Monika Höfer

European pome fruit genetic resources evaluated for disease resistance

Pome fruit genetic resources collections constitute a highly valuable resource not only for fruit breeding but also for direct use by nurseries, growers, and home gardeners. In order to use these resources efficiently and sustainably, reliable evaluation data on fruit and tree characteristics must be generated. Here we focus on pome fruit genetic resources evaluated phenotypically and genotypically for susceptibility to apple scab (Venturiainaequalis), powdery mildew (Podosphaeraleucotricha), fire blight (Erwiniaamylovora), pear rust (Gymnosporangiumsabinae) and storage diseases (e.g., Penicilliumexpansum). Examples are presented of several ongoing projects throughout Europe, with the aim to evaluate fruit genetic resources for disease susceptibility and potential use in breeding and for commercial use. The COST action 864 has fostered international cooperation in the evaluation of pome fruit genetic resources, and some of these evaluations therefore involve research groups from several of the participating countries.

Assessment of phenotypic variation of Malus orientalis in the North Caucasus region

Malus orientalis Uglitzk. is the predominant Malus species of the Caucasian forests distributed in the north of Anatolia, Armenia, Russia as well as in Iran. It is considered as one of the probable minor ancestors of domestic apples. Although M. orientalis has a lower diversity of fruit quality, other valuable traits such as later blooming, adaptation to a wider array of habitats, and capacity for longer storage of the apples should be taken into account for improving the genetic makeup of the domestic apple. A joint expedition of scientists of the Julius Kühn-Institute from Germany and the Nikolaj I. Vavilov Research Institute of Plant Industry from Russia was performed into the North Caucasus region during August/September 2011. Altogether 101 M. orientalis accessions were collected from eight sites at the North Caucasus. Twenty-six traits such as size, color, shape, flavor and firmness of fruit and tree habit were used for phenotypic evaluation of the accessions. A high phenotypic diversity within the collected material of M. orientalis was indicated. Accessions characterized by suitable fruit traits like bigger size, larger cover color, less bitterness and better firmness as well as more sweetness and better flavor were found. However, small-sized flavorless fruits were also detected. Tree habit varied widely from upright to weeping. Subsequently, a comprehensive phenotypic and genetic evaluation of M. orientalis increases the knowledge of diversity, may provide new resources of agronomically important traits for breeding purposes, and gives support to determine accessions for a core collection.

Phenotypic and genetic analysis of the German Malus Germplasm Collection in terms of type 1 and type 2 red-fleshed apples.

Red fruit flesh is a desirable trait in apple breeding, because red-fleshed apples are a novelty and therefore considered to be more attractive to consumers and contain more health beneficial compounds. The red fruit flesh coloration is based on an increased level of cyanidin 3-galactoside, an anthocyanin whose biosynthesis is regulated by the MYB-type transcription factors MdMYB10 or MdMYB110a, respectively. A repeated segment in the MdMYB10 promoter allele R6 results in a gain-of-function mutation visible as red pigmentation of fruit skin and flesh and all vegetative tissues. Red-fleshed apple genotypes containing this R6 allele belong to the type 1 red-fleshed apple, which is known to be linked to some negative traits like astringent taste and internal flesh browning disorder. In type 2 red-fleshed apples the fruit flesh coloration is not inevitably linked with skin and leaf color. This red-fleshed apple phenotype, which is a result of increased expression of MdMYB110a, seems to be more useful for breeding, but it can be found rather seldom. In the present study 357 Malus accessions of the German Malus Germplasm Collection were evaluated for red fruit flesh coloration and the presence of the MdMYB10 R1 (not mutated) and R6 promoter alleles. Among them a total of 40 accessions were identified which contain the R6 allele. 37 accessions showed a red coloration of the fruit flesh. All these accessions belong to type 1 red-fleshed apple. No type 2 red-fleshed apple could be found. Three accessions with R6 allele had non-red-fleshed apples. 312 other non-red-fleshed accessions contained only the R1 allele. Five non-red-fleshed accessions contained a new promoter allele with an unexpected size of ~1 kbp. Sequencing of this allele detected the insertion of a non-autonomous apple transposon.

