Fruit Size and Crop Load Influences Diurnal Growth in Peach

Peach and other Rosaceae fruits exhibit sigmoidal diurnal fruit growth with shrinkage and rehydration during the day and growth at night. Productivity can be enhanced at harvest by cumulative increase in fruit size by either higher diurnal growth rates or longer periods of diurnal growth or both. We report here results from two diurnal fruit growth studies. The first study (2005-06) compared diurnal growth of 23 medium (36.9 +/- 0.39 mm) and 25 large (40.6 +/- 0.70 mm) fruits from the processing peach cultivar 'Tatura 204'. The second study (2006-07) compared diurnal growth of 36 small fruits of one size from 'Tatura 204' at each of two crop loads-Non-thinned (21.0 +/- 2.9 fruit per trunk cross sectional area (TCSA)) and thinned (5.0 +/- 0.002 fruit per TCSA thinned at reference date). The daily phases of growth were determined by assessment of points of inflection on diurnal growth curves generated from 20 minute readings over stage 3 of rapid fruit development. These phases were end of growth/start of shrinkage; end of shrinkage; start of rehydration; and start of growth which were used to determine the daily periods and rates of shrinkage, rehydration and growth. Our simulation results suggested 10 fruits as optimal to reliably determine the differences in the points of inflection due to fruit sizes. The crop load experiment showed a significant increase in growth rate under the thinned treatment but no alteration in the phases of growth. In the fruit size experiment larger fruit had both a significantly higher growth rate and a longer period of growth than medium sized fruit. Whilst the start of diurnal fruit growth in peach has previously been shown to be delayed by water stress, under non-water stressed conditions both the time of fruit growth commencement and cessation were important determinants of fruit size.