M. Juan

Girdling increases carbohydrate availability and fruit-set in citrus cultivars irrespective of parthenocarpic ability

Summary The effects of girdling performed at various dates were evaluated during two consecutive years in high- and low-bearing commercial orchards of ‘Fortune’ mandarin and ‘Clausellina’ Satsuma mandarin. The time-dependent response was evaluated through fruitlet abscission, final fruit-set and yield as related to carbohydrate contents in developing fruitlets. A few days after treatment, girdling increased the soluble sugars content (SSC) in fruitlets, reduced the daily fruit drop, and thereby diminished abscission. Application of girdling to low-bearing ‘Fortune’ mandarin orchards was most effective 15 d before anthesis (DBA) and 35 d after anthesis (DAA). It increased yield by 125%. In high-bearing orchards, the best results were achieved by girdling 35 DAA, which increased yield by 28%. In both orchards, the effect of girdling declined gradually from 35 DAA to the end of fruit drop. SSC values were found to be positively correlated with fruit-set at 25 DAA, but this tendency was reversed by 50 DAA. This study showed that the effects of girdling are time-dependent, and that yield can be improved in cultivars of different parthenocarpic ability.

Loquat fruit size is increased through the thinning effect of naphthaleneacetic acid

The thinning effect of naphthaleneaceticacid was examined in loquat trees (Eriobotryajaponica Lindl.). The effect depended on theconcentration applied and on the treatment date. Themost effective treatment found to thin fruit andincrease the average fruit size was the application of20 mg l−1 of naphthaleneacetic acid 10–15 daysafter anthesis. Treatment reduced the fruit resistanceto puncturing and improved total soluble solidsconcentration and coloration and, consequently,harvest time was markedly advanced.

EFFECTS OF RINGING BRANCHES ON FRUIT SIZE AND MATURITY OF PEACH AND NECTARINE CULTIVARS

SummaryRinging branches at pit hardening resulted in larger fruits and enhanced fruit colouring of peaches and nectarines. Because both together determine the time of harvest, fruit from ringed trees were picked earlier. Further, ringing resulted in advanced fruit ripening compare with controls. Results obtained were similar to those reported for girdling. Ringing is easier and quicker than girdling and represents a useful technique to improve fruit quality.

Synthetic auxin 3,5,6-TPA promotes fruit development and climacteric in Prunus persica L. Batsch

SummaryThe application of 3,5,6-TPA advances fruit maturation of peaches and nectarines through different mechanisms, depending on the fruit development stage at treatment. Treatments applied at pit hardening encourage the development of fruit, which grow faster, reach the climateric stage earlier, and can be harvested earlier. The effect is direct, since the number of fruits per tree is not reduced by the treatment and also can be obtained by applying the auxin locally to a small number of fruits per tree. Treatments applied a few days before climateric increase ethylene production without affecting fruit growth.

Effect of the synthetic auxin 2,4-DP on fruit development of loquat

Application of the butylglycol ester of 2,4-DP increased final fruit size in loquat without causing fruit thinning. Its effectiveness depended on the concentration applied and treatment date. When applied at the onset of the cell enlargement fruit stage, 25 mg l−1 was the most effective treatment. Fruit diameter distribution showed a significant shift to the larger size for treated trees; further, fruit colour break and maturation were encouraged and harvest time was earlier than in untreated trees.

Rootstock influence on the incidence of rind breakdown in ‘Navelate’ sweet orange

