Red rust disease occurring in some fruits species in Cameroon

Abstract

The knowledge of the red rust disease remains limited in Cameroon, with a view to developing a control method. This work consisted in studying red rust on some fruit species such as Annona muricata (soursop), Dacryodes edulis (safou), Psidium guajava (guava) and Theobroma cacao (cocoa). Diseased leaves were collected in the field in the Maham site, in west region of Cameroon.The symptomatology of disease (colour, number and diameter of lesions) was studied. Coefficient of variation ( %) was calculated. The incidence and severity of the disease was assessed in the different orchards surveyed. The measurement of the different structures of the thallus (length, width of sporangia and sporangiophores) was carried out using a microscope with a micrometer. The disease is characterized by circular orange to orange-brown spots on the upper surfaces and rarely on the lower surface. Number of lesions, varied from 245–510 respectively with D. edulis and T cacao. Lesion diameters varied from 0.1−1 cm, 0.1−7 cm, 0.1−1.5 cm in safou (African pear), guava and soursop respectively. The length and width of sporangiophores varied from 280.5−714×10.2−25.5 µm for A. muricata, 408−612×15.3−25.5 µm for Dacryodes edulis, 433.3−663×15.3−20.4 µm for P. guajava and 484.5−612×20.4−35.7 µm for T. cacao. The number of sporangiophores varied from 1 to 11 at the maximum threshold. But, number of sporangia was the same in the four species, 1−9. The pathogenicity test was negative. The data measurements show that the specie observed is Cephaleurus virescens which is a parasitic alga. The data obtained are a basis for the development of an integrated control strategy against this emerging disease