Experimental approaches for agro-ecological management of black leaf streak in dry and humid tropical conditions

Abstract

Black leaf streak (BLS), caused by the phytopathogenic fungus Pseudocercospora fijiensis, leads to leaf necrosis and often to a substantial reduction in fruit yield. It also causes the fruit to ripen early by reducing the time between harvest and the beginning of natural ripening, called green life (GL). The usual method of control is by spraying fungicides, but this type of management is challenged worldwide due to the high costs, regulation of products, environmental concerns and the development of resistance. Integrated pest control is an alternative management method based on the combination of agronomic practices that can slow down the development of the epidemic, and limit damage to the fruit. Two experiments were conducted in the Dominican Republic and Martinique, to evaluate the performance of an innovative prototype cropping system with no chemical control. This system is based on optimal growth management, to reduce stress and enhance the leaf emission rate, combined with the systematic removal of necrotic parts of the leaves, which strongly limits ascopore sporulation and reduces the effect of BLS on GL. Depending on the conditions and cycles, the reduction in bunch weight with the prototype system versus chemical control ranged from O to 15%. Bananas were harvested at the same physiological age in the prototype and in the control. The bananas harvested from plants with as low as zero leaves left at harvest retained a good aptitude for conservation, with up to 40 days of GL, on average. The limited impact on fruit weight observed suggests that physiological compensation phenomena through remobilization of resources inside the plant (stem, bunch, suckers) occur. Above all, the removal of necrotic leaves prevented a significant negative effect on early fruit ripening when the bananas were harvested at the correct physiological age, and enabled export of the fruit despite the small number of leaves remaining on the plant at harvest. These results offer perspectives for the development and transfer of alternative practices to chemical control.