Corn (Zea mays) rusts (Puccinia sorghi, P. polysora, Physopella zeae) I. Review

Abstract

The present review is mainly concerned with the genetical control of the corn rusts, as well as with their correlated problems. Such a study is important, ii one intends to improve resistance by means of a genetical treatment of corn. In his forward, the author emphasizes the losses caused by Puccinia polysora as 40% and only 0,5 to 1.0% ascribed to P. sorghi. These pathogenic agents are identified in a brief historical summary. Also reviewed were their life cycles and morphology to enhance proper field identification, and so that their physiology and parasitism pattern may be more fully understood. In the chapter on physiological races the possible existence of breeds in rusts is given; there were no results in reducing the number of pathogenic types in experiments to improve P. sorghi breeds, and no advances were registered in homozygosity of pathogenic factors. The author emphasized the fact that the understanding of the host-parasite interaction and the definitions, symbols and concepts of complementary fit among interacting genotypes is essencial for advancing the study of genetical unity and of ascertaining geometrical shape of the molecules governing resistance. The complementary activity pattern and the differential series that enabled U.S. workers to isolate 15 P. sorghi races are mentioned also. With reference to inherited resistance, some studies were reported on the analysis of an allelic series for resistance to P. sorghi in the short chain of chromosome 10 of corn (Rp rp). There is a possibility of interference of closely linked genes. Though information on Physopella zeae and Puccinia polysora are scarce analysis are reported on initial genes (Rpp¹ and Rpp²), so that a differential series for P. Polysora races can be established in the future. The author observed that experimental studies on the production of rust resistant breeds of corn must follow a certain sequence, so that resistante hybrid corn lines for commercial purposes can be obtained. Adequate measures now become necessary in Brazil to stimulate efficiency in future experiments. Research work should indicate when and how genetical control of corn leaf rust should be exercised. Since losses in large scale forming were only 0.5% for P. sorghi the author is of the opinion that a specific program is not presently urgent in this instance. On the subjects reported herein little was found in Brazilian literature, only a note on occorrence of P. sorghi in corn plantations of Brazil.