Major pear diseases: exploring fire blight susceptibility and pear decline phytoplasma variability

Among the pear diseases fire blight and pear decline are two of the most important. Chapter 1 and 2 describe the main characteristics of fire blight and its causative agent Erwinia amylovora, and of phytoplasmas and their associated diseases. In Chapter 3 are reviewed some selected aspects of resistance in plant-pathogen interactions. Chapter 4 reports the results of the isolation and virulence evaluation through experimental inoculations under greenhouse conditions, of eight E. amylovora strains on “Abbé Fetel” and “Conference”, as well as re-isolations from infected “Old Home” pear plants. The selected virulent strain (EaFP621) was used for the phenotyping in two consecutive years of a crossing population of “Abbé Fetel” x “Old Home” segregating for the fire blight resistance trait. The genotyping, using high-density genetic maps of the parentals, and the phenotyping of the above population allowed the identification of a major QTL in LG2 and a minor QTL at the end of LG4 of “Old Home”. Various candidate genes putatively related to resistance have been identified within the QTL region. Chapter 6 focus on the fire blight resistance evaluation in apple. In particular, eight apple rootstocks and three advanced selections were phenotyped for fire blight resistance. The influence of scion/rootstock combinations was also tested. Chapter 7 focus on ‘Candidatus Phytoplasma pyri’ associated with pear decline and the multilocus analysis of five genetic loci, on samples collected in Italy in the last 25 years to evaluate strain molecular variability. Characterization of non-ribosomal genes was applied as effective tool to study the epidemiology of phytoplasmas and to investigate the presence of virulent strains. The markers applied may allow to trace back the route of phytoplasmas spread through infected insects and plant propagation material trade.