A Sorghum F-Box Protein Induces an Oxidative Burst in the Defense Against Colletotrichum sublineola.

The hemibiotrophic fungal pathogen Colletotrichum sublineola is the causal agent of anthracnose in sorghum (Sorghum bicolor), resulting in leaf blight, stalk rot, and head blight in susceptible genotypes, with yield losses of up to 50%. The development of anthracnose-resistant cultivars can reduce reliance on fungicides and provide a more sustainable and economical means for disease management. A previous genome-wide association study of the sorghum association panel identified the candidate resistance gene Sobic.005G172300 encoding an F-box protein. To better understand the role of this gene in the defense against C. sublineola, gene expression following infection with C. sublineola was monitored by RNA sequencing in seedlings of sorghum accession SC110, which harbored the resistance allele, and three accessions that harbored a susceptible allele. Only in SC110 did the expression of Sobic.005G172300 increase during the biotrophic phase of infection. Subsequent transcriptome analysis, gene co-expression networks, and gene regulatory networks of inoculated and mock-inoculated seedlings of resistant and susceptible accessions suggest that the increase in expression of Sobic.005G172300 induces an oxidative burst by lowering the concentration of ascorbic acid during the biotrophic phase of infection. Based on gene regulatory network analysis, the protein encoded by Sobic.005G172300 is proposed to target proteins involved in the biosynthesis of ascorbic acid for polyubiquitination through the SCF E3 ubiquitin ligase, causing their degradation via the proteasome.

Genetic diversity, population structure and anthracnose resistance response in a novel sweet sorghum diversity panel.

Sweet sorghum is an attractive feedstock for the production of renewable chemicals and fuels due to the readily available fermentable sugars that can be extracted from the juice, and the additional stream of fermentable sugars that can be obtained from the cell wall polysaccharides in the bagasse. An important selection criterion for new sweet sorghum germplasm is resistance to anthracnose, a disease caused by the fungal pathogen Colletotrichum sublineolum. The identification of novel anthracnose-resistance sources present in sweet sorghum germplasm offers a fast track towards the development of new resistant sweet sorghum germplasm. We established a sweet sorghum diversity panel (SWDP) of 272 accessions from the USDA-ARS National Plant Germplasm (NPGS) collection that includes landraces from 22 countries and advanced breeding material, and that represents ~15% of the NPGS sweet sorghum collection. Genomic characterization of the SWDP identified 171,954 single nucleotide polymorphisms (SNPs) with an average of one SNP per 4,071 kb. Population structure analysis revealed that the SWDP could be stratified into four populations and one admixed group, and that this population structure could be aligned to sorghum's racial classification. Results from a two-year replicated trial of the SWDP for anthracnose resistance response in Texas, Georgia, Florida, and Puerto Rico showed 27 accessions to be resistant across locations, while 145 accessions showed variable resistance response against local pathotypes. A genome-wide association study identified 16 novel genomic regions associated with anthracnose resistance. Four resistance loci on chromosomes 3, 6, 8 and 9 were identified against pathotypes from Puerto Rico, and two resistance loci on chromosomes 3 and 8 against pathotypes from Texas. In Georgia and Florida, three resistance loci were detected on chromosomes 4, 5, 6 and four on chromosomes 4, 5 (two loci) and 7, respectively. One resistance locus on chromosome 2 was effective against pathotypes from Texas and Puerto Rico and a genomic region of 41.6 kb at the tip of chromosome 8 was associated with resistance response observed in Georgia, Texas, and Puerto Rico. This publicly available SWDP and the extensive evaluation of anthracnose resistance represent a valuable genomic resource for the improvement of sorghum.

Exploring boron applications in modern agriculture: A structure-activity relationship study of a novel series of multi-substitution benzoxaboroles for identification of potential fungicides.

Several boron-containing small molecules have been approved by the US FDA to treat human diseases. We explored potential applications of boron-containing compounds in modern agriculture by pursuing multiple research and development programs. Here, we report a novel series of multi-substitution benzoxaboroles (1-36), a compound class that we recently reported as targeting geranylgeranyl transferase I (GGTase I) and thereby inhibiting protein prenylation (Kim et al., 2020). These compounds were designed, synthesized, and tested against the agriculturally important fungal pathogens Mycosphaerella fijiensis and Colletotrichum sublineolum in a structure-activity relationship (SAR) study. Compounds 13, 28, 30, 34 and 36 were identified as active leads with excellent antifungal MIC95 values in the range of 1.56-3.13 ppm against M. fijiensis and 0.78-3.13 ppm against C. sublineolum.

Metabolomic Analysis of Defense-Related Reprogramming in Sorghum bicolor in Response to Colletotrichum sublineolum Infection Reveals a Functional Metabolic Web of Phenylpropanoid and Flavonoid Pathways.

