HILGEMAN: GRAPEFRUIT — CLIMATE STUDIES 99 couragement, observations and suggestions in 2. Steams, Charles R. Jr., J. T. Griffiths, W. L. Thomp son, and E. J. Deszyck. Progress report on concentrated compiling and assembling data for this presenta sprays on citrus in Florida. Proceedings, Fla. State Hort. tion. Soc, 1951. 3. Steams, Charles R. Jr., W. L. Thompson, R. B. LITERATURE CITED Johnson, and E. J. Deszyck. Method of Applying insecti 1. Griffiths, James T., C. R. Steams, and W. L. Thomp cides with different spray machines. Proceedings, Fla. son. Possibilities for the use of concentrated sprays on State Hort. Soc, 1952. citrus in Florida. Proceedings, Fla. State Hort Soc, 1950. EFFECT OF CLIMATE OF FLORIDA AND ARIZONA ON GRAPEFRUIT FRUIT ENLARGEMENT AND QUALITY; APPARENT TRANSPIRATION AND INTERNAL WATER STRESS1 r. h. hilgeman2 Introduction 'Valencia' oranges grown in Florida have a Abstract thinner peel and more juice but lower percen tages of acid and total soluble solids than Ari Fruit enlargement rates, changes in physical zona fruit (3). Similar differences in grape characteristics and water relationships were fol fruit are indicated by maturity studies (6) (8). lowed between July and November in Florida in These differences have been associated with the 1964 and in Arizona in 1965. widely different climatic conditions (3). How In Florida, due to summer rains and clouds, ever, detailed comparisons of the responses of relatively uniform fruit enlargement rates were trees to each environment have not been made, maintained. With soil water below 10 cbs. ten except with trunk growth of 'Valencia7 oranges sion, heavy rains increased enlargement rates (4). This investigation was designed to evaluate and intensified internal pressures on the peel. responses associated with typical commercial In Arizona, blossoming was 45 days later, fruit trees, grown with normal culture practices in was only % as large as Florida fruit on July 1 each area. It is recognized that differences in but grew more rapidly. Fruit enlargement rates soils, stocks and cultural practices, particularly varied widely between irrigations. Internal pres use of arsenical sprays, influence tree responses sure on the peel was low. and fruit characteristics, as well as climate. In Florida, continuously high soil water and This report compares the effects of climatic low internal water deficits in July, August and conditions in the 2 areas on (A) fruit enlarge September apparently induced high juice con ment rates and physical and chemical character tent and thin peel. The high juice content re istics; (B) apparent transpiration from leaves sulted in lower solids and acid percentages than and internal water deficits. found in Arizona. On sunny Florida days, apparent transpira Materials and Methods tion was similar to Arizona, although atmos pheric vapor pressure deficits were about 3 times Five large, vigorous 'Redblush' grapefruit higher in Arizona; internal water deficits were trees on rough lemon stock, about 18 years old, markedly higher in Arizona. were selected in a commercial grove growing lUniversity of Arizona Agricultural Experiment Sta on fine sand soil, about 11 miles south of Winter tion Journal Series paper No. 1173. Garden, Florida. Trees received adequate fer 2Horticulturist, University of Arizona Citrus Experi ment Station, Tempe, Arizona. The author was employed tilization and insect control and were sprayed as collaborator by the USDA, ARS Crops Research Division at Orlando, Florida, during 1964, while on Sabbatical leave. with arsenical materials. Irrigation was with 100 FLORIDA STATE HORTICULTURAL SOCIETY, 1966 perforated pipe sprinklers with most of the wa each area between July and November in 1964 ter falling in alternate rows. No "off-season" in Florida and 1965 in Arizona. fruit was present; twig growth occurred irreg Maximum and minimum temperatures were ularly during the summer. obtained in U. S. Weather Bureau shelters, lo Four moderately vigorous 'Marsh' grapefruit cated about 5 miles from the trees in Florida trees on sour orange stock of similar size, but and about 100 yards from them in Arizona. In 33 years old, were selected at the University of Florida, the accumulative precipitation between Arizona Citrus Experiment Station, near Phoe fruit measurement intervals was measured at nix, Arizona. The trees were growing in calcare the test trees. In Arizona, precipitation was ous, gravelly, sandy loam, soil moderatly fertil measured daily at the thermometer station. ized with nitrogen, clean cultivated, and irri Irrigations are indicated in Figure 1. About gated by flooding between borders under the 2 to 3 inches of water were applied in Florida. tree. No "off season" bloom occurred and sum In Arizona, 5 to 6 inches were applied to either mer growth was light. one side or to the entire soil area as indicated Similar observations were made on trees in in Figure 1. Tensiometers were placed at 18 400 .FRUIT ENLARGEMENT DAILY ENLARGEMENT RATE A PRECIPITATION Florida .