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- Author or Editor: Peter C. Andersen x
The influence of bilateral cordon (BC) and cane training systems and level of pruning severity on vegetative and reproductive characteristics of Vitis hybrid `Suwannee' were determined from 1987 to 1989. In 1987, yield and quality were similar on BC- and cane-trained vines. In 1988, shoot count, yield, and quality were similar regardless of training system and pruning severity (50, 70, or 90 nodes per vine). When data from both training systems were combined, yield was related to the number of shoots. Vines pruned more severely compensated by producing more shoots from non-count (non-node) positions on the canes, cordon, or spurs. Similarly, in 1989 yield and berry quality were not affected by training system or levels of pruning severity (50, 70, 90, or 110 nodes), although berry weight was affected by training system, and shoot count and shoot length were affected by level of pruning severity. Interactive effects of training system and pruning level were not significant in either year. An analysis of combined data for 1989 indicated that yield was affected by the number of nodes and shoots. Thus, `Suwannee' may be trained to the BC system, which is more readily adapted to mechanization. Pruning to a specific number of nodes per vine was not critical.
Abstract
Diurnal characteristics of the grape bleeding phenomenon were investigated for four muscadine (Vitis rotundifolia Mich.) grape cultivars. Shoots 6 to 12 mm in diameter of 8-year-old ‘Fry’, ‘Noble’, ‘Cowart’, and ‘Jumbo’ were cut to 60- to 140-mm-long spurs on 3 Apr., and the naturally occurring exudate was collected in foil-covered Erlenmeyer flasks. Water flux (Jv), osmotic potential (Ψs), and total solute flux (Js) were monitored diurnally from bleeding spurs. A distinct diurnal trend in Jv occurred with a minimum during early evening and a maximum during late morning. The Ψs of the exudate varied only slightly diurnally, thus the total quantity of solute moved from the root to the shoot was several times greater during the day than during the night. Water flux and Ψs were cultivar- and time-dependent. The Ψs of the exudate varied from −53.4 to −27.7 kPa. Maximum Js occurred at 1000 hr and was ≈ 0.250 mmol·s−1·m−2 for all cultivars except ‘Cowart’.
There is increasing interest in the culture of satsuma citrus in the states bordering the northern Gulf of Mexico. Yield, tree size, and fruit quality of mature ‘Owari’ and ‘Brown Select’ satsuma (Citrus unshiu Marcovitch) on Poncirus trifoliata (L.) Raf. (‘Rubidoux’ and ‘Flying Dragon’) were evaluated in north Florida. Canopy area and volume, yield, and fruit quality data were analyzed as a 2 × 2 factorial design with scion and rootstock as the main effects. There were no scion × rootstock interactions. Overall average yield per tree was 16, 88, 91, 143, and 101 kg in 2010, 2011, 2012, 2013, and 2014, respectively. Yield was influenced by scion (higher for ‘Brown Select’) in three of five years, and by rootstock every year (higher for ‘Rubidoux’). Yield per tree was ≈2-fold greater for trees on ‘Rubidoux’ compared with ‘Flying Dragon’; the highest yield was recorded for ‘Brown Select’ on ‘Rubidoux’. Yield per m2 canopy area was often similar since canopy area was often ≈2-fold greater for trees on ‘Rubidoux’. For three of the five years, fruit weight was greater for ‘Brown Select’ (average = 157 g) than ‘Owari’ (average = 146 g), with no rootstock effect. Soluble solids of juice averaged 10.0 °Brix and were higher for trees on ‘Flying Dragon’ than on ‘Rubidoux’ in three of five years. Juice pH averaged 3.67 and was unaffected by scion or rootstock. Trees were not subjected to freeze protection and were not damaged by minimum temperatures as low as −9.4 °C, except for 2014/15. A rating of defoliation after a freeze on 19 Nov. 2014 (−5.6 °C) indicated that cold hardiness varied by scion (greater for ‘Brown Select’) and rootstock (greater for ‘Rubidoux’). Differences in cold hardiness did not persist when assessed later in the winter. Successful satsumas production can be achieved in north Florida in the absence of a severe freeze event.
Leaf physiology and growth parameters of Aucuba japonica (Thunb.) cv. Variegata were assessed under conditions of full sun (photosynthetic photon flux = 1531 to 2073 μmol·m-2·s-1) and under shadecloth (light transmittance of 69%, 47%, and 29% full sun) over 2 years. Two days after treatment initiation, net CO2 assimilation (A) was proportional to light level, although stomata1 conductance to water vapor (gs) was not influenced by shading. Subsequently, A, gs, transpiration rate, and water use efficiency of 100% sun-grown plants were often <50% that of shade-grown plants. After 1 month of exposure to 100% sun, leaves were chlorotic and necrotic; plant appearance was normal for plants grown under shadecloth. The growth index and total, leaf, stem, and root dry weights were inversely related to light level. Relative water content and chlorophyll concentration in leaves that had expanded before treatment initiation were reduced with increasing levels of irradiance, but these variables were not altered in leaves produced after treatment initiation. Plants from all treatments experienced dieback when transplanted to the field under conditions of full sun. We conclude that A. japonica is shade obligate, performing best with exposure to 47% of full sunlight.
