Take home messages

• Avoid paddocks prone to waterlogging, with poorly drained areas, or a history of lucerne, medics or chickpea Phytophthora root rot (PRR)
• Use the most PRR resistant varieties (rated MR) where there is a risk of PRR
• Be aware that although more chickpea varieties now have improved resistance to PRR substantial yield losses (40-68%) can still occur, even in a relatively dry season if one soil saturation rainfall event occurs
• Crosses between chickpea and wild Cicer species, such as the breeding lines CICA1328, CICA1718 and CICA1812, offer improved levels of resistance to PRR.

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 as a general management tool for PRR.  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 chickpea variety.

Detailed information on control of PRR in chickpea is available at the Pulse Australia website.

Current commercial varieties differ in their resistance to P. medicaginis, with Yorker, PBA HatTrickand PBA Seamerhaving the best resistance and are rated MR, while Jimbour is MR-MS, Flipper and Kyabra are MS and PBA Boundary and PBA Drummond have the lowest level of resistance at S. PBA Boundary and PBA Drummond should not be grown in paddocks with a history of PRR, lucerne, medics or other known hosts such as sulla.

From 2007 to 2018 trials at the DAF Qld Hermitage research Facility, at Warwick QLD have evaluated a range of varieties and advanced PBA breeding lines for the extent of yield loss from PRR.  In dry seasons, trials are planted into pre-irrigated sites, with for example 50 mm of irrigation applied before sowing in 2018.  Trials consist of two treatments being: 1) Plus PRR - seed treated with thiram + thiabendazole only and plots inoculated at planting with a mixture of oospores from 10 P. medicaginis isolates and receive no metalaxyl soil drenches; and 2) Minus PRR - seed treated with thiram + thiabendazole + metalaxyl and plots receive regular soil drenches with metalaxyl (Note: metalaxyl is not currently registered as a soil drench in chickpea).  This metalaxyl treatment has prevented infection by the PRR pathogen in all trials since 2007.  The difference in yield between the metalaxyl-treated plots and untreated plots is used to calculate the yield loss caused by PRR.

The level of PRR which developed in 2018 was lower than that achieved in 2017 with a subsequent reduction in the extent of yield loss.  In 2017, losses ranged from 29% for CICA1328 to 95% for PBA Boundary(rated S). However, in 2018, CICA1328 had no significant yield loss from PRR and the most susceptible entry PBA Drummond (S) lost 68% (Table 1).

The lower yield losses in the 2018 trial reflect low early season levels of PRR resulting from below average rainfall in July, August and September (total 15 mm).  However, 22 mm of irrigation applied in late September and frequent October rainfall (128 mm) favoured development of PRR later in the season which caused moderate yield losses in more susceptible entries.

The high yields of advanced breeding lines which are crosses between a chickpea (Cicer arietinum) line and a wild Cicer species in the presence of PRR was a highlight in the 2018 experiment. Three lines in particular, CICA1328, CICA1718 and CICA1812, produced over 2 t/ha in the plus PRR treatment and correspondingly had the lowest % yield losses.   The yield of these three lines in the plus PRR treatment were significantly higher than all other entries which lacked non-wild Cicer genetics, with the exception of PBA HatTrickand Yorker (Table 1). The breeding lines CICA1718 and CICA1812 are being multiplied as possible new variety releases.

Table 1. Yield of chickpea varieties and breeding lines in the absence (Minus PRR) and presence (Plus PRR) of Phytophthora root rot and % yield loss from PRR in the 2018 trial (sown 16 Jul) at Warwick QLD.  (P yield=0.047; lsd yield = 0.77 t/ha)

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

Hundred seed weights of samples showed that seed of good size was produced by all breeding lines and varieties in 2018 despite PRR infection (Table 2).  In addition, two entries that had lower than average seasonal yields (CICA1521 and Kyabra) also had significantly larger seed in the presence of PRR.  This larger seed reflects reduced seed numbers per plant, plant recovery from PRR during dry spells and lower plant density (due to PRR losses) providing greater soil moisture during pod fill.

Table 2. Hundred seed weights (HSD, g) of chickpea varieties and breeding lines in the absence (Minus PRR) and presence (Plus PRR) of Phytophthora root rot in the 2018 trial at Warwick QLD  (P HSD= 0.030; lsd HSD = 1.525 g)

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

Acknowledgements

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.  We thank Gail Chiplin, Aaron Fryer and Katie McIvor for technical support.

Contact details

Sean Bithell
NSW Department Primary Industries
Mb: 0429 201 863
Fx: 02 6763 1100
Email:  sean.bithell@dpi.nsw.gov.au

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

GRDC codes: DAN00176, DAN00212, DAQ00186, BLG205 & BLG209 within DAN00213: Grains Agronomy & Pathology Partnership - A strategic partnership between GRDC and NSW DPI