Flower Induction – Hormonal and Substrate Control

1. Flower Induction – Hormonal and Substrate Control Karthik-Joseph John Horticultural Sciences Department University of Florida

2. Monselise and Halevy. 1964. Chemical Inhibition and Promotion of Citrus Flower Bud Induction.

3. Introduction Gibberellic acid inhibits flower formation in apples, pears, peaches and many other plants First paper to study the effect of GA on citrus flower induction Study the GA effect on citrus and to better understand the timing of bud induction Use of anti-GA or other growth regulators to induce flowering in lemons as an alternative to withholding irrigation

4. Materials and Methods Experiment 1: Shamouti oranges – 1 branch/tree on the southern part of each tree Treatments – 200 ppm of GA sprays for 3, 4, 5 or 6 times at 2-week intervals from November 3 4 replications per treatment Flowers were counted on the branches on April 5 Sprouting vegetative buds were recorded on January 1 and February 12

5. Materials and Methods Experiment 2: Eureka lemons – 2 branches/tree on the south-eastern side Treatments – 2 sprays of 0.2% Cycocel, 0.2% B Nine, 50ppm BTOA or 500ppm GA Flower buds, flowers and fruitlets less than 2 cm in diameter were counted on Nov. 4 Withhold irrigation for 2 months starting mid-august???

6. Results and Discussion Experiment 1: GA spray inhibited flower formation GA treatment delayed flower differentiation No statistics

7. Results and Discussion Very few flowers differentiate if GA effect lasts during the main induction period No statistics

8. Results and Discussion Experiment 2: No flowering in control and GA treated trees BTOA induced maximum flowering No statistics

9. Results and Discussion Effect of BTOA on citrus leaves Rolling of leaf margins in leaves of the new growth produced under the influence of the chemical Formation of flower clusters at the apex of the young branches “Leaf symptoms found with GA are well known”

10. Overview Abstract is missing Experimental design is not mentioned Only southern part of the tree is used – so results may not represent the overall effect What is the basis for selecting the conc. of GA? No statistical analysis In experiment 1, data for measurements on Jan 1 is missing No details on the leaf symptoms due to GA Typing error?

11. Discussion

12. Guardiola et al. 1977. Gibberellic acid and flower bud development in sweet orange.

13. Introduction • The inhibitory effect of GA is used to control alternate bearing • The mechanism of the inhibitory action is unknown Earlier hypothesis: • GA interferes with flower induction • GA may reverse flower bud to a vegetative apex through an indirect mechanism • A different mechanism of action of GA on flowering is observed

14. Materials and Methods Sweet orange trees – Navelate and Washington navel No other details were given in materials and methods

15. Results and Discussion GA sprays during winter greatly reduced flowering The effect depends on the concentration and time of application Absolute values were not presented

16. Results and Discussion There is decrease in the leafless type of inflorescences with a parallel increase in the vegetative shoots

17. Results and Discussion Number of leaves per shoot increased but there was no change in the number of flowers

18. Results and Discussion Inhibition in flowering is mainly due to decrease in number of shoots of RF and S types

19. Results and Discussion The buds in the more apical nodes started growth earlier and in a greater number than in the more basal GA did not affect the proportion of shoots which abscise during early phases of development No statistics shown in figure

20. Overview The main effect of GA lies in the inhibition of bud development Insufficient information about the materials and methods Statistical analysis is not show for the figure Results and interpretation were difficult to understand

21. Discussion

22. Davenport. 1983. Daminozide and Gibberellin Effects on Floral Induction of Citrus latifolia.

23. Introduction Tahiti limes grown in southern Florida are ever bearing Heavy flushes of flowers – Jan., Feb. and March Fewer flowers – several times throughout the year Majority of production – summer months It is desirable to induce heavy flowering in any flush to increase off season crop

24. Materials and Methods 18 year old Tahiti lime trees 3 treatments – 0.1mM GA, 2500 ppm daminozide and distilled water control 4 replications per treatment First experiment: Treatments applied in mid-August at the onset of summer flush 3 sprays in one week period Daminozide concentration – 500 ppm Total number of new shoot and shoot type were observed in mid-September

