die Phenylpropanoidbiosynthese von Birne abhängig von dem Genotyp und der Blattentwicklung, sowohl auf eine Infektion mit dem Feuerbranderreger Erwinia amylovora als auch auf eine Behandlung mit dem Wachstumsregulator Prohexadion-Ca (Regalis) reagiert. Desweiteren konnte in den Experimenten belegt werden, dass Prohexadion-Ca der einzige Einflussfaktor ist, welcher aufgrund einer kompetitiven Hemmung eines Schlüsselenzyms neben den quantitativen Modifikationen im Phenylpropanoidstoffwechsel auch qualitative Veränderungen bewirkt. Diese normalerweise nicht in Birnenblättern vorkommenden neuartigen Metabolite wurden als das 3-Deoxyflavonoid Luteoliflavan und das Flavanon Eriodictyol 7-glukosid identifiziert. The meaning of phenolic compounds, their role in resistance and the influence to their biosynthesis by different exogenic and endogenic factors was investigated in this work with pear plants. Dependent on the cultivar and the leaf development, it was shown that the phenylpropanoid metabolism of pear react to infection by the fire blight pathogen Erwinia amylovora as well as to a treatment with the growth regulator prohexadione-Ca (Regalis). In addition it was observed, that due to a competitive inhibition of a key enzyme, prohexadione-Ca is the only influencing factor which causes quantitative and qualitative modifications in the biosynthesis of phenylpropanoids. These novel metabolites, which are normally not synthesised in pear leaves, were identified as the 3-deoxyflavonoid luteoliflavan and the flavanone eriodictyol 7-glucoside.