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- Author or Editor: Frederick S. Davies x
Potted apple trees (Malus domestica Borkh. cv Empire) were grown either in the greenhouse at 40% of available photosynthetically active radiation (PAR), or outdoors for 9 weeks. Although greenhouse trees displayed much lower specific leaf weights than outdoor trees, net photosynthetic (Pn) rates were comparable at light saturation. Half the trees in each group were subjected to 3 successive soil preconditioning treatments. Preconditioning the trees by withholding water did not affect Pn, transpiration (E), or stomatal conductance (ks) during a subsequent drought period in outdoor trees; however, preconditioning increased ks in greenhouse trees. Water-use efficiency increased for both greenhouse and outdoor trees as stomata closed and soil water potential decreased. Total growth and root:shoot ratios were unaffected by either light or soil preconditioning, indicating that potted apple trees are adaptable to different environmental conditions.
Ethylene production by senescing flowers of calamondin (Citrus madurensis Lour.), at rates as high as 15 nl/g fresh weight-hour did not necessarily induce absicission. Moreover, combinations of gibberellic acid (GA), calcium dihydrophosphate and 6-benzylamino purine (BA), which are known to increase fruit set in citrus, did not significantly decrease ethylene production. Abscission of calamondin fruitlets and increases in fruit set appear to be independent of ethylene production.
Root conductivity was measured in decapitated 18-month-old citrus rootstocks using a modified pressure chamber apparatus. Carrizo citrange [Citrus sinensis (L.) Osbeck × Poncirus trifoliata L. (Raf.)], a frost-hardy species, exhibited a log-linear decrease in conductivity over a temperature range from 40 to 10°C. Rough lemon (C. jambhiri Lush.), a frost-susceptible species, also exhibited decreasing conductivity from 40 to 20°, but conductivity was similar at 10 and 20°. No endogenous diurnal cycling of root conductivity was observed in Carrizo citrange root-stocks.
Containerized ‘Woodard’ and ‘Tifblue’ rabbiteye blueberries (Vaccinium ashei Reade) were placed outdoors and flooded at various times throughout the season to determine the effects of flooding on survival, growth, and abaxial diffusive resistance (ADR) of the leaf. Plants survived but were severely damaged by 49 to 58 days of flooding at soil temperatures of 20 to 31°C, regardless of the cultivar. Developmental stage had little effect on survival. Shoot growth ceased, and ADR increased after 7 days of flooding. ADR is an accurate indicator of short term flooding stress, but not of survival. Removal of roots underwater from plants flooded for 25–45 days significantly decreased ADR, indicating root resistance is an important component of total resistance. Shoot growth was less and ADR increased sooner for plants growing in a peat:pine bark (1:1 v/v) mixture than in native soil (Leon fine sand); however, time of survival was similar in both media types.
Stomatal conductance, abscisic acid levels, and water potential components (water, osmotic, and rurgor potentials) were measured in irrigated and non-irrigated open pollinated seedlings of ‘Northern Spy’ apples (Malus domestica Borkh.). Although non-irrigated seedlings typically displayed water potentials of 0.2 to 0.6 MPa lower than those of irrigated seedlings, turgor potentials remained comparable in both groups, Because diurnal osmotic adjustment was also greater for non-irrigated seedlings. Abscisic acid (ABA) levels in the leaf increased linearly in response to changes in leaf turgor, rather than water potential. Stomatal conductance was independent of bulk leaf ABA levels and was poorly correlated with leaf turgor potential above a critical value of 0.7 MPa.
The objectives of this study were to determine whether juice quality of `Valencia' sweet orange [C. sinensis (L.) Osb.] is affected by the type of inflorescence on which fruit are borne, and to determine the contribution of inflorescence type to within-tree variation in juice quality. During the 1998-99 and 1999-2000 seasons, fruit size and juice quality [soluble solids concentration (SSC) and titratable acidity (TA)] of fruit from `Valencia' sweet orange trees on Carrizo citrange rootstock [Poncirus trifoliata (L.) Raf. × C. sinensis (L.) Osb.] planted in 1987 at Howey-in-the-Hills, Fla., were measured. A 2×2 factorial design (inflorescence type × canopy position) with leafy and leafless inflorescence types, and southwest top and northeast bottom canopy positions was used. The type of inflorescence on which fruit were borne had a minor effect on juice quality, and inflorescence type and juice quality were not directly associated. Rather, juice SSC was associated with the effect of inflorescence type on fruit size, as small fruit tended to have higher SSC than large fruit, regardless of the type of inflorescence on which fruit were borne. The relatively small difference in SSC between fruit borne on leafy and leafless inflorescences (≈3% of mean SSC) was an indirect result of fruit size. Therefore, fruit borne on leafy inflorescences, which tend to be of larger size compared with fruit borne on leafless inflorescences, tended to have marginally lower SSC. Acid content and ratio of SSC: TA were not related to inflorescence type. In addition, the type of inflorescence on which fruit were borne made only a nominal contribution to variability in juice SSC, in contrast to the major contribution of canopy position to within-tree variation in juice SSC. Factors other than inflorescence type are important components of within-tree variation in juice SSC.
