Submitted to: Plant Disease Management Reports
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/22/2013
Publication Date: 3/11/2013
Citation: Chen, X., Garner, J.P., Liu, Y. 2013. Evaluation of chemical seed treatments for control of stripe rust in wheat under controlled conditions. Plant Disease Management Reports. 7:ST003. Interpretive Summary: Chemical seed treatments were tested for any effects and duration of effects on control of stripe rust on both winter wheat and spring wheat under controlled conditions. A randomized complete block design experiment with three replications and five plants in each replication was used including a non-treated control. Infection type and severity was assessed for each plant twice after inoculation. Disease index and area under the disease progress curve (AUDPC) was calculated for each plant. Relative AUDPC was calculated as percentage of the non-treated control. The relative AUDPC data were subjected to analysis of variance and means were compared to determine the difference among the treatments. The majority of the treatments significantly reduced the disease, but the control effects only lasted up to 15 days after planting. For stripe rust, which is a multi-cyclic disease caused by an airborne pathogen, all of the tested seed treatments appear not able to provide protection long enough to have significant value in the disease management, which was also shown in the field studies under natural infection conducted at Pullman, WA during the 2011-2012 wheat growth season. This study indicates that chemicals with a long-lasting effect (at least for a month) are needed to be used as seed treatments for reduce stripe rust.
Technical Abstract: The study was conducted under controlled conditions in a greenhouse in Pullman, WA. Seed of winter wheat ‘PS 279’ and spring wheat ‘Lemhi’ were treated by chemical companies with various chemicals. Seed of the two susceptible cultivars without treatment were used as non-treated controls. Five seeds of the same treatment were planted in a 3 x 3 x 3 in. plastic pot filled with a potting mixture of 24 L peat moss, 8 L perlite, 12 L sand, 12 L commercial potting soil mix, 16 L vermiculite, and 250 g 14%-14%-14% (available N-P-K) Osmocote fertilizer (Scotts Miracle-Gro Company, Marysville, OH) for the seedling tests (shoot, early tillering, and late tillering stages). Plants were grown in a rust-free greenhouse prior to inoculation. For plants of PS 279 tested at early jointing to flowering stages, two-leaf seedlings of 10 days after planting were kept in a vernalization chamber at 2-4oC with 14 h light/10 h dark for 60 days. Five vernalized plants of the same treatment were transplanted into a 7 x 7 x 7 in. plastic pot filled with the potting mixture described above and grown in a rust free greenhouse. Plants of different growth stages or days after planting were inoculated with a mixture of fresh urediniospores of Puccinia striiformis f. sp. tritici PST-100, a predominant race identified throughout the U.S. in the recent years, and talc at a 1:20 ratio using a brush to uniformly cover the upper surface of two top leaves. Inoculated plants were kept in a dew chamber for 24 h at 10oC without light, and then moved into a growth chamber with a diurnal temperature cycle gradually changing from 4oC at 2:00am to 20oC at 2:00pm and a 16-h light/8-dark cycle for the seedling tests (GS1 - GS3 in the following tables), or with a 10oC to 30oC diurnal cycle and the same light/dark cycle for the later growth stages (GS4 – GS7 in the first table) of PS 279. For each growth stage experiment, a complete randomized block design was used with three pots as blocks and five plants per pot. Stripe rust infection type (IT) based on a 0-9 scale with ITs 8 and 9 combined as IT 8 and severity from 0 to 100% (percentage of inoculated leaf area infected) were recorded for each plant twice, 15 days and 20 days after inoculation. Disease index (DI) was calculated using the formula: DI = (IT x severity) / (8 x 100) x 100. Area under disease progress curve (AUDPC) was calculated for each plant using the two sets of DI data. Relative AUDPC was calculated as percent of the non-treated control and were subjected to analysis of variance and means were separated by Fisher’s protected LSD test. In the winter wheat tests, all Valent Corporation seed treatments (TRT) significantly reduced stripe rust only at the early stages (GS1 and GS2) 10 and 15 days after planting, except for TRT1 (Nipsit Inside Insect 5.00 FS 1.000 fl oz/cwt). TRT3 [Metlock 3.70FS 0.090 floz/cwt + V10209 2.65FS 0.150 fl oz/cwt + Nipsit Inside Insect 5.00FS 1.000 fl oz/cwt (Metconazole 2.5)], TRT4 [Dividend Extreme 0.96SS 3.000 fl oz/cwt + Nipsit Inside Insect 5.00FS 1.000 fl oz/cwt (Difenocon-18 gai)], and TRT5 [Dividend Extreme 0.96SS 3.000 fl oz/cwt + Rancona 3.80FS 0.051 fl oz/cwt + Nipsit Inside Insect 5.00FS 1.000 fl oz/cwt (Difenocon 18 gai + Ipconazole 1.5)] were better than the other treatments based on the test of 15 days after planting, reducing the relative AUDPC value by about 57% compared to the non-treated control (NTC). Similar results were obtained in the spring wheat tests of first two growth stages (GS1 and GS2). However, TRT1 did not reduce stripe rust in the tests of inoculations of 10 and 16 days after planting, but had significant lower rust AUDPC value than NTC in the test of inoculation 32 days after planting (GS3). All treatments had significantly lower rust than NTC in the test of inoculation 32 days after inoculation, except TRT4 (Dividend Extreme 0.96SS 3.000 fl oz/c