Can you explain the difference between crop varieties that are tolerant, resistant and susceptible to a particular pest?

Researcher Kirsty Owen from the University of Southern Queensland (USQ) says knowing the difference is critical for producers responding to one of the northern wheat industry’s thorniest problems.

The root lesion nematode, Pratylenchus thornei reduces the ability of crop roots to take up water and nutrients, leaving a sickly plant with yellowing lower leaves and poor tillering.

Populations build in susceptible crops, can survive fallow periods and have the ability to carry over between cropping seasons, and there are no registered chemical control methods.

Tolerance is the ability of a plant to produce good yields in the presence of P. thornei and its opposite is intolerance, while resistance is the ability of the plant to prevent nematode reproduction. Its opposite is susceptibility.

Kirsty says crop varieties may be tolerant but susceptible, that is, they produce good yields but allow the nematode to increase in population. The ideal combinations for management of P. thornei are varieties that are both tolerant and resistant.

In USQ’s study of chickpeas, wheat and the build-up and decline of P. thornei in the farming system, researchers found that while chickpea varieties may not suffer yield loss, the crop’s tolerance may lead to a build-up of nematodes that affects the following crop.

When P. thornei was present in paddocks at damaging populations (greater than 2/g soil), management relied on growing tolerant crop varieties that don’t suffer yield loss and increasing the number of resistant crops in the cropping sequence to reduce populations.

Trials showed that:

Chickpeas generally have a good level of tolerance to P. thornei but because most varieties are susceptible, populations of the nematode will increase to attack future crops

The tolerance of a wheat variety and the populations of P. thornei at the time of planting will determine the degree of yield loss at the end of the season

Intolerant wheat varieties should be avoided when P. thornei populations are at damaging levels, but even moderately tolerant varieties may suffer yield loss.

Growers and agronomists can learn how to sample for root lesion nematodes and interpret the results by taking part in PreDicta®B courses run by SARDI; download an app that has ratings for resistance; use the NVT site comparison tool to find tolerance ratings; and tap into their local crop variety guides for more information.

Further Information:

Kirsty Owen

Research Fellow (Crop nematology)

Centre for Crop Health

Institute for Agriculture and the Environment

University of Southern Queensland, Toowoomba, Qld

07 4631 1239

[email protected]

Resources GRDC Update Paper: https://grdc.com.au/resources-and-publications/grdc-update-papers/tab-content/grdc-update-papers/2018/03/chickpeas,-wheat-and-pratylenchus-thornei-build-up-and-decline-in-the-farming-system.-chickpeas-a-combination-of-susceptibility-and-moderate-tolerance

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