Susceptibility of European pear germplasm to Cacopsylla pyri under Mediterranean climatic conditions

The response of 160 European pear genotypes to the attacks of Cacopsylla pyri in natural conditions of infestation was studied in the ex situ germplasm collection of the IVALSA Institute - CNR located in Follonica (Grosseto, Italy) during three years. ANOVA showed that both the year and the period of survey have a significant effect upon pear infestation assessed by seven variables. The overall average values of the studied accessions for the variables taken into account were used for grouping the genotypes into 5 putative classes of susceptibility by cluster analysis. Four variables (number of colonies, small nymphs, large nymphs and length of the colonies) selected on the basis of discriminant analysis allowed us to classify 70% of the cultivars into the correct group of susceptibility by jackknifed classification matrix. Taking into account the mean values of the variables and their upper and lower limits all the genotypes were grouped into 5 different classes of susceptibility. On the whole, the number of highly tolerant or resistant cultivars were 8.1% of the investigate genotypes; part of them were ancient cultivars of Italian origin as 'Eletta Morettini', 'Fiorenza', 'Gentile', 'Moscatellina', 'Pera Volpina VP7', 'Precoce di Cassano' and 'Precoce di Masi', but there were also the French 'Notaire Lepin' and 'Président Loubet', the German 'Forelle' and the American 'Starking Delicious'. The remaining 91.9% of the germplasm collection showed different levels of susceptibility to psylla attack. The largest part of the genotypes (56.9%) was identified as slightly susceptible, often with minor infestation (that is some isolated larvae, few colonies and reduced honeydew) only in one or two out of three years. Several cultivars (46.3%) were scored as susceptible, suffering medium or high damage, including the widespread cultivated 'Conference', 'Doyenné du Comice', 'Highland' 'Curè', 'Etrusca', 'Kaiser', and 'William', these last 3 being classified as highly susceptible. The influence of the environment and growth condition of trees are discussed together with screening methods applied for the evaluation of pear susceptibility to psylla attack reported in world literature.