Controlling Phytophthora root rot (PRR) in chickpea crops is a two-step process, says Dr Kevin Moore, a plant pathologist from the New South Wales Department of Primary Industries (DPI) in Tamworth.
The years 2010 and 2012 were very wet or had periods of saturated soil conditions in the chickpea-growing regions of the north, and subsequent PRR outbreaks and waterlogging caused substantial damage to some chickpea crops in those areas.
In a paper presented at the March GRDC Research Update in Goondiwindi, Queensland, Dr Moore emphasised that although there are no in-crop control measures for PRR, there are two steps that reduce the risk of damage.
“The first management step is evaluating paddocks based on history and experience, and avoiding planting in high risk paddocks.
Chickpea breeder Ted Knights (left) with
pathologist Dr Kevin Moore in a trial plot
of PBA HatTrick chickpeas.
“The second key step for minimising PRR effect is correct varietal selection and that is what the national chickpea improvement team has been working on at Tamworth and Warwick,” Dr Moore says.
Dr Moore leads the chickpea component of a GRDC-funded research project that includes investigating the effects of PRR on commercial chickpea varieties, advanced breeding lines and hybrids with wild relatives of chickpea.
PRR is favoured by wetter-than-average seasons, as occurred in 2010, or by periods of soil saturation in average seasons, as happened in the early part of 2012.
PRR can sometimes be confused with waterlogging, but there are differences between them (see Table 1). Knowing the differences is important because management of the two disorders is different.
Current commercial varieties differ in their resistance to Phytophthora medicaginis, the pathogen responsible for PRR. Trials at Tamworth, NSW, and Warwick, Queensland, have shown varietal reactions of:
- best resistance – Yorker;
- lower resistance – PBA HatTrick, Flipper, Jimbour and Kyabra; and
- least resistance – PBA Boundary, most kabuli chickpeas.
“PBA Boundary and other susceptible varieties should not be grown in paddocks with a history of PRR, lucerne, medics or other hosts of P. medicaginis,” Dr Moore says.
To try to overcome the problem of varietal susceptibility to PRR in chickpeas, chickpea breeders at Tamworth developed hybrids by crossing chickpeas with a wild Cicer species.
The work was initially carried out by Ted Knights and is being continued by Dr Kristy Hobson (NSW DPI).
Dr Moore and Dr Mal Ryley, a pathologist with the Queensland Department of Agriculture, Fisheries and Forestry (DAFF), then challenge the hybrids with P. medicaginis to determine susceptibility.
“So far, the results look promising,” Dr Moore says. “Data from a 2012 trial at Warwick indicates that these hybrids have significantly higher levels of resistance to P. medicaginis than the most resistant commercially available variety, Yorker.”
This work is continuing this year and will be expanded in a new GRDC project focused specifically on Phytophthora. However, the availability to growers of new varieties with these higher levels of resistance is at least five years away.
Will PRR be a problem for 2013 chickpea growers? PRR, like all diseases, will occur if these three conditions are met:
- availability of a susceptible host;
- presence of the pathogen; and
- environmental conditions favourable for infection and disease development.
If growers plant chickpea varieties with the highest resistance to P. medicaginis in paddocks that have no recent history of PRR or medics, it is very unlikely that PRR will occur, even if conditions are favourable.
TABLE 1 Differences between waterlogging and Phytophthora root rot (PRR) in chickpea crops.
| Phytophthora organism consumes roots
|| Roots die from lack of oxygen
| Can affect plants of any age
|| Plants are most susceptible during flowering and pod fill
| Symptoms develop within seven days after infection
|| Symptoms develop within two days of waterlogging
| Plants easily pulled from the soil after damage
|| For the first few days after the waterlogging event, plants
not easily pulled from the soil and roots are not rotted
Conversely, if a susceptible variety is grown in a paddock known to have had PRR or medics in the past five to seven years, and conditions favour disease, there is a high probability that the crop will be infected by the pathogen and that the crop, or parts of it, will be killed by the disease. Under very favourable conditions, such as repeated soil saturation, even resistant varieties such as Yorker can succumb.
“As with all disease problems, PRR is only one aspect that a chickpea grower should consider,” Dr Moore says, “but by following these simple steps, growers can avoid the huge losses that can be caused by PRR, especially if there is a history of it in their local area."
Dr Kevin Moore
0488 251 866
Dr Moore’s full paper, presented at the GRDC Research Update, is available on the GRDC website:
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