Legume varieties differ in their response to nematodes
Research conducted by: Neil Halpin, Jenny Cobon and Angela Marshall, Queensland Department of Agriculture and Fisheries for the GRDC Grower Solutions Group – Coastal and Tablelands, Bundaberg node
Legumes are a key tool to reduce cane-specific soil pathogens in the sugarcane farming system. Even legume cultivars that host plant parasitic nematodes do not allow nematode populations to grow to the same extent as some other crops potentially grown in the rotation.
Legumes are a poor host (and therefore a good choice) compared to tomato for root-knot nematode and corn for root-lesion nematode.
For example, when 10,000 eggs that were added to tomato plants resulted in over 548,000 nematodes compared to 390 to 7000 nematodes for the worst legume crop option!
There are differences in the number of nematodes hosted by the different peanut and soybean crop varieties.
If root-knot nematodes Meliodogyne incognita or Meliodogyne javanica are of concern, the best legume cultivars to plant to suppress the nematode population are A6785 soybean, Kairi peanut or Holt peanut.
If root-lesion nematodes Pratylenchus zeae are of greatest concern then Fernside soybean is also a good option, along with A6785, Holt and Kairi.
The trial details
Growers in the coastal Burnett requested information on the impact of legume choice (either soybean or peanuts) or of varieties on sugarcane nematode populations. The aim of this work was to address the research question: Does the choice of legume crop variety make a difference to parasitic nematode populations?
To address this question three pot trials were established one for each nematode species: Meliodogyne incognita (a root knot nematode), Meliodogyne javanica (the most common root knot nematode) and Pratylenchus zeae (lesion nematode). In each of these trials the following cultivars were sown:
- Peanut cultivar – Holt
- Peanut cultivar – Kairi
- Soybean cultivar – A6785
- Soybean cultivar – Bunya
- Soybean cultivar – Fernside
- Soybean cultivar – Hayman
- Soybean cultivar – T183-3
- Soybean cultivar – T015-3
- Tomato (in root knot trial only)
- Sweet corn (in lesion trial only)
The crops were sown into pots of pasteurised sand (to ensure that there were no nematodes present) and grown for two weeks to establish a healthy root system.
Root-knot nematode results
For the two root-knot nematode (RKN) trials 10,000 eggs were added to each pot and the crop was grown for 14,000 heat units. The tops were then removed, roots washed free of sand, and nematode eggs extracted from the roots by soaking in a bleach solution. The nematodes were caught in a 38μm sieve and eggs counted.
For Meliodogyne incognita there were significant differences in nematode egg numbers T183-3c ≥ Bunya c ≥ Hayman c > Fernside b ≥ T103-5 ab ≥ A6785 a ≥ Kairi a ≥ Holt a in Figure 1.
Figure 1: The number of root knot nematode (Meliodogyne incognita) recovered per plot after being inoculated with 10,000 eggs and grown for 14,000 heat units
Figure 2: The number of root knot nematode (Meliodogyne javanica) recovered per plot after being inoculated with 10,000 eggs and grown for 14,000 heat units
However, legumes are a far better crop rotation choice than crops like tomatoes that are known hosts of RKN, see Figure 3.
Figure 3: The number of RKN nematodes extracted from the roots of legumes in comparison to tomatoes after 10,000 eggs were added to pots then the crop grown for 14,000 heat units
For lesion nematodes (Pratylenchus zeae) the crops were sown into pots of pasteurised sand (to ensure that there were no nematodes present) and grown for two weeks to establish a healthy root system. 1,000 juvenile lesion nematodes were added to each pot and the crop was grown for 10 weeks. The tops were then removed, roots washed free of sand and nematode eggs extracted from the roots by chopping the roots into segments then being placed in a misting chamber for 7 days. The solution was sieved over a 38μm sieve and eggs counted.
Lesion nematode numbers recovered differed by crops and choice of variety. The highest number of lesion nematodes recovered was on soybean variety T183-3 c ≥ Bunya c ≥ Hayman c ≥ T013-5 bc ≥ Fernside b ≥ A6785 b > peanut Holt a ≥ Kairi a Figure 4.
However, legumes were a relatively poor host (good choice) in comparison to other rotation choices. For example, in the sweet corn pots in excess of 7400 nematodes were recovered; compared to 197 in the worst of the legume pots.
Figure 4: The number of lesion nematodes recovered 10 weeks after adding 1,000 juvenile Pratylenchus zeae nematodes
Please note that a variety followed by the same letter is NOT statistically different.
For more information about managing nematodes : Legume crops improve soil health and reduce losses from nematode pests in coastal farming systems