Summary The influence of three rootstocks, Carrizo citrange (Citrus sinensis (L.) Osb. × Poncirus trifoliata (L.) Raf.), Cleopatra mandarin (Citrus reshni Hort. ex Tanaka) and sour orange (Citrus aurantium L.) on the incidence and severity of rind breakdown in ‘Navelate’ sweet oranges was studied over seven years in four orchards. The proportion of affected fruit was greater in trees on Carrizo citrange (60% on an average) followed by Cleopatra mandarin (38%) and then on sour orange (9%). There were also significant differences in the severity of the disorder among rootstocks; more than 35% and 20% of fruit from trees on Carrizo citrange and Cleopatra mandarin, respectively, were rejected for commercialization, whereas only 4% of fruit on sour orange was rejected. Cryo-scanning electron microscopy (SEM) of fruit peduncles showed that average diameter of xylem vessel elements of peduncles of fruits on Carrizo citrange rootstock were 6% and 17% larger than those on Cleopatra mandarin and sour orange, respectively. Defoliation of fruit-bearing branches reduced water loss from fruit, maintained fruit peel water potential at a higher value than that of fruit on undefoliated branches and reduced the proportion and severity of affected fruit. It is concluded that fruit-tree water relationships are related to rind breakdown in ‘Navelate’ oranges and low fruit water content might be responsible for the disorder.

Effects of fruit load on flower bud initiation and development in peach

Summary This study aims to quantify the effects of fruit crop-load on flowering and to determine the relationships between flowering and phloem sap carbohydrate and nitrogen content fractions from budding to dormancy in ‘Zincal 5’ nectarine. Fruit load significantly reduced the number of flowers per tree both indirectly, by reducing the number of shoots per tree and the number of nodes per shoot, and directly, by reducing the number of floral buds per node. The intensity of the response depended on the number of fruits developed per tree. Trees that kept all fruits up to senescence flowered 35% less than trees thinned by hand to 40% of fruits at pit hardening, and 55% less than trees completely thinned in bloom by hand. Trees that kept all fruits had significantly lower glucose and sorbitol contents in the phloem sap of mixed branches up to harvest date and full vegetative growth, respectively, but no significant relationships were found between the concentrations of these carbohydrates and flowering intensity in the following Spring. Sucrose and fructose did not show any significant difference in regard to crop-load. In fibrous roots, starch content was not related to fruit load up to dormancy, indicating that starch content is not associated with flower bud induction and differentiation. The nitrate-nitrogen fraction was significantly higher, and the ammonium-nitrogen fraction was significantly lower, in trees that tended to flower less, suggesting some disturbance in nitrate reduction in these trees.

The effect of 2, 4-DP on fruit development in apricots (Prunus armeniaca L.)

Abstract The application of 25 mg l−1 2, 4-DP (2, 4-diclorophenoxypropionic acid butylglycol ester) at pit hardening, increased final fruit size and advanced fruit maturation in apricots. Fifteen days after treatment the differences in diameter between control and treated fruit reached a maximum and remained constant until harvest. This effect coincided with a decrease in leaf weight and, at an advanced stage of development, leaf area. This suggests a competitive relationship between fruit development and vegetative growth, although a direct effect of 2, 4-DP on fruit development cannot be discarded.

Histological and physiological study of purple spot of loquat fruit

Abstract We describe the structure of purple spot of loquat (Eriobotrya japonica Lindl.) by comparison between affected and non-affected fruit, using light and scanning electron microscopy (SEM) procedures. Water permeability rates of isolated cuticles and mineral fruit composition were also measured. SEM and light microscopy show that purple spot initially appears at the deepest rind cell layers as a fringe of compact and empty cells. As purple spot intensity increases, the number of affected cells also increases to include all rind tissue. Affected cells show a shrunken cytoplasm with an extrusion of cellular material out of the plasmalemma. Flesh cells are not damaged. The cuticle of affected fruit showed no sign of damage or disruption and the water permeability of isolated cuticles showed no consistent differences between injured and healthy fruits. Mineral composition in flesh tissue of affected and healthy fruit was similar. However, in epidermal tissue concentration of K, Fe and Cu were higher in affected fruit than in healthy fruit.

Effects of fruit thinning on fruit growth, sugars and purple spot in loquat fruit (Eriobotrya japonica Lindl.)

Summary This work examines the effects of fruit thinning on fruit growth, sugar accumulation and incidence of purple spot in loquat (Eriobotrya japonicaLindl.). Thinning increased fruit growth and sugar contents of fruit. As total sugar concentration correlated significantly with the proportion of affected fruit, we conclude that thinning increased markedly the proportion of fruit affected by the disorder. Carbohydrate accumulation may be the factor responsible for the incidence of purple spot by accelerating fruit development.