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

Resumo

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 DoornikHansen 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 Buíque, in the state of Pernambuco, and São Raimundo Nonato, Canto do Buriti and Pio IX, in Piauí, 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.