Chestnut blight fungus (Cryphonectria parasitica Murrill Barr) ; diversity and impact on sweet chestnut (Castanea sativa Mill.) populations

Abstract

Devet populacija gljive Cryphonectria parasitica, patogena pitomoga kestena, s geografskog područja Hrvatske i Slovenije genotipizirano je upotrebom 11 mikrosatelitnih biljega. Analizom podataka ustanovljena je vrlo velika genska raznolikost populacija ovog patogena na istraživanim područjima te je postavljena hipoteza o dva neovisna unosa ove gljive na područje Hrvatske i Slovenije, od kojih je prvi najvjerojatnije bio sa zapada tijekom 50-tih godina XX. stoljeća, a drugi s jugoistoka, vjerojatno kasnije. Historiografski podaci ukazuju da je upravo na području Lovrana prvi puta zabilježena pojava raka kore kestena, stoga je lovranska voćnjak/šuma s nasadima prirodne populacije kestena i cijepljenih maruna podrobnije istražena. Analizom mikrosatelitnih genotipova kestena utvrđena je velika raznolikost prirodne populacije kao i klonalno porijeklo maruna, cijenjenog kultivara kestena. Osim toga zabilježen je neočekivano velik broj aktivnih rakova kore kao i nedostatak zarastajućih rakova – kalusa, upravo na marunima, unatoč prisutnosti hipovirulentih izolata gljive C. parasitica na ovom području. Istraživanje je pokazalo da se, za razliku od prirodne populacije kestena, lovranski marun slabije oporavlja od ove bolesti.Nine populations of sweet chestnut pathogen Cryphonectria parasitica, from Croatia and Slovenia were genotyped using 11 microsatellite markers. Data analysis revealed high gene diversity of this pathogen in the studied area. Therefore a hypothesis of two independent introduction events of this fungus in the area of Croatia and Slovenia was proposed: the first one from west during the 1950's, and the second from southeast, probably occurring later. Historical data indicate the Lovran county as the first place where chestnut blight was observed in Croatia, therefore Lovran orchard/forest with naturally growing chestnuts and grafted marrons was further studied. Microsatellite analysis of the chestnuts showed a very diverse natural population as well as clonal origin of the marron, a cherished chestnut cultivar. Besides that, an unexpectedly large number of active cankers as well as the lack of healing cankers – calli, was observed on marrons, despite of presence of hypovirulent strains of C. parasticia in this area. This research revealed that, unlike naturally growing trees, the marrons recovery from this disease is much slower