Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2011
Publication Date: 5/1/2011
Citation: Prom, L.K., Perumal, R., Erattaimuthu, S., Erpelding, J.E., Montes-Garcia, N., Odvody, G., Greenwald, C., Jin, Z., Frederiksen, R., Magill, C. 2011. Virulence and molecular genotyping studies of Sporisorium reilianum isolates in sorghum. Plant Disease. 95:523-529. Interpretive Summary: Sorghum head smut is an important fungal disease caused by Sporisorium reilianum. The fungus can live in the soil for many years. Since the spores of the fungus in the soil do not germinate at once, field screening for resistance to this disease is difficult due to the lack of a reliable and effective method of inoculation. In this study, we found that a modified syringe inoculation method was the most effective in screening for resistance to head smut. We also report for the first time the existence of new races (Races 5 and 6) of the head smut pathogen in Texas. In addition, the genetic differences at the DNA level of 32 head smut isolates collected from several locations in Texas were determined using 16 AFLP primer combinations (EcoRI +1/ MseI+1). The results showed that 82% of the head smut isolates from sorghum can be placed in four small clusters with 81.5% similarity. The study also identified 30 AFLP markers that can be used in determining different races of sorghum head smut.
Technical Abstract: Head smut, caused by the fungal pathogen Sporisorium reilianum, has been reported with increasing frequency in the grain sorghum growing areas of Texas. To facilitate analysis of changes in pathogen virulence, four inoculation techniques were examined: soil and teliospore mixture, seed coating, media placement and syringe injection. Of the four, syringe injection was determined to be the most effective. Inoculations of sorghum host differentials BTx643, BTx7078, BTx635, SC170-6-17 (TAM2571), SA281 (Early Hegari), and Tx414 showed 23 of 32 Texas isolates were race 4. Two isolates from College Station, Texas, were classified as race 1, but no race 2 or 3 isolates were found. New virulent races 5 and 6 were identified among isolates from south Texas. Using 16 AFLP primer combinations, genetic diversity was assessed in DNA samples from 49 S. reilianum isolates, including: 44 sorghum isolates from Texas, USA, two from Uganda, and one from Mali; and two maize isolates from Mexico. Single-base extensions with EcoRI and MseI primers in the selective amplification increased the number of informative polymorphic bands. High genetic dissimilarity (50%) was observed between isolates originating from maize and those originating from sorghum. The resultant dendrogram, made using cluster analysis, grouped the Texas S. reilianum isolates into four small clusters with =82% similarity. Other than for two race 6 isolates from Weslaco, Texas, no evidence for geographical or other restrictions on gene flow was evident.