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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 resistant varieties and growing techniques (vegetable crops)

Several growing techniques have been tested in combination with resistant varieties to combat root-knot nematodes in vegetable crops sustainably. These techniques (intercrop management, solarisation) are evaluated over four-year periods in agricultural systems, and their acceptability in the industry assessed.

By Terre-Ecos, translated by Inge Laino
Updated on 04/03/2015
Published on 01/22/2015

Sorghum crop. © INRA
Sorghum crop © INRA

A study carried out from 2007 to 2010 with 30 partners representing all stakeholders showed that root-knot nematodes are a major concern of Mediterranean growers; more than 40% of farms are affected and the few chemical products that are still authorized to combat the pest do not work well. “Many solutions have been tested: solarisation, intercrop management with green “nematicide” fertilisers, and crop rotation with non-host plants. But none of them, used in isolation, is satisfactory on all counts: agriculturally, environmentally and economically”, explains Caroline Djian-Caporalino, scientific head of the Gedunem project (1).

Combining alternative techniques

The Gedunem project aims to propose and evaluate protected vegetable cropping systems using a combination of resistant varieties and several technical innovations. This involves boosting the efficiency of parasite control while preserving, in the long term, the few resistance genes available by diminishing the inoculum pressure exerted on these genes. Launched in 2012 for a period of four years, it groups together experiments carried out in four sites in France and one in Morocco. Modelling work is carried out in parallel to study the proposed systems in the long term. It has revealed, among other things, that the best strategies for keeping virulent nematodes at bay are still those that alternate between resistant and susceptible plants.

Working in close collaboration with growers

“Work is carried out in tandem with professionals in the farming world”, continues Caroline Djian-Caporalino. “Making crop systems compatible with the constraints farmers face is all-important. These systems must be acceptable in terms of yield, organisation of work, cost, risk, etc.”. That is why, in addition to nematologists, geneticists, soil ecologists, pathologists and researchers, agronomists also look to the growers themselves to find out what obstacles stand in the way of the proposed multi-annual systems. These obstacles are then identified and removed. “For example, we are trying to reduce the down time between different crops, which certain producers consider too long”, explains the project head. “We are also trying to find a way to avoid systematic annual summer cropping on the same plot since it rules out the possibility of solarisation. We have to stop working at plot level and broaden our scope to the entire farm, as a single sustainable system to be managed over several years”.
 
(1) Gedunem project: Technical and varietal innovations for the sustainable management of root-knot nematodes. Partners: INRA PACA and Alénya, IRD Montpellier, Grab (organic agriculture research group), Aprel (French Association for research and experiments on vegetable crops), Var Chamber of Agriculture.

Contact(s)
Scientific contact(s):

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

Alternative techniques

-  Conventional or biofumigant sorghum used as green fertiliser: in intercropping, used for four to six weeks then buried for at least ten days. Biofumigant sorghum releases gases that are toxic for nematodes. Experiments have shown that conventional sorghum can be just as effective, with a different mode of action: its roots trap nematodes, triggering a hypersensitive reaction that hinders their development (necrosis of root cells surrounding nematodes). Both types of sorghum have led to a 95% reduction of nematode population in the soil.

-  Me1/Me3-resistant pepper used as green fertiliser in intercropping: this constitutes a real innovation since the peppers, with two genes that are resistant to nematodes, were created with a view to serving as rootstock for marketed peppers that are susceptible to the pest. Used as green fertiliser, the pepper plants have proven to be effective nematode traps, arresting development completely. Their roots colonise the soil quickly, making a reduction in growing time from ten to six weeks feasible. The rate of buried dry matter is equal to that of sorghum when used conventionally. This technique reduces nematode populations by more than 99%.

-  Solarisation: this technique consists of flooding the soil in summer, then covering it with tarpaulin to let the sun do its work. When temperatures exceed 60°C, nematodes die. This technique works more or less well depending on temperature and how well the soil is covered. Like the preceding techniques, when solarisation is carried out correctly, nematode populations in the soil are reduced enough to delay resistance circumvention in resistant tomatoes and peppers grown for commercial purposes.