Below is from blogs that I wrote in 2015. The principles of factors involving stalkrot continues in fields today.
With a B.S. degree in Botany from Iowa State I was lucky to teach biology in Sarawak as a Peace Corps volunteer in 1963 and 1964. Probably like all teachers, I soon discovered how little I knew about my subjects. Among the many benefits of that job was the short term. It was assumed that one would leave, and for me that meant grad school and a chance to learn more about plants and fungi. After more studies in Botany and Mycology I took a job with a seed corn company in which studies of plants and fungi was forced to face the realities of corn grown in many environments and considered as a crop instead of individual plants. I was hired because of the corn industry concerns that their crop’s vulnerability to disease had been exposed with race T of southern corn leaf blight in 1970. I, nor the seed company, had real clear ideas of what a plant pathologist should do in a company breeding corn seed varieties. I had a lot to learn.
After southern corn leaf blight danger subsided, corn breeders advised me that their toughest problem was obtaining resistance to stalk rot. So I was a guy with an interest in biology of plants faced with a complex problem. Why does stalk rot occur in one plant but not the next? Single cross hybrid plants are, at least theoretically, genetically identical. The fungi accused of causing stalk rot are ubiquitous and surely readily available to attach each plant. So, why this plant and not the next?
A dead plant with yellow lower stalk is adjacent to a genetically identical plant with a green live lower stalk. Why? I first hypothesized these could be the plants that emerged late, as if it developed from seed that germinated slowly because of deteriorating quality. In the field nursery with many hybrids tags were put by plants that showed only 3 leaves and other tags placed by seedlings just emerging when most adjacent plants were showing 5 leaves. These plants were followed through the season. Late emerging plants definitely did not develop stalk rot. Some of those that were only emerging when tagged actually disappeared but if not they were completely barren. Those tagged with 3 leaves had narrow stalks and tassels that were much smaller and with fewer branches than surrounding plants, silks emerging later than other plants and averaged about 20% of the yield of majority plants- but no stalkrot. I showed the plants to the fellow that evaluated winter growouts for purity of new seed lots. He said that confirmed his opinion that some plants he saw that looked like they could be inbred selfs were actually late emerging plants. To make sure that these were not inbreds, the next year I hand planted 5 hybrids leaving interplant space for planting the same hybrids later between the initial planting. These intentional late emergence plants looked the same as in the first year’s observation. Late emergers apparently suffer from competition resulting in having very small stalks and yield but the stalks remain green. Late emerging plants do not yield but also do not explain why adjacent plants do not behave the same in terms of stalk rot.
The concept that late emerging plants do not perform well and that seed quality is a significant component to good grain yields was observed by many others before that experiment in 1973, but it was new to me. It also set me on path to find a better method of evaluating purity of hybrid seed lots as well as finding other explanations as to why a dead plant would occur adjacent to a green one only a few inches apart. It is probably significant that commercial hybrids of 2015 have a lot less ‘flex’ than those of 1973, but the basic importance of uniform emergence remains.
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About Corn Journal
The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.