Fire blight, caused by the gram-negative bacterium Erwinia amylovora (Burrill) Winslow et al., is a dangerous disease of pome fruits, including pear. A pear breeding program for fire blight resistance was initiated in 2003 at the Department of Pomology, Warsaw University of Life Sciences, Poland. Since several Asian species are considered to be potential sources of resistance to fire blight, the susceptible Pyrus communis 'Doyenne du Comice' was crossed with the resistant P. ussuriensis. The F1 full-sib progeny composed of 155 seedlings was tested for susceptibility to fire blight by artificial shoot inoculation. A framework linkage map of both parents was constructed based on 48 AFLP and 32 SSR markers and covered a length of 595 cM and 680 cM in 'Doyenne du Comice' and P. ussuriensis, respectively. For the first time a putative QTL for fire blight resistance in P. ussuriensis linkage group 11 was identified. Another putative QTL in linkage group 4 of 'Doyenne du Comice' seems to indicate that sources of fire blight resistance can be identified also in the susceptible cultivars.
L'Aptien-Albien du Nord de l'Espagne est caractérisé par de grandes masses calcaires lenticulaires décamétriques à hectométriques constituées par des empilements de mud-mounds. Ces mud-mounds possèdent un noyau construit lithifié très précocément avec une charpente réticulée micritique et bacinellide (type thrombolite) attribuée à l'action d'algues bleu-vert et de bactéries. Les cavités interréticu-laires sont généralement complètement oblitérées par de la micrite claire d'origine également cyanobactérienne : les cavités stromatactoïdes sont rares. Les cristallisations et recristallisations sparitiques à l'intérieur du noyau peuvent être aussi d'origine microbienne. Les grands mud-mounds se développaient selon la séquence suivante : 1-niveau bioclastique basai (faciès A) ; 2-noyau construit, en forme de dôme avec des fortes pentes (30 à 50°) ou de lentille sigmoïde, avec charpente réticulée micritique (faciès B) relayée latéralement par une charpente réticulée bacinellide (faciès C) puis par des faciès à la fois bioconstruits et accumulés (faciès D) ; 3-placage protecteur et couches de recouvrement. Ils se formaient sur de fortes pentes, en bordure des plates-formes à rudistes et orbitolines et face à des milieux de bassin plus profonds et ouverts. Leur implantation et leur développement se faisaient en domaine infralittoral sous la limite d'action des vagues mais l'édification se poursuivait jusque dans la zone intertidale (placage organique protecteur et couches de recouvrement) et pouvait subir des émersions temporaires (éogenèse d'eaux douces).
Several old cultivars, and breeding clones of European pear Pyrus communis L. originating from Belgium, England, Sweden, and Switzerland were evaluated for their resistance/susceptibility to fire blight. Studies were carried out during three consecutive years 2007–2009 in the greenhouse of Warsaw University of Life Sciences, Poland. Strain 691 of Erwinia amylovora was used for artificial infection of plants. Genotypes included in this study considerably varied in their resistance to fire blight. The most resistant was the old English cultivar ‘Hessle’. The other two genotypes, i.e., ‘Gränna Rödpäron’ originating from Sweden, and Pyrus communis FG 1606 from Switzerland were included in a group of low susceptible ones. The most susceptible were Cra Py H 18, Cra Py V 22 and Cra Py W 14 from Belgium.
Since several Asian pear species are considered to be potential source of fire blight resistance, we crossed 'Doyenné du Comice', the susceptible European cultivar, with four Asian pear species. The aim of the study was to establish the level of resistance of each genotype and the mode of transmission of fire blight resistance to each F 1 full-sib progeny. The best sources of resistance were P. ussuriensis 18 and P. ussuriensis var. ovoidea 8 ranked to resistant and highly resistant, respectively. Although pear resistance to fire blight is suggested to be polygenic, distribution of phenotypes in 'Doyenné du Comice' × P. ussuriensis var. ovoidea 8 hybrid family suggests the possibility of monogenic inheritance with the dominance of resistance derived from P. ussuriensis var. ovoidea 8. Polygenic inheritance of pear resistance to fire blight was identified in cross combinations of 'Doyenné du Comice' with P. pyrifolia 6, and contributed by the major gene, with P. ussuriensis 18 and P. calleryana 12. Transgressive segregation was observed within the progenies of susceptible, moderately susceptible and resistant parents.
Studies realized in 2008 and 2009 proved that Neo Arbolin Extra (10 g GA4+7 and 50 g BA in 1 l of solution) and Neo Arbolin (18 g GA4+7 and 18 g BA in 1 l of solution) applied separately or with Algamino Plant (18% extract from seaweeds and 10% of potassium salt of amino acids) stimulated the development of axillary buds on apple maiden trees of ‘Ligol’, ‘Golden Delicious’ and ‘Mutsu’ cultivars grafted on M.9 rootstock, thus enhancing the number of feathers longer than 10 cm. Preparations were applied twice, from the middle of June to July 9. Results differed between years, which may be related to different weather courses during the growing seasons. Neo Arbolin Extra at a concentration 30 ml·l−1 with adjuvant addition (Adpros 5 ml·l−1) gave the best results in branching of maiden trees of three examined cultivars. Trees treated with those preparations twice produced more than 10 feathers (> 10 cm) in the year highly favoring maiden tree growth and more than 6 feathers in the less favorable year. Algamino Plant did not influence apple tree branching.
Polish apple cvs: 'Ligol', 'Odra' and 'Primula' served for studies of self-incompatibility. Basing on available sequence data, a new set of primers upstream and downstream of the hypervariable (HV) region of apple S-RNases were designed. Using the RT-PCR method, cDNA was amplified on RNA isolated from styles. PCR products were cloned and sequenced. A new trans-generic S-RNase allele, designated as Skb (GenBank accession no. EU443101), was discovered in cvs 'Odra' and 'Primula'. Nucleotide sequence alignment revealed that Skb-RNase shows 98% identity to SaucS19-RNase from Sorbus aucuparia and 97% identity to CmonS17-RNase from Crataegus monogyna. The occurrence of extensive intergeneric hybridization among extant Pyrinae is considered since the deduced amino acid sequence of Skb-RNase from M. 9 domestica showed higher similarity to CmonS17 from C. monogyna, SaucS19-RNase from S. aucuparia, St from Malus transitoria, S5-RNase and S3-RNase from Pyrus pyrifolia, and S40-RNase from P. ussuriensis than to S-alleles from Malus 9 domestica and all of them are grouped in the same cluster of phylogenetic tree. In respect to extremely high similarities between aforementioned S-RNases it could be possible that these alleles existed before the separation of Malus, Pyrus, Sorbus and Crataegus genera. Within Malus, the SkbRNase from M. 9 domestica and St-RNase from M. transitoria show 100% identity of the HV region at the deduced amino acid level, suggesting that these S-RNases diverged more recently than the other Malus S-RNases. In 'Ligol', the agronomically most important cultivar in Poland, the S2 and S9 were identified.
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