Posted on Dec 01, 2010
In Kansas, Fusarium stalk rot and charcoal rot are the primary stalk rots that cause yield loss and lodging in sorghum. Fusarium stalk rots (caused byFusarium spp. including F. thapsinum, F. proliferatum, and F. andiyazi) are important when high temperatures and drought stress occur during head initiation and caryopsis formation followed by exposure to cooler and wetter conditions. However, charcoal rot (caused by Macrophomina phaseolina) occurs during prolonged post-flowering drought stress and does not require a period of cooler temperatures or higher moisture in order to manifest itself. From 1994-2008, the mean actual grain sorghum yields in Kansas averaged 212 million bushels (MBu) per year and ranged from 143 to 368 MBu during this period. As early as 1996, Doug Jardine (Extension Row Crops Pathologist, KSU), noted that stalk rots (especially Fusarium stalk rot) cause 5-10% yield losses per year in Kansas and continued to note consistent disease. This suggests that attainable yields would have averaged 223 to 234 MBu during this period. Such yield impacts of both stalk rots are also seen in other sorghum producing states including Texas and Nebraska.
A goal of this project is to assess losses in sorghum seed weight and quality due to stalk rots in dryland production systems. This will be accomplished through the identification of drought-tolerant germplasm possessing acceptable end of season yield parameters and lodging resistance after stalk inoculations with Fusarium spp. and Macrophomina phaseolina after flowering. It is clear that resistance to Fusarium stalk rots and charcoal rot are genetically and mechanistically divergent; previous efforts have identified some dominant resistance to Fusarium stalk rots. However, responses to the various Fusarium pathogens (see above) differ greatly and inoculations with these needs to be tested in greater detail. Secondly, the best source of tolerance to stalk rot diseases and resultant lodging is a strong stalk. To assess structural resistance to stalk rots in diverse sorghum germplasm, stalk strength will be assessed at multiple plant developmental stages using a rind penetrometer. This is a hand-held instrument that measures the amount of force required to penetrate the rind of the sorghum stalk, and the amount of resistance associated with this force requirement is related to rind thickness and composition. Stalk strength will be further evaluated by obtaining crude fiber, cellulose, lignin, and silica measurements from stalk samples throughout the experiment. Additionally, a 300-line sorghum diversity panel will be screened to catalogue the diversity of stalk rot pathogens (with emphasis on Fusariumspp.) and stalk strengths will be acquired using rind penetrometry.
The control of stalk rot, especially through better understanding of pathogen biology and screening and enhancement of genetic material for use in breeding programs is an essential activity which will result in lodging resistant and increased yielding hybrids. In order to do this, interconnected strategies must be adopted: (1) identify germplasm with improved stalk strength and tolerance to pre-harvest lodging, and (2) identify germplasm with resistance (quantitative, partial, or complete) to the stalk rot pathogens, and (3) ensure that identified germplasm possesses post-flowering drought-tolerance and concomitant tolerance to charcoal rot.