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Articles by Thomas Isakeit
Total Records ( 5 ) for Thomas Isakeit
  Thomas Isakeit , Louis K. Prom , Michael Wheeler , Lorraine S. Puckhaber and Jinggao Liu
  The objective of this study was to determine the mycotoxigenic potential of 12 Fusarium isolates (10 species), including six isolates (4 species) from sorghum. The species were: F. thapsinum, F. semitectum, F. proliferatum and F. chlamydosporum isolated from molded sorghum seed; F. poae, F. graminearum and F. sporotrichioides from barley seed with Fusarium head blight; F. acuminatum from wheat seed; F. verticillioides from infected corn seed; and F. nygamai isolated from soil. Fumonisin and zearalenone concentrations were measured following incubation on autoclaved sorghum seed for 21 days at 25°C, while fusaric acid was measured in mycelia harvested from Czapek Dox broth cultures. F. thapsinum (SC8 and CS121) and F. semitectum (SC7) produced fusaric acid only (4.59-64.13 mg g-1). F. graminearum (KB172) and F. semitectum (CS152) produced zearalenone only (73.4 and 799.3 μg g-1, respectively). F. proliferatum (CS183), F. verticillioides (TX02) and F. nygamai produced both fumonisin (1.92-6.05 μg g-1) and fusaric acid (39.4-234.17 mg g-1). F. poae (KB652), F. acuminatum (Ark), F. chlamydosporum (CS102) and F. sporotrichioides (KB662) did not produce any of these three mycotoxins. Five of the six Fusarium isolates (three species) isolated from sorghum had mycotoxigenic potential. Fusarium spp. naturally occurring on sorghum in the field have the potential to contribute to mycotoxin contamination, either singly or in combination.
  Louis K. Prom , Hugo Cuevas , Thomas Isakeit and Robert Droleskey
  Foliar phase of anthracnose, caused by Colletotrichum sublineolum is the most important leaf disease of sorghum. Due to the hyper-variable nature of the fungus, continuous evaluation of sorghum germplasm to identify new sources of resistance is imperative. Field and greenhouse evaluations for anthracnose resistance, especially with large numbers of sorghum lines/accessions can be expensive, time consuming and require large spaces and labor. In this study, 16 sorghum lines were evaluated by putting a drop of the mixture of C. sublineolum isolates suspension on each side of the midrib of adaxial excised leaves plated on half-strength potato dextrose agar medium and concurrently as whole plants inoculated with a mixture of C. sublineolum isolates-colonized grain and conidial suspension in the greenhouse. Each line exhibited the same reaction when challenged with C. sublineolum either using the excised leaf assay or screened in the greenhouse, indicating that the excised leaf assay is as effective in identifying susceptibility or resistance to the anthracnose pathogen. In both screening methods, SC748 was the only resistant line. The excised leaf assay was completed in 4 days while the greenhouse evaluation was arrested 44 days post-inoculation. Thus, the excised leaf method could offer several advantages in screening sorghum for anthracnose resistance such as reducing the time for conducting the experiment, labor, space and increasing the number of isolates that can be tested within a short period.
  Louis K. Prom , Ghada Radwan , Ramasamy Perumal , Hugo Cuevas , Seriba O. Katile , Thomas Isakeit and Clint Magill
  Background and Objective: Globally, grain mold is a major hurdle affecting sorghum productivity and quality. This disease is caused by complex fungal pathogens, among them Fusarium thapsinum and Curvularia lunata are the major fungi prevalent in many sorghum growing regions. This study examined the effect of inoculating a mixture of F. thapsinum and C. lunata on 60 sorghum converted lines with five adapted inbred lines as checks. Materials and Methods: Sorghum lines and checks were evaluated in field trials at the Texas AgriLife Research Station. Plants were inoculated with a mixture of F. thapsinum and C. lunata at 50% bloom. Results: The overall result showed that SC 725 (PI 534101), SC 218 (PI 534127), SC 691 (PI 534050), SC 91 (PI 534145) and Sureno exhibited grain mold severity of 2.3 or less. This level of grain mold infection was lower than the scores exhibited by the two resistant checks RTx 2911 (2.8) and SC 719-11E (2.5). Significant negative correlation (r = -0.385, p = 0.002) between grain mold and germination indicated the impact of these two fungi infection on germination rates. The significant negative correlation detected between germination and daily maximum temperature during the evaluation period shows planting of sorghum cultivars/hybrids that mature during periods of dry moderate weather will avoid problem of grain mold infection. Conclusion: The identified four converted lines for grain mold resistance in this study is recommended to use in breeding program to introgress grain mold resistance genes into other adapted sorghum inbred lines to increase the yield and seed quality traits.