25. Materials and Methods Second experiment: First spray was done in mid-December, prior to spring flush 2 weekly sprays of 500 ppm daminozide followed by 4 weekly sprays of 1000 ppm These were followed by 2500 ppm daminozide prior to and during the spring flush GA and control were applied at all times

26. Results and Discussion The flush was vegetative which is typical for that time of year No tendency to flower in daminozide treatment GA increased the number of shoots produced The morphology of vegetative shoots in the GA treatment was comparable to control and daminozide treatment

27. Results and Discussion GA treatment shifted shoot type from predominantly flowering to mainly vegetative Daminozide inhibited flowering

28. Overview Materials and methods were not organized together Details of experimental design and statistical analysis were not mentioned The data from the west side of the trees are not reliable – the western side was crowded due to closely placed adjacent rows and so there was shading and also the sprays were unable to cover completely on this side

29. Discussion

30. Garcia-Luis et al. 1986. Inhibition of flowering in vivo by existing fruits and applied growth regulators in Citrus unshiu

31. Introduction Flowering in citrus is inversely related to the previous crop This could be due to an interference in the build-up of reserves and hormonal imbalance This study investigates the time course of flowering inhibition by the fruit This effect is compared to the application of GA Also studied the effect of kinetin, ABA and 2,4-D

32. Materials and Methods 10 year old Owari Satsuma mandarin Randomized Block Design with single whole tree replicates 5 µL drop of 200 ppm solution of growth regulator was placed directly on the bud Growth regulators GA, ABA, kinetin and 2,4-D were used 10 most apical buds from each twig from previous summer were selected 20 twigs were selected for each compound Application – from middle Dec. to middle Jan. Whole tree spray was also done using the chemicals

33. Results and discussion Only GA reduced the number of sprouted nodes

34. Results and discussion Similar response was obtained when GA and kinetin were applied to entire tree instead of locally to the buds

35. Results and discussion Influence of time of GA application on flowering No statistics

36. Results and discussion Influence of time of GA application on spouting

37. Overview Most data support the work done earlier The inhibitory effect of GA and kinetin on bud sprouting contrasts with the promotive effect found when applied to non-flowering seedlings and young trees Good experimental design Statistics is done but no statistics is shown for figure 3

38. Discussion

39. Koshita et al. 1999. Involvement of endogenous plant hormones (IAA, ABA, GAs) in leaves and flower bud formation of satsuma mandarin (Citrus unshiu Marc.)

40. Introduction This paper investigates the effect of the levels of endogenous plant hormones in relation to flowering The relation to other plant hormones was not simultaneously investigated The aim of this study is to clarify the relationship between flower bud formation and plant hormones (IAA, ABA, GA1/3, GA4/7) contents

41. Materials and Methods 25 year old satsuma mandarin 8 lateral branches consisting of only vegetative shoots were chosen in each tree 4 of them are ringed 60 fruit bearing shoots are selected in each tree

42. Results and Discussion

43. Results and Discussion IAA and ABA contents in the leaves

44. Results and Discussion GA content in the leaves

45. Overview In October, higher endogenous GA levels may be one of the reasons for vegetative growth in the following spring In Dec. and Feb. only slight difference was observed in GA content between bearing and vegetative shoots – this supports the work of others Increase of leafless inflorescence and enhancement of ABA in Dec. and Feb. and of IAA in Dec. suggests that endogenous ABA and IAA may affect flower bud development

46. Discussion

47. Jona et al. 1971. Further Studies on the Effect of Nucleic Acids on Shoot and Flower Formation in Citrus Trees.

48. Introduction FUdR is a specific DNA synthesis inhibitor which promotes flowering in citrus This controls flower formation at the stage of cell division in the growing apex This paper deals with the effects of this chemical on flower and shoot formation The role of cell division in flower formation was studied by applying FUdR and TdR during the induction and differentiation period

49. Materials and Methods 36 year old Shamouti orange trees TdR and FUdR were applied either alone or in combinations at 10-3 M Each chemical solution was brushed on leaves, stem and buds of 10 spring branches beginning Oct. 17 Application was repeated at 10 day intervals There were 2 series of treatments. In one the last treatment was applied on Dec. 17 and in another on Jan. 18

50. Results and Discussion Effects on the number of sprouting buds during the spring flush No statistics