Field management of Rotylenchulus reniformis on pineapple combining crop rotation, chemical-mediated induced resistance and endophytic bacterial inoculation
Résumé
In Martinique or La Reunion, French authorities recently banned the use of pesticides for the management of "soil-borne pathogens" on pineapple after several decades of intensive monoculture where the natural balance between beneficial and harmful communities of soil organisms has disappeared. Today, increasing infestation of pineapple by the nematode R. reniformis and other "soil-borne pathogens" causes severe damage to the crop. New cropping systems with innovative ecological nematode management are needed. An eco-friendly cropping system, which comprised rotation of sunn hemp (C. juncea), pineapple, a natural grass fallow and another cash crop, eggplant, consistently reduced the inoculum of nematodes. Nematode populations were reduced by 86.4%, 82% and 46.5% respectively under pineapple, sunn hemp and grass fallow compared to infestations of eggplant (3456 nematodes .100g(-1) of soil) after several rotations. Integrating a chemical induction of systemic resistance or application of an endophytic bacteria recovered from pineapple roots, Bacillus sp. GVS2, helped maintain low populations of nematodes during the vegetative cycle. On two pineapple varieties, MD2 and Victoria (Queen), two different treatments were applied monthly in the field, methyl jasmonate (10(-4) M, 10 ml per plant), or a suspension of Bacillus sp. GVS2 (10(8) CFU ml(-1), 10 ml per plant) isolated from pineapple roots. After eight months, the nematode populations were reduced respectively on MD2 and Victoria (Queen) by 58.3% and 50.3% with the methyl jasmonate and by 59.6% and 54.3% with the Bacillus sp. GVS2 compared to controls. Because of the efficiency of sunn hemp in reducing the inoculum of nematodes, no significant differences in vegetative growth were observed using the D leaf weight and the estimated root length densities (RLD). The potential of pest management through eco-friendly cropping systems for pineapple with a biocontrol for nematodes with no pesticide is discussed.
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