Articles
Selection of new almond rootstocks with resistance to Phytophthora in California
Article number
1406_12
Pages
77 – 82
Language
English
Abstract
Many California almond orchards have experienced a high incidence of tree death caused by Phytophthora spp.
Depending on the Phytophthora sp. and environmental conditions, tree death resulted from rootstock crown and root rot (CR), scion canker (SC), or both.
Problems with CR have intensified, especially where the industry has shifted from predominant use of ‘Nemaguard’ peach rootstock to use of peach-almond hybrid rootstocks.
From 2019 to 2022, Phytophthora species P. cambivora, P. cinnamomi, P. crassamura, P. mediterranea, and P. niederhauserii have a mode of attack which primarily targets the crown and root as rot while P. acerina and P. pini will manifest scion canker and P. cactorum will cause both issues in the host.
We evaluated commercially available rootstock standards and experimental hybrid rootstocks for resistance to Phytophthora. The selections were established in sandy loam soil in rows bordered by berms and irrigated with dual drip lines.
In the first year after planting, substrates bearing P. cactorum and P. niederhauserii were used to infest soil around each tree; sterile substrate was the control.
Then, at monthly intervals during the growing season, drip lines were used to achieve 24-h water saturation episodes around all root crowns, and pear fruits were floated as bait to verify infective potential of Phytophthora. Both species of Phytophthora infected pears and rootstocks, but P. cactorum predominated.
Among rootstock standards, based on incidence and extent of crown rot, ‘Nemaguard’ and ‘Lovell’ had low susceptibility to Phytophthora, whereas ‘Hansen 536’ and most other peach-almond hybrids had high susceptibility; ‘Viking’ and ‘BB 106’ had moderate susceptibility.
Among 35 experimental hybrids, seven exhibited low susceptibility, 25 were highly susceptible, and three were moderately susceptible.
Our results suggest that some of the new hybrid rootstocks can provide Phytophthora resistance in backgrounds with horticultural advantages over conventional peach and plum rootstocks.
Depending on the Phytophthora sp. and environmental conditions, tree death resulted from rootstock crown and root rot (CR), scion canker (SC), or both.
Problems with CR have intensified, especially where the industry has shifted from predominant use of ‘Nemaguard’ peach rootstock to use of peach-almond hybrid rootstocks.
From 2019 to 2022, Phytophthora species P. cambivora, P. cinnamomi, P. crassamura, P. mediterranea, and P. niederhauserii have a mode of attack which primarily targets the crown and root as rot while P. acerina and P. pini will manifest scion canker and P. cactorum will cause both issues in the host.
We evaluated commercially available rootstock standards and experimental hybrid rootstocks for resistance to Phytophthora. The selections were established in sandy loam soil in rows bordered by berms and irrigated with dual drip lines.
In the first year after planting, substrates bearing P. cactorum and P. niederhauserii were used to infest soil around each tree; sterile substrate was the control.
Then, at monthly intervals during the growing season, drip lines were used to achieve 24-h water saturation episodes around all root crowns, and pear fruits were floated as bait to verify infective potential of Phytophthora. Both species of Phytophthora infected pears and rootstocks, but P. cactorum predominated.
Among rootstock standards, based on incidence and extent of crown rot, ‘Nemaguard’ and ‘Lovell’ had low susceptibility to Phytophthora, whereas ‘Hansen 536’ and most other peach-almond hybrids had high susceptibility; ‘Viking’ and ‘BB 106’ had moderate susceptibility.
Among 35 experimental hybrids, seven exhibited low susceptibility, 25 were highly susceptible, and three were moderately susceptible.
Our results suggest that some of the new hybrid rootstocks can provide Phytophthora resistance in backgrounds with horticultural advantages over conventional peach and plum rootstocks.
Authors
G.T. Browne, N.J. Ott, M.A. Yaghmour, B.C. Fekete
Keywords
rootstock, Prunus, susceptibility, crown rot, root rot, scion canker, disease
Groups involved
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