A comparison of screening techniques for Fusarium head blight of wheat in South Africa

[摘要] English: Fusarium head blight is one of the most important wheat diseases under irrigation and currently there are no cultivars resistant to this disease in South Africa. The main aim of this study was to determine the virulence of Fusarium graminearum isolates, to test growth and sporulation on different media and to do screening for resistance in the greenhouse and field. Twenty Fusarium graminearum single spore isolates from the Prieska region were evaluated in the greenhouse to determine the virulence of the isolates on a susceptible wheat cultivar. The isolates that were most virulent were A191, A145, A144, A149, A204 and A223. These isolates did not differ significantly from each other in the greenhouse test. Five of these isolates were used in the laboratory to determine which solid medium can be used to produce an abundance of spores. Potato dextrose agar, carrot agar, malt extract agar with 5 g chopped maize straw and mung bean agar were used. The growth of the isolates was measured over a seven day period. From the data it was evident that malt extract agar and mung bean agar were the best media to use for growth within the seven day period. Each of the media was tested weekly for up to four weeks to determine which of the isolates produced the most spores when given optimum conditions. Mung bean agar was the best medium to use for spore production. Considering the other media, potato dextrose agar may be used for identification, multiplying and storage of Fusarium isolates. Carrot agar is suitable to induce spore production, but is generally used as a medium for fertility studies. Malt extract agar containing sterile, chopped maize straw may be used for growth rather than for inducing spore formation. A lower amount of malt extract should be used to reduce the amount of maltose in the medium to increase spore production. Isolate A191 was used in the other two greenhouse tests. The first test was to determine the best inoculation technique for inducing FHB. Five different cultivars were included, namely SST825, SST822, Krokodil, Frontana and a derivative of Sumai #3 (SUM3/3/CS/LE.RA//CS/4/YANGMAI 158). Three techniques were used, namely cotton wool, straw and spray inoculation. From the data obtained it was clear that the cotton wool method was the best inoculation method to use to test Type II resistance. In a second greenhouse test, 13 lines from the 9th SRSN, CIMMYT, Mexico, were tested with isolate A191 using the cotton wool technique. The results showed that there were no differences between the moderately susceptible SST825 and numbers 74 and 54 (Type II resistance). The second group can be classified as a moderately resistant group that included numbers 54, 39, 21, 34, 50, 47, 19, 5, 57, 61 and 3. Number 14 was classified as resistant and the Sumai #3 derivative as a very resistant cultivar. Two field trials were executed in 2007 and 2008, respectively. The 9th SRSN from CIMMYT, Mexico, were included in the trials for both years. The field experiment consisted of the honeycomb moving grid design. The isolates used for both years included numbers were A144, A145, A146, A149, A151, A156, A159, A161, A166, A167, A169, A176, A183, A187, A191, A194, A204 A221, A223 and A269. These isolates were prepared on mung bean medium, harvested and sprayed four times, at two-day intervals, onto wheat plants during flowering. The environmental conditions for the 2007 trial were excellent for infection. Data from 2007 showed that entry 66 was susceptible. Thirty-three lines showed resistance, 29 lines showed moderate resistance and five showed moderate susceptibility. SST806 and Marico were used as a susceptible and moderate resistant control, respectively. The environmental conditions for 2008 were not conducive and very low levels of infection were obtained. Grain spawn was used in conjunction with spray inoculation to improve the inoculum pressure during 2008. Although extra inoculum was added, a low infection percentage was noted. Thus, field trials should be executed for at least three seasons before meaningful recommendations can be made.

[发布机构] University of the Free State