Juice quality of `Valencia' sweet orange [Citrus sinensis (L.) Osb.] trees on Carrizo citrange [C. sinensis × Poncirus trifoliata (L.) Raf.] or rough lemon (C. jambhiri Lush.) rootstocks was determined for fruit harvested by canopy quadrant and separated into size categories to ascertain the direct role of rootstock selection on juice soluble solids concentration (SSC) and soluble solids (SS) production per tree of citrus fruit. SS production per fruit and per tree for each size category was calculated. Juice quality was dependent on rootstock selection and fruit size, but independent of canopy quadrant. Fruit from trees on Carrizo citrange had >20% higher SSCs than fruit from trees on rough lemon, even for fruit of the same size. Large fruit accumulated more SS per fruit than smaller fruit, despite lower juice content and SSC. Within rootstocks, SS content per fruit decreased with decreasing fruit size, even though SSC increased. Rootstock effect on juice quality was a direct rather than an indirect one mediated through differences in fruit size. The conventional interpretation of juice quality data that differences in SSC among treatments, e.g., rootstocks or irrigation levels, or fruit size, are due to “dilution” of SS as a result of differences in fruit size and, hence, juice volume, is only partly supported by these data. Rather, accumulation of SS was greater for fruit from trees on Carrizo citrange than rough lemon by 25% to 30%.
Citrus rootstocks have well-known effects on tree size, crop load, fruit size, and various fruit quality factors. Fruit from trees budded on invigorating rootstocks are generally larger with lower soluble solids concentration (SSC) and titratable acidity compared to fruit from trees budded on less invigorating rootstocks. Although it is unclear how rootstocks exert their influence on juice quality of Citrus L. species, plant water relations are thought to play a central role. In addition, the larger fruit size associated with invigorating rootstocks and the inverse relationship between SSC and fruit size implies that fruit borne on trees on invigorating rootstocks have lower SSC due to dilution effects in larger fruit. To determine how rootstock type affects sugar accumulation in fruit of Citrus species, controlled water-deficit stress was applied to mature `Valencia' sweet orange [C. sinensis (L.) Osb.] trees on Carrizo citrange [C. sinensis × Poncirus trifoliata (L.) Raf.] or rough lemon (C. jambhiri Lush.) rootstocks. Withholding water from the root zone of citrus trees during stage II of fruit development decreased midday stem water potential and increased the concentrations of primary osmotica, fructose and glucose. Sucrose concentration was not affected, suggesting that sucrose hydrolysis took place. Increased concentrations of sugars and SSC in fruit from moderately water-stressed trees occurred independently of fruit size and juice content. Thus, passive dehydration of juice sacs, and concentration of soluble solids, was not the primary cause of differences in sugar accumulation. Controlled water-deficit stress caused active osmotic adjustment in fruit of `Valencia' sweet orange. However, when water-deficit stress was applied later in fruit development (e.g., stage III) there was no increase in sugars or SSC. The evidence presented supports the hypothesis that differential sugar accumulation of citrus fruit from trees on rootstocks of contrasting vigor and, hence, plant water relations, is caused by differences in tree water status and the enhancement of sucrose hydrolysis into component hexose sugars resulting in osmotic adjustment. Therefore, inherent rootstock differences affecting plant water relations are proposed as a primary cause of differences in sugar accumulation and SSC among citrus rootstocks.
One-year-old potted `Peach' mango (Mangifera indica L.) trees were flooded at soil temperatures of 15, 22.5 or 30°C. Hypertrophied lenticels were observed after 5-6 days at 30°C and 6-8 days at 22.5°C, but were not observed after 30 days at 15°C. Cells of hypertrophied lenticels were more spherical and randomly arranged than those of nonhypertrophied lenticels, resulting in increased intercellular airspace. Lenticel hypertrophy also occurred on sterns of trees which were kept moist from intermittant misting, and on excised and intact stem sections. Therefore, formation of hypertrophied lenticels in mango occurs independently of root anaerobiosis and is dependent on floodwater temperature.
The influence of floodwater dissolved O2 content on stem lenticel hypertrophy and endogenous ethylene evolution from mango trees, and the influence of exogenous ethylene on mango stem lenticel hypertrophy was examined. In general, floodwater O2 contents of 1-7 ppm resulted in lenticel hypertrophy within about 6 days of flooding, whereas floodwater O2 contents of 15 ppm delayed hypertrophy until about day 9. After 14 days of flooding, there were more than twice the number of hypertrophied lenticels per tree with floodwater O2 contents of 1-7 ppm than with O2 contents of 15 ppm. Ethylene evolution from aerobic stem tissue increased 4- to 8-fold in trees exposed to floodwater with 1-2 ppm O2, increased 2-fold for trees exposed to 6-7 ppm O2, but remained constant with 15 ppm floodwater dissolved O2 content. During a 10-day flooding period, trees in floodwater with 15 ppm dissolved O2 content, and given exogenous ethylene, developed extensive stem lenticel hypertrophy, whereas no hypertrophy developed on stems of trees receiving no exogenous ethylene and maintained in floodwater with 15 ppm O2. These data suggest that ethylene plays a role in promoting stem lenticel hypertrophy in flooded mango trees.