Contents lists available at ScienceDirect Scientia Horticulturae journal homepage: www.elsevier.com/locate/scihorti Quantifcation of lenticels in Japanese plum cultivars and their efect on total fruit peel permeance Imke Kritzinger ⁎ , Elmi Lötze Department of Horticultural Science, Faculty of AgriSciences, University of Stellenbosch, South Africa ARTICLE INFO Keywords: Fruit cuticle Moisture loss Prunus salicina Lindl. Transpiration Mass loss ABSTRACT Fruit peel vapour permeance is an indicator of the propensity of fruit to lose moisture. Permeance is afected by cuticle composition, as well as stomata, lenticels and cracks in the cuticle. Stomata play a signifcant role in controlling the transpiration of leaves. Since lenticels on fruit often form from non-functional stomata, this study determined whether lenticels contribute to peel permeability in Japanese plums and whether this varies between cultivars. In 2015/16 as well as 2016/17, ‘Laetitia’ and ‘Songold’ were investigated and in 2016/17, ‘African Delight™’ and ‘Sapphire’ were added to the study. Fruit were sampled from three weeks before commercial harvest until the commercial harvest date. On each sampling date, the peel permeability of individual fruit was determined and the number of open lenticels quantifed. Lenticel numbers and peel permeability of fruit both difered signifcantly between fruit of diferent cultivars and between seasons. Signifcant correlations between permeability and the number of open lenticels were found only in ‘Songold’, ‘African Delight™’, and ‘Sapphire’ fruit. The percentage of open lenticels are therefore not the determining factor of total fruit peel permeability or the tendency of plums to lose moisture. Cuticle composition seems to play a more important role in determining fruit moisture loss. 1. Introduction Fruit mass loss is mostly due to the loss of water vapour through transpiration and to a lesser extent, the loss of carbon in the respiration process (Pieniazek, 1944). Therefore, fruit peel water vapour per- meance (P’ H20 ) is a good indicator of the propensity of a product to lose moisture, as it quantifes the ease with which water vapour can escape from the fruit (Maguire et al., 2000). The rate of transpiration and thus, moisture loss, is infuenced by both external and internal factors. External factors include temperature, relative humidity (RH) and air movement over the fruit surface (Pieniazek, 1944), while internal factors include cuticle composition and openings in the fruit peel such as wounds, cracks, stomata and lenticels (Maguire et al., 2000; Veraverbeke et al., 2003). The cuticle is a lipid membrane, consisting of cutin and waxes that covers the epidermal cells (Belge et al., 2014; Holloway, 1982; Schreiber and Schönherr, 2009). Its main function is to act as a barrier to transpirational moisture loss, while still allowing gas exchange and transpiration controlled by the stomata (Riederer and Schreiber, 2001; Yeats and Rose, 2013). The waxes associated with the cuticle are the main determinants of the hydrophobic nature of the cuticle (Díaz-Pérez et al., 2007) and can reduce the rate of moisture loss through transpiration by up to 25 times (Wills et al., 2007). This becomes especially important after harvest, when fruit do not receive additional moisture from the tree to replace the moisture lost to the atmosphere (Díaz-Pérez et al., 2007). So, the state of the fruit peel at harvest can have a signifcant efect on its postharvest quality (Léchaudel et al., 2013). In leaves, the cuticle blocks moisture loss to such an extent that transpiration occurs mostly through the stomata (Veraverbeke et al., 2003; Yeats and Rose, 2013). However, in fruit that contain stomata, the guard cells generally become non-functional as the fruit mature (Tamjinda et al., 1992). In sweet cherries, the stomata are non- func- tional by Stage III of fruit growth and are fxed in a partially open position (Peschel et al., 2003). Lenticels often develop from these non- functional stomata (Dietz et al., 1989; Everett et al., 2008; Veraverbeke et al., 2003). They are sunken openings that are larger than the stomata and, because they do not have functional guard cells, they form open pores in the fruit peel. However, lenticels can be packed with suberised cells or covered with epicuticular wax, thus closing the lenticel opening (Turketti et al., 2012). The cuticular layer is usually thinner over len- ticels and the small holes in the cuticle, formed by the lenticels, cause discontinuities in the cuticle (Tamjinda et al., 1992). Therefore, these small holes in the cuticle can act as avenues for water vapour to escape https://doi.org/10.1016/j.scienta.2019.04.082 Received 12 December 2018; Received in revised form 28 April 2019; Accepted 29 April 2019 ⁎ Corresponding author. E-mail address: imkekrit@gmail.com (I. Kritzinger). Scientia Horticulturae 254 (2019) 35–39 0304-4238/ © 2019 Published by Elsevier B.V. T