The effect of <i>Azotobacter chroococcum</i> on the resistance of red clover to <i>Colletotrichum destructivum</i>

Anthracnose, caused by fungi of the Colletotrichum genus, represents a serious threat to the profitable cultivation of red clover worldwide. This disease also has a significant economic impact on red clover production in Serbia. This study examined the susceptibility of 19 red clover genotypes of different origins and one genotype of Medicago truncatula (Pramedi) to the pathogen Colletotrichum destructivum. Additionally, the study included Azotobacter chroococcum, known for its beneficial effects on plant health. The resistance of the tested red clover genotypes was evaluated under two treatments: Inoculation with the C. destructivum isolate and combined inoculation with C. destructivum and A. chroococcum. Treatments that included a combination of A. chroococcum and C. destructivum generally led to increased resistance or tolerance of red clover varieties to C. destructivum compared to treatments where plants were exposed only to the C. destructivum isolate. Among the tested genotypes, Wilo exhibited the highest resistance in both treatments. In contrast, the most susceptible genotypes were Krusevac-9, Krusevac-32, Krusevac-39, Nigula, Lea, Diana and Pramedi. The potential application of biological control measures specifically, inoculation of red clover plants with Azotobacter species was investigated as a strategy for controlling C. destructivum, the causal agent of anthracnose in forage legumes.