  Louis K. Prom , Hugo Cuevas , Ramasamy Perumal , Thomas Isakeit and Clint Magill
  Background and Objective: Anthracnose incited by Colletotrichum sublineola is the most important foliar disease of sorghum worldwide. The hyper-variable nature of the pathogen requires continual evaluations of sorghum germplasm to identify sources with different resistance genes. Thus, this research was undertaken to determine the inheritance of two Sudanese lines PI570726 and PI569979 to pathotype 30 and BT×378 (Redlan) to pathotypes 30 (P30) and 35 (P35) of the anthracnose pathogen. Materials and Methods: Crosses between these three sorghum lines and a susceptible parent PI609251 were performed and the resulting F2 populations were evaluated in greenhouse. Seeds were planted in 1-gallon cans and 30 d post planting, plants were inoculated with the anthracnose pathotypes. Individual plants from each cross were scored based on a scale of 1-5, where 1 = No symptoms or chlorotic flecks on leaves; 2 = Hypersensitive reaction; 3, 4 and 5= Infected leaf lesions with acervuli formation. Results: Chi-square test for the F2 populations of BT×378×PI609251 against P30 and P35, segregated in the expected Mendelian ratio 3 (resistant): 1(susceptible) fashion, indicating that resistance in BT×378 to P30 and P35 of C. sublineola obtained from the USA is governed by a single dominant gene. Segregation analysis for the PI569979×PI609251 and PI570726×PI609251 F2 populations revealed 1:3 ratio of resistance to susceptible, indicating that resistance in PI569979 and PI570726 to P30 was conditioned by a recessive trait. Conclusion: Resistance in the sorghum line BT×378 was shown to be dominant and will therefore be more desirable for use in breeding for anthracnose resistance, especially in sorghum hybrid production.
  Louis Kajac Prom , Hugo Cuevas , Thomas Isakeit , Ramasamy Perumal and Saradha Erathaimuthu
  Background and Objective: Grain mold is one of the major biotic constraints to sorghum production worldwide. This disease complex is associated with many genera of fungi, including mycotoxigenic Fusarium species. Yield losses can be high, especially when susceptible lines are planted in areas with wet conditions later in the growing season. The aim of this study was to determine the frequency of fungal genera/species contaminating sorghum seeds, grain mold severity, seed weight and germination rate. Materials and Methods: During the 2016 and 2017 growing seasons, 62 sorghum lines were collected from Puerto Rico and Mexico. Panicles from these locations were threshed and the seed samples were put in separate paper bags and stored at 7°C in a refrigerator in the laboratory. Seed samples were evaluated for grain mold severity, seed mycoflora, seed weight and germination rate. Results: In Isabela, Puerto Rico, Fusarium thapsinum was the dominant fungal species isolated from sorghum grain, followed by Aspergillus spp. and F. semitectum in 2016 and 2017, F. semitectum was the most frequently isolated fungal species. In Guayanilla, Puerto Rico and Puerto Vallarta, Mexico, FIESC (Fusarium incarnatum, F. acuminatum, F. equiseti and F. semitectum Complex) were the dominant species isolated from sorghum seed samples. Among the sorghum lines evaluated for grain mold severity, KS-963 collected from Guayanilla, Puerto Rico, exhibited a moderate resistance response to grain mold, while the other sorghum lines were either moderately susceptible or susceptible. Across locations, KS-835 exhibited the highest seed weight (4.7 g) while PI534152 exhibited the lowest seed weight (1.0 g). Germination rates ranged from 100-0% among the sorghum lines surveyed. Conclusion: While F. thapsinum, F. nygamy and C. lunata are considered the most common grain molding species, the frequency of recovery of these three fungal species in some sorghum growing regions, including locations surveyed in this study, may be low. Thus, in grain mold resistance studies, selecting the most dominant fungal species in a sorghum growing region and using them as inocula in either the field or greenhouse is more practical and beneficial.
 
 
 
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