The metabolome of a biological system provides a functional readout of the cellular state, thus serving as direct signatures of biochemical events that define the dynamic equilibrium of metabolism and the correlated phenotype. Hence, to elucidate biochemical processes involved in sorghum responses to fungal infection, a liquid chromatography-mass spectrometry-based untargeted metabolomic study was designed. Metabolic alterations of three sorghum cultivars responding to Colletotrichum sublineolum, were investigated. At the 4-leaf growth stage, the plants were inoculated with fungal spore suspensions and the infection monitored over time: 0, 3, 5, 7, and 9 days post inoculation. Non-infected plants were used as negative controls. The metabolite composition of aqueous-methanol extracts were analyzed on an ultra-high performance liquid chromatography system coupled to high-definition mass spectrometry. The acquired multidimensional data were processed to create data matrices for multivariate statistical analysis and chemometric modeling. The computed chemometric models indicated time- and cultivar-related metabolic changes that reflect sorghum responses to the fungal infection. Metabolic pathway and correlation-based network analyses revealed that this multi-component defense response is characterized by a functional metabolic web, containing defense-related molecular cues to counterattack the pathogen invasion. Components of this network are metabolites from a range of interconnected metabolic pathways with the phenylpropanoid and flavonoid pathways being the central hub of the web. One of the key features of this altered metabolism was the accumulation of an array of phenolic compounds, particularly de novo biosynthesis of the antifungal 3-deoxyanthocynidin phytoalexins, apigeninidin, luteolinidin, and related conjugates. The metabolic results were complemented by qRT-PCR gene expression analyses that showed upregulation of defense-related marker genes. Unraveling key characteristics of the biochemical mechanism underlying sorghum-C. sublineolum interactions, provided valuable insights with potential applications in breeding crop plants with enhanced disease resistance. Furthermore, the study contributes to ongoing efforts toward a comprehensive understanding of the regulation and reprogramming of plant metabolism under biotic stress.

Severidade da antracnose e produtividade de sorgo granífero em resposta a doses crescentes de nitrogênio / Anthracnose severity and yield of grain sorghum in response to increasing nitrogen doses

O presente estudo objetivou avaliar a severidade da antracnose e a produtividade de diferentes genótipos de sorgo em resposta a doses crescentes de nitrogênio. Os experimentos foram conduzidos em duas safras agrícolas: safra 2009/2010 (safra I) e safra 2010/2011 (safra II). O preparo do solo na área experimental foi realizado de forma convencional. Na safra I foram utilizados quatro genótipos de sorgo BRS 310, CMSXS 0144015, CMSXS 9920045 e CMSXS 9920044, enquanto que na safra II apenas os genótipos BRS 310 e CMSXS 0144015 foram avaliados. Aos 45 dias após o plantio (DAP) foram aplicados os tratamentos que consistiram de doses de nitrogênio (67; 112; 157; e 202 kg ha-1) em adubação de cobertura. Aos 60 DAP, iniciou-se a avaliação da severidade da antracnose utilizando escala de notas. Na colheita, determinou-se a produtividade de grãos nos tratamentos. Houve variação nos níveis de severidade da antracnose e na produtividade de grãos dos genótipos de sorgo em função das doses de nitrogênio aplicadas. Os genótipos de sorgo CMSXS 9920045 e BRS 310 apresentaram menor e maior suscetibilidade à antracnose, respectivamente. No genótipo BRS 310, a doença progrediu mais rapidamente na safra I que apresentou maior umidade relativa.

The present study aimed to evaluate the severity of anthracnose and yield of different genotypes of sorghum in response to increasing levels of nitrogen. For this, experiments were conducted in two agricultural seasons: crop season 2009/2010 (crop season I) e crop season 2010/2011 (crop season II). The soil preparation in the experimental area was performed in conventional manner. In the crop season I were used four sorghum genotypes BRS 310, CMSXS 0144015, CMSXS 9920045 e CMSXS 9920044, whereas in the crop season II only the genotypes BRS 310 and CMSXS 0144015 were evaluated. At 45 days after planting (DAP) were applied the treatments which consisted of nitrogen doses (67; 112; 157; and 202 kg ha-1) in topdressing. At 60 DAP, was began the evaluation of anthracnose severity using notes scale. At the harvest it was determined the yield for each treatment based on the mass of grain. There was variation in levels of anthracnose severity and grain yield in the sorghum genotypes in response to nitrogen levels applied. The sorghum genotypes CMSXS 9920045 and BRS 310 showed smaller and higher susceptibility to anthracnose, respectively. In genotype BRS 310, the disease progressed more rapidly in the crop season I that showed major relative humidity.

Bioprospection of yeasts as biocontrol agents against phytopathogenic molds

Yeasts isolated from sugar cane and maize rhizosphere, leaves and stalks were screened against the phytopathogenic molds Colletotrichum sublineolum and Colletotrichum graminicola, both causal agents of the anthracnose disease in sorghum and maize, respectively. Strains identified as Torulaspora globosa and Candida intermedia were able to inhibit the mold growth, with the first species also exhibiting killer activity. No previous report on the application and potentiality of these yeasts as biocontrol agents were found neither the killer phenotype in Torulaspora globosa.