ProCa Treatments Research Articles

Effects of prohexadione-calcium with three rates of phosphorus and chlormequat chloride on vegetative and generative growth of tomato

The aim of this study was to analyze the effects of prohexadione-calcium [(Regalis ® )(100 mg L -1 )] and chlormequat chloride (2000 mg L -1 ) on vegetative and generative growth of tomato plant. An underlying aim was to evaluate the growth of plants treated with pro-Ca with three phosphorus rates (40, 80 and 120 mg L -1 ). Pro-Ca was applied to plants either as a spray or medium drench, while chlormequat chloride was applied only as a spray. Results show that inhibiting effect of pro-Ca and chlormequat chloride applications on seedling height were significant and these two chemicals produced smaller seedlings compared to the control. Height reduction with chlormequat chloride was 56%, while with pro-Ca treatments it varied from 46 to 55%. Effects of chemicals on total weight of two trusses were not significant, although spray of pro-Ca together with the 40 mg L -1 phosphorus rate was promising in relation to chlormequat chloride and control plants. Based on the results of this study, it seems likely that pro-Ca, having an inhibiting effect on stem elongation without a negative effect on total weight of two trusses would be sufficient to control stem elongation. However, further researches are needed to suggest a strong opinion whether the pro-Ca treated tomato plants give same responses in every independent application of this chemical. Key Words : Prohexadione-calcium, chlormequat chloride, growth rate, seedling height, tomato.

PLANTING YEAR PROHEXADIONE-CALCIUM TREATMENT INCREASES THE CROPPING POTENTIAL AND YIELD OF STRAWBERRY

The yield of strawberry (Fragaria x ananassa Duch.) is dependent on the number of inflorescences initiated in the apical meristems of the main and branch crowns. Branch crown formation is enhanced by short-day (SD) conditions while long-day (LD) conditions promote runner formation from the axillary buds of the main crown. Gibberellin (GA) and GA biosynthesis inhibitor application studies indicate that the fate of axillary buds is also affected by GA. We tested if prohexadione-calcium (ProCa), the inhibitor of GA biosynthesis, could be used to regulate vegetative and generative growth of strawberry in northern European conditions. SD cultivars 'Polka' or 'Honeoye' were sprayed with 0-200 mg/L ProCa concentrations during the planting year in six experiments. ProCa had a positive effect on both cultivars, but the results varied between the experiments. ProCa reduced the number of runners in five experiments and increased crown branching in three experiments during the treatment year. Reduced runnering and/or increased number of crown branches correlated with 23-53% increase on the number of inflorescences and, consequently, berry yield in four cases during the following year. In conclusion, in the northern European climate runner and branch crown formation can be controlled with single timely ProCa treatment during the planting year resulting in a significant increase of the yield during the following season.

Vegetative Growth and Flowering of Primocane Raspberry ‘Ariadne’ as Affected by Prohexadione–calcium Treatments

Maintaining an appropriate balance between vegetative and generative growth is a prerequisite for profitable raspberry (Rubus idaeus L.) production. The objective of our study was to test the effect of prohexadione–calcium (ProCa) on vegetative growth and flowering of primocane fruiting red raspberry ‘Ariadne’ in greenhouse conditions. ProCa was applied either once or twice in a concentration of 100 ppm or 200 ppm. Double applications of ProCa reduced cane height by 33 cm (100 ppm) or by 46 cm (200 ppm). Growth reduction was the result of shortening of the internodes, because total node number in plants was unaffected. Furthermore, cane diameter was reduced in plants treated with 200 ppm ProCa. ProCa treatments reduced the total aboveground dry weight by 32% to 55% but did not affect the allocation of dry weight into different plant parts. All ProCa treatments reduced the number of flowers by 22% to 42%. In conclusion, ProCa proved effective in controlling vegetative growth of red raspberry. However, because the number of flowers was reduced, ProCa cannot be recommended for growth regulation of primocane fruiting raspberry without further studies.

Physiological effects of prohexadione-calcium in apple trees: effects on parameters related to photoproductivity

SummaryDifferent prohexadione-Ca (RegalisTM, Pro-Ca) treatments were applied as foliar sprays to ‘Royal Gala’ and ‘Smoothee Golden Delicious’ apple trees to asses its effects on different physiological traits, under the growing condition of the Middle Ebro Valley (Spain). The application of Pro-Ca resulted in a decrease in leaf area, as well as fresh and dry leaf weights, and an increase in specific leaf weight. Greater light penetration through the canopy was recorded, indicative of a lower canopy density, resulting both from the inhibition of shoot growth and leaf extension growth. In addition, increases in leaf chlorophyll concentrations, and photosynthetic rates were found, which could account for the lack of effect of Pro-Ca on overall tree growth.

