The identification and use of fire blight resistance genes in breeding programmes worldwide is thought to be the most eco-friendly means of tackling the threat posed by the very devastating and erratic fire blight disease of apples, especially as most commercial cultivars are highly susceptible to the causal bacterium – Erwinia amylovora; and the use of antibiotics treatment being forbidden in Germany. The crabapple, Malus fusca, had been found to be highly resistant to fire blight with a strong resistance quantitative trait loci (QTL) mapped on chromosome 10 (Mfu10). Recently, a putative candidate gene underlying Mfu10 was proposed. The candidate gene called FB_Mfu10 was identified on the sequence of a resistant BAC clone, 46H22, spanning the M. fusca fire blight resistance locus. FB_Mfu10 was predicted to possess eight exons and 880 amino acids that encode receptor-like kinase proteins including a bulb-type mannose-specific binding (B-lectin) domain, a catalytic domain of the serine/threonine kinases and interleukin-1 receptor-associated kinases (STKc_IRAK), and the PAN/apple-like domain. These domains are similar to domains of genes that confer resistance to fungal and bacterial disease in other plant species. Furthermore, the amplification of the open reading frame (ORF) on resistance and susceptible clones and the subsequent sequencing of amplicons led to the discovery of eight base pair difference in the first exon that leads to a 28 amino acid difference between resistant and susceptible genotypes and clones.
Therefore, the key objective of the proposed study is to validate the function of FB_Mfu10 in complementing studies. This research is especially necessary as the only functionally proven fire blight gene in Malus, FB_MR5 from M. ×robusta5, is broken down by highly virulent and mutant strains of E. amylovora. It is expected that when validated, FB_Mfu10 will provide resistance to strains breaking FB_MR5 since till date no strain has been able to overcome the resistance of M. fusca which FB_Mfu10 underlies.
Climate change is already impacting on flowering, hence increasing the risk of crop failures in Germany and New Zealand. Whereas in Germany a shift towards earlier flowering can be observed to a period where night frosts can lead to losing a complete crop, in New Zealand winters are becoming too mild for proper flowering because of too few chilling units. In this project, we will initiate research on the contribution of QTL and candidate genes (CGs) to flowering time, starting with known ones and continue with the detection of further genetic factors ruling chilling requirements (bud dormancy release), heat requirements (bud break), and flowering time. The knowledge gained within this project will finally be used to develop molecular markers for breeding. The entire project is based on two complementary approaches (Figure S1) focusing on the same goal. The first approach based on QTL mapping using a F1-population segregating for flowering time. The German partner will do this. The second approach based on genome-wide association studies (GWAS). The New Zealand partner will do this. CGs already known from the literature will be validated and evaluated for allelic variation. The obtained information will be integrated into both aforementioned approaches. Both partners will do this together. The partners will jointly develop the experimental setup for both approaches, discuss the phenotyping and genotyping strategies, collaborate in CGs sequencing and functional validation and share all information and results. They will also collaborate in marker development and validation. The outcomes of this research will enable the selection of new apple cultivars adapted to climate change.