Call to action/take home messages

• Two seasons of trials (2016 and 2017) under high Phytophthora root rot (PRR) pressure showed the importance of varieties with good PRR resistance.
• Under heavy PRR pressure in 2016, of the three MR rated varieties, Yorker (1.29 t/ha) performed significantly better than PBA HatTrick (0.40 t/ha), while PBA Seamer had yields intermediate (0.95 t/ha) between the two.
• The 2016 trial showed that the best PRR resistance occurred in two breeding lines that are crosses with a wild relative of chickpea.
• The 2017 trial which had extensive PRR losses (minimum loss 78%), was also affected by frosts and cool temperatures delaying podset. In addition, hotter than average conditions in September also led to early plant death. The 2017 results showed that a lines PRR yield loss can be confounded by the lines ability to set and retain pods under sub-optimal conditions.

Varietal resistance to Phytophthora root rot

Phytophthora medicaginis, the cause of Phytophthora root rot (PRR) of chickpea is endemic and widespread in southern QLD and northern NSW, where it carries over from season to season on infected chickpea volunteers, lucerne, native medics and as resistant structures (oospores) in the soil. Although registered for use on chickpeas, metalaxyl seed treatment is expensive, does not provide season-long protection and is not recommended. There are no in-crop control measures for PRR and reducing losses from the disease are based on avoiding risky paddocks and choosing the right variety.

Detailed information on control of PRR in chickpea is available at: Chickpea: Managing Phytophthora Root Rot

Current commercial varieties differ in their resistance to P. medicaginis, with Yorker, PBA HatTrick and PBA Seamer having the best resistance and are rated MR (historically Yorker has been slightly better than PBA HatTrick), while Jimbour is MS - MR, Flipper and Kyabra are MS and PBA Boundary has the lowest resistance (S). PBA Boundary should not be grown in paddocks with a history of PRR, lucerne, medics or other known hosts such as sulla.

From 2007 to 2017, PRR resistance trials at the DAF Q Hermitage Research Facility, Warwick QLD have evaluated a range of varieties and advanced PBA breeding lines. Each year the trial is inoculated with P. medicaginis at planting. There are two treatments, (i) seed treatment with thiram +thiabendazole and metalaxyl plus regular soil drenches with metalaxyl* and (ii) seed treatment with thiram + thiabendazole only and no soil drenches. The first treatment has prevented infection by the PRR pathogen in all of these trials. The difference in yield between the metalaxyl-treated plots and non metalaxyl treated plots is used to calculate the yield loss caused by PRR.

*Soil drenching with metalaxyl is not a registered or legal practice for use in chickpeas and has been used purely as a research tool to provide a PRR protected treatment.

The trials were irrigated during extended periods of low rainfall with dripper tape once or twice per season to provide adequate soil moisture for PRR disease development.

Varietal resistance in 2016 and 2017 trials

Yield losses were high across all entries in the 2016 trial, with only two entries (CICA1328 and D06344>F3BREE2AB027) sustaining less than 50% yield loss.

In the 2016 trial, there were significant effects (P < 0.001) for the PRR protected treatment, variety effects and the interaction between the PRR protected and variety treatments. For the interaction, yields amongst varieties that were PRR protected did not differ, but there were large differences among varieties not protected for PRR (Table 1). Especially for CICA1328 and D06344>F3BREE2AB027 which had higher yields than all other varieties, there were several different levels separating the yields of groups of varieties (group 1 CICA1328 & D344, group 2 CICA1007 & Yorker, group3 CICA1521 & PBA Seamer, group 4 PBA HatTrick & PBA Boundary) in this treatment. The 2016 trial again confirmed the superior PRR resistance of the PBA breeding line CICA1328 and D344 which are both crosses between a chickpea (Cicer arietinum) line and a wild Cicer species.

Table 1. Yields of chickpea varieties and breeding lines protected from Phytophthora root rot, and % yield losses from PRR in a 2016 trial at Warwick QLD. (P yield <0.001; lsd yield = 0.63 kg/ha)

^A These lines are crosses between chickpea (C. arietinum) and a wild Cicer species

The extent of yield losses to PRR across entries in 2017 was unprecedented with the minimum yield loss of 83% for CICA1328. The 2017 season had an unusual combination of climatic conditions including heavy frosts affecting flowering and podset (see following section for more details). These conditions had a large effect on the performance of material in the 2017 trial, which may reflect the effect of these conditions on performance rather than direct effects of PRR on yields. Therefore we recommend caution in the interpretation of the 2017 PRR varietal resistance results.