Nursery plant production controlled by prohexadione-calcium and mechanical treatments in strawberry cv. ‘Honeoye’

SummaryResponses to an inhibitor of gibberellin biosynthesis, prohexadione-calcium (Pro-Ca) at 0.01% (w/v), applied at three different times during nursery plant production, was tested in June-bearing strawberry (Fragaria ananassa Duch.) cultivar ‘Honeoye’ under cool-climate, long-day conditions. The effects of mechanical manipulation, detaching runner plants from the mothers, were also tested on the same dates. The treatment dates were 12 August, 24 August and 2 September 2004 which corresponded to day-lengths of 16, 15 and 14 h, respectively. After lifting on 11 November, and sorting into size categories, the plants were cold-stored and their performance was subsequently investigated under greenhouse conditions. Mother plant growth was decreased by the first two Pro-Ca treatments. A Pro-Ca application on 12 August also decreased the number of runners, and the total number of daughter plants was reduced by 30%.This reduction was highest in the smallest plant category, which was the most abundant.All Pro-Ca treatments increased the dry mass of the crown and the roots of plants in the smallest size category. The Pro-Ca treatment on 12 August enhanced crown-branching in the largest size category, and increased the number of inflorescences in these plants when grown in the greenhouse. All Pro-Ca treatments increased the number of flowers in inflorescences of plants in the smallest size category. In contrast, plant production did not benefit from the detachment of runners from mothers, suggesting that this nursery practice has no advantageous consequences.

Differential effects of prohexadione-calcium on red colour development in ‘Royal Gala’ and ‘Fuji’ apples

SummaryTwo different spray programmes for split application of prohexadione-calcium (ProCa) were tested on ‘Royal Gala’ and ‘Fuji’ apple trees (Malus domestica Borkh.) to evaluate their effect on red colour development in the fruit. Applications of ProCa split into two sprays at full-bloom and 60 d after full-bloom (DAFB) were sufficient to control shoot growth in these cultivars. A third application (95 DAFB) did not result in any additional beneficial effects. In addition to obtaining significant reductions in shoot elongation, reductions in leaf area were also noted. No effects on yield or on various fruit quality parameters resulted from the ProCa treatments, with one important exception, fruits from ‘Fuji’, a late-season cultivar, displayed a greater percentage of fruit surface with red colour. Simultaneously, a deeper red colour was recorded on the blushed side of the fruit, resulting from greater concentrations of anthocyanins and carotenoids. In contrast, fruits of ‘Royal Gala’, a mid-season cultivar, did not show differences in fruit colouration following treatment with ProCa.

Prohexadione-calcium modifies growth and increases photosynthesis in strawberry nursery plants

Prohexadione-calcium (ProCa) at an active ingredient concentration of 62.5 mg L-1 was applied as a foliar spray to Camarosa and Sweet Charlie strawberry (Fragaria × ananassa Duchesne) plants in growth chambers to assess its effects on dry weight allocation and growth over 42 d. The height, leaf number, leaf area, and specific leaf area (SLA) of daughter plants and the total dry weights of their leaves, stems and roots were all affected by ProCa treatments. Treated plants weighed less than untreated plants for the first 28 d after treatment, but by 42 d, all plants were similar in total weight regardless of treatment. ProCa-treated plants consistently allocated more dry weight to roots, and proportionally less to shoots, and were reduced in height, leaf area and SLA. ProCa increased net photosynthesis in plants grown in growth chambers and in the field. Plants grown in the field responded to ProCa earlier, and their photosynthetic rates were higher (i.e., 23–34% higher in daught ers and 34–41% higher in mothers) than those grown in growth chambers. Key words: Fragaria × ananassa, gibberellin biosynthesis inhibitor, growth analysis, net photosynthesis

Shoot growth control of pear trees ( Pyrus communis L.) with prohexadione-calcium

Prohexadione-calcium (ProCa) is a gibberellin biosynthesis inhibitor with limited persistence and low toxicity that has recently been registered as a shoot growth retardant for apples in North America (Apogee ®) and Europe (Regalis ®). We investigated the response of six different pear cultivars (‘Rosemarie’, ‘Forelle’, ‘Packham's Triumph’, ‘Flamingo’, ‘Early Bon Chretien’ and ‘Golden Russet Bosc’) to ProCa in the Western Cape, South Africa, over the period 1999–2003. ProCa treatments ranging from 50 to 250 mg l −1 were applied between one and three times per season and were compared with girdling and control treatments. ProCa application reduced shoot growth in all of the cultivars. ‘Forelle’, was least responsive and showed a reduction in 2002/2003 but not 2001/2002. ‘Rosemarie’, ‘Flamingo’, ‘Packham's Triumph’ and ‘Golden Russet Bosc’ were most responsive, with shoot growth being reduced by up to 50% of the control for the latter two cultivars. The response to number of applications and ProCa concentration was not consistent across cultivars. ‘Early Bon Chretien’, for example, only responded to high ProCa concentration, whereas ‘Rosemarie’ was very responsive at the lowest ProCa concentration. ProCa application improved fruit set but decreased final fruit size in some of the cultivars, particularly in ‘Rosemarie’. It also caused a decrease in return bloom in ‘Forelle’ and ‘Packham's Triumph’. The response of different cultivars to girdling, in terms of shoot growth and fruit set was highly variable. Girdling tended to increase final fruit size and return bloom. ProCa shows potential as a shoot growth retardant for the pear cultivars investigated, but the response of reduced fruit size in some cultivars requires mitigation. Future research on combined girdling and ProCa treatments may be instructive.