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.
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.
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.
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.
Individual plants varied considerably, but peach and apricot were more sensitive to waterlogging than was plum. No differences were established between peach and apricot. All 3 species became more sensitive as temperature was increased between 17 and 27°C. More than half of the plum seedlings survived at 17°C whereas all plants of the other 2 species died. A scion of a more tolerant species did not overcome the sensitivity of the roots.
Both cyanogenic glycoside content and the proportion of it that was hydrolyzed during waterlogging were higher in peach than in plum roots. Exposure of detached root systems of all 3 species to anaerobic conditions caused HCN to be released. The rate of cyanogenesis increased with both temperature and time. Peach and apricot roots were alike in HCN evolution whereas plum roots were lower, with release of HCN being barely detectable at 22°C. Cyanogenesis was significant in peach and apricot at as low as 17°C.
A close association exists among differential sensitivity, glycoside hydrolysis, and cyanogenesis in the absence of O2. However, the latter may be secondary, though contributory, to cellular disorganization as a cause of sensitivity.
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.
Alternate bearing in the pistachio (Pistacia vera L.) is brought about by abscission of inflorescence buds during July and August when seed growth and development take place. There was rapid accumulation of sugars and conversion to fat in the nuts at that time, but sugar and starch levels in the bark and wood of nut-bearing branches were not appreciably different from those in similar tissues of non-bearing branches. The inflorescence bud-drop phenomenon does not appear the result of carbohydrate deficiency.
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.
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.