Effect of climate and geographical conditions on the occurrence of cashew gummosis in the northeast of Brazil

Abstract

Cashew gummosis is one of the main diseases of the cashew in the semi-arid region of the northeast and is characterised by a decline in the plants and a reduction in stand. Lasiodiplodia theobromae, the causal agent, is an endophytic fungus that eventually takes on pathogenic characteristics; however, the environmental conditions that cause this change in behaviour are still unknown. It is assumed that stress in the host caused by environmental changes stimulate pathogenicity. The aim of this study was to define the relationship between climate and geographical factors and the occurrence of gummosis. Rainfall data, maximum and minimum temperature, thermal amplitude, and the altitude of 14 micro-regions in the northeast were compared and classified into five frequencies of disease occurrence: 0 (no occurrence), 1 (rare occurrence), 2 (frequent occurrence), 3 ( generalised occurrence) and 4 (generalised high-severity occurrence). The data were submitted to the Doornik-Hansen test for multivariate normality, and principal component analysis was carried out using the correlation matrix between the climate and geographical variables and occurrence of the disease. Areas of disease severity were correlated (Pearson’s correlation). Only thermal amplitude, altitude and latitude were associated with the different areas of gummosis occurrence. The districts of Buique, in the state of Pernambuco, and Sao Raimundo Nonato, Canto do Buriti and Pio IX, in Piaui, with the highest incidence of the disease, had the highest values for thermal amplitude, altitude and latitude. Whereas the districts of Pacajus and Beberibe had a lower occurrence of gummosis, with lower values for thermal amplitude, altitude and latitude.