In Queensland, 80% of strawberry (Fragaria ×ananassa) production occurs between Brisbane and the Sunshine Coast with a major concentration in the Wamuran-Caboolture area located ≈50 km north of Brisbane. During the production season, from late fall (May) through early spring (September), rainfall is typically low (mean monthly rainfall ≈61 mm), but rainfall events are highly variable. Fruit are exposed to prevailing weather conditions and may suffer rain damage (Herrington and Chandler, 2006).
“Immediate rain damage” on strawberries is expressed during or soon after the rainfall, whereas “delayed rain damage” becomes obvious only as the fruit develops 1 week or more after the rainfall (Herrington et al., 2009). “Immediate rain damage” takes the form of “water soaking,” etching, and cracking to the stem end (neck, shoulder), body, and tip of affected fruits (Fig. 1). “Delayed rain damage,” which requires further investigation, includes a higher than expected proportion of deformed fruit, irregularly cracked fruit, and mottled or blotchy fruit. The investigations reported here are restricted to a consideration of only the “immediate” form of rain damage to strawberries grown in southeast Queensland.
The “immediate rain damage” on strawberry may result from the physical impact of rainfall (i.e., its energy) and/or the water (potential and turgor relationships) derived from the rainfall. Increased turgor caused by rapid uptake of water is the assumed mechanism for rain damage in many fruit species (Opara et al., 1997). Although the energy of impacting raindrops (van Dijk et al., 2002) can be sufficient to bruise “soft” fruit (Holt and Schoorl, 1982), the incidence of high rain damage on some firm-fruited cultivars in southeast Queensland (Herrington et al., 1996) implies that the response of the fruit surface to the free water (i.e., a turgor relationship) rather than the impact of the raindrops per se is probably the major factor influencing resistance to rain damage in strawberry.
Studies in cherry (Prunus avium L.) indicate water uptake by fruit may occur by diffusion through the cuticular membrane, flow through tissue junctures, guard cells or stomatal pores, and through microscopic cracks in the cuticular membrane (Beyer et al., 2005; Peschel and Knoche, 2005). Microscopic cracking of the cuticular membrane is increasingly recognized as an important entry point for water in other fruit (Glenn and Poovaiah, 1989; Knoche et al., 2004) and surface moisture can induce microcracks in the cuticular membrane (Knoche and Grimm, 2008), although their formation is not necessarily related directly to water uptake (Knoche and Peschel, 2006).
Microcracking is exacerbated in european plum (Prunus domestica L. ssp. domestica) by the increased strain that results from developmental features such as fruit expansion and the cessation of cutin deposition in the cuticular membrane with advancing maturity (Knoche and Peschel, 2007). However, we found no specific reports in strawberry on the diffusion of water through the cuticular membrane or the mechanism leading to rain damage. The location on the fruit surface (Gilbert et al., 2007), environmental factors such as surface water or high humidity (Knoche and Peschel, 2006), and cultural factors such as irrigation and fruit thinning (Gilbert et al., 2007) can also influence cracking in other crops.
Rain damage in strawberries typically results in substantial economic losses from rejected fruit as well as increased harvesting, grading, and packing costs coupled with lower prices from reduced consumer demand as a result of poor fruit quality (Herrington et al., 2009). Incorporation of genetic resistance to rain damage into strawberry cultivars released for commercial production in southeast Queensland will reduce both the risk and severity of these losses.
The studies reported here estimate the genetic control (i.e., heritability) of resistance to rain damage, particularly damage resulting from water soaking and surface etching because initial observations indicated that these were the most frequent damage types. However, even if selectable genetic variance exists, selection for resistance relies on the occurrence of sufficient rainfall at an appropriate stage of fruit maturity so that degrees of resistance among genotypes can be determined. The uncertainty of such rainfall events makes selection for resistance in the field difficult. An indirect method to evaluate resistance to rain damage (in the absence of a rain event) would therefore be useful. Soaking fruit in water has been used to simulate rain damage in apples [Malus ×sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] in a controlled manner (Byers et al., 1990) and cherries (Glenn and Poovaiah, 1989), but such methods have not been applied to strawberry. We therefore conducted an additional series of experiments to test if soaking fruit in deionized water may approximate rain damage sufficiently to be used as an indirect assessment method in strawberry breeding.
