Dynamic analysis of resistance in Colombian elite Hevea brasiliensis genotypes as a breeding strategy for enhancing South American leaf blight management under disease non-escape conditions in the Amazon region

Abstract

South American Leaf Blight (SALB) stands as the primary limitation to the establishment of new rubber (Hevea brasiliensis) crops in Latin America. This study aimed to assess the temporal dynamics of resistance to SALB in 99 elite Colombian genotypes and the IAN 873 cultivar (control) of H. brasiliensis in small-scale clone trials conducted under conditions with a high disease prevalence in the northwestern Colombian Amazon. Resistance monitoring was carried out on a monthly basis and analyzed over five climatic periods. Three variables were recorded: attack severity (AT, ranging from 0 to 4), reaction type (TR, ranging from 1 to 6) and stromal density (ST, ranging from 0 to 4). The maximum scores for TR and ST were used to classify the level of resistance of the genotypes. Highly significant differences in the mean values of AT, TR and ST among the genotypes, across the periods, and in the interaction between genotype and period were found. Over time, an increase in symptoms (AT) and signs (TR and ST) of SALB was observed. During the rainy periods, SALB intensity was highest, resulting in a leaf area affected ranging from 16–30%. Eight genotypes exhibited partial resistance (PR) (TR < 5 and ST < 2), while 16 genotypes demonstrated complete resistance (CR) (TR < 3 and ST = 0), and 76 genotypes were highly susceptible (HS) (TR > 5 or ST > 2). The temporal analysis early on identified 23 Colombian superior genotypes with varying degrees of SALB resistance, which can be a valuable breeding resource for improving SALB management in the Colombian Amazon region.