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.
Two Globodera rostochiensis and two G. pallida populations (pure and mixed) were analysed by identification methods based on morphology/morphometrics. To assess the accuracy of the identification, PCR analysis was performed on the same specimens. The investigation comprised juveniles, cysts and males. Seven of the most commonly used morphological/morphometric characters were examined: stylet length, length of stylet shaft plus knobs and stylet knob shape of second-stage juveniles; number of cuticular ridges between anus and vulval basin, distance between anus and vulval basin and Granek's ratio of cysts; and spicule shape of males. Altogether, 480 specimens were analysed and assessed. There were statistically significant differences between means of the G. rostochiensis and G. pallida populations in most characters and, in part, between populations of the same species. However, no individual morphological-morphometric character proved to be discriminant for species determination as in all cases there was a large overlap. A statistical discriminant analysis showed that with our populations, the values of a commonly used table of characters for separation of the two species had to be adjusted in order to produce the break points. By judging more than one character, the identification process could be considerably improved, suggesting the possibility of designing a computerised expert system.
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