Immunomodulator and marker-assisted identification of Allium genotypes containing immunological memory against anthracnose

Abstract

Allium cepa (onion) suffers significant yield losses due to anthracnose disease caused by Colletotrichum gloeosporioides. Current control methods, such as biocontrol agents, have limited effectiveness, while agrochemical applications pose risks to human health and the environment. Genomics-assisted breeding can be useful in getting a diverse genetic pool of wild Allium species to improve disease resistance in cultivated varieties. In this study, we used 42 intron length polymorphic and 22 chloroplast-based SSR markers to identify wild Alliums for anthracnose resistance. Genetic analysis using the marker data showed that two wild types, 6AfistAKO-17 and 15Afistul, are very different from the cultivated types. Immunomodulator benzo-thiadiazole-7-carbothioic acid S-methyl ester evoked a long-lasting immune response in wild Alliums. Transcriptome profiling showed that 131 immune-related genes were more than twice as active in wild Alliums compared to cultivated ones. These included MAPKs (7 genes), WRKY transcription factors (10), R genes (19), MYB transcription factors (28), cytochrome P450s (46), transcriptional activators (14), and other immune-associated genes (7). The results from the anatomical analysis showed that wild Alliums have more callose in their vascular bundles, thicker wax on their leaf surfaces, and closed stomata, which were confirmed by fluorescence and scanning electron microscopy, indicating that wild Alliums have a stronger immune system than the cultivated Alliums. Our findings suggest that wild Alliums possess both immunity and immune memory-related genes. This study suggests that molecular markers could help transfer the immunity-related genes from wild Alliums to cultivated Alliums to protect them from anthracnose infestation.