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- Author or Editor: R. H. Hilgeman x
‘Valencia’ cultivars (‘Campbell’ old line, ‘Campbell’ nucellar, ‘Frost’ nucellar, ‘Olinda’, ‘Cutter’, ‘Wood’, and ‘Chapman’) were budded on rough lemon (Citrus jambhiri Lush.), sour orange (C. aurantium L.), ‘Cleopatra’ (C. reshni Hort ex Tan.) and ‘Willowleaf (C. delicosa Tenore) mandarins.
The first 5 were California cultivars with buds imported from the USDA Sub Tropical Fruit Station, Indio. The ‘Wood’ and ‘Chapman’ were local cultivars. All cultivars were disease free, excepting stubborn. Trees were planted in October 1959 near Peoria, Arizona and at 2 other locations.
‘Campbell’ old line produced highest yield at all locations. Fruit shape and quality were satisfactory, and tree growth vigorous. Up to 1966, trees on rough lemon rootstocks had the highest yield. Between 1968 and 1971, no difference in yield on trunk growth existed between trees on rough lemon, and ‘Willowleaf’ mandarin rootstocks. Lowest yield trees were on ‘Cleopatra’ mandarin.
‘Marsh’ grapefruit (Citrus paradisi Macf.) trees 32 years old, 5.1 m tall and 6.6 m wide were pruned with 5 methods: 1) light −4.5 m tall and 5.4 m wide; 2) moderate −3.6 m tall and 4.5 m wide; 3) severe −2.1 m tall and 2.4 m wide to main scaffolds (buckhorned); 4) Low-High – severe pruning of lower 1.8 m followed by severe pruning of upper part 3 and 5 years later; 5) control – deadwood removed. Yields, fruit size and grade and trunk growth were obtained for 6 years after pruning.
In the 1st year, yields and US No. 1 grade decreased, fruit size and trunk growth increased as the amount of fruiting wood removed became greater. No fruit was set on severely pruned trees. In the 2nd year yields on the lightly pruned trees were similar to the control. Moderately and severely pruned trees had normal yields in the 4th year. Thereafter, severely pruned trees produced more US No. 1 grade fruit which was slightly larger than fruit on the control trees. 6 years after pruning the severely pruned trees were 4.6m high and 5.2 m wide whereas the unpruned trees were 5.7 m and 7.3 m.
‘Valencia’ orange scions on sour orange rootstock, planted in 1935 at Tempe, Arizona, in calcareous sandy loam, were grown from 1949 through 1968 under 4 irrigation programs: high—15 irrigations a year, 1.72 m water applied; moderate—10 irrigations a year, 1.35 m water applied; low—5 irrigations a year, 0.95 m water applied; high-low—high, March to July, and low, August to February, 9 irrigations a year, 1.18 m water applied.
Yields were similar in high, moderate and high-low trees; reduced in low trees. Trunk growth was proportionately reduced as less water was applied. High soil water produced larger tree canopies than moderate, low and high-low, which were similar. Summer shoot growth was stimulated in high trees, limited by fruiting and soil water deficits in moderate and high-low regimes, and promoted by reduced yields in low trees. Low soil water reduced total feeder roots and increased the proportion below 60 cm. Fruit sizes were similar in high and moderate, markedly reduced in high-low and variable in low schedules. Total soluble solids in fruit increased as less water was applied after mid-July. Peel thickness was similar in high and moderate and thinner than in low and high-low.
High yields from the high-low regime show there is no advantage in maintaining high soil water during the entire year. Moderate stresses after July induced highest soluble solids in fruit, maintained smaller trees which facilitated picking, and prevented iron chlorosis.
Leaves from ‘Washington’ navel and ‘Valencia’ oranges, ‘Dancy’ and ‘Kinnow’ mandarins and ‘Marsh’ grapefruit were analyzed for 5 years. Significant differences between cultivars were found for N, P, K, Ca, Mg and Fe levels but not for Zn, Cu and Mn. Concentrations of the potentially toxic elements, Na, Cl, B, and Li, were significantly different at low non-toxic levels. Lowest values occurred in oranges and highest in ‘Kinnow’ mandarin and ‘Marsh’ grapefruit. Compared with rough lemon, sour orange rootstock decreased N in ‘Valencia’, increased K in ‘Kinnow’ and increased Ca and decreased Mn, Na, B and Li in all cultivars. There were wide annual variations in N, K, P, Ca, Mg, Zn, Mn and Cu levels in all cultivars.
Surveys were made of Li in leaves, irrigation water and soil in groves of 37 to 43 year old ‘Marsh’ grapefruit on sour orange rootstock. Lithium in leaves increased during the late summer. Leaves with 50 to 60 ppm Li in September generally developed necrotic lesions on margins below the tip in November when they contained 60 to 90 ppm Li and abscissed within 1 to 4 months. Lithium varied widely between spring-cycle leaves on the same tree and within the leaf where it accumulated in the lesions. Severe Li toxicity symptoms were associated with 0.18 to 0.25 ppm Li in the irrigation water, 0.7 to 1.0 ppm in the soil and from 68 to 232 ppm in spring-cycle leaves in November. Vigorous growth and high yields occurred with 24 to 34 ppm Li in the leaves, 0.07 to 0.11 ppm Li in the irrigation water and 0.3 to 0.4 ppm in the soil. Severe leaf symptoms with Li content as high as 175 ppm were induced by soil applications of LiCl under field conditions.
Comparisons were made of the composition of ‘Valencia’ oranges, Citrus sinensis Osbeck, from orchards in 6 major climatic zones used for citrus culture in the U. S. Six orchards, selected in a compact area in each location, were measured and sampled at intervals during 2 crop seasons. The locations were: Orlando, Fla.; Weslaco, Tex.; Tempe, Ariz.; Indio, Calif.; Riverside, Calif.; Santa Paula, Calif. Statistical evaluations showed that the seasonal trends for most measurements differed significantly among locations.
Observations on flowering showed that full-bloom occurred from 1 to 2 months later in the Far-Western locations than in Texas and Florida. The extremes of the interval between an thesis and the beginning of ripening (a 9 to 1 ratio of total soluble solids to acid in juice) varied from 71/2 to 81/2 months in Weslaco, to 14 to 15 months in Santa Paula, but earliness or lateness of maturity could not be relatd in any simple, obvious manner to the characteristic of the seasonal temperature regimes in the 6 locations. In general, rinds were thinner, smoother and slower to color, and fruits larger, and juicier in Orlando and Weslaco than in the Far-Western locations. Total soluble solids and ascorbic acid in juice at comparable stages of maturity were not influenced in a predictable manner by location, although significant differences occurred in a given season. Of the juice constituents, the acids appear to be the most consistently influenced by climatic conditions during the rapid growth and maturation periods of fruit development. The warmer the climate, the more rapid was the rate of decrease of total acid concentration. Seediness of fruit was influenced by both location and season. Measurements of comparable samples of fruit obtained from widely divergent climatic parameters suggest that the numerous growth and metabolic processes involved in ripening of citrus fruits have independent internal controlling mechanisms. Apparently these processes interact in different ways with external environmental factors, and are not dominated by a pervasive, common internal maturity factor.