Ergot: A New Disease Threat to Sorghum in the Americas and Australia

Sorghum, Sorghum bicolor (L.) Moench, is the world’s fifth most important cereal crop, cultivated on about 45 million hectares for food, feed, beverage, and fodder. The most significant technological change since the 1960s has been the development and use of F1 hybrid seed (14), which has lead to a dramatic improvement in the crop’s productivity. Sorghum cultivation in intensive, commercialized systems where yields average 3 to 5 t ha-1 relies almost totally on hybrid seed. In contrast, yields vary widely and average less than 1 t ha-1 in low-input production systems

A Disease of Pearl Millet in Zimbabwe Caused by Pantoea agglomerans

Necrosis at the leaf tips and margins of pearl millet (Pennisetum glaucum (L.) R. Br.) was observed in 1995 in a Pseudomonas syringae resistance screening nursery near Bulawayo, Zimbabwe. Straw-colored lesions with a chlorotic edge often extended the leaf length, and were atypical of the round spots, with a brown margin, caused by P. syringae (1). Bacteria were isolated from cut lesions macerated in water by dilution streaking onto King's medium B and nutrient agar. A gram-negative, nonfluorescent, fermentative, rod-shaped bacterium, forming yellow colonies on nutrient agar was consistently observed. Three pots of 10, 2-to 3-week-old seedlings of a susceptible cultivar, 852B, were inoculated with a 108 CFU per ml suspension from cultures by misting or injection into the whorl. In three experiments, the treatment and uninoculated control were incubated at 25°C and 95% relative humidity for 48 h before transfer to the greenhouse. The original symptoms of watersoaking at leaf tips and margins were observed after 4 days. Necrotic lesions surrounded by chlorotic tissue were observed a day later. Fluorescence on King's medium B, and levan, oxidase, potato-rot, arginine dihydrolase, 2-keto gluconate, nitrate reduction, gelatin, phenylalanine deaminase, and acid from starch tests were negative. Tobacco hypersensitivity, acid from sucrose and glycerol, aesculin hydrolysis, lipase, indole production, and growth on tetrazolium chloride were positive. The identification of the pathogen to the species level as Pantoea agglomerans (Ewing and Fife 1972) Gavini et al. 1989, formerly Erwinia herbicola, was by fatty acid analysis by the International Mycological Institute (Egham, Surrey, UK). P. agglomerans was recorded as a pathogen of pearl millet in India in 1958 (2)

Ergot - a Global Threat to Sorghum

The current status of ergot (Claviceps sorghi and C. africana) of sorghum is reviewed. The biology, epidemiology, control, host plant resistance and integrated management strategies of the disease are discussed

Simple sequence repeat markers useful for sorghum downy mildew (Peronosclerospora sorghi) and related species

