Sclerotinia impacts on chickpea yield and the role of Predicta B to differentiate between species and inoculum load of sclerotinia
Sclerotinia impacts on chickpea yield and the role of Predicta B to differentiate between species and inoculum load of sclerotinia
Take home message
- There are three species of Sclerotinia present in chickpea crops in the northern cropping region. Sclerotinia populations may increase under susceptible crops including canola and chickpeas
- Of the three species, in two years of chickpea yield loss experiments Sclerotinia minor consistently caused higher grain yield loss (34–54%) than Sclerotinia sclerotiorum (10–26%) or Sclerotinia trifoliorum (7–15%)
- A new Predicta® B soil test can be used to identify which Sclerotinia species are present in paddocks. Predicta B results may allow paddocks to be monitored over time to gauge Sclerotinia inoculum concentration responses to changes in crop rotations.
Background
Infection of the stem base by Sclerotinia causes stem rot of chickpea, whilst a second infection route occurs from aerially dispersed ascospores infecting chickpea foliage. Analysis of over 100 Sclerotinia disease records for northern NSW chickpea crops showed that 48% were Sclerotinia minor, 32% were Sclerotinia sclerotiorum and 24% were Sclerotinia trifoliorum (Bithell et al., 2023). It was unknown what scale of yield loss Sclerotinia disease of chickpea can cause and which Sclerotinia species has the most effect on chickpea production.
In addition, the monitoring of soil pathogen populations with the Predicta® B based method did not previously individually identify the three Sclerotinia species and distinguishing between Sclerotinia sclerotiorum and Sclerotinia trifoliorum is time consuming and requires specialist mycological techniques. Therefore, we sought to develop species specific molecular detection and quantification methods to provide Predicta B based monitoring of Sclerotinia species and inoculum concentrations in paddocks.
Methods
Four yield loss experiments were carried out on chickpea, PBA Seamer, at the Trangie Agricultural Research Centre. Each experiment was a randomised complete block design, using five-row 15 m2 plots, with 4 replicates. Treatments were: three Sclerotinia species, Sclerotinia minor, S. sclerotiorum and S. trifoliorum applied as sterilised barley and millet grain infected with the Sclerotinia species and included in the chickpea seed packets at sowing; and five inoculum concentrations (0, 0.8, 1.7, 3.4, 6.7 g inoculum/m2). The two 2022 experiments were not irrigated and there was 398 mm of in-crop rain. The 2023 experiments received 106 mm of in-crop rain. One 2023 experiment was managed with supplementary irrigation using a lateral irrigator and had 18.0, 17.5 and 20.0 mm applied at 55, 76 and 105 days after sowing (DAS), respectively. The second 2023 experiment received salvage irrigation to ensure ongoing survival of the experiment, with applications of 9.0 and 12.5 mm at 76 and 105 DAS, respectively.
Results
Emergence
Emergence counts were made in fixed quadrat areas of each plot. In the wet conditions of the 2022 season emergence of control plots at 21 plants/m2 was lower than the 35 plants/m2 target. Combined results for the two 2022 experiments are presented in this report as these experiments did not differ in irrigation management. In 2022 increasing Sclerotinia inoculum concentration significantly reduced emergence by 7 to 16 plants/m2, P<0.001, LSD 2.4 plants/m2, Table 1) although there was no significant effect of Sclerotinia species (P>0.05, LSD 1.9 plants/m2).
Table 1. Percentage reduction of a) emergence and b) seedling PBA Seamer population of Sclerotinia minor, S. sclerotiorum, or S. trifoliorum inoculated plots relative to nil inoculum control plots across three experiments: 2022 combined, 2023 supplementary irrigation (SUI) and salvage irrigation (SAI).
a. Emergence reduction (%) | ||||
---|---|---|---|---|
Species/Exp. | 2022 combined | 2023 SUI | 2023 SAI | Average |
S. minor | 46 | 61 | 60 | 55.7 |
S. sclerotiorum | 46 | 30 | 33 | 36.3 |
S. trifoliorum | 40 | 23 | 25 | 29.3 |
Average | 44 | 38 | 39.3 | 40.4 |
b. Seedling population reduction (%) | ||||
Species/Exp. | 2022 combined | 2023 SUI | 2023 SAI | Average |
S. minor | 10 | 7 | 6 | 7.7 |
S. sclerotiorum | 6 | 4 | 0 | 3.3 |
S. trifoliorum | 3 | 0 | 1 | 1.3 |
Average | 6.3 | 3.7 | 2.3 | 4.1 |
In the dry conditions of 2023, the population density of seedlings in control plots met the 35 plants/m2 target. In both 2023 experiments for species effects across all inoculum concentrations, S. minor (19 plants/m2) had significantly (P<0.001, LSD 2.33 plants/m2) less emerged seedlings than both S. sclerotiorum and S. trifoliorum (26 and 28 plants/m2, respectively). There was also a significant species by inoculum concentration interaction (P<0.01), whereby for all four Sclerotinia inoculum concentrations (0.8 to 6.7 g/m2) there was a significant reduction in emergence for S. minor inoculated plots relative to S. sclerotiorum and S. trifoliorum emergence at the same inoculum concentrations. For the supplementary irrigation experiment at the highest inoculum concentration S. sclerotiorum had less plants that S. trifoliorum.
The effects of Sclerotinia on the establishment of chickpea are summarised by comparing the average counts of all Sclerotinia-inoculated treatments relative to the nil inoculum control plots for each species to determine the percentage of emergence reduction from Sclerotinia disease (Table 1a). The overall average percentage of emergence reduction across all experiments from S. minor was highest (56%), although substantial reductions also occurred for S. sclerotiorum (36%) and S. trifoliorum (29%).
