Morphological and anatomical leaf characteristics of some European and Asian pear cultivars

Abstract

The objective of this study was to determine morphological and anatomical leaf characteristics and stomatal traits of three European (Pyrus communis L.) cultivars, three Asian [Pyrus pyrifolia (Burm. f.) Nakai] pear cultivars together with one interspecies hybrid (P. pyrifolia x P. communis 'Bartlett') and link them with the resistance to pathogens. Pear trees were grown under the standard practice without irrigation. Fully developed leaves were picked from the middle part of the extension shoots at the beginning of the July. Leaf traits were measured on leaves picked the same day. Anatomy of leaves was determined under light microscopy (LM) while scanning electron microscopy (SEM) was used for the examination of the stomata cells. Asian pear cultivars ('Kousui', 'Nijisseiki' and 'Niitaka') had much higher leaf parameters (width, length, stem length and leaf area) than the European cultivars ('Conference', 'Williams Bartlett', 'Abbate Fetel') and interspecies hybrid ('Kieffer Seedling'). Midrib parameters (length and width) were the highest in 'Kosui' and 'Nijisseiki'. Leaves of 'Kieffer Seedling' and 'Abbate Fetel' were the thickest, mainly due to increased palisade and spongy parenchyma thickness. The leaf stomata density significantly varied among the pear cultivars, ranging from 89.53 stomata mm(-2) ('Nijisseiki') up to 134.07 stomata mm(-2) ('Housui'). SEM proved that Asian pear cultivars and 'Kieffer Seedling' shared 'paracytic' stomata type, while European pear cultivars had 'anomocytic' stomata type. Cluster analysis distinguished pear cultivars into two distinct groups, where European cultivars formed first sub-cluster and Asian together with 'Kieffer Seedling' second subcluster. Midrib traits and stomata type made a clear separation between the clusters. These results might suggest that thickness of midrib could be a huge barrier for Psylla sp. probing in Asian pears, thus representing one of the key factors in the resistance of these cultivars.