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M.M. Peet

The environmental and physiological causes of cracking or splitting of soft fruits and citrus as they ripen are not well understood. This paper explores factors contributing to radial cracking in tomatoes, gives suggestions for prevention of cracking, and suggests directions for future research. Fruit cracking occurs when there is a rapid net influx of water and solutes into the fruit at the same time that ripening or other factors reduce the strength and elasticity of the tomato skin. In the field, high soil moisture tensions suddenly lowered by irrigation or rains are the most frequent cause of fruit cracking. Low soil moisture tensions reduce the tensile strength of the skin and increase root pressure. In addition, during rain or overhead irrigation, water penetrates into the fruit through minute cracks or through the corky tissue around the stem scar. Increases in fruit temperature raise gas and hydrostatic pressures of the pulp on the skin, resulting in immediate cracking in ripe fruit or delayed cracking in green fruit. The delayed cracking occurs later in the ripening process when minute cracks expand to become visible. High light intensity may have a role in increasing cracking apart from its association with high temperatures. Under high light conditions, fruit soluble solids and fruit growth rates are higher. Both of these factors are sometimes associated with increased cracking. Anatomical characteristics of crack-susceptible cultivars are: 1) large fruit size, 2) low skin tensile strength and/or low skin extensibility at the turning to the pink stage of ripeness, 3) thin skin, 4) thin pericarp, 5) shallow cutin penetration, 6) few fruits per plant, and 7) fruit not shaded by foliage. Following cultural practices that result in uniform and relatively slow fruit growth offers some protection against fruit cracking. These practices include maintenance of constant soil moisture and good Ca nutrition, along with keeping irrigation on the low side. Cultural practices that reduce diurnal fruit temperature changes also may reduce cracking. In the field, these practices include maintaining vegetative cover. Greenhouse growers should maintain minimal day/night temperature differences and increase temperatures gradually from nighttime to daytime levels. For both field and greenhouse tomato growers, harvesting before the pink stage of ripeness and selection of crack-resistant cultivars probably offers the best protection against cracking. Areas for future research include developing environmental models to predict cracking and exploring the use of Ca and gibberellic acid (GA) sprays to prevent cracking.

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Eric Curry

+ external amorphous wax layers attenuating and scattering the transmitted light; 2) ineffective or insufficient removal of cellular material; and/or 3) inability to identify newly forming cell imprints because of the thinness of the cutin outlining the new

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Yuliya A. Salanenka, Martin C. Goffinet, and Alan G. Taylor

30 min. Cutin and suberin give a red–orange color with Sudan III–IV and a blue–black color with Sudan black B ( Krishnamurthy, 1999 ). For fluorescent microscopy of lipids, neutral red ( Lulai and Morgan, 1992 ), rhodamine B, and auramine O ( Gahan

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W. Robert Trentham, Carl E. Sams, and William S. Conway

. Further study could substantiate these variables. The cuticle, secreted by and coating the epidermal tissue of higher plants, is a complex material consisting of two unique lipids, cutin and wax. A definable amount of the wax is embedded within the cutin

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Bishnu P. Khanal, Rejina Shrestha, Leonie Hückstädt, and Moritz Knoche

surface enlarges and the cuticle is strained. Because wax acts as a filler in the strained polymer network of the cutin matrix ( Petracek and Bukovac, 1995 ), the deposition of wax essentially “fixes” strain ( Khanal et al., 2013a ). Second, wax decreases

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Isaac T. Mertz, Nick E. Christians, and Adam W. Thoms

). We hypothesize that the hydrophobicity of these AAs will make them more mobile through the epicuticular wax and cutin of the leaf cuticle. According to Schönherr (1976) , once through the cuticle and inside the plant, this hydrophobicity could

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Isaac T. Mertz, Nick E. Christians, and Adam W. Thoms

hydrophobicity of the BCAA makes them more mobile through the epicuticular wax and cutin of the leaf cuticle, compared with other AA and standard N sources (e.g., urea). Once inside the leaf, the hydrophobicity of BCAA could also promote diffusion through the

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Bishnu P. Khanal and Moritz Knoche

composite material comprising both cellular and polymeric components. The cuticle is the outermost layer. It is a lipophilic polymer film with cutin and wax as the major constituents ( Dominguez et al., 2011a ; Heredia, 2003 ). The cuticle functions as a

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Eric A. Curry, Carolina Torres, and Luis Neubauer

). The cutin and the waxy surface undergo microcracking in which there occurs a simultaneous “tearing” of the cutin/wax matrix and “repairing” with wax platelet regrowth. Under optimal conditions, this process allows the cuticle to enlarge while still

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Yuliya A. Salanenka and Alan G. Taylor

tissues (plasma membrane, waxes, cutin, suberin, etc). Lipophilicity is quantified as log K ow (where K ow is the octan-1-ol/water partition coefficient). The relationship of log K ow and plant tissue uptake reveals a Gaussian curve with a range from