Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/27/2002
Publication Date: 2/1/2003
Citation: STACK, J.P., PEDERSEN, J.F. EXPRESSION OF SUSCEPTIBILITY TO FUSARIUM HEAD BLIGHT AND GRAIN MOLD IN A1 AND A2 CYTOPLASM OF SORGHUM BICOLOR (L.) MOENCH.. PLANT DISEASE. 2003. Interpretive Summary: Over 97% of grain sorghum hybrids are based on one cytoplasmic (A1) background raising concern for vulnerability to disease due to genetic uniformity. In other studies, A2 cytoplasm was determined acceptable for developing commercial hybrids to increase genetic diversity. Panicle and grain diseases are major constraints to sorghum production throughout the world. Commercial hybrids vary in susceptibility to these diseases that affect yield and quality. Multiple Fusarium spp. are associated with Fusarium head blight in Nebraska. Grain mold of sorghum is caused by several fungal species, the most prevalent in Nebraska being species of Alternaria, Cladosporiu,, and Fusarium. In this experiment conducted at three environmentally diverse sites we demonstrated that in four sorghum hybrids, no differences existed between A1 and A2 cytoplasms for susceptibility to head blight and grain mold. These hybrids varied dramatically in degree of susceptibility to head blight and grain mold allowing for assessment of cytoplasmic affects over a range of disease incidence and severity. The A2 cytoplasm did not affect disease development. Consequently, using A2 cytoplasm to increase cytoplasmic genetic diversity of grain sorghum hybrids, should not increase risk due to these two diseases.
Technical Abstract: Panicle diseases are major constraints to sorghum [Sorghum bicolor (L.) Moench] production in the Northern Great Plains. Host plant resistance is the primary management option. Essentially all commercial sorghum hybrids contain A1 cytoplasm. This raised concern about the risk to disease as a result of genetic uniformity. To determine the influence of cytoplasmic background on the expression of susceptibility to panicle diseases, F1 hybrids with four nuclear genotypes in each of two cytoplasms (A1 and A2) were planted in three geographic locations. Fusarium head blight (F. semitectum Berk. & Ravenel, Fusarium spp.) ranged in incidence from 13% to 100% and grain mold, caused by several species, ranged in incidence from 5% to 100% across all locations. There was a significant effect of hybrid on the incidence of head blight and grain mold and the severity of grain mold at all three locations. Cytoplasm had no significant effect at any location. The use of A2 cytoplasm to incorporate genetic diversity into grain sorghum hybrids should not pose added risk from head blight or grain mold.