Resistance estimation to Phytophthora palmivora in cacao genotypes using artificial inoculation and natural infection in the field

Abstract

Black pod disease (BPD) is a severe biotic disorder affecting cacao trees in tropical regions generating an estimated global production reduction of approximately 20 to 30%. Accordingly, this study aimed to investigate the correlation between two artificial inoculation methods for Phytophthora palmivora and their potential association with natural infection in cacao clones. Incidence (%) and severity in detached pods (average lesion diameter) and leaf discs (disease severity index) were evaluated. The inoculation in pods at 6 DAI (Days After Inoculation) indicated the highest lesion diameter values for clone CCN51 (9.83 cm); hence, it was categorized as the most susceptible. Conversely, clones IMC67 (5.30 cm) and PA46 (5.27 cm), with the lowest lesion diameter values, were classified as moderately susceptible. Similar outcomes were observed in the leaf disc infection test, corroborating the susceptibility categorization of all six clones at 10 DAI. The leaf disc infection method showed a significantly positive correlation with the detached pod infection method, highlighting the feasibility of employing leaf inoculation to classify clones based on their susceptibility to BPD. Significant differences in aggressiveness were established between the isolates from different Colombian cacao regions. These findings were consistently reflected in the field, where the CCN51 clone exhibited the highest susceptibility compared to TSH565 and ICS95. This research proposes using the leaf technique to assess the aggressivity of Phytophthora palmivora isolates in cacao trees in Colombia.