Jacob Thompson and Dr. Von D. Jolley, Agronomy and Horticulture

The objective of this research was to determine if iron-efficiency controlled by one gene is a more predictably inherited trait than when iron-efficiency is controlled by multiple genes.

In the calcareous soils of the upper Midwest soybean becomes deficient in iron. This deficiency causes a yellowing of the leaves known as chlorosis. Alleviating the deficiency by either foliar or soil application of iron is not economical, but without treatment the plants will die. The only economical alternative currently practiced is the development of iron-efficient cultivars.(4) Some cultivars exhibit iron stress responses which make the iron in the soil available for the plant. These cultivars are referred to as iron-efficient.Those unable to exhibit these responses are iron-inefficient.

A major drawback in breeding for iron chlorosis resistance is accurate and timely screening of genotypes. Results in field nurseries may not produce consistent results due to environmental changes and soil heterogeneity, and often years of data must be collected to produce accurate estimates of chlorosis resistance. In field nurseries, it is also difficult to determine resistant cultivars because cultivars differ in their development of chlorosis symptoms. Because of these constraints, screening for efficient cultivars in controlled environments such as greenhouses and growth chambers has been successful.(3)

Jolley et al. used iron reduction capacity as a predictor of chlorosis resistance using genotypes representing a broad range of iron efficiencies.(2) They have since successfully implemented the technique in dry bean.(1) Iowa State University researchers have developed soybean lines by crossing genotypes in which a single-gene controlled iron stress inheritance is expressed, or in which inheritance is controlled by multiple genes. They have done molecular-genetic marker research and field chlorosis trials with the offspring of these crosses. We used iron reduction capacity to determine if lines in which iron efficiency is controlled by one gene can be distinguished from those lines whose iron stress response is controlled by multiple genes. We selected randomly 7 crosses from the 300 lines provided by Iowa State University and are currently in the process of measuring the iron reduction capacity to predict the degrees of resistance or susceptibility to iron deficiency chlorosis. Due to problems encountered with new lights in our growth chamber our experiments have been delayed. These problems were overcome by changing the lights and by conducting smaller trial experiments to see if the plants could grow properly. The plants did responded appropriately and the results of the first 7 crosses, currently being measured, will be compiled within the next few weeks. These findings will link known inheritance characteristics to a quick and efficient screening technique leading to a faster release of iron-efficient cultivars that are needed on millions of acres.

References

1. Ellisworth, J.W., Jolley, V.D., Nuland, D.S., Blaylock, A.D. 1997. Screening for resistance to iron deficiency chlorosis in dry bean using iron reduction capacity. J. Plant Nutr. 20:1489- 1505.
2. Jolley, V.D., Fairbanks, D.J., Stevens, W.B., Terry, R.E., Orf, J.G. 1992. Root iron reduction capacity for genotypic evaluation of iron efficiency in soybean. J. Plant Nutr. 15:1679-1690.
3. Jolley, V.D., Cook, K.A., hansen, N.C., Stevens, W.B. 1996. Plant physiological responses for genotypic evaluation of iron efficiency in strategy I and strategy II plants- a review. J. Plant Nutr. 19:1241-1255
4. Weiss, M.G. 1943. Inheritance and physiology of efficiency in iron utilization. Genetics 28:253-268.