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Distillate flower abscission (PFA) was measured for four cultivars of walnut (Juglans regia L.): `Serr', `Sunland', `Howard', and `Chandler'. Mean PFA for `Serr' over 7 years was greater than for the other cultivars and there were no differences among any of the latter. The high PFA potential of `Serr', shown here and earlier, was not expressed in `Sunland', even though both cultivars have one common parent. There was no association of PFA with either of two rootstock. Flowering index did not differ among cultivars and was not related to PFA.
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
With normal pear leaves, soluble carbohydrates (sorbitol, sucrose, glucose, fructose) and starch were higher in green than in abscising, yellow senescent ones. Considerable accumulation of these components occurred in curl leaves which were about to abscise. Greatly reduced transport of photosynthetically fixed 14C from the leaves occurred in curl-affected trees. Normal leaves photosynthesized and exported C even when abscission was imminent as long as chlorophyll was present. Curl-affected leaves abscised earlier while considerable photosynthetic potential remained. As normal leaves approached senescence their N content decreased dramatically. Curl-affected leaves abscised when N levels were still high. Curl deprives the tree of potentially utilizable carbohydrate and N resources through inhibition of translocation and premature abscission. These effects of curl may explain reduced vigor and productivity as well as difficulties in establishing young trees. It is postulated that curl and decline are not solely graft union problems.
Abstract
Although few seedlings of jojoba [Simmondsia chinensis (Link) C. K. Schneid] developed foliar symptoms when their roots were waterlogged at 23°C for 42 days, root systems of all plants were irreversibly damaged. At 33°, symptoms developed more rapidly, but again all plants died when treatments were prolonged to obtain foliar effects on a high proportion of plants. The limit of survival at 33° was when about 50% of the seedlings expressed symptoms. Jojoba is intermediate in sensitivity to waterlogging based upon direct comparisons with walnut (very sensitive) and pear (very tolerant).
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.
Abstract
The pistillate flower of walnut is a complex structure (10, 13, 14) and is referred to as a pistil for simplicity. Pistils emerge terminally on shoot or spurs after different degrees of vegetative extension from mixed buds (9, 14). Such growth can range from essentially nil to about 1 m. Pistils are borne on a short peduncle (Fig. 1). Two pistils per peduncle are most common, but one or three, or (rarely) more, can occur. Flowers are wind-pollinated and all cultivars are considered to be cross- and self-fruitful (9, 14). Pistils become receptive very shortly after emergence from the shoot apex when the two stigma lobes begin to separate. Fertilization of ovules is necessary for nut development to maturity, but pollination and fertilization are not required for early growth of the ovary (14). Ovaries of nonpollinated flowers will enlarge at rates similar to those of fertilized ones for several weeks before abscising, when about 1 to 2 cm in diameter.