For the 2017 trial, protecting for PRR significantly increased yields (P < 0.001) and there were also significant differences amongst varieties, although there was no significant interaction between the PRR protected and variety treatments (Table 2). For the variety effect (P yield < 0.05; lsd yield = 0.38 kg/ha) CICA 1328, 1624 and 1713 had higher yields than CICA 1521, and CICA 1328, 1424, 1624, 1718, 1713, PBA Seamer and Yorker, those seven entries also had higher yields than PBA Boundary.

Table 2. Yields of chickpea varieties and breeding lines protected from Phytophthora root rot, and % yield losses from PRR in a 2017 trial at Warwick QLD. (interaction, P yield = 0.57; lsd yield = 0.54 kg/ha)

^A These lines are crosses between chickpea (C. arietinum) and a wild Cicer species

Seasonal effects on yields and varietal resistance rankings

It is well known that Phytophthora requires periods of soil saturation for disease development. In addition, a range of seasonal factors also affect the performance and yield of chickpeas. Using the last four seasons, we sought to identify factors affecting PRR disease and yields, and especially factors that could explain the unprecedented PRR losses in the 2017 trial.

The yield of PRR protected PBA HatTrick was used to indicate the yield potential of a season, and the % yield loss from PRR for key entries used to compare the extent of PRR development in differing material across seasons (Table 3). Yield results for PBA HatTrick show that the 2016 season had the highest yield potential (yields for PBA Boundary support this) and the 2015 season the lowest yield potential. The most PRR susceptible material is PBA Boundary with high % losses every season; the most resistant material is CICA1328 with consistently the lowest losses each season. Results for these two entries clearly show that the 2014 season had the lowest PRR disease pressure.

The 2014-2017 results for PBA HatTrick and PBA Boundary show the 2016 season was the most PRR conducive of the four seasons, however for CICA1328, 2015 was more conducive than 2016, and that 2017 was more conducive than 2015.

Data from the BOM station at Hermitage was used to identify associations between differing PRR trial seasons (Table 4). For the 2014 season, PBA Boundary, PBA HatTrick and CICA1328 had the lowest % yield losses, and rainfall across the four seasons was lowest in June and July 2016. These conditions may have limited the extent of early PRR infection. In contrast in 2016, PBA Boundary and PBA HatTrick had the largest % yield losses and 2016 rainfall was very high in June, August and September (> 300mm). These conditions may have supported both early infection events and later disease development in spring.

The 2017 season which saw very high % yield losses across all entries also had the lowest August and September rainfall of the four seasons, so the extent of spring rainfall does not explain the 2017 % yield losses and therefore suggests the role of other factors. For the 2017 season, mean minimum temperatures were below the 1994-2013 average temperatures for July, August and September (Table 4). The number of days in 2017 with minimum temperatures below 0°C and 2°C was higher than average in July, August and September (data not presented). September 2017 was also unusual as it had the highest average maximum temperature of the four seasons and was higher than the long term average.

Table 3. Results from the 2014, 2015, 2016 and 2017 seasons for yields of PBA HatTrick and PBA Boundary, and PRR % yield losses for PBA HatTrick, PBA Boundary and CICA1328.

Table 4. Average minimum and maximum monthly air temperatures and monthly rainfall totals for four chickpeas seasons at Hermitage (BOM station 41525) including longer term (1994-2013) average data for these measurements.

The 2017 season was unusual in that in many of the non PRR protected plots, plants were observed to die before setting pods. Unsuccessful and delayed flowering and podset was a key feature of the 2017 season, with temperature data showing that conditions unsuitable for successful flowering and podset occurred very late in the 2017 season. In addition, the combination of low minimum temperatures in September 2017 limiting podset and high maximum temperatures which increased the evaporative demand and so stress on PPR infected plants with compromised root systems, may explain the high yield losses due to PRR infection in 2017.

If these conclusions are valid, then the yields of non PRR protected treatments may reflect both the ability of an entry to successfully set pods under sub-optimal conditions and the entry’s PRR resistance. For example, this may explain why non PRR protected PBA HatTrick in the 2017 season had for the first time in four seasons a higher (although not significantly higher) yield that CICA1328.

Acknowledgements

Thanks to growers and agronomists for help with crop inspections and submitting specimens, to Woods Grains, Goondiwindi for planting material for trials. This research is made possible by the significant contributions of growers through both trial cooperation, field access and the support of the GRDC, the authors would like to thank them for their continued support.

Contact details

Sean Bithell
NSW Department Primary Industries
Ph: 0429 201 863
Fax: (02) 6763 1100
sean.bithell@dpi.nsw.gov.au

Kevin Moore
NSW Department Primary Industries
Ph: 0488 251 866
Fax: (02) 6763 1100
kevin.moore@dpi.nsw.gov.au

Varieties displaying this symbol beside them are protected under the Plant Breeders Rights Act 1994