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Increased preharvest fruit drop rates and reduced fruit sizes are common symptoms associated with Huanglongbing (HLB) in sweet orange. Small fruit may be more likely to drop during preharvest fruit drop. The objective of the current study was to determine whether fruit size could be used as an indicator of the preharvest fruit drop likelihood. Nearly 1400 fruit were surveyed over the following three timepoints across two years: 11 Mar 2022, 15 Apr 2022, and 22 Mar 2023. Each fruit was evaluated to determine the equator and peduncle diameter, fruit detachment force (FDF), type of detachment (mechanically broken or abscission), and lopsidedness. The total soluble solids content was determined for a subset of fruit. The FDF was consistently lower in abscising fruit than in mechanically broken fruit, suggesting that the physiological process of abscission had begun in these fruit and that they were more likely to drop. The fruit diameter was significantly smaller in abscising fruit than in mechanically broken fruit on 11 Mar 2022 and 22 Mar 2023, but not on 15 Apr 2022. Similarly, the fruit diameter and FDF were also significantly and positively correlated, but this relationship was weaker at time points late in the season (closer to harvest). These findings suggest that small fruit are indeed more likely to drop early in the preharvest period. The abscising fruit had total soluble solids contents similar to those of the mechanically broken fruit. Therefore, we hypothesized that the smaller fruit ceased growing and are able to respond to abscission signals earlier than the larger fruit. Therefore, any strategies to mitigate fruit drop, such as the use of plant growth regulators, should be applied early in the season when the fruit are still actively growing. When growth ceases, the fruit are vulnerable to drop.
Anthocyanins are beneficial bioflavonoids that have numerous roles in human health maintenance, disease prevention, and overall well-being. In addition, anthocyanins are key to the consumer appeal of many ornamental plants. Most citrus (Citrus L.) plants do not produce anthocyanins under warm tropical and subtropical conditions. Anthocyanin pigments, responsible for the “blood” color of blood orange [Citrus sinensis (L.) Osbeck], are produced after exposure to cold conditions during the fruit’s development. The transcription factor Ruby is responsible for the production of anthocyanin in blood orange. Functionally, similar genes exist in other fruit crops such as grape [Vitis vinifera L. (VvmybA1 and VvmybA2)] and apple [Malus ×domestica Borkh (MdMYB10)]. Here, VvmybA1 and Ruby genes were constitutively expressed in ‘Mexican’ lime (Citrus aurantifolia Swingle). This cultivar performs optimally under Florida’s humid subtropical environment and has a short juvenile phase. Constitutive expression of VvmybA1 or Ruby resulted in anthocyanin pigmentation in the leaves, stems, flowers, and fruit. An increased pigmentation of the outer layer(s) of stem tissue was observed in ‘Mexican’ lime overexpressing the VvmybA1, whereas lower anthocyanin levels were observed in plants overexpressing Ruby. Enhanced pigmentation was also observed in the young leaves; however, pigment intensity levels decreased as the leaves matured. Flower color ranged from light pink to fuchsia and the fruit pulp of several ‘Mexican’ lime lines were maroon; similar to a blood orange. The results demonstrate that expression of anthocyanin-related genes can affect temporal pigmentation patterns in citrus. It also opens up the possibility for the development of modified blood orange and other cultivars adapted to the subtropical environment.
Abstract
2-Chloro-9-hydroxyfluorene-9-carboxylic acid (chlorflurenol) 3 at 50 or 100 ppm increased fruit production of a gynoecious cucumber (Cucumis sativus L. cv. MSU 713-5) under field conditions of both normal and reduced pollination. A monoecious cultivar, ‘Wisconsin SMR 18’, treated with (2-chloroethyl) phosphonic acid (ethephon) and then chlorflurenol produced over twice as many fruit as the control when pollen was plentiful, and more than 4 ⨯ as many when pollen supply was limited. Ethephon sprays alone increased pistillate flower formation on the monoecious cultivar but did not increase fruit set. Chlorflurenol treatments increased the proportion of fruit in the smaller, more valuable size grades and appear advantageous for mechanically harvested pickling cucumbers.