Homalodisca coagulata (Say) is a xylem-feeding leafhopper that is the principal vector of many economically important diseases resulting from infection by Xylella fastidiosa (i.e., plum leaf scald, phony peach disease). We have previously established that high abundances and high consumption rates of H. coagulata occur on host species with high amide concentrations in the xylem fluid. Several lines of research suggest that selection of “marginal hosts” (those that typically have low abundances of leafhoppers) may be influenced by ovipositional, as well as feeding, preferences. In northern Florida, Euonymus japonica consistently has the highest densities of eggs and young nymphs, but is only a marginal host for adults. Adults caged on this host feed little and have a short longevity. In contrast, young insects (second instar) caged on the host have high survivorship rates and assimilate dietary nutrients with high efficiency. H. coagulata are abundant on Prunus germplasm in northern Florida during the month of June, but only occasionally visit Prunus after this period. In a study of 10 Prunus scion/rootstock combinations, we established that abundances of H. coagulata on Prunus during the peak period were correlated to leafhopper consumption rates. During summer, when Prunus serves as a marginal host, leafhopper abundances are tightly coupled to fecundity rates. Understanding of ovipositional preference may be central to our understanding of Xylella acquisition. These preliminary experiments suggest that leafhoppers may sample xylem fluid during ovipositional selection, as they preferentially select ovipositional sites that have proper nutrient profiles for development of young nymphs (“mother knows best”). Although consumption rates are low for marginal hosts, repeated probing for ovipositional preference may contribute to the spread of diseases caused by X. fastidiosa.
Diurnal variations in the chemical composition of xylem fluid have been established for many plant species exhibiting positive root pressure; similar patterns have not been well documented in transpiring plants. Diurnal changes in plant water status and xylem fluid chemistry were investigated for `Flordaking' peach [Prunus persica (L.) Batsch], `Suwannee' grape (Vitis hybrid), and `Flordahome' pear (Pyrus communis L.). Xylem tension was maximum at 1200 or 1600 hr and declined to <0.5 MPa before dawn. Xylem fluid osmolarity ranged from 10 to 27 mm and was not correlated with diurnal patterns of xylem tension. The combined concentration of amino acids and organic acids accounted for up to 70%, 45%, 55%, and 23% of total osmolarity for irrigated P. persica, nonirrigated P. persica, Vitis, and P. communis, respectively. The concentration of total organic compounds in xylem fluid was numerically greatest at 0800 or 0900 hr. For irrigated P. persica the osmolarity of xylem fluid was reduced by 45% from 0800 to 1200 hr, 1 h after irrigation, compared to only a 12% reduction from 0800 to 1200 hr for nonirrigated trees. Asparagine, aspartic acid, glutamine, and glutamic acid were mainly responsible for diurnal changes in the concentration of total amino acids and organic N for P. persica; the diurnal variation in organic N for Vitis was due to glutamine. Arginine, rather than the amides, was the primary source of organic N in xylem fluid of P. communis, and there was no consistent diurnal change in the concentration of amino acids or organic N. The predominant organic acids in all species examined were citric and malic acids. No consistent diurnal trend occurred in the concentration of organic acids or sugars in xylem fluid.
The effects and interactions of water stress and nutrient solution on water relations and concentrations of amino acids, organic acids and sugars in xylem fluid of `Methley' plum (Prunus salicina Lindl.) and `Carolina Beauty' crape myrtle (Lagerstroemia indica L.) during midday were determined. Container-grown plants were irrigated with water or nutrient solution (i.e., osmolarity = 138 mm) for 15 days, then irrigation was either continued or terminated for the next 5 days. The experiments were analyzed as factorial designs for each species separately, with the nutrient solution and irrigation status the last 5 days as the main factors. Xylem fluid tension increased ≈ 2- to 3-fold and leaf conductance to water vapor and transpiration were reduced ≈ 10-fold by withholding irrigation for both species; plant water relations of L. indica were also influenced by the nutrient solution. For both species, the osmolarity of xylem fluid was not altered by withholding irrigation. The predominant organic compounds quantified in both species were amides (i.e., glutamine and asparagine), arginine, and citric and malic acids. Sugars represented a small proportion (i.e., generally ≤ 1%) of total osmolarity. Irrigation altered the chemical profile of amino acids and organic acids to a greater degree than the nutrient solution. Water stress induced a 3-fold increase in total organic acids in xylem fluid of both species. The osmolarity and the concentration of most organic compounds in xylem fluid of P. salicina were not significantly affected by the nutrient solution. Arginine increased markedly in concentration by withholding irrigation or with the application of nutrient solution for L. indica. The concentration of most organic compounds did not vary greatly in response to variations in soil water or nutrient status. In conclusion, soil water-or nutrient-mediated changes in plant water relations exceeded changes in xylem fluid chemistry.