Control of foliar rusts of wheat in South Africa with special emphasis on Puccinia striiformis f. sp.Tritici

[摘要] English: Stripe rust, caused by Puccinia striiformis Westend. f. sp. tritici Eriks., has becomean endemic disease of wheat (Triticum aestivum L.) in South Africa after beingobserved for the first time near Moorreesburg, Western Cape, during August 1996.Pathotypes (pts.) detected in surveys were 6E16A- with virulence toYr2,6,7,8,11,14,17 and Yr19, and 6E22A- with added virulence to Yr25. Stripe rustisolates found on Hordeum murinum L. in the Western Cape were identified as pt.6E 16A- whereas both pts. 6E 16A- and 6E22A- were collected from Bromuscatharticus Vahl in the eastern Free Sate. The possible role that grass species mayplay in the over-summering of the stripe rust pathogen has not yet been fullyestablished. However, stripe rust infections have been found on summer-sownwheat in the south Western Cape during 1998, volunteer wheat growing in thesummer and autumn months in the eastern Free State from 1998 to 2000, and onsummer-sown wheat in Lesotho. The reaction of 55 South African and 18 foreign wheat cultivars wasdetermined to pts. 6E16A- and 6E22A- in both the seedling and adult plant stage.The occurrence of stripe rust head infections was studied using 16 spring wheatcultivars and 17 supplemental lines. Six of the 55 local wheat cultivars expressedseedling resistance, 18 appeared heterogeneous and 31 were susceptible. Themean area under the disease progress curve (AUDPC) determined in the field for 42cultivars over a three year period showed that 11 cultivars expressed high levels ofcomplete or adult plant resistance (AUDPC <200). Twelve cultivars expressedintermediate levels of resistance (AUDPC 200 to 500) and 19 displayed AUDPCvalues of 500 to 1598. The percentage head infection was positively correlated tostripe rust severity on flag leaves. Of the 18 foreign cultivars evaluated 10 wereresistant in both seedling and adult plant stages. The remaining eight cultivars weresusceptible as seedlings but showed high levels of adult plant resistance in the field.Field trials were conducted from 1997 to 1999 to determine the effect of stripeand leaf rust (P. triticina Eriks.) epidemics on yield and quality of wheat. Five triazolefungicides, applied at two growth stages on three cultivars in the south WesternCape during 1997, resulted in a mean decrease of 31% in the AUDPC calculated for stripe rust infection. The application of fungicides closely to, or just after heademergence, resulted in a 65 to 74% decrease in the occurrence of stripe rust headinfections. In contrast, head infection was reduced by only 8% when fungicides wereapplied at the seven leaf stage. Combined seven and flag leaf treatments withpropiconazole, averaged over the three cultivars, resulted in a 56% yield increase,followed by increases of 49%, 44%, 39% and 25% with tebuconazole, flutriafol,bromuconazole, and flusllazole, respectively. In the absence of disease during 1998no fungicide treatment resulted in a significant yield or hectolitre mass increase inany of the trials.The application of eight fungicides at both seven and flag leaf stages atLanggewens in the Western Cape during 1999, resulted in a mean decrease of 65%in the AUDPC, calculated for leaf rust severity. Combined seven and flag leaftreatments resulted in a mean yield increase of 56%, followed by 50 and 15% for theflag leaf and seven leaf treatments, respectively. Over treatments applied, yieldincreases varied from 24% for bromuconazole to 53% forepoxiconazole/carbendazim. Furthermore, the application of a flag leaf, andcombined seven and flag leaf treatments, resulted in a significant increase inhectolitre mass. During 1999 the combination of triticonazole seed treatment with apropiconazole flag leaf spray on the cultivar Gariep in the eastern Free Stateresulted in a 91% decrease in the stripe rust AUDPC, and an associated 36% yieldincrease. Hectolitre mass increased by 3% and protein content decreased by 4% forthe latter treatment. Triticonazole seed treatment had a 54% decrease in theAUDPC resulting in 16 and 2% yield and hectolitre mass increase, respectively. Thebest control of stripe rust was obtained with a combined seven and flag leaftreatment with propiconazole, as well as triticonazole seed treatment combined witha seven and flag leaf treatment of propiconazole. The latter two treatments resultedin a 49% yield increase.The results obtained in yield loss studies emphasise the importance ofresearch aimed at the genetic control of rust diseases of wheat in South Africa.Effective and longlasting genetic control can only be obtained by coordinating futureresearch, continuous monitoring of changes in the pathotype population, the regular collection of germ plasm carrying new or unused sources of resistance,characterising current sources of resistance, and by deploying available sources ofresistance in a responsible manner. The result of successful genetic control is notonly aimed at preventing the repeated application of fungicides, but also at reducingrisk in wheat production, thereby ensuring more stable yields of high quality.

[发布机构] University of the Free State