Plant population and disease symptoms
Repeat counts of seedlings at approximately one month after the emergence counts (9 August in 2022, 17 July in 2023) were made in the same fixed quadrat areas of each plot each year. Symptomatic or dead seedlings were observed in marked quadrat areas at these times for each of the three Sclerotinia species; only plants with stem base infection were observed. Seedlings with stem base symptoms were collected and analysed. Samples of mycelium from the stem base of dying plants provided cultures with typical Sclerotinia characteristics. DNA analysis using SARDI’s Predicta B test of stem base tissue from dead seedlings confirmed infection by each of the three Sclerotinia species.
The effect of Sclerotinia disease on seedling death of chickpea were also summarised on a percentage of seedling loss basis (Table 1b). The overall average percentage of emergence reduction across all experiments from S. minor was highest at 8% whereas the overall values for the other two Sclerotinia species were less than 5% on average.
Effects on yield
In 2022 there was a significant (P=0.006, LSD 412.2 kg/ha) interaction between the Sclerotinia species and inoculum concentration where S. minor at the second (2011 kg/ha) and third (1366 kg/ha)inoculum concentration treatments had a significantly lower grain yield than S. trifoliorum (2424 and 228 kg/ha) only, but at the fourth and highest inoculum concentration treatment S. minor (780 kg/ha) had a significantly lower grain yield than both S. trifoliorum (1704 kg/ha) and S. sclerotiorum (1352 kg/ha).
In 2023 for the supplementary irrigation experiment S. minor had significantly (P<0.001) lower grain yields (range 173 to 1126 kg/ha) than S. sclerotiorum and S. trifoliorum at all inoculum concentrations, whereas S. sclerotiorum (919 kg/ha) had a lower grain yield than S. trifoliorum(1064 kg/ha) only at the highest inoculum concentration. For the salvage irrigation experiment S. minor also had significantly (P = 0.005) lower grain yields (range 389 to 1073 kg/ha) than S. sclerotiorum (range 1080 to 1392 kg/ha) and S. trifoliorum (range 1025 to 1433 kg/ha) at all inoculum concentrations, but the grain yields of S. sclerotiorum and S. trifoliorum did not differ at any common level of inoculum concentration.
The effects of Sclerotinia on chickpea grain yield is summarised on a percentage of grain yield lost to Sclerotinia disease basis (Table 2). The percentage yield loss to S. minor was highest across all three experiments. In two of three experiments S. sclerotiorum had a higher percentage loss (18–26%) than S. trifoliorum (7–12%), but in one 2023 experiment S. trifoliorum had a 5% greater yield loss than S. sclerotiorum.Overall the results from two seasons of experiments indicate that S. minor can cause proportionally large (>30%) yield loss in both wet and dry seasons, but the largest losses are likely to occur in dry seasons.
Table 2. Percentage grain yield loss of PBA Seamer in Sclerotinia minor, S. sclerotiorum, and S. trifoliorum inoculated plots across three experiments: 2022 combined, 2023 supplementary irrigation (SUI) and salvage irrigation (SAI). Untreated controls in 2022 yielded 2498 k/ha, untreated controls in 2023 the SUI in yielded 1493 kg/ha and in the SAI yielded 1439 kg/ha.
Species/Exp. | 2022 combined | 2023 SUI | 2023 SAI | Average |
---|---|---|---|---|
S. minor | 34 | 54 | 48 | 45.3 |
S. sclerotiorum | 26 | 18 | 10 | 18.0 |
S. trifoliorum | 7 | 12 | 15 | 11.3 |
Average | 22.3 | 28.0 | 24.3 | 24.9 |
Sclerotinia inoculum measurement
The new Sclerotinia Predicta B species tests successfully detected inoculum of the three Sclerotinia species. Table 3 presents results for one of the 2023 experiments which showed that, at planting, the inoculum concentrations of the three Sclerotinia species treatments did not differ significantly. However, following harvest of the 2023 chickpea experiment S. minor and had significantly higher values than S. sclerotiorum and S. trifoliorum.
In addition, the Sclerotinia Predicta B species tests were able to detect inoculum in the roots of chickpeas and other pulse crops from paddocks where isolates of these pathogens had been collected. This new capability may allow paddocks to be monitored over time to gauge Sclerotinia inoculum concentration responses to changes in crop rotations.
Table 3.Sclerotinia minor, S. sclerotiorum, or S. trifoliorum soil DNA extraction results (kilo copies DNA/g soil) post planting or postharvest in the Trangie 2023 supplementary irrigation experiment of PBA Seamer, residual df = 42, P value and least significant difference (LSD) values presented.
Species | S. minor | S. sclerotiorum | S. trifoliorum | P | LSD |
---|---|---|---|---|---|
Post planting kDNA copies | 1094 | 648 | 978 | 0.32 | 609.9 |
Postharvest kDNA copies | 2712 | 1181 | 177 | <0.001 | 1111.7 |
References
Bithell SL, Devkota R, Moore K and Lindbeck K (2023) Sclerotinia of chickpea in northern New South Wales. Australian Pulse Conference. 21-23 March 2023, Toowoomba, Qld.
Acknowledgements
The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC, the author would like to thank them for their continued support.
Contact details
Sean Bithell
NSW Department of Primary Industries
4 Marsden Park Rd, Tamworth NSW 2340
Mb: 0429 201 863
Email: sean.bithell@dpi.nsw.gov.au
Leigh Jenkins
NSW Department of Primary Industries
Trangie Agricultural Research Centre, Trangie, NSW 2823
Mb: 0419 277 480
Email: leigh.jenkins@dpi.nsw.gov.au
Date published
August 2024
Varieties displaying this symbol are protected under the Plant Breeders Rights Act 1994.
GRDC Project Code: DPI2206-023RTX,