INTERAÇÃO ENTRE Pratylenchus brachyurus E Macrophomina phaseolina NA CULTURA DA SOJA

Abstract

Soybean is the main commodity in Brazil and occupies an area of approximately 39.9 million hectares. However, crop yield is still affected by susceptibility to pests and root diseases, some of which are amplified by the fungus-nematode association. The association between two or more phytopathogens can cause an exacerbated expression of symptoms in the plant, negatively affecting the growth and development of the plant. Two experiments were perfomed in a greenhouse with the objective of evaluating the interaction between Pratylenchus brachyurus and Macrophomina phaseolina in soybean. The experiments were installed in a randomized block (DBC) experimental design. Experiment I consisted of 5 treatments and 10 replications, with sowing in 900mL pots, and the plants were conducted up to 70 days after sowing (DAS). Experiment II consisted of 5 treatments and 15 replications, with sowing in 8L pots, where the plants were conducted up to 105 days after sowing (DAS), in order to allow production evaluation. The treatments evaluated were: i. plants without soil infestation (control); ii. soil infested with M. phaseolina inoculum at the time of sowing; iii. soil infested with M. phaseolina at the time of sowing and with P. brachyurus seven days after sowing; iv. soil infested with P. brachyurus seven days after sowing and v. soil infested with P. brachyurus seven days after sowing and M. phaseolina 14 days after sowing. The severity of lesions on roots, number of nematodes in the soil and root, plant development, yield components and gas exchange analysis were evaluated. Statistical analyzes were performed using Minitab statistical software. In a general analysis, it was concluded that the damage caused by the interaction between P. brachyrus and M. phaseolina: (i) causes an increase in severity when predisposed by P. brachyurus and in conditions of higher temperatures; (ii) does not support the increase in nematode population in soil and roots; (iii) does not interfere with photosynthesis (A), since there was no statistically significant difference between treatments inoculated with soil-dwelling phytopathogens; (iv) it causes a decrease in plant development parameters when the infection initially occurs by P. brachyurus and (v) for some of the analyzed variables, the interaction predisposed by P. brachyurus presented a synergistic effect, confirming the hypothesis that the nematode opens doors for fungal infection and can lead to increased damage and reduced productivity.