Indução da supressividade à murcha-de-fusário do caupi pela adubação verde

Abstract

The cowpea (Vigna unguiculata) is a crop of great economical and strategic importance, mainly for the Northeast region of Brazil. In the state of Pernambuco, the main cowpea production areas are located in Agreste and Sertão regions. Fusarium wilt, caused by Fusarium oxysporum f.sp. tracheiphilum, is an important cowpea disease worldwide. This work aimed to evaluate the potential of green manure in inducing suppressiveness to Fusarium wilt as well as to identify the factors related to suppressivity. The experiment was carried out in greenhouse conditions. A sandy loam soil with no native populations of F. oxysporum was used. Eleven treatments were compared after soil infestation with F. oxysporum f.sp. tracheiphilum. Different combinations of non-cropping, cowpea (cv. BR-17 Gurguéia) and green manures (showy crotalaria, sunn hemp, mucuna, lablab, canavalia and pigeonpea), in four growing seasons, were compared. Disease severity evaluations along with microbial and chemical characteristics of soil were carried out at the end of the 2nd and 4th growing seasons. For the two evaluations, the incorporation of sunn hemp into the soil led to smallest levels of severity (SVD) of cowpea Fusarium wilt. There was no correlationbetween F. oxysporum population density in soil and SVD. For the first evaluation (2nd season), SVD was negative correlated (r = -0.69) with Bacillus sp. population. Thus, this bacteria was regarded a suppressiveness factor. For the 4th growing season, no significant correlation between SVD and soil microbiological characteristics was found. These results suggest that other mechanisms are involved in disease suppressivenes. Despite the reduction in SVD by sunn hemp incorporation, more studies are necessary to clarify the factors inducing suppressiveness to Fusarium wilt before sunn hemp is recommended for commercial plantations. It is worth considering that the disease suppression in greenhouse conditions does not guarantee similar levels of suppression in commercially cultivated areas under diverse conditions of soil, environment conditions, and management.