Host-pathogen studies of common rust of maize in South Africa

[摘要] English: Maize (Zea mays L.) is one of South Africa's most important grain crops because of its significance as a staple diet among a large proportion of the population. Maize is alsoan important component of livestock feed and is used in the manufacturing of severalindustrial products. Observations during the past few seasons showed an increasedoccurrence of common rust, caused by the fungus Puccinia sorghi Schwein. This gaverise to questions from maize producers and researchers regarding the epidemiology,economic impact and control measures of the disease.The spore stages of this macro-cyclic fungus, as they occur on both the primary(maize) and alternate (Oxalis corniculata, creeping sorrel) hosts in South Africa, weredescribed. Detailed schematic illustrations as well as microscopic records of the fivespore stages were prepared. A survey was done to determine the occurrence of thesexual stage on creeping sorrel in the main maize producing areas in South Africa.Most aecial infections were observed in KwaZulu-Natal, implying this region to be asource of new recombinant pathotypes. On request of the PAN NAR Seed Company(Pty) Ltd., all viable maize accessions in their germ plasm collection were tested forreaction to common rust infection. Out of 2594 lines only 185 were resistant in theglasshouse as well as in the field, while 426 were resistant in the glasshouse but notin the field. This information should help PANNAR to make certain decisions about rustresistance or susceptibility in their breeding material.Spray trials with different fungicides and maize cultivars showed that positiveyield increases can be obtained. Eria®+Eria® and Amistar®+Eria® showed the bestresults. The effects of fungicides were, however, dependent on the level of adult plantresistance, locality, as well as the occurrence of other diseases.Even though maize breeders realize that single gene resistance does not ensurelong-term protection against rust, breeding approaches allow combination of suchgenes with non-specific adult plant resistance. The inheritance of Rp1-A, Rp1-C, Rp1-G, Rp1-L, Rp3-D, Rp3-E and Rp3-F in F2 progenies were studied to provide breederswith information on the ease of following single genes in segregating populations.Although all the genes indicated monogenic inheritance, F2 segregation ratios fromcrosses inbred 1 X Rp 1-L and inbred 1 X Rp 3-F differed significantly from theexpected 3 resistant: 1 susceptible ratio. Chi-square tests for homogeneity showed thatwhite and yellow seed colour did not, as expected, influence the inheritance of Rp1-A,Rp1-C, Rp1-G, Rp1-L, Rp3-0 and Rp3-E. Based on the distinct expression of infectiontypes, breeders should be able to efficiently select for these genes in cultivardevelopment.

[发布机构] University of the Free State