Incidence and severity of ergot (Claviceps africana Frederickson, Mantle and de Milliano) in two male-sterile sorghum lines as a function of distance from pollen source and its impact on seed production and quality
Sorghum ergot, caused by the fungus Claviceps africana Frederikson, Mantle and de Milliano, was first recorded in the State of Guanajuato, Mexico, in August 1997. In this year, the disease was observed in the Bajio Experiment Station in two sorghum (Sorghum bicolor L. Moench) seed production fields, one seeded with the lines E15A × E15B and the other for the hybrid A155 × R8509. Both fields had an area of 2000 m2, a female to male row ratio of 8:4, 0.76 m row width and 0.10 m spacing between plants. Six random plots (replications) 5-m in length were delimited for evaluation. Each plot included 16 rows (8 female rows bordered by 4 pollinator rows on either side). Disease incidence, ergot severity and seed yield were determined in female rows 1, 3, 5 and 8 and in male rows 1 and 3. Regression analyses between distance from pollen emission source and disease incidence, disease severity and seed yield were performed, for each field. At harvest, two composite samples: one from the four female rows and another from the two male rows were made for each replication. These samples were used to evaluate physical, physiological and sanitary seed quality through comparisons to the control seed obtained in the same year for E15A × E15B and A155 × R8509 hand seed increases from ergot uncontaminated nursery plots located within the Experimental Station. Treatment means were compared by Student's t-test. Results indicated that yield reduction, ergot incidence and severity were lower in the female rows of the line than in those of the hybrid seed production field. As the distance increased from the pollen source to the female row the ergot incidence increased from 42 to 67% in the farthest row (3.04 m), 19 to 22% for ergot severity and seed yield decreased from 45 to 56%. The effect of ergot on seed quality was low but the number of sclerotia reached 6 to 10 per kilogram of seed. The proportion of small seeds was 6% greater than in the controls. Ergot affected seed physiological quality by decreasing viability, vigour and germination of seed by between 17 and 25%. Ergot-contaminated seed was more readily colonized by a greater number of fungi than the control seed.
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Document Type: Research Article
Publication date: July 1, 2006
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