Banks, B.D., Mao, I.L. & Walter, J.P. 1985 Robustness of the restricted maximum likelihood estimator derived under normality as applied to data with skewed distributions J. Dairy Sci. 68 1785 1792
Beyer, M., Lau, S. & Knoche, M. 2005 Studies on water transport through the sweet cherry fruit surface: IX. Comparing permeability in water uptake and transpiration Planta 220 474 485
Byers, R.E., Carbaugh, D.H. & Presley, C.N. 1990 ‘Stayman’ fruit cracking as affected by surfactants, plant growth regulators, and other chemicals J. Amer. Soc. Hort. Sci. 115 405 411
Considine, J. & Brown, K. 1981 Physical aspects of fruit growth—Theoretical analysis of distribution of surface growth forces in fruit in relation to cracking and splitting Plant Physiol. 68 371 376
Considine, J.A. 1982 Physical aspects of fruit growth: Cuticular fracture and fracture patterns in relation to fruit structure in Vitis vinifera J. Hort. Sci. 57 79 91
Dieters, M.J., White, T.L. & Hodge, G.R. 1995a Genetic parameter estimates for volume from full-sib tests of slash pine (Pinus elliottii) Can. J. For. Res. 25 1397 1408
Dieters, M.J., White, T.L., Littell, R.C. & Hodge, G.R. 1995b Application of approximate variances of variance components and their ratios in genetic tests Theor. Appl. Genet. 91 15 24
Dieters, M.J., Hodge, G.R. & White, T.L. 1996 Genetic parameter estimates for resistance to rust (Cronartium quercuum) infection from full-sib tests of slash pine (Pinus elliottii), modelled as functions of rust incidence Silvae Genet. 45 235 242
Gilbert, C., Chadoeuf, J., Vercambre, G., Genard, M. & Lescourret, F. 2007 Cuticular cracking on nectarine fruit surface: Spatial distribution and development in relation to irrigation and thinning J. Amer. Soc. Hort. Sci. 132 583 591
Gilmour, A.R., Thompson, R. & Cullis, B.R. 1995 Average information REML: An efficient algorithm for variance parameter estimation in linear mixed models Biometrics 51 1440 1450
Glenn, G.M. & Poovaiah, B.W. 1989 Cuticular properties and postharvest calcium applications influence cracking of sweet cherries J. Amer. Soc. Hort. Sci. 114 781 788
Harding, P.H. 1983 Testing and cultivar evaluation 371 382 Moore J.N. & Janick J. Methods in fruit breeding Purdue University Press West Lafayette, IN
Herrington, M., Prytz, S., Greer, G.N., Hutton, D.G. & Moisander, J.A. 1996 Strawberry cultivar improvement (Queensland—subtropical Australia) Final Report for Horticultural Research and Development Corporation, Project No. Fr143
Herrington, M.E., Woolcock, L., Wegener, M., Dieters, M. & Moisander, J. 2009 Cultivar differences in tolerance to damage by rainfall Acta Hort. 842 483 486
Kendall, M.G., Stuart, A. & Ord, J.K. 1987 Kendall's advanced theory of statistics. Vol. 3, Design and analysis, and time series Oxford Univ. Press New York, NY
Knoche, M., Beyer, M., Peschel, S., Oparlakov, B. & Bukovac, M.J. 2004 Changes in strain and deposition of cuticle in developing sweet cherry fruit Physiol. Plant. 120 667 677
Knoche, M. & Peschel, S. 2006 Water on the surface aggravates microscopic cracking of the sweet cherry fruit cuticle J. Amer. Soc. Hort. Sci. 131 192 200
Knoche, M. & Peschel, S. 2007 Deposition and strain of the cuticle of developing European plum fruit J. Amer. Soc. Hort. Sci. 132 597 602
Marshall, D.A., Spiers, J.M., Stringer, S.J. & Curry, K.J. 2007 Laboratory method to estimate rain-induced splitting in cultivated blueberries HortScience 42 1551 1553
Moing, A., Renaud, C., Christmann, H., Fouilhaux, L., Tauzin, Y., Zanetto, A., Gaudillère, M., Laigret, F. & Claverie, J. 2004 Is there a relation between changes in osmolarity of cherry fruit flesh or skin and fruit cracking susceptibility? J. Amer. Soc. Hort. Sci. 129 635 641
Peschel, S. & Knoche, M. 2005 Characterization of microcracks in the cuticle of developing sweet cherry fruit J. Amer. Soc. Hort. Sci. 130 487 495
van Dijk, A., Bruijnzeel, L.A. & Rosewell, C.J. 2002 Rainfall intensity-kinetic energy relationships: A critical literature appraisal J. Hydrol. (Amst.) 261 1 23
Westfall, P.H. 1987 A comparison of variance component estimates for arbitrary underlying distributions J. Amer. Stat. Assoc. 82 866 874