Sex expression in cucumber (Cucumis sativus L.) and muskmelon (C. melo L.) was correlated with endogenous ethylene production. Plants of gynoecious (all female) sex types of the two species produced more ethylene than monoecius (male-female) plants. Sex expression in cucurbits is influenced by genetic, environmental, and hormonal factors. Monoecious strains of cucumber (Cucumis sativus L.) and muskmelon (C. melo L.) bear staminate (male) and pistillate (female) flowers. Gynoecious strains normally produce only pistillate flowers. Other cucumber and muskmelon strains produce staminate or pistillate and, in addition, perfect (hermaphroditic) flowers in various combinations. For example, andromonoecious strains are those that begin with staminate flowers and, eventually, also produce hermaphroditic flowers. Exogenous application of auxin (1, 2) and inhibitors of gibberellin biosynthesis (3) promote monoecious strains to form pistillate flowers, that is, increase femaleness. Application of gibberellin promotes formation of male flowers in monoecious and gynoecious phenotypes of cucumber (4, 5). Sex expression can be modified by daylength and temperature. Generally, short days and cool temperatures favor femaleness, while long days and high temperatures favor maleness, although there are exceptions (6). Determinations of endogenous growth substances indicate that strains with genetically strong female sex expression contain more auxin (7) and less gibberellin-like substances (8) than strains with strong male sex expression. There are certain differences between species; for example, gibberellin application does not cause male flower formation in gynoecious muskmelon (9). However, the results obtained with hormone applications and hormone determinations suggest the hypothesis that sex expression in cucurbits is controlled by an endogenous auxin-gibberellin balance (3, 7, 8, 10).Ethylene and 2-chloroethylphosphonic acid (ethephon), an ethylene-releasing compound, have recently been shown to promote femaleness in cucurbits (11, 12); thus, the effect of ethylene is similar to that of auxin. Exogenous application of auxin increases ethylene production by cucumber plants (13

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The history of flower and fruit thinning, along with the commercially important physiological effects of thinning are discussed. Adjuvants and thinning chemicals and their physiological effects, as well as their applications are presented. The influence of photosynthetic reserves on the fruit set and chemical thinning of apples following ovule fertilization are also discussed. Notes are presented on chemicals that induce flower bud formation without thinning.

Shading (92%) of `Redchief Delicious' apple (Malus domestics Borkh.) trees for 10-day periods from 10 to 20, 15 to 25, 20 to 30, and 25 to 35 days after full bloom (DAFB) caused greater fruit abscission than shading from 5 to 15, 30 to 40, 35 to 45, or 47 to 57 DAFB. Fruit 8 to 33 mm in diameter (10 to 30 DAFB) were very sensitive to 10 days of shade, even though fruit sizes of 6 to 12 mm are considered the most sensitive to chemical thinners. In a second test, shading for 3 days caused fruit thinning; 5 days of shade in the periods 18 to 23, 23 to 28, and 28 to 33 DAFB caused greater thinning than 11 to 16 or 33 to 38 DAFB. Shading reduced photosynthesis (Pn) to about one-third that of noncovered trees. Terbacil (50 mg·liter-1) + X-77 surfactant (1250 mg·liter-1) applied with a hand-pump sprayer 5, 10, or 15 DAFB greatly reduced fruit set and caused some leaf yellowing, particularly in the earliest treatments. Terbacil reduced Pn by more than 90% at 72 hours after application. Shoot growth of trees defruited by shade or terbacil was equivalent to defruited or deblossomed trees; ethephon (1500 mg·liter-1) inhibited tree growth and defruited trees. No terbacil residues were dectected in fruit at harvest from applications made 5, 15, 20, 25, or 30 DAFB. Eleven of 12 photosynthesis-inhibiting herbicides were also found to thin `Redchief Delicious' apple trees. Shading caused more thinning than terbacil at the later applications, which may reflect poorer absorption and/or lesser photosynthetic inhibition than when terbacil was applied to older leaves.

In northern Virginia, over 80% of the apple crop is grown for processing. Many trees are propagated on vigorous rootstocks and require much pruning, especially in the tops. To reduce costs and labor needs, many growers prune every second or third year. When trees are not pruned, shading caused by growth in the current season or in nonpruned years is detrimental to pest control, fruit quality, and yield.Several plant growth regulators have been evaluated for their potential to reduce vegetative growth of tree fruits, thereby reducing pruning costs and improving fruit quality. Several reviews (Faust, 1984;Looney, 1983;Luckwill, 1970;Miller, 1988;Williams, 1984) dealing with many of these compounds indicate that most have several effects of greater commercial value than control of vegetative growth.The objectives of the experiments reported here were to evaluate the effects of prohexadione-calcium (3-oxido-4-propionyl-5-oxo-3cyclohexene-carboxylate), formulated as BAS-125 ("Apogee" ® ), on a) vegetative growth of apple and peach trees, b) fruit size and quality, and c) response to thinning chemicals. MATERIALS AND METHODSGeneral. Randomized complete-block designs were used in all experiments. Trees were blocked by location within rows, by rootstock, and/or by flower density rating. All experiments had six blocks except for Expts. 1, 4, 5, and 6. Trees were sprayed with either a low pressure hand-wand sprayer or a Swanson three-point-hitch airblast sprayer with both fans adjusted to one side, which doubled air output and increased nozzle numbers.In several experiments (Expts. 1-4), a 10-fruit sample was collected from each tree at harvest for quality evaluations, which included flesh firmness, soluble solids concentration, starch staining, percentage of red color, and incidence of water core. Flesh firmness of both peach and apple fruit was measured on two sides of each fruit with an Effegi penetrometer (model FT327; McCormick Fruit Tech, Yakima, Wash.) fitted with an 11.1-mm tip. Soluble solids concentration (SSC) was estimated with an Atago hand-held refractometer (model N1; McCormick Fruit Tech), utilizing a composite sample of juice resulting from penetrometer testing for each replicate of each treatment. Each apple fruit was cut in half transversely, and severity of water core was rated on a scale of 0 to 5 (0 = none, 5 = severe). Flesh starch was evaluated by dipping half of each apple in a solution of I 2 /KI for ≈15 s. The degree of staining was rated on a scale of 0 to 5 where 1 = staining of the entire cut surface and 5 = absence of starch (Poapst et al., 1959).In the dormant season (Expts. 1-4), average shoot length of the longest top two shoots, length of the five longest scaffold shoots, total length of shoots longer than 30 cm, weight and basal and terminal shoot diameters of these scaffold shoots, nodes/cm of the basal 40 cm, nodes/cm of the upper 30 cm of shoots, and time required to prune each tree, number of cuts/tree, and pruning weights/cm 2 trunk cross-sectional area (TCSA) per tree were recorded...