J. Besset

Fruit quality and leaf photosynthesis in response to microenvironment modification around individual fruit by covering the fruit with plastic in nectarine and peach trees

Summary The effects of covering fruit with clear plastic film during the final stage of rapid fruit growth were investigated on ‘Big Top’ nectarine and ‘Opal’ peach over three years. Covering fruit with plastic film modified the microenvironment around the fruit, particularly by increasing relative humidity and temperature during the day. These modifications influenced fruit development, fruit quality and leaf photosynthesis. Covering fruit with plastic film significantly reduced the dry matter content, either for fruit flesh or for total fruit, the content of total soluble solids in fruit fresh, and leaf photosynthesis under high light intensities (photosynthetically active radiation in excess of 1000.m.mol.m–2.s–1) as compared with uncovered control fruit. The relationship between photosynthetic rate and other leaf physiological responses showed that the depression of photosynthetic CO2 assimilation was related to reduced stomatal aperture and increased leaf temperature. It is suggested that the stomatal aperture may be considered as the trigger or promoter and leaf temperature as the regulator of photosynthesis under a lower sink-source ratio.

Peach fruit growth in relation to the leaf-to-fruit ratio, early fruit size and fruit position

Summary To study the influences of assimilate availability, early fruit size and fruit position on fruit growth, experiments were conducted on an early-maturing peach (Prunus persica) cv.‘Alexandra’ in 1992 and a late-maturing peach cv.‘Suncrest’ in 1993. Leaf-to-fruit ratio (LFR) was used to manipulate assimilate availability. For each LFR, the distribution patterns of fruits along the fruit-bearing shoot were adjusted to one of four situations: 1) fruits were uniformly distributed on the leafy shoots; 2) fruits were located on the basal part of the fruit-bearing shoot with leaves on the distal part; 3) fruits were located on the distal part of the fruit-bearing shoot with leaves on the basal part; or 4) half of the fruits were distributed along the leafy shoots and the other half on the distal part of the fruit-bearing shoot. The fruit-bearing shoot base was girdled and the apical bud was removed. Fruit growth was expressed as dry weight calculated from continuously measured diameter. The effects of LFR, fruit position and early fruit size were analysed using a linear mixed-effects model. The results showed that LFR increased fruit dry weight and advanced fruit maturity date. Early fruit size had a significant influence on fruit growth. Fruit position slightly influenced its growth. Fruit closer to leafy shoots appeared to have higher fruit growth than more distal fruit, especially when there was intense assimilate competition. However, in most cases, the effect of fruit position was not significant.

Effects of fertilizer rates and dates of application on apricot (cv Bergeron) cropping and pitburn

Abstract Various nitrogen (N) and potassium (K) fertilizer rates and dates of application were assessed in an apricot orchard. High N fertilization enhanced vegetative growth, yield and average fruit weight and aggravated fruit pitburn incidence. Increasing K fertilization enhanced fruit soluble solids and colouring, but did not affect pitburn. Pre-harvest versus post-harvest applications of fertilizers did not influence vegetative growth, yield or average fruit weight, but tended to reduce fruit soluble solids and colouring. At all times of evaluation of pitburn, there was a positive correlation between fruit N content and pitburn incidence. Furthermore, for a given fruit N content, pitburn appeared to increase with the duration of conservation. A high fruit N content has to be considered as a main predisposing factor for pitburn in apricot. A negative correlation between pitburn incidence and fruit Ca content also was detected a week after harvest.

Does dry matter partitioning to fruit in early- and late-ripening peach (Prunus persica) cultivars confirm the branch autonomy theory?

Summary We studied dry matter partitioning to fruit by establishing different patterns of fruit distribution between and within main branch units (scaffolds) on early (cv. ‘Alexandra’) and late (cv. ‘Suncrest’) maturing cultivars of peach (Prunus persica L. Batsch). The desired fruit loads were obtained by differential thinning of scaffolds and the commercial crop-load per tree was maintained. Each tree had four main scaffolds, one of these scaffolds was lightly thinned (High-crop scaffold), another one was heavily thinned (Low-crop scaffold) and the different fruit bearing stems (FBS) were alternately lightly thinned or heavily thinned in two scaffolds (Alternative-scaffold). Growth of fruits and of leafy shoots on all FBS were measured periodically from hand-thinning 30 and 50 days after full-bloom (DAFB) until harvest for cvs. ‘Alexandra’ and Suncrest, respectively. The mean fruit dry weight (DW) per FBS was strongly affected by fruit distribution between and within scaffolds in the late cv. ‘Suncrest’, indicating that branch autonomy was functional at the level of FBS in this case. In the early cv. ‘Alexandra’, mean fruit DW per FBS in each scaffold was similar, suggesting C-transfer between individual FBS. Branch autonomy could not be explained by fruit sink-strength being equal in both cultivars. In contrast to generative growth, vegetative growth was similar between scaffolds in both cultivars suggesting its independence from fruit sink removal.

The consequences of cultural practices on growth and cropping of peach trees subjected to localized irrigation: Effects of soil management, nitrogen fertilization and tree density

SUMMARYCultural practices were studied in peach tree orchards irrigated with microsprinklers, herbicide strips being maintained along the tree rows. Differences in fruit cropping between treatments varied in the same way as tree vigour, the most vigorous trees having the highest production capacities. Concerning soil management, ground cover vegetation (permanent or temporary) improved fruit production compared with soil cultivation. According to leaf analysis, ground cover vegetation appeared to ameliorate the conditions of trees nutrition. This effect was probably mainly due to increasing soil resistance to compaction; applying organic matter was not effective in improving the performance of trees grown with soil cultivation compared with those grown with ground cover vegetation. Increasing fruit tree density also contributed to increased fruit production. Nevertheless, more than 600 trees per hectare did not allow further increase in fruit yield for the experimental cultivar. Lastly, nitrogen fertiliza...