Biokemijska osnova otpornosti lista jabuke na infekciju bakterijom Erwinia amylovora

Erwinia amylovora is the most frequently found necrogenic bacterium on apple (Malus domestica Borkh.) trees, which causes progressive necrosis and blight of host plants. Rapid spread of bacteria through the host tissue can lead to the loss of entire trees in one growing season. In this work, the aim is to investigate long-lasting biochemical responses in leaves of two apple cultivars (Enterprise and Golden delicious). Several histochemical (polyphenols, suberin and callose) and biochemical parameters (total polyphenols, superoxide dismutase – SOD, ascorbate peroxidase – APX and guaiacol peroxidase – GPOD) were screened 60 days after Erwinia inoculation in order to find their potential correlation with plant resistance mechanisms to the pathogen attack. Differential susceptibility to the pathogen attack observed between the investigated cultivars was in accordance with previous studies that characterized Enterprise as less susceptible and Golden delicious as more susceptible cultivar. Infected leaves of Golden delicious expressed symptoms seen as large brown areas at the abaxial side mostly placed at the leaf margin and necrosis also found peripherally, while damage in Enterprise leaves was observed as small brown spots and sporadic leaf edge necrosis. Increased SOD and GPOD activities combined with decreased polyphenol content as well as wide cuticle suberization in cultivar Enterprise should be considered as reliable biochemical parameters characterizing its ability to develop certain resistance to the pathogen infection. Furthermore, the absence of callose deposition in leaves of Enterprise confirmed our findings that thick suberized cuticle is likely the main defense mechanism that enables long-term efficient protection of apple leaves against biotic stress caused by Erwinia attack.Erwinia amylovora je najčešća nekrogena bakterija koja na jabuci (Malus domestica Borkh.) uzrokuje progresivnu nekrozu i palež lista biljke domaćina. Brzo širenje bakterije kroz tkivo domaćina može uzrokovati gubitak čitavih stabala u jednoj vegetacijskoj sezoni. Svrha je ovoga rada bila istražiti dugotrajni biokemijski odgovor u listovima dvaju kultivara jabuke (Enterprise i Golden delicious). Nekoliko histokemijskih (polifenoli, suberin i kaloza) i biokemijskih parametara (ukupni polifenoli, superoksid dismutaza – SOD, askorbat peroksidaza – APX i gvajakol peroksidaza – GPOD) određeni su 60 dana nakon inokulacije bakterije Erwinia amylovora da bi se utvrdila eventualna korelacija s mehanizmima otpornosti biljaka na napad patogena. Različita osjetljivost dvaju kultivara na napad patogena u skladu je s prijašnjim studijama koje Enterprise karakteriziraju kao manje osjetljiv i Golden delicious kao više osjetljiv kultivar. Inficirani listovi kultivara Golden delicious pokazali su simptome u obliku velikih smeđih područja na rubovima naličja lista i perifernu nekrozu, dok su se na inficiranim listovima kultivara Enterprise pojavile sitne smeđe točke i mjestimična nekroza na rubu lista. Povećane aktivnosti SOD-a i GPOD-a zajedno sa smanjenim udjelom polifenola, a i zadebljana suberinizirana kutikula na listovima kultivara Enterprise, trebale bi biti pouzdani biokemijski parametri što karakteriziraju njegovu sposobnost pri stjecanju otpornosti na infekciju patogenom. Osim toga, izostanak kaloznih depozita na listovima kultivara Enterprise potvrđuje rezultate autora da je debela suberinizirana kutikula glavni obrambeni mehanizam koji omogućava dugotrajnu učinkovitu zaštitu listova jabuke protiv biotičkoga stresa uzrokovanog bakterijom Erwinia amylovora