Characterisation of Alternaria radicina isolates and assessment of resistance in carrot (Daucus carota L.)

Alternaria radicina ist der Erreger der weltweit auftretenden Schwarzfäule an der Möhrenwurzel. Von Möhren- (Daucus carota) bzw. Petersilienblättern (Petroselinum crispum) wurden vier Alternaria spp. Isolate gewonnen und in Relation zu den Alternaria Arten A. radicina, A. carotiin­cultae und A. petroselini der Alternaria Sektion Radicina, charakterisiert und differenziert. Untersucht wurden Koloniewachstumskriterien, morphologische Merkmale und die Intensität der Sporulation. Typisch für A. radicina Isolate ist die Bildung gelber Pigmente auf angesäuer­tem Kartoffeldextroseagar (APDA). Die Pathogenität der Alternaria Isolate wurde durch Bioassays von Blattsegmenten eines Differenzial-Wirtspflanzensortiments bestehend aus vier Arten aus der Familie Apiaceae untersucht. Verschiedene Möhrensorten und eine Wildform wurden genutzt, um die Aggressivität der Pathogene zu charakterisieren. Die Krankheitssymptome wurden durch digitale Bildanalyse (Digital image analysis system, DIAS, LemnaTec, Deutschland) quantifiziert. Weiterhin konnte mit Hilfe des DAS-ELISA die Erregervermehrung im gesamten pflanzlichen Gewebe erfasst werden. Drei Isolate konnten als A. radicina identifiziert werden und eins als A. petroselini. Zwei A. radicina Isolate unterschiedlicher Aggressivität wurden genutzt, um die Resistenz eines 14 Genotypen umfassenden Möhrensortiments zu bewerten.Alternaria radicina is a fungal pathogen that causes the black rot disease of carrot. Four Alternaria spp. isolates associated with black rot symptoms collected from carrot (Daucus carota) and parsley (Petroselinum crispum) were characterised and differentiated in relation to the closely related Alternaria species A. radicina, A. carotiincultae and A. petroselini belonging to the Alternaria sect. Radi­cina. The Alternaria isolates were differentiated for their growth rates and colony margins. A typical feature of A. radicina isolates is the production of high amounts of yellow pigments on acidified potato dextrose agar (APDA). Furthermore, sporulation intensity and conidia morphology were determined to classify the potential new A. radi­cina isolates. The pathogenicity of the Alternaria isolates was determined by bioassays with detached leaves of four Apiaceae species. Different carrot cultivars and one wild relative were used to estimate aggressiveness of the isolates. The disease symptoms were quantified in bio­assays using a digital image analysis system (LemnaTec). Additionally, a DAS-ELISA with polyclonal antibodies was used to detect the development of fungal pathogens. As result of the morphological and molecular characteris­tics as well as the pathogenicity assay, three isolates were verified as A. radicina and one as A. petroselini. Finally, two isolates with different aggressiveness were used to screen a set of 14 carrot genotypes for resistance to A. radi­cina

Investigating the genetic control of plant development in spring barley under speed breeding conditions

Key message: This study found that the genes, PPD-H1 and ELF3, control the acceleration of plant development under speed breeding, with important implications for optimizing the delivery of climate-resilient crops. Abstract: Speed breeding is a tool to accelerate breeding and research programmes. Despite its success and growing popularity with breeders, the genetic basis of plant development under speed breeding remains unknown. This study explored the developmental advancements of barley genotypes under different photoperiod regimes. A subset of the HEB-25 Nested Association Mapping population was evaluated for days to heading and maturity under two contrasting photoperiod conditions: (1) Speed breeding (SB) consisting of 22 h of light and 2 h of darkness, and (2) normal breeding (NB) consisting of 16 h of light and 8 h of darkness. GWAS revealed that developmental responses under both conditions were largely controlled by two loci: PPDH-1 and ELF3. Allelic variants at these genes determine whether plants display early flowering and maturity under both conditions. At key QTL regions, domesticated alleles were associated with late flowering and maturity in NB and early flowering and maturity in SB, whereas wild alleles were associated with early flowering under both conditions. We hypothesize that this is related to the dark-dependent repression of PPD-H1 by ELF3 which might be more prominent in NB conditions. Furthermore, by comparing development under two photoperiod regimes, we derived an estimate of plasticity for the two traits. Interestingly, plasticity in development was largely attributed to allelic variation at ELF3. Our results have important implications for our understanding and optimization of speed breeding protocols particularly for introgression breeding and the design of breeding programmes to support the delivery of climate-resilient crops