Translucent Kernel Syndrome
A rash of reports have come in during the past two weeks of an odd grain filling problem that can be best described as a translucent kernel syndrome. The initial symptoms of this oddity are the appearance of plump, translucent, liquid-filled kernels scattered randomly among already-dented kernels throughout an otherwise normal-looking ear. The abnormal kernels subsequently shrivel dramatically as the kernel matures, resulting in a shriveled kernel appearance not unlike mature sweet corn kernels.
The proportion of affected kernels on an individual ear range as high as 50 percent. The proportion of plants affected in a field is more difficult to determine, but has usually been reported to be found throughout whole fields.
The occurrence of this phenomenon has been reported primarily from northwest Indiana. Initially, there appeared to be common planting date link of the first week of May, but subsequent reports have indicated a wider range of planting dates. There is some evidence of a common corn inbred link, but we are still investigating that detail. Few other common threads apparently connect these reports.
At first glance, one is tempted to diagnose these kernels as aborted, perhaps from excessive heat or drought conditions shortly after pollination. Indeed, typical kernel abortion symptoms are evident in fields throughout Indiana this year. However, the pattern of "typical" kernel abortion usually involves those kernels at the tip end of the cob and rarely includes a random scattering of aborted kernels throughout the ear. Furthermore, "typical" kernel abortion at blister or early milk stages of kernel development usually result in very small shriveled kernels.
The ears that we have seen have not exhibited significant kernel abortion at the ear tips. Additionally, the shriveled kernels are nearly full size, not the usual small aborted size. Furthermore, the cobs themselves are essentially normal sized and do not indicate any other symptom of stress. Plants in the affected fields are also normal in appearance and size.
Another initial reaction to the random pattern of affected kernels is to blame Fusarium infection. Although Fusarium has been isolated from some of the symptomatic kernels, it has not been consistently isolated from all of the symptomatic kernels and thus does not appear to be the primary cause of the symptom itself.
The symptom and pattern of occurrence on an ear resembles that of a particular corn genetic mutant known as "defective kernel" or "dek". A number of variations of this kernel mutant are illustrated in the book "Mutants of Maize" (M. Gerald Neuffer, University of Missouri, Columbia; Edward H. Coe, USDA, ARS, PGRU, Columbia; and Susan R. Wessler, University of Georgia, Athens. 1997). Images of some of the "dek" mutants are available on the Web at http://www.agron.missouri.edu/Coop/images/MOM.html . By no means have we confirmed that this genetic kernel mutant is the culprit behind the translucent kernel syndrome being reported this year, but the random pattern on the affected ears does hint at genetic segregation.
If you have come across this strange phenomenon, please contact Bob Nielsen, firstname.lastname@example.org, 765/494-4802 and indicate the geographic location, planting date, hybrid, herbicides applied, and any other pertinent information that may be useful in diagnosing this odd kernel development problem. Ear samples can be sent in to the Purdue Plant & Pest Diagnostic Lab. Contact the PPDL at 765/494-7071 for details on submitting samples.