Tolerance and susceptibility of commercial stone fruit rootstocks for plant-parasitic nematodes

We evaluated high potential stone fruit rootstocks for their host status to ring (Criconemoides xenoplax) and root-knot (Meloidogne spp.) nematodes.

We evaluated different pot sizes, inoculation periods as well as different potting mediums. The best results were achieved using 2400ml pots, steam sterilised 2:1 fine bark to medium textured sand. Inoculated trees must stay in a glass house at 25ºC for at least 6 months. We have also compared the results in pots to results in a commercial orchard situation where ring nematodes occur.

From results it is clear that all rootstocks used, sustain high numbers of ring nematodes. The rootstocks Marianna, Flordaguard, Atlas and Garnem have statistical significant higher numbers of ring nematodes than the other rootstocks used, except Guardian. The rootstocks GF 677, Maridon, 5A-5-34, 7B-25-21 and Viking are in the 50% range when Marianna is defined as 100%. The rootstock GF 677 is significantly more sensitive than Kakamas seedling for root-knot nematodes. Both GF 677 and Kakamas seedling rootstocks are more sensitive for root-knot nematodes than Marianna, Maridon, Flordaguard, 5A-5-34, 7B-25-21, Garnem and Viking (5A-5-34 and 7B-25-21 are ARC-bred rootstocks).

To correlate these results with field data, soil samples were taken in a plum orchard with several rootstocks, during 2008 (after plant), 2012 and 2014. During 2014 the ring nematode numbers in the root zone of Marianna was significantly higher than those in the root zone of other rootstocks. There was a high increasing tendency in ring numbers from 2012 to 2014 in the root zones of Marianna, Maridon, Tsukuba 5 as well as GF 677 whilst the rootstocks Chuche-Picudo, Atlas and Flordaguard show a decrease. Ring numbers in the root zone of Viking, SAPO 778 clonal and seedling have never increase above the 500 ring nematodes/300cm³ described as damaging. Results from California indicate that the rootstocks Flordaguard, Cadaman and Atlas have a higher than 100% (Nemaguard defined as 100%) rating with Garnem also showing a tendency to be high.

Looking at the bigger picture, it is clear that there is no commercial rootstock that can be described as resistant to ring nematodes. All results agree that the rootstock Marianna is a good host to ring nematodes and others like Maridon, Flordaguard, Cadaman, Atlas and Garnem must also be suspected to be in the higher rankings. The rootstocks Kakamas seedling and GF 677 are good host to root-knot nematodes, Guardian and Atlas is resistant with Marianna, Maridon, Flordaguard, Garnem and Viking resistant/immune to root-knot nematodes. Correctly performed pot experiments can provide valuable results about the host status (reproduction) of stone fruit rootstocks to ring and root-knot nematodes. To evaluate the influence of rootstocks on the performance (tolerance) of the scion (yield, fruit weight) long term field experiments are necessary. Such results from field trials indicate that Marianna, Maridon, GF 677 and Flordaguard is negatively affected if ring nematode numbers are higher than 500/300 cm³. Performances of trees on Atlas, Garnem and Cadaman are less affected.