Articles
Clonal Paradox rootstock comparison on Howard walnut in Californias Northern Sacramento Valley
Article number
1346_80
Pages
641 – 646
Language
English
Abstract
Paradox hybrid seedling (Juglans hindsii × Juglans regia) is the most widely grown walnut rootstock in Northern California due to its high vigor, adaptability to marginal soils, and improved resistance to Phytophthora root and crown rot.
However, it remains susceptible to disease from soil-borne pathogens.
Micropropagation technology has resulted in commercial availability of three clonal Paradox walnut rootstocks, RX1, VX211, and Vlach. Clonal rootstocks have less genetic variability than open-pollinated rootstocks, resulting in more uniform growth and the ability to select for specific pathogen resistance.
A replicated and randomized trial in Californias Northern Sacramento Valley (Los Molinos) was planted as bareroot rootstock in March of 2009 as part of a commercial Howard walnut orchard.
The study compared the clonal rootstocks RX1, VX211 and Vlach to Paradox seedling (Paradox) and the grower control: nursery June budded Vlach. Field grafting was a tremendous challenge at this site, and the nursery June budded Vlach trees had a scion (Howard) growth advantage of as much as 26 months compared to the field grafted treatments.
To evaluate these treatments, scion cross-sectional area, photosynthetically active radiation (PAR) intercepted underneath the canopy, dry in shell yield per plot and tree (kg), as well as the percentage of edible yield, jumbo walnuts, light kernels and mold were determined.
Due to the substantial scion growth head start, June budded Vlach exhibited significantly larger scion cross-sectional area than grafted rootstocks.
Among grafted rootstocks, there were few significant differences in growth, although RX1 showed the lowest relative scion cross-sectional area and PAR. Field grafted rootstocks showed no overall significant differences in yield or nut quality.
The soil-borne disease tolerances and resistances touted with clonal Paradox rootstocks may take more time to result in higher tree survival and therefore greater yield versus Paradox seedlings.
However, it remains susceptible to disease from soil-borne pathogens.
Micropropagation technology has resulted in commercial availability of three clonal Paradox walnut rootstocks, RX1, VX211, and Vlach. Clonal rootstocks have less genetic variability than open-pollinated rootstocks, resulting in more uniform growth and the ability to select for specific pathogen resistance.
A replicated and randomized trial in Californias Northern Sacramento Valley (Los Molinos) was planted as bareroot rootstock in March of 2009 as part of a commercial Howard walnut orchard.
The study compared the clonal rootstocks RX1, VX211 and Vlach to Paradox seedling (Paradox) and the grower control: nursery June budded Vlach. Field grafting was a tremendous challenge at this site, and the nursery June budded Vlach trees had a scion (Howard) growth advantage of as much as 26 months compared to the field grafted treatments.
To evaluate these treatments, scion cross-sectional area, photosynthetically active radiation (PAR) intercepted underneath the canopy, dry in shell yield per plot and tree (kg), as well as the percentage of edible yield, jumbo walnuts, light kernels and mold were determined.
Due to the substantial scion growth head start, June budded Vlach exhibited significantly larger scion cross-sectional area than grafted rootstocks.
Among grafted rootstocks, there were few significant differences in growth, although RX1 showed the lowest relative scion cross-sectional area and PAR. Field grafted rootstocks showed no overall significant differences in yield or nut quality.
The soil-borne disease tolerances and resistances touted with clonal Paradox rootstocks may take more time to result in higher tree survival and therefore greater yield versus Paradox seedlings.
Publication
Authors
C. Reyes, L. Milliron, A. Fulton, R. Buchner
Keywords
VX211, RX1, Vlach, June budded, field grafted, micropropagation, PAR
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