Articles
Field testing of resistance of novel hybrid clonal walnut rootstocks to soilborne biotic stresses
Article number
1420_5
Pages
33 – 40
Language
English
Abstract
Continued breeding and selection strives for walnut rootstocks with improved, combined resistance to multiple soilborne pathogens, including Agrobacterium tumefaciens (At) (crown gall), Phytophthora species (Pspp) (crown and root rot), and Pratylenchus vulnus (root lesion nematode, RLN). In a factorial field experiment, resistance to At and Pspp in four new clonal rootstocks was compared to the three commercially available clonal rootstocks (‘RX1’, ‘VX211’ and ‘Vlach’). In May 2015, trees were planted in replicate genotype subplots nested within inoculation main plots (Pspp, At, and non-inoculated). Trees were bud-grafted to ‘Chandler’ in September 2015. Inoculation treatments were applied in May 2017. In 2020, crown gall incidence and gall size rating were measured at the trunk bases.
In November 2020, all root systems were excavated and sampled to assess incidence of crown and root rot associated with Pspp. At the same time, root infections with P. vulnus of natural soil infestations were quantified in the non-inoculated replicates. ‘VX211’ and ‘Vlach’ exhibited the highest gall ratings in response to At that were significantly higher than ‘RX1’. The novel experimental genotype K3 had significantly lower gall ratings than the three commercial clones.
Gall ratings on novel genotypes 11-991, STJM4 and 29JM8 were not significantly different from those of ‘RX1’ or K3. High incidence of crown and root rot (CR) from Pspp was found in K3, ‘Vlach’ and ‘VX211’. The Phytophthora-resistant ‘RX1’ had no CR, nor did 11-991. Experimental genotypes 29JM8 and STJM4 displayed a near zero incidence of CR. Novel K3 showed consistently low nematode infections, similar to the standard clones, whereas 29JM8 and STJM4 supported higher numbers than the standards.
Nematode populations on genotype 11-991 fell between these two extremes.
Bud-grafting success, tree mortality, and tree growth were also documented.
The results showed high potential for using genetic resistance to combat these soilborne biotic stresses.
In November 2020, all root systems were excavated and sampled to assess incidence of crown and root rot associated with Pspp. At the same time, root infections with P. vulnus of natural soil infestations were quantified in the non-inoculated replicates. ‘VX211’ and ‘Vlach’ exhibited the highest gall ratings in response to At that were significantly higher than ‘RX1’. The novel experimental genotype K3 had significantly lower gall ratings than the three commercial clones.
Gall ratings on novel genotypes 11-991, STJM4 and 29JM8 were not significantly different from those of ‘RX1’ or K3. High incidence of crown and root rot (CR) from Pspp was found in K3, ‘Vlach’ and ‘VX211’. The Phytophthora-resistant ‘RX1’ had no CR, nor did 11-991. Experimental genotypes 29JM8 and STJM4 displayed a near zero incidence of CR. Novel K3 showed consistently low nematode infections, similar to the standard clones, whereas 29JM8 and STJM4 supported higher numbers than the standards.
Nematode populations on genotype 11-991 fell between these two extremes.
Bud-grafting success, tree mortality, and tree growth were also documented.
The results showed high potential for using genetic resistance to combat these soilborne biotic stresses.
Publication
Authors
K. Jarvis-Shean, J. Hasey, C. Leslie, G. Browne, A. McClean, N.J. Ott, A. Westphal, D. Kluepfel
Keywords
hybrid Paradox rootstocks, Phytophthora, Agrobacterium, nematodes, ‘VX211’, ‘RX1’, ‘Vlach’, 11-991, K3, 29JM8, STJM4
Groups involved
Online Articles (45)