The inheritance of anthracnose (Colletotrichum sublineola) resistance in sorghum differential lines QL3 and IS18760

Genetic Diversity and Classification of Colletotrichum sublineola Pathotypes Using a Standard Set of Sorghum Differentials

Anthracnose, incited by Colletotrichum sublineola, is the most destructive foliar disease of sorghum and, under severe conditions, yield losses can exceed 80% on susceptible cultivars. The hyper-variable nature of the pathogen makes its management challenging despite the occurrence of several resistant sources. In this study, the genetic variability and pathogenicity of 140 isolates of C. sublineola, which were sequenced using restriction site-associated sequencing (RAD-Seq), resulted in 1244 quality SNPs. The genetic relationship based on the SNP data showed low to high genetic diversity based on isolates' origin. Isolates from Georgia and North Carolina were grouped into multiple clusters with some level of genetic relationships to each other. Even though some isolates from Texas formed a cluster, others clustered with isolates from Puerto Rico. The isolates from Puerto Rico showed scattered distribution, indicating the diverse nature of these isolates. A population structure and cluster analysis revealed that the genetic variation was stratified into eight populations and one admixture group. The virulence pattern of 30 sequenced isolates on 18 sorghum differential lines revealed 27 new pathotypes. SC748-5, SC112-14, and Brandes were resistant to all the tested isolates, while BTx623 was susceptible to all. Line TAM428 was susceptible to all the pathotypes, except for pathotype 26. Future use of the 18 differentials employed in this study, which contains cultivars/lines which have been used in the Americas, Asia, and Africa, could allow for better characterization of C. sublineola pathotypes at a global level, thus accelerating the development of sorghum lines with stable resistance to the anthracnose pathogen.

Inoculation and Screening Methods for Major Sorghum Diseases Caused by Fungal Pathogens: Claviceps africana, Colletotrichum sublineola, Sporisorium reilianum, Peronosclerospora sorghi and Macrophomina phaseolina

Sorghum is the fifth most important crop globally. Researching interactions between sorghum and fungal pathogens is essential to further elucidate plant defense mechanisms to biotic stress, which allows breeders to employ genetic resistance to disease. A variety of creative and useful inoculation and screening methods have been developed by sorghum pathologists to study major fungal diseases. As inoculation and screening methods can be keys for successfully conducting experiments, it is necessary to summarize the techniques developed by this research community. Among many fungal pathogens of sorghum, here we summarize inoculation and screening methods for five important fungal pathogens of sorghum: Claviceps africana, Colletotrichum sublineola, Sporisorium reilianum, Peronosclerospora sorghi and Macrophomina phaseolina. The methods described within will be useful for researchers who are interested in exploring sorghum-fungal pathogen interactions. Finally, we discuss the latest biotechnologies and methods for studying plant-fungal pathogen interactions and their applicability to sorghum pathology.

The Effects of Epicuticular Wax on Anthracnose Resistance of Sorghum bicolor

Cuticular waxes are mixtures of hydrophobic compounds covering land plant surfaces and play key roles in plant resistance to abiotic and biotic stresses. However, it is still not clear whether the epicuticular wax could protect the plants from infection by anthracnose, one of the most important plant diseases worldwide, which seriously infects sorghum and causes great yield loss. In this study, Sorghum bicolor L., an important C4 crop with high wax coverage, was selected to analyze the relationship between epicuticular wax (EW) and anthracnose resistance. In vitro analysis indicated that the sorghum leaf wax significantly inhibited the anthracnose mycelium growth of anthracnose on potato dextrose agar (PDA) medium, with the plaque diameter smaller than that grown on medium without wax. Then, the EWs were removed from the intact leaf with gum acacia, followed by the inoculation of Colletotrichum sublineola. The results indicated that the disease lesion was remarkably aggravated on leaves without EW, which showed decreased net photosynthetic rate and increased intercellular CO₂ concentrations and malonaldehyde content three days after inoculation. Transcriptome analysis further indicated that 1546 and 2843 differentially expressed genes (DEGs) were regulated by C. sublineola infection in plants with and without EW, respectively. Among the DEG encoded proteins and enriched pathways regulated by anthracnose infection, the cascade of the mitogen-activated protein kinases (MAPK) signaling pathway, ABC transporters, sulfur metabolism, benzoxazinoid biosynthesis, and photosynthesis were mainly regulated in plants without EW. Overall, the EW increases plant resistance to C. sublineola by affecting physiological and transcriptome responses through sorghum epicuticular wax, improving our understanding of its roles in defending plants from fungi and ultimately benefiting sorghum resistance breeding.

Transcriptome analysis provides insights into the bases of salicylic acid-induced resistance to anthracnose in sorghum

Key Message Transcriptome analysis of SA sensitive and tolerant lines indicates that SA enhances anthracnose resistance in sorghum by upregulating the expression of some immune-related genes and pathways.Abstract Anthracnose caused by the hemibiotrophic pathogen Colletotrichum sublineolum is one of the most destructive diseases of sorghum, the fifth most important cereal crop in the world. Salicylic acid (SA) is a phytohormone essential for plant immunity; however, the role of SA in sorghum resistance to anthracnose has not been well explored. In this study, we found that Colletotrichum sublineolum infection induced the expression of SA-responsive genes and that exogenous SA enhanced resistance to anthracnose in the sorghum line BTx623. To rule out the possibility that SA triggers anthracnose resistance in sorghum by its direct toxic function on pathogen, an SA-tolerant line, WHEATLAND, was identified, and we found that SA treatment could not induce anthracnose resistance in WHEATLAND. Then, SA-induced transcriptome changes during Colletotrichum sublineolum infection in BTx623 and WHEATLAND were analyzed to explore the molecular mechanism of SA-triggered resistance. SA pretreatment regulated the expression of 2125 genes in BTx623 but only 524 genes in WHEATLAND during Colletotrichum sublineolum infection. The cutin, suberine and wax biosynthesis pathway involved in the plant immune response and the flavonoid biosynthesis pathway involved in anthracnose resistance were enriched in BTx623-specifically upregulated genes. Additionally, some immune-related genes, including multiple resistance genes, were differentially expressed in BTx623 and WHEATLAND. Taken together, our results revealed the mechanisms of SA-induced anthracnose resistance in sorghum at the transcriptional level and shed light on the possibility of enhancing sorghum resistance to anthracnose by activating the SA signaling pathway by molecular breeding.