Publisher Summary This chapter discusses the general field of cytoplasmic inheritance of pollen sterility. In five discoveries, the expression of the cytoplasmically induced sterility was influenced by nuclear genes. Investigation of the genetics of fertility restoration of both the United States Department of Agriculture (USDA) and the Texas types of cytoplasmic sterility has shown that in either case a single dominant gene is sufficient to restore pollen fertility to most cytoplasmic male-sterile inbreds although there are complications with certain genetic backgrounds and in certain environments. Specific tester genotypes enable one to differentiate USDA from Texas cytoplasms because some genotypes are sterile in one cytoplasm but not the other, some are sterile in both, and some are pollen fertile in both. This type of test can be applied to all discoveries of cytoplasmic male sterility to see if they resemble either the USDA or the Texas source or if they have a different spectrum of interactions with genotype. Cytoplasmic male sterility in corn is characterized by having two distinct forms, the USDA and the Texas. Both types interact with the nucleus to the extent that their sterility-inducing potential is revealed only by certain genes, and the number of the genes is relatively few for each cytoplasm. The Texas type has been shown to affect, to a small degree, the rate of growth and final size of the corn plant, independently of its effect on pollen sterility.

Cytoplasmic Pollen Sterility in Corn

Models for the maintenance of females in gynodioecious species are reviewed. Some new results are given concerning digenic models and models of cytoplasmic inheritance with restorer genes, when the cytoplasmic and nuclear factors may have fitness effects in addition to their effects on male fertility. It is suggested that many gynodioecious species may be interpreted as having a cytoplasmic-genic inheritance of male-sterility, and that this interpretation would resolve a number of difficulties. However, much of the evidence is circumstantial, and complete details of the genetics are not available for any case of natural polymorphism for male-sterility. This makes it impossible to test the population genetics theories in a more precise way. It is clear, however, that both the digenic and the cytoplasmic-genic model require large fitness differences if a polymorphism for females is to be maintained. Some evidence exists in maize for the type of fitness effect required by the cytoplasmic-genic model.

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A further study of the problem of the maintenance of females in Gynodioecious species

The Role and Regulation of the Anthesis-Silking Interval in Maize

We have proposed breeding a maize (Zea mays L.) ideotype that will maximally utilize an optimum production environment. This environment should include: a) adequate moisture; b) favorable temperatures throughout the growing season; c) adequate fertility; d) high plant densities; e) narrow row spacings; and f) early planting dates. The maize ideotype that should produce optimally when grown in such an environment would be characterized by: a) stiff, vertically-oriented leaves above the ear (leaves below the ear should be horizontally oriented); b) maximum photosynthetic efficiency; c) efficient conversion of photosynthate to grain; d) short interval between pollen shed and silkemergence; e) ear-shoot prolificacy; f) small tassel size; g) photoperiod insensitivity; h) cold-tolerance in germinating seeds and young seedlings (for genotypes grown in areas where early-planting would require planting in cold, wet soils); i) as long a grain-filling period as practically possible; and j) slow leaf senescence.

An ideotype of maize

SUMMARY This review focuses on the mechanisms determining yield in maize, sunflower and soybean, the three major summer crops of the Argentinean Pampas. Emphasis is given to the capture of light by the crop canopy and the processes determining grain set and grain filling. A strong correlation between grain yield and the physiological status of crops or plants at crop-specific critical periods is confirmed. This basic physiological information is used (i) to evaluate and understand the effect of agricultural management practices on crop yield and (ii) as the source of concepts and quantitative relationships for crop simulation models. Finally, we discuss the relevance of the described physiological processes for crop breeding.

Physiological Determinants of Crop Growth and Yield in Maize, Sunflower and Soybean

THE influence of detasseling on the performance of corn has been studied since the last decade of the last century. Some of the early research workers found that detasseling decreased yield, while others found that it did not. The early work was reviewed adequately by Grogan. Grogan stated that the removal of immature tassels seemingly results in diversion of some of the energy and nutrients normally expended in pollen production to grain production. He predicted that under the same environment male-sterile plants which produce no pollen would react in a manner similar to their detasseled fertile counterparts.

M. S. Zuber

Papers

Interaction of Detasseling, Sterility, and Spacing on Yields of Maize Hybrids 1