Medicinal plants, Bacillus subtilis BV09 and precision agriculture in the management of Meloidogyne spp.

Abstract

Lettuce and tomato are vegetables of high commercial value widely consumed around the world. Root-knot nematodes (Meloidogyne spp.) are soil-borne pathogens that causes galls formation in the root system of both affecting plants’ growth, which can cause losses in more than 80% of production in lettuce and tomato crops. To control plant-parasitic nematodes, integrated management is necessary, adopting cultural, chemical and biological control practices. Some medicinal plants can be used to control Meloidogyne spp. due to its ability to produce metabolites with nematicidal properties. In this context, the objective was to evaluate the effect of cultivating medicinal plants intercropped with lettuce and tomato on the management of root-knot nematode in these crops. Considering the importance of the integrated management in nematodes control and the search for alternatives less aggressive to the environment, in the field experiment applications of Bacillus subtilis BV09 (microbiological nematicide), elimination of infested roots, and fallow. Aerial images captured by unmanned aerial vehicles (UAV) can provide important information for decision-making in cultural treatments, detection and management of plant diseases, therefore, aerial images were carried out to monitor the crops. Initially, three medicinal species were selected: Allium sativum (garlic), Catharanthus roseus (Madagascar periwinkle), and Achillea millefolium (yarrow). Tagetes patula (marigold) was used as a positive control. These were grown intercropped with lettuce and tomato in pot (experiments 1 and 2). The substrate was infested with eggs or second-stage juveniles (J2) of Meloidogyne javanica and the pots were kept in a greenhouse until the evaluation of the number of eggs in plant roots. Medicinal plants intercropped with lettuce or tomato promoted a reduction in the total population of M. javanica per pot. In laboratory, it was found attractiveness of roots and root exudates, reduced penetration and affected the development of J2 in the roots of Madagascar periwinkle and marigold, while J2 showed a random response to yarrow and garlic root exudates. In the field (experiment 3) the effect of garlic cultivation and the application of B. subtilis BV09 on the management of Meloidogyne incognita was evaluated, as well as the use of aerial images to monitor the disease. Garlic cultivation intercropped with lettuce, application of B. subtilis BV09, fallow soil and elimination of infested roots were efficient in reducing M. incognita population in the field. The production per garlic plant was improved by intercropping with lettuce and B. subtilis BV09 application, while the production per lettuce plant was affected by the intercropping when garlic plants were large, due to competition for nutrients and solar radiation. Intercropping enabled achieving high total income from lettuce and garlic crops, as the total income obtained from lettuce monoculture. In laboratory, it was observed that B. subtilis BV09 application altered the chemical composition of lettuce and garlic root exudates, affecting the chemotactic response of M. incognita. Aerial images obtained with UAV allowed the evaluation of lettuce plants' growth over time, presenting the potential for use in the detection of root-knot nematode affected areas when plants show reduced growth.