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- Author or Editor: P. B. Catlin x
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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
Pistillate flowers from walnut trees having > 80% pistillate flower abscission (PFA) were examined from the time of anthesis until shortly before abscission. In addition to normally developing flowers, two types of abortive flowers were found. One abnormal flower type, seen in only two cases, lacked a developed embryo sac and had cellular degeneration in the nucellus. The second type of damaged flowers, which were more commonly observed, had apparently normal development of the nucelli and embryo sacs, but cell and tissue necrosis became evident beginning at the tip of the stigma, in the integuments, and throughout the placental evaginations. No cell or tissue damage was observed until after ovary growth in these flowers had stopped. We conclude that this second type of damage is associated with PFA.
Abstract
Individual Egyptian apricot (Prunus armeniaca L.) seedlings differed considerably in their response to 87 and 174 mm NaCl in nutrient solution supplied to roots. Wilting and/or necrosis of leaves were indices of sensitivity and survival. Damage occurred sooner, and more plants were affected at 174 mm salt. Some seedlings survived longer than others at both levels of NaCl. Root systems were reduced with prolonged treatment and some root death appeared to occur. Root damage occurred in some plants before toxicity symptoms appeared on leaves. Attempts to identify further apricot germplasm with improved tolerance to salinity appear warranted.
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
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).
Nitrogen (N) deficiency reduced biomass and altered N allocation within large walnut tree canopies (Juglans regia L. cv Serr). N-fertilized control trees contained 2.5 times more N in current year spurs, leaves and fruit than did those of N-deficient trees. The N content and biomass allocated to kernels was reduced in N-deficient canopies to a greater extent than was al location to current year shoots and foliage. N removal in abscised leaves and fruit was 3 times greater in canopies of fertilized trees than in N-deficient trees.
A non-destructive method is described to calculate total spur, leaflet and fruit numbers. Calculations were based on ratios of fruit counts on selected scaffold limbs to total fruit number per tree. Dry weight and N content of representative spurs, leaflets and fruit permitted estimation of whole canopy biomass and N content in these organs. N contained in current year spurs and the N lost from the tree in fruit and leaf litter were calculated for both N-fertilized control and N-deficient trees.
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.
In both laboratory and field experiments, excessive pollen has been found to be a major cause of pistillate flower abscission (PFA) and reduced yields of sensitive English Walnut cultivars (CVs) (especially “Serr”). In the field, PFA and reduced yields develop when substantial overlap of male and female walnut bloom occurs. PFA and poor yields can be further aggravated when pollenizing CV's have been included into an orchard to maximize pollen availability for the commercial CV Field experiments, conducted in 1992 and 1993, demonstrated that mechanically shaking trees to remove male flowers pre-bloom from either pollenizer CV's or the main CV reduced pollen load, PFA, and substantially improved yields.