<p>Abstract</p> <p>Background</p> <p>A recent outbreak of sorghum downy mildew in Texas has led to the discovery of both metalaxyl resistance and a new pathotype in the causal organism, <it>Peronosclerospora sorghi</it>. These observations and the difficulty in resolving among phylogenetically related downy mildew pathogens dramatically point out the need for simply scored markers in order to differentiate among isolates and species, and to study the population structure within these obligate oomycetes. Here we present the initial results from the use of a biotin capture method to discover, clone and develop PCR primers that permit the use of simple sequence repeats (microsatellites) to detect differences at the DNA level.</p> <p>Results</p> <p>Among the 55 primers pairs designed from clones from pathotype 3 of <it>P. sorghi</it>, 36 flanked microsatellite loci containing simple repeats, including 28 (55%) with dinucleotide repeats and 6 (11%) with trinucleotide repeats. A total of 22 microsatellites with CA/AC or GT/TG repeats were the most abundant (40%) and GA/AG or CT/TC types contribute 15% in our collection. When used to amplify DNA from 19 isolates from <it>P. sorghi</it>, as well as from 5 related species that cause downy mildew on other hosts, the number of different bands detected for each SSR primer pair using a LI-COR- DNA Analyzer ranged from two to eight. Successful cross-amplification for 12 primer pairs studied in detail using DNA from downy mildews that attack maize (<it>P. maydis & P. philippinensis</it>), sugar cane (<it>P. sacchari</it>), pearl millet (<it>Sclerospora graminicola</it>) and rose (<it>Peronospora sparsa</it>) indicate that the flanking regions are conserved in all these species. A total of 15 SSR amplicons unique to <it>P. philippinensis </it>(one of the potential threats to US maize production) were detected, and these have potential for development of diagnostic tests. A total of 260 alleles were obtained using 54 microsatellites primer combinations, with an average of 4.8 polymorphic markers per SSR across 34 <it>Peronosclerospora, Peronospora and Sclerospora </it>spp isolates studied. Cluster analysis by UPGMA as well as principal coordinate analysis (PCA) grouped the 34 isolates into three distinct groups (all 19 isolates of <it>Peronosclerospora sorghi </it>in cluster I, five isolates of <it>P. maydis </it>and three isolates of <it>P. sacchari </it>in cluster II and five isolates of <it>Sclerospora graminicola </it>in cluster III).</p> <p>Conclusion</p> <p>To our knowledge, this is the first attempt to extensively develop SSR markers from <it>Peronosclerospora </it>genomic DNA. The newly developed SSR markers can be readily used to distinguish isolates within several species of the oomycetes that cause downy mildew diseases. Also, microsatellite fragments likely include retrotransposon regions of DNA and these sequences can serve as useful genetic markers for strain identification, due to their degree of variability and their widespread occurrence among sorghum, maize, sugarcane, pearl millet and rose downy mildew isolates.</p

Evaluation of sorghum germplasm used in US breeding programmes for sources of sugary disease resistance

Ergot or sugary disease of sorghum has become an important constraint in North and South American countries that rely on F1 hybrid seeds for high productivity. The objective of this research was to determine the vulnerability of various germplasm sources and publicly bred sorghum lines to sugary disease (Claviceps africana) in the United States. Flower characteristics associated with sugary disease resistance were also studied. A-/B-line pairs, R-lines, putative sources of resistance and their hybrid combinations with an A3 cytoplasmic male-sterile source were evaluated using a disease incidence, severity, and dual-ranking system. Trials were planted in a randomized complete block design with three replications and repeated in at least two planting dates. Planting dates and pedigrees had significant effects on overall ranking for resistance. A-lines were most susceptible to sugary disease. R-lines were more susceptible than B-lines with respect to incidence and severity of the disease. Newer releases of A- and B-lines were more susceptible to sugary disease than older releases. Sugary disease reaction of A-lines was a good indicator of disease reaction of B-lines. Tx2737, a popular R-line, was highly susceptible to sugary disease in spite of being a good pollen shedder because the stigma emerged from glumes 2±3 days before anthesis. The combination of flower characteristics associated with resistance were least exposure time of stigma to inoculum before pollination, rapid stigma drying after pollination, and small stigma. An Ethiopian male-fertile germplasm accession, IS 8525, had good levels of resistance. Its A3 male-sterile hybrid had the highest level of resistance in the male-sterile background. IS 8525 should be exploited in host-plant resistance strategies

