Twenty-five random decamer primers were used to evaluate the level of polymorphism between Persian walnut and the Northern California black walnut. Sixty-six randomly amplified polymorphic DNA (RAPD) markers were identified using an interspecific walnut backcross population [(Juglans hindsii × J. regia) × J. regia]. Segregation data from these polymorphisms were joined to a previously published set of restriction fragment-length polymorphism (RFLP) marker data to expand the genetic map of walnut to 107 markers in 15 linkage groups.
Abstract
Seedlings of Juglans hindsii Jeps. and J. regia L. reacted similarly and were much more sensitive to waterlogging at root temperatures of 33°C than those of Pterocarya stenoptera DC. At 23°C,J. regia expressed symptoms of waterlogging earlier than J. hindsii. Paradox plants, hybrids between the 2 walnut species, were more tolerant than J. hindsii but are still considered highly sensitive to anaerobiosis. These results support the contention that use of J. regia seedlings as rootstocks to avoid blackline introduces greater potential for damage if soils become saturated. Some plants of each type which demonstrated increased tolerance have been selected. Levels of abscisic acid, or changes therein did not appear to be useful parameters in screening walnut seedlings for tolerance to waterlogging. Phenolic compounds decreased in roots of waterlogged plants. Although the magnitude of change in phenols was the same in Juglans and Pterocarya plants, it occurred over a much longer period with the latter. Phenols lost from roots may be a secondary phenomenon but contribute to hypersensitivity of Juglans to waterlogging.
Walnuts (Juglans spp.) are difficult-to-root woody plants. The rolABC genes (rolA + rolB + rolC), derived from the bacteria Agrobacterium rhizogenes, have been shown to increase the rooting potential of other difficult-to-root woody plants. We inserted the rolABC genes into somatic embryos of a `Paradox' hybrid (J. hindsii × J. regia) clone PX1 using the A. tumefaciens gene transfer system. A transgenic sub-clone, designated PX1 rolABC 2-2 was selected and compared to the untransformed clone for a variety of phenotypic characteristics, including rooting potential. Transformed and untransformed shoots were budded onto seedling J. regia rootstock in the greenhouse and established in the field. Transformed trees displayed reduced internode length, an increase in lateral branching, and wrinkled leaves. In another test, a commercial persian walnut cultivar J. regia `Chandler' was grafted onto rooted cuttings of both the untransformed and transformed plants. The presence of the rolABC genes in the rootstock had no visible effects on the grafted scion. Several of these trees were excavated from the field and the root systems of each genotype were examined for root number, diameter, and biomass. Trees with the rolABC rootstock had significantly more small diameter roots compared to the controls and less recovered biomass. Tests of the rooting potential of leafy semi-hardwood cuttings for two years resulted in 14% to 59% rooting of the transformed cuttings compared to 51% to 81% rooting of the control. Both transformed hardwood cuttings and microshoots in tissue culture also rooted significantly less (52% and 29% respectively) than untransformed hardwood cuttings and tissue cultured shoots (82% and 54% respectively). Thus, although the rolABC genes induced a shorter internode length and a more fibrous root system (typical of rol-tranformed plants), they were not useful for increasing the rooting potential, and as rootstock they did not affect the phenotype of the scion.
Abstract
Walnut trees planted at 50’ × 30’ grew more slowly than xtrees at 50’ × 40’ or 50’ × 50’. Yields per tree were similar at all spacings early in the orchard’s life, but unit area yields later increased proportionately to the number of trees per acre. Long-term monetary returns above fixed costs were far greater as the number of trees per acre increased.
, percentage of root crown length rotted and B , percentage of root rot. On x axis, cal = Juglans californica , nig = J. nigra , reg = J. regia , hin = J. hindsii , maj = J. major , mic = J. microcarpa , and ste = Pterocarya stenoptera . Fig. 2
Armillaria root disease affects orchards in all Juglans regia (Persian walnut)-growing regions of California ( Gardner and Raabe, 1963 ). The causal agent is Armillaria mellea (Basidiomycota, Physalacriaceae), which attacks walnut and other
hybrid walnut, and I determined to make the experiment of fertilizing the flowers of the California species with pollen from the Persian” ( Whitson et al., 1914, 1915 , p. 138). The California walnut species has since been identified as Juglans hindsii
(typically Juglans hindsii × J. regia ) ( Mircetich et al., 1998 ). Compared with NCB ( J. hindsii ) and Persian walnut ( J. regia ) rootstocks, PH is more resistant to several species of Phytophthora ( Matheron and Mircetich, 1985b ; Mircetich and
Abstract
We compared the responses to root-zone waterlogging of seedlings of Juglans nigra L. and Juglans hindsii (Jeps.) Rehder. On the average, the two species did not differ in sensitivity to waterlogging, but substantial variation in sensitivity between individual plants within phenotypes was observed. Both species are highly sensitive to root-zone waterlogging.
Abstract
Genetic variation in vigor, phenology, and branching in juvenile seedlings of Juglans californica and J. hindsii was investigated. Significant differences between species were detected in traits that reflect vigor (height, diameter, volume), in phenological traits (dates of leafing out and leaf drop), and in branching. J. californica was generally more vigorous, more branched, leafed out earlier, and dropped leaves later than J. hindsii. When species were analyzed separately, seed source was a highly significant source of variation for phenological traits and branching in J. hindsii. Upper estimates of heritability for phenological traits ranged from 0.47 to 0.88. The results of this study suggest that J. hindsii may have had a history of differentiation and adaptation to latitude, elevation, or other climatic characters. Conservation of germplasm resources in J. hindsii will be essential to maintain the purity of the species and to provide resources for studying the species and breeding rootstock for J. regia, the Persian walnut.