£ t(M\ o DAILY TRUNK SHRINKAGE Florida Fig. 1.—Seasonal growth of fruit, daily fruit enlargement rates, and trunk shrinkage as affected by precipitation and irrigation in Florida in 1964 and Arizona in 1965. HILGEMAN: GRAPEFRUIT — CLIMATE STUDIES 101 and 30 inch depth at the drip of the trees. weighed within 15 seconds after removal from Fruit Enlargement and Characteristics; Trunk the tree and after 2 minutes exposure at its Measurements. Forty fruits were measured near original place on the tree. Loss of water is sunrise at 2 to 5 day intervals as shown in Fig reported as mg of water/g fresh wt./hr. The ure 1. Circumference measurements were con leaf petiole was then placed in water, transfer verted to volume, according to tables of Taylor red to a saturated atmosphere and weighed 26 and Furr (15). Fruit shrinkage during the day to 32 hours later. The percentage water de was reported as percent of volume loss based on ficit was calculated by dividing the gain in volume near sunrise. Fritts dendographs were weight by the hydrated leaf weight. In Arizona, placed on trunks of two trees in a previously observations were started near sunrise. In Flor described manner (4) to obtain daily records of ida, they were delayed from 1 to 3 hours later trunk shrinkage. until the dew had evaporated. Wet and dry Five fruits per tree were collected on dates bulb temperatures were obtained from sling shown in Table 2. Fruit was weighed, volume psychrometers at intervals during the day. determined by water displacement and specific gravity calculated. Juice was extracted with a Results and Discussion Sunkist extractor, pressed through cheesecloth and weighed. Total soluble solids were meas Climatic Conditions. The mean monthly temper ured as sucrose with an Abbe refractometer. atures and total precipitation set forth in Table Acid was determined by titration with standard 1 show Florida rainfall was near normal in July alkali. and August. The hurricane caused 9.73 inches Apparent Transpiration and Internal Water between September 8 to 13. No rain fell between Stress. Apparent transpiration was estimated October 14 and November 27. The normal Ari by methods used by Oppenheimer and Mendel zona mean temperatures in July and August (12). Spring flush leaves weighing between 1.0 were associated with maximum and minimum and 1.5 g were used in both areas. A leaf was temperatures about 2° F above and below nor- Table 1, Temperature and precipitation in Florida and Arizona July Aug. Sept. Oct. Nov. Florida 1964 Mean max. F. 90 91 tib1 81 78 Mean min. °F. 72 73 71 63 60 Departure from 0 0 + 1 - 2 + 3 normal a/ °F. Total precip. in. 3.22 c/ 7.67 ll.ij.7 .65 1.08 Days with precip• 9 19 10 k 1 Departure from + .71 + k.2k - 3.31 - .k9 normal a/ in. Arizona 1965 Mean max. °F. 107 107 9« 77 Mean mino °F. 72 69 61 Departure from 0 0 - k + 2 + k normal b/ °F. Total precip • in. .36 .81 .51 .I4.O 1.36 Days with precip. 2 1 3 Departure from J - -U5 - .10 - .20 + .70 normal b/in. Departure of mean temperature and precipitation from normal at: a/ Orlando, Florida; b/ Tempe, Arizona. 0/ Precipitation at test grove between July 17 and 31. 102 FLORIDA STATE HORTICULTURAL SOCIETY, 1966 mal. In September, minimum temperatures were largement rates dropped rapidly, although a below 50° F on 4 days (low 45° F). Rainfall light rain and a drop in temperature occurred was well below normal until late November and soil water was available. Internal pressures when 1.28 inches fell on November 23 and 25. sufficient to cause contraction of the peel upon cutting did not develop at any time. Part. 1. Fruit Enlargement, Trunk Shrinkage, Daily Trunk Shrinkage. The trunk shrinks or Fruit Quality expands during the day as the internal water FRUIT ENLARGEMENT. Full bloom was supply changes (4) (10). Figure 1 shows the about March 1 in Florida and April 15 in Ari amount of daily diameter shrinkage. zona. Fruit enlargement rates and daily shrink Florida. Rain and cloudy days retarded age changed with age so the 45 day age differ shrinkage on about 50 percent of the days be ence induced differences in these values on the tween July 17 and September 22. On days with same dates (Fig. 1). Enlargement of similar age heavy, almost continuous rainfall, almost none fruit was about equal; however, the absolute ocurred (July 26; Sept. 9, 10, 11 and 15). Dur values for fruit size are not basic to this study. ing sunny days without rain, large shrinkage Florida. Between July 17 and Oct. 9 rela took place. tively uniform gradually decreasing daily During the dry October-November drouth growth rates were maintained by rainfall dur period, daily shrinkage was more uniform with ing each measurement interval.