A new species complex including Claviceps fusiformis and Claviceps hirtella

Isolates of Claviceps species with lunate to fusiform macroconidia were collected from panicoid grasses in Texas and Zimbabwe and described as new species based on anamorphs since no teleomorphs were available. Characterization was based upon morphology and partial sequences of rDNA and β-tubulin. The isolates grouped into two stronglysupported clades. The first clade contained ancestral C. hirtella and C. fusiformis from pearl millet (Pennisetum glaucum) in clade terminal position with Texas isolates from native cup grass (Eriochloa sericea) and pearl millet grouped between them. The second clade consisted of African isolates from Urochloa and Eragrostis. The isolates from Texas from pearl millet and buffel grass (Cenchrus ciliaris) and isolates from E. sericea were described as new species, Sphacelia texensis and Sphacelia eriochloae, respectively. Both species had morphology, DNA markers, and alkaloid production that was intermediate between those features exhibited in C. fusiformis and C. hirtella. The African isolates from Urochloa and Eragrostis were also described as a new species, Sphacelia lovelessii. In shaken cultures, C. hirtella readily produced a whole range of clavines with agroclavine and festuclavine predominating, but ergometrine was also detected. Claviceps fusiformis produced mainly agroclavine and elymoclavine, S. eriochloae produced mainly agroclavine, elymoclavin and festuclavine and the cultures of S. texensis contained small amounts of agroclavine and festuclavine. Only traces of clavines were found in cultures of S. lovelessii of the second clade. The alkaloid content of infected florets in the sphacelial (honeydew) developmental stage was also measured. Only C. fusiformis and S. eriochloae produced alkaloids in planta at this early stage

Presumptive identification of Pseudomonas syringae, the cause of foliar leafspots and streaks on pearl millet in Zimbabwe

The aetiology of a leafspot disease of pearl millet (Pennisetum americanum [P. glaucum]) in Zimbabwe was investigated using Koch's postulates. Bipolaris sp., Exserohilum sp. and bacteria, were isolated from lesions, but only bacterial isolates produced the original symptoms following inoculation of a susceptible pearl millet line, 852B. Biochemical and physiological tests, including LOPAT, indicated that the bacterium was the fluorescent pseudomonad, Pseudomonas syringae. This represents the first report of P. syringae on pearl millet in Afric

New Claviceps species from warm-season grasses

Eight undescribed species of Claviceps were recognized from the combinations of molecular and morphological characters. The teleomorph was observed only for Claviceps setariicola. Phylogenetic affinities of the new species inside the genus were revealed by a 5.8S-ITS-28S nrDNA analysis. Claviceps chloridicola, C. tenuispora, C. setariicola and C. setariiphila are related to C. maximensis; C. truncatispora is a sister species to C. pusilla. Claviceps clavispora and C. langdonii cluster with species colonizing maize and sorghum. The position of C. loudetiae is unclear. Comparisons with herbarium specimens showed C. setariicola as a well-established species on Setaria spp. in the southern USA. C. tenuispora was recorded on Cenchrus and Pennisetum in Brazil, USA, and Zimbabwe. C. setariiphila was found on S. geniculata in Brazil. C. chloridicola, C. loudetiae and C. truncatispora occurred in African savannas on Chloris, Loudetia, and Hyparrhenia spp., respectively. C. clavispora was found on Paspalum sp. and Urochloa sp. in Mexico and C. langdonii colonized Dichanthium spp. in the southern USA and probably in Mexico. The occurrence of C. pusilla on pearl millet in the USA (Texas) is reported and the record of C. sulcata on Urochloa brizantha in Brazil is confirmed by nrDNA sequence comparison with an African herbarium specimen. No alkaloids were detected in sclerotia and/or sphacelia of the new species

Genome wide association analysis of sorghum mini core lines regarding anthracnose, downy mildew, and head smut

In previous studies, a sorghum mini core collection was scored over several years for response to Colletotrichum sublineola, Peronosclerospora sorghi, and Sporisorium reilianum, the causal agents of the disease anthracnose, downy mildew, and head smut, respectively. The screening results were combined with over 290,000 Single nucleotide polymorphic (SNP) loci from an updated version of a publicly available genotype by sequencing (GBS) dataset available for the mini core collection. GAPIT (Genome Association and Prediction Integrated Tool) R package was used to identify chromosomal locations that differ in disease response. When the top scoring SNPs were mapped to the most recent version of the published sorghum genome, in each case, a nearby and most often the closest annotated gene has precedence for a role in host defense