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Querina (R) florina, apple variety resistant to apple scab. © INRA, LE LEZEC Marcel

Novel mechanisms for more sustainable resistance to disease

Combining resistance based on different mechanisms (apple)

Research on resistance to apple scab is focussing on creating new varieties of apple combining resistance based on different mechanisms of action.

By Pascale Mollier, translated by Inge Laino
Updated on 03/30/2015
Published on 01/22/2015

Lesions on fruit and leaves caused by apple scab © RIDE Michel
Lesions on fruit and leaves caused by apple scab © RIDE Michel

Several resistance mechanisms identified

Several QTLs (1) of resistance to apple scab (2) have already been characterised and used to create varieties of resistant apple trees: QTL T1 on the one hand, and the QTL F11/F17 synergistic combination on the other. Research within the framework of the ARAMIS programme (3) has shown that these QTLs have different mechanisms of action. T1 is thought to act upon recognition of the fungus and is particularly effective in specialty strains.The F11/F17 combination, on the other hand, is thought to trigger defence mechanisms in apple trees that prevent the multiplication of the fungus, and acts mainly on common strains. There have been reports of weakened efficiency in untreated orchards where these two types of resistance are used in isolation.

Combining resistance mechanisms

“Based on this data, we think that the combination of these two types of QTLs with different characteristics and mechanisms of action will be more efficient in keeping the evolution of the pathogen in check”, explains Charles-Eric Durel, head of INRA’s ARAMIS programme. A mathematical model that allows scientists to simulate the inhibitory effect of different combinations of QTLs on pathogen populations has proven the merit of this approach: for increased sustainability in resistance, QTLs with different modes of action - those that control pathogens’ capacity to colonise and those that control their ability to reproduce -must be used together.

Experiments currently underway should allow scientists to verify this hypothesis in the field by end-2015. They will do this by measuring the adaptive response of apple scab strains taken from apple trees containing T1, F11 and F17, and identifying the metabolic pathways activated differently in the plant by these two types of QTL.

“These findings will be a starting point for selecting resistant varieties, but we must also take production-related criteria into account to avoid potential conflict between resistance and productivity”, concludes Charles-Eric Durel.

(1) QTL (quantitative trait loci): region of the genome whose polymorphic nature explains in significant part the variability of a measured trait.

(2) Apple scab is caused by the ascomycete fungus Venturia inaequalis. It is the most economically devastating disease of apple trees, requiring 15-20 treatments per year for those varieties susceptible to the pathogen.

(3) ARAMIS: Apple partial Resistance durability Assessed through Metabolic pathways and pathogen adaptation to Selective pressures.

Scientific contact(s):

  • Charles-Eric Durel UMR1345 IRHS Research Institute for Horticulture and Seeds (Joint Research Unit)
Associated Division(s):
Plant Biology and Breeding, Plant Health and Environment, Environment and Agronomy
Associated Centre(s):
Pays de la Loire

Apple scab

No region used for growing apples has escaped apple scab, a disease linked to the ascomycete fungus Venturia inaequalis. It causes brown or black lesions on leaves, buds or fruit, and sometimes even on the wood of apple trees.

Infected fruit is downgraded, driving down their market value. Moreover, if surface lesions are then invaded by a secondary parasite (Trichothecium, Monilia), the fruit rots and is no longer fit for consumption. Apple scab is the most economically devastating disease of apple trees (15-20 treatments/yr for susceptible varieties).