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Small fruit size is a limiting factor in marketing apples ( Malus × domestica ). Several techniques have been used to improve this trait, among them blossom and fruit thinning with plant growth regulators such as auxins and cytokinins to reduce crop load. In the present study, carried out in three consecutive years (2011–2013), we evaluated the photosynthesis inhibitor metamitron (MM) as a thinner for ‘Gala’ apples. MM applied twice at 150 g/ha (in the form of 0.085% Brevis ® ) at the 6- and 10-mm diameter stages, or once at 180 g/ha (0.1% Brevis ® at 1200 l/ha) at the 6-mm stage, resulted in significant thinning. Consequently, the average time spent on hand thinning was reduced from 40–80 day/ha to 10–20 day/ha. However, crop load was only slightly affected, depending on the year. In “ON” years, there was a considerable and significant shift to larger fruit size. The relatively low effective doses of MM, compared to those used in Europe and the USA, were likely due to the higher night temperatures for 3 weeks postapplication, which increased respiration and caused assimilation deficiencies during that critical period of fruit development. No negative effects were observed on the return bloom in the following year.

Introduction. Small fruit size is a limiting factor in marketing apple (Malus ×domestica ). Several techniques have been used to improve fruit size, among them blossom and fruit thinning with plant growth regulators such as auxins and cytokinins to reduce crop load. Materials and methods. In the present study, carried out in 3 consecutive years (2012–2014), we evaluated the photosynthesis inhibitor metamitron (MM) as a thinner for ‘Golden Delicious’ apple. Results. MM applied once at 180–225 g ha-1 (150–190 mg L-1 in the form of 0.1%–0.125% Brevis® at 1200 L ha-1 ) at the 6-mm fruit-diameter stage increased dark-adapted chlorophyll fluorescence, measured as a reduction in Fv/Fm values and resulted in significant fruit thinning. Consequently, the average time spent on hand thinning was reduced from 20–30 days ha-1 to 2–5 days ha-1 and there was a considerable and significant shift to larger fruit size. Discussion. The relatively low effective doses of MM compared to those used in Europe and the USA were likely due to the higher night temperatures for 3 weeks postapplication, which increased respiration and caused assimilation deficiencies during that critical period of fruit development. Conclusion. In a warm growing environment the thinner MM is highly effective on apple, since only one application (FB+7) of relatively low dose (190 mg L-1 MM as 0.125% Brevis® ) is enough for optimal fruitlet thinning.

The vegetative and reproductive performances of ‘Coscia’ pear ( Pyrus communis L.) grown on nine rootstocks [OHF 69, OHF 97, OHF 217, OHF 333, OHF 513 and BP 1 ( P. communis ), clonal seedling (Davis AxB) of Pyrus betulifolia and quince BA 29 and EMA ( Cydonia oblonga )] were compared during a 9-year period. The trial was conducted at the Experimental Station ‘Avnei Eitan’ in northern Israel (elevation 400 m above sea level, a.s.l.), on a well-drained soil with pH 7.1. Trees were planted in December 1998, spaced at 4.0 m × 2.0 m and trained with a central axis. The most vigorous trees were on P. betulifolia seedlings, followed by the four OHF rootstock (69, 97, 333, 513) and BP 1 (with no significant difference between them). All the above rootstocks demonstrated greater vigor than OHF 217 and quince BA 29 or EMA. The highest cumulative yields per tree were harvested from trees on the four OHF rootstocks (69, 97, 333, 513) and P. betulifolia followed by the BP 1. The two quince rootstocks, as well as OHF 217, had the lowest cumulative yield and the lowest yield of large fruit. A positive correlation was found between the vigor of the tree, as affected by the rootstock, and both the total yield and the fruit size. We conclude that in a warm climate, yield efficiency is not the only parameter that should be taken into account, and building a strong tree for a weak cultivar is the first requirement for establishing an orchard.