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Fungal Development and Callose Deposition in Compatible and Incompatible Interactions in Melon Infected with Powdery
Paola Beraldo-Hoischen1, Caroline Hoefle2, Ana I López-Sesé1
1Instituto de Hortofruticultura Subtropical y Mediterránea "La Mayora", Consejo Superior de Investigaciones Científicas-Universidad de Málaga (IHSM-CSIC-UMA), Estación Experimental "La Mayora", Avda. Dr. Wienberg, s/n, E-29750 Algarrobo-Costa, Málaga, Spain.
Abstract:
Two post-haustorial resistance mechanisms (types I and II) against powdery mildew, caused by Podosphaera xanthii, have been described previously in melon according to the arresting of fungal development and the timing of hypersensitive response (HR) in host cells. In our work, host-pathogen interactions between races 1, 2, and 5 of Podosphaera and several melon accessions carrying different resistance genes, have been characterized by observing several parameters, such as the number of fungal penetration points with callose accumulation, the number of epidermal cells with callose accumulation in their cell walls, and the number of conidiophores developed. Influence of temperature was observed in some cases affecting the timing of fungal development arrest. According to our results, besides the compatible interaction, four different resistance behaviors in the plant-pathogen interaction have been observed herein: type I and II, as described previously, as well as an earlier and a later type II: IIa and IIb, respectively. Melon genotypes showing post-haustorial resistance mechanism types IIa and IIb against powdery mildew, seem to show different behavior according to temperature, affecting fungal development, mainly those genotypes carrying QTL of linkage group V for powdery mildew resistance, such as "TGR-1551".
Insights
Melon powdery mildew resistance involves two main mechanisms, with new subtypes IIa and IIb identified. Temperature influences these resistance types, particularly in genotypes with specific resistance genes.
Area of Science:
- Plant Pathology
- Plant Genetics
- Mycology
Background:
- Powdery mildew, caused by *Podosphaera xanthii*, is a significant disease in melon.
- Two post-haustorial resistance mechanisms (Type I and II) are known in melon, defined by fungal development arrest and hypersensitive response (HR) timing.
Purpose of the Study:
- To characterize host-pathogen interactions between *Podosphaera xanthii* races and melon accessions.
- To identify and describe new resistance mechanisms against powdery mildew in melon.
Main Methods:
- Assessed fungal penetration points with callose accumulation.
- Quantified epidermal cells with callose accumulation.
- Counted developed conidiophores.
- Observed the influence of temperature on fungal development arrest.
Main Results:
- Identified four resistance behaviors: compatible, Type I, Type II, and two new subtypes, IIa (earlier) and IIb (later).
- Temperature influenced fungal development arrest in some melon genotypes.
- Genotypes with Type IIa and IIb resistance, especially those with linkage group V QTLs like 'TGR-1551', showed temperature-dependent responses.
Conclusions:
- Melon exhibits diverse post-haustorial resistance mechanisms against powdery mildew, including novel subtypes IIa and IIb.
- Temperature is a critical factor modulating the effectiveness of these resistance mechanisms, particularly in specific genetic backgrounds.
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