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Nerine peach. © INRA, MONET René

Pathogen-related harvest losses: analysis and quantification

Methods for the control of orchard pests

Michel Génard and Isabelle Grechi, who are leading the ModQual project, have modelled the impacts of pests on peach and mango. The solutions differ depending on whether the pest attacks the fruit directly or the vegetative parts of the tree.

Updated on 09/12/2016
Published on 01/12/2016

The scientists thus developed a model for the impact of pests and pathogens on temperate and tropical perennial crops such as peach and mango.  They were able to distinguish two types of pest and pathogen: those with direct effects on the crop by attacking the fruit, such as brown rot of peach or fruit fly on mango, and those with indirect effects which attack the foliage, such as green peach aphid.

Green peach aphid: damage that extends over several years, controlled by nitrate fertilisation

Peach aphid (Myzus percicae). © INRA, Elodie Naessens
Peach aphid (Myzus percicae) © INRA, Elodie Naessens

“For green peach aphid with an indirect impact, our model is able to analyse harvest losses in the longer term”, explains Michel Génard. The simulations have confirmed that the aphids cause losses as from the second year; by disturbing vegetative growth, they affect production the next year.  Over ten years, their effects become increasingly important, whatever the initial degree of infestation.

“We varied the levels of leaf nitrogen and our model showed that the positive effect on yields of nitrate fertilisation “wiped out” the negative effect of the aphids.  Averaged over ten years, the positive effect of fertilisation was stronger than the effect of the aphids."

Reducing attacks on fruits by manipulating their size or degree of ripeness

Fruits harvested from peach trees subjected to water restrictions during the cell division period (stress 1), during stone hardening (stress 2) or during the cell expansion period (Stress 3), or subjected to continuous stress during periods 1, 2 and 3.. © INRA, Inra PSH Avignon
Fruits harvested from peach trees subjected to water restrictions during the cell division period (stress 1), during stone hardening (stress 2) or during the cell expansion period (Stress 3), or subjected to continuous stress during periods 1, 2 and 3. © INRA, Inra PSH Avignon

The impact of a fruit pest can be mitigated by manipulating fruit size or date of harvest.  This was shown by the model applied to a pest causing direct damage to mango: the fruit fly.

“Growing conditions that stress the fruits mean they ripen less rapidly.  At a fixed harvest date, the mangos are certainly of poorer quality, but they are also less infested by the flies: the model indicates mean losses of 1.6%, versus 6.6% under non-stressful conditions” explains Isabelle Grechi.  “Similarly, earlier and more frequent picking can reduce the infestation of mangos: a loss of 5.4% with an early harvest, versus a loss of 20% when harvesting at greater ripeness.”

For brown rot of peach, one million ideotypes (1) have been tested by varying six genetic parameters.  It appears that it is not possible to breed ideotypes with large, very sweet fruits that are little susceptible to brown rot, whatever the cultivation practices.  On the other hand, the model predicts the existence of ideotypes producing medium-sized, sweet fruits that are little susceptible to rot. These traits can be obtained by applying water stress to large-fruiting varieties.

The ModQual project has thus highlighted the importance of a compromise between yield and quality to the sustainable management of pest resistance.

(1) In agronomy, an ideotype is a variety of cultivated plant that is bred for its ability to profit optimally from a given environment.

Contact(s)
Scientific contact(s):

Associated Division(s):
Environment and Agronomy, Plant Health and Environment
Associated Centre(s):
Provence-Alpes-Côte d'Azur