The effects of ethylene on plants have been recognized since the Nineteenth Century and it is widely known as the phytohormone responsible for fruit ripening and for its involvement in a number of plant growth and development processes. Elucidating the mechanisms involved in the ripening of climacteric fruit and the role that ethylene plays in this process have been central to fruit production and the improvement of fruit quality. The biochemistry, genetics and physiology of ripening has been extensively studied in economically important fruit crops and a considerable amount of information is available which ranges from the ethylene biosynthesis pathway to the mechanisms of perception, signaling and control of gene expression. However, there is still much to be discovered about these processes and the objective of this review is to present a brief historic account of how ethylene became the focus of fruit ripening research as well as the development and the state-of-art of these studies at both biochemical and genetic levels.

The production of five new somatic hybrids with potential for improved disease resistance is reported herein. Protoplast isolation, fusion, and plant regeneration was achieved from Caipira sweet orange (Citrus sinensis L. Osbeck) as an embryogenic parental source and Volkamer lemon (C. volkameriana Pasquale), Cleopatra mandarin (C. reticulata Blanco), and Rough lemon (C. jambhiri Lushington) as non-embryogenic parental sources. Fusion involving Cleopatra mandarin and Rangpur lime (C. limonia L. Osbeck) as embryogenic parental sources with Sour orange (C. aurantium L.) also resulted in somatic hybrid plants. Somatic hybridization was confirmed by leaf morphology evaluation, chromosome counting, and randomly amplified polymorphic DNA (RAPD) analyses. Somatic hybrids may combine complementary characteristics from both parental sources and have potential for tolerance to blight and citrus tristeza virus (CTV).

Thinning is a cultural practice that leads to balance between fruit yield and quality. It is carried out in a short period of time and requires qualified workforce, whose shortage ends up increasing costs. This study aimed at evaluating the thinning effect of metamitron on peach trees at different periods of time after bloom. The experiment was carried out in a commercial orchard of 'Sensação' peach trees located in Morro Redondo, Rio Grande do Sul (RS) state, Brazil, in 2015-2016 crops. Treatments were the application of 200 mg L-1 metamitron, 20, 30, 40, 50 and 60 days after full bloom (DAFB), and manual thinning 40 DAFB. Fruit abscission, effective fructification, period of manual and chemical thinning, number of fruits and yield per plant, mean fruit mass and fruit caliber were evaluated. When metamitron was applied 40 DAFB, percentages of fruit abscission and fruit set, besides the number of fruits, were similar to the ones found when manual thinning was carried out. The intensity of the thinning effect of metamitron in peach trees depends on the application period.

High effective peach fruit set results in an excessive amount of fruits, requiring thinning accomplishment, which is a manual practice and demands specialized labor, raising production costs. In this sense, chemical thinning may be an alternative to improve the peach production chain. The objective of this work was to evaluate the efficiency of 6-benzyladenine (BA) on chemical thinning and the effect of different BA dosages on peach production and color characteristics of 'Maciel' fruits. Treatments consisted of plants without thinning (Control), sprayed BA at doses of 100 mg L-1 , 200 mg L-1 and 400 mg L-1 , applied 45 days after full bloom (DAPF) and hand thinning at 45 DAPF. The applications of different dosages were carried out by spraying, using backpack spraying equipment. Percentage of thinning abscission, number of fruits per plant, yield per plant, fruit mass, color and average fruit diameter were evaluated. The doses of 200 and 400 mg L-1 BA for thinning increased the percentage of fruit abscission and fruit mass. The doses of 400 mg L-1 BA presented lower yield per plant, but fruits with higher average mass. Increasing BA dose reduced the number of fruits per plant. Hand thinning and 400 mg L-1 BA resulted peach fruits with larger diameter. BA application to thin peaches did not alter the fruit skin color. Therefore, BA may be a chemical thinning alternative for 'Maciel' peach cultivar, because it reduces the time of thinning in plants when compared to manual thinning. For an efficient chemical thinning with BA the product dose must be taken into account, along with climatic conditions and the cultivar.

In the peach tree cultivation, the producer has the challenge of obtaining good quality fruits and maintaining production in a balanced way over the years. Thinning favors these parameters and reduces the fruit load on plants. Manual thinning commonly practiced on peach trees requires high labor and increases production costs. Chemical thinning as an alternative to manual thinning, which depending on the species, time and concentration, has demonstrated high efficiency. The aim of this study was to evaluate the effect of metamitron applied at different seasons and concentrations on the chemical thinning of peach trees in southern Brazil. Experiments were conducted in a commercial peach orchard (‘Maciel’ cultivar), in the municipality of Morro Redondo, Rio Grande do Sul, Brazil, during the 2015 and 2016 harvests. In experiment 1, metamitron at concentration of 200 mg L-1 was applied at 20, 30, 40, 50 and 60 days after full bloom and manual thinning performed at 40 days after full bloom. In experiment 2, metamitron was applied at concentrations of 100 mg L-1, 200 mg L-1, 300 mg L-1 and 400 mg L-1 and manual thinning at 40 days after full bloom, in addition to control plants. Fruit abscission, fruit set, total number of fruits per plant, yield per plant, average mass and fruit diameter were evaluated. Metamitron at concentration of 200 mg L-1 has thinning effect when applied before 40 days after full bloom. Metamitron concentration of 100 mg L-1 applied at 40 DAFB promoted fruit abscission superior to manual thinning. Therefore, the application of metamitron to ‘Maciel’ peach trees close to full bloom at concentration of 100 mg L-1 results in thinning practice similar to manual thinning.

Nowadays, despite of being a typically temperate fruit crop, peach is found in subtropical and even tropical altitude zones, due to breeding efforts. Genetic knowledge and phenotypic and environmental parameters directly or indirectly influence the characters of economic importance in peach, and they are of great importance for breeding programs orientation. The aim of this study was to estimate heritability of a color shade character of peach flesh, measured by the Hue angle, chroma and lightness to evaluate its distribution in the populations, testing the possible existence of maternal effect. Results showed that parameters related to color shade of peach flesh have a medium heritability. Parents selection based on phenotype allows a medium genetic improvement for the mentioned character. This heritability is predominantly additive, without maternal effect. The Hue angle is the correct parameter to be used to classify and study yellow-flesh peaches and nectarines in relation to their color shade. However, the multivariate analysis of principal components, using the three parameters Hue angle, chroma and lightness, is an alternative of high accuracy.

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Aims: The objective of this study was to evaluate peach fruits quality after chemical thinning using metamitron at different times in the South of Brazil. Study Design: The experimental design was in randomized blocks, with five replications of three plants, fruits were harvested and evaluated the central plant in the plot, and twenty fruits were evaluated in each replicate.