Evaluation of Rubus genetic resources on their resistance to cane disease

Raspberry cane disease, caused by a complex of fungi, is amongst the most devastating problems for raspberry production. Using resistant or highly tolerant genotypes is a promising strategy. However, until now, cultivars with good field resistance for German fruit growers as well as the primary causal pathogens of cane disease present in the eastern part of Germany, Saxony state are still unknown. The primary objective of this study was to identify the primary disease causing organisms and resistant Rubus germplasm for future breeding efforts. From 2012 to 2014, we evaluated the degree of susceptibility to cane diseases on 213 raspberry cultivars at two different locations using a rating scale. We also identified the main fungi growing on infected canes. Our results suggest that Fusarium avenaceum is the main fungus causing cane disease in Saxony. The Rubus hybrid cultivars ‘Tayberry’ (2n = 6x = 42), ‘Buckingham Tayberry’ (2n = 6x = 42) and ‘Dorman Red’ (2n = 2x = 14) displayed the highest levels of field resistance at both locations. Moreover, we established an in vitro assay for resistance evaluation which correlates significantly with field data and is particularly suitable for quick assessment of resistance against F. avenaceum in breeding material. Future breeding programs, aiming at cultivars with enhanced resistance towards cane diseases can use the presented data for parental selection and may employ our in vitro F. avenaceum inoculation method for parental testing and progeny selection.

Cryopreservation of fruit germplasm

Most temperate fruit species are genetically heterozygous and vegetatively propagated. Active collections of fruit genetic resources in Germany are generally maintained in the field, e.g., as potted plants for Fragaria and as trees for pome and stone fruit species. The plant material in active collections should be kept in duplicate to ensure security in case of disease or environmental disaster. The aim of this study was to develop an efficient complementary conservation strategy for fruit genetic resources. Although costly, fruit tree cultivars can be duplicated as field collections at a second site within the framework of the German Fruit Genebank, which is a decentralized fruit-specific network. Wild species accessions, particularly those of the genera Malus spp. (apple) and Fragaria spp. (strawberry) as well as strawberry cultivars, can also be duplicated by means of cryopreservation. In the current study, long-term cryopreservation was initiated for 194 Fragaria genotypes. A protocol combining vitrification with cold acclimation was effective and highly reproducible, with an average regrowth rate of 86%. In Malus, a general cryopreservation protocol based on dormant winter buds was adopted. Based on the results provided in this study, a combination of traditional ex situ conservation and cryopreservation can greatly improve the stability and security of fruit germplasm conservation.

Molecular and flow cytometric evaluation of pear (Pyrus L.) genetic resources of the German and Romanian national fruit collections

A total of 188 German and 28 Romanian pear accessions were evaluated using flow cytometry and molecular markers to detect homonymous and synonymous genotypes, triploids, which are not useful for breeding, and genotypes having favorable traits for breeding. Genotyping was done using a set of 11 simple sequence repeat markers proposed by the European Cooperative Program for Plant Genetic Resources, along with a standard set of six reference pear genotypes used in previous studies. The observed number of alleles ranged between 21 and 38 per locus. Twenty-three accessions could be confirmed as triploids. Because of the expected cross-incompatibility they are only of limited interest for breeding. The study confirmed that 180 of the 188 tested German accessions represent unique genotypes, while some accessions were found to be genetically identical. In parallel additional markers, which are known to be linked to resistance/susceptibility to major pathogens (e.g. black spot, aphid, fire blight, and apple scab), were applied to the German accessions. The comparative screening of the Romanian pear genetic resources demonstrated that only a few accessions with identical/very similar names to German accessions really have an identical fingerprint. Mislabeling and homonymous designation of different genotypes seems to occur frequently in different collections.

Russisch-Deutsche Kaukasusexpedition 2011

Vom 22. August bis 4. September 2011 fand eine gemeinsame Sammelreise von Wissenschaftlern des Julius Kuhn-Institutes (JKI) und russischen Wissenschaftlern des Nikolai I. Vavilov Forschungsinstitutes fur Pflanzenbau (VIR) im nordlichen Kaukasus statt. Ziel der Expedition war es, genetische Ressourcen von im Kaukasus vorkommenden Obstarten zu sammeln und diese in die Genbanken der beteiligten Institute zu uberfuhren. Das gesammelte Material wird von den beteiligten Partnern gleichermasen evaluiert und auf das Vorkommen wertgebender Eigenschaften gepruft, um nachfolgend neues Ausgangsmaterial fur kunftige Zuchtungsarbeiten bereitzustellen und Core-Kollektionen fur die Obstarten abzuleiten. Stichworter: Apfel, Birne, Malus orientalis, Pyrus caucasica, Russland, genetische Ressourcen, Obstarten Russian-German expedition into the Caucasus 2011 Summary From August 22nd to September 4th, 2011 a joint expedition of scientists from Germany and Russia of the Julius Kuhn-Institute (JKI) and the Nikolaj I. Vavilov Research Institute of Plant Industry (VIR) into North Caucasus has been taken place. The expedition was aimed on collection of fruit genetic resources in this region and their introduction into national collections for fruit genetic resources of both countries. Subsequently, the collected material will be evaluated by the participating partners regarding sources of agronomical important traits in order to provide new resources for breeding purposes, and aid in determining accessions for core collections of the fruit species. Keywords: apple, pear, Malus orientalis, Pyrus caucasica, Russia, fruit species, genetic resources