Biostimulant compositions and their use in processes for the interruption of bud dormancy

Abstract

Biostimulant compositions for bud growth in fruit trees comprising bacteria capable of producing HCN, and processes for stimulating bud growth of fruit trees in vivo are described.

Description

DESCRIPTIONTitleBIOSTIMULANT COMPOSITIONS AND THEIR USE IN PROCESSES FOR THE INTERRUPTION OF BUD DORMANCYTechnical field

[0001] The invention relates to the field of products and agronomic practices in agriculture and, in particular, to the removal of bud dormancy in fruit trees.Present status of the art

[0002] As is known, fruit species typical of temperate zones (such as apples, pears, kiwifruit, table grapes, cherries, peaches, nectarines, apricots, blueberries, plums) require a period of vernalization in order to break bud dormancy.

[0003] The "chilling requirement" for removing bud dormancy varies from species to species and also among different cultivars of the same species. This issue is particularly important in Actinidia (kiwifruit), since the cultivation area of this crop is expanding considerably, including new regions suitable due to pedological characteristics (e.g., Greece, Southern Italy, especially Calabria), but with winters too mild to allow uniform bud break. For similar reasons, the problem also arises in general for pome and stone fruits (apple, pear, apricot, plum, peach, nectarine, cherry), which likewise suffer from excessively mild winters.

[0004] The lack of uniform bud break results in a reduction in the number of buds opening and a delay in flowering, which often occurs asynchronously, with a low number of flowers and poor pollination, leading to consequences both on fruit yield and on fruit quality and size.

[0005] Until a few years ago, plant growth regulators (pesticides) based on HCN (such as Dormex® or Hi-Cane®) were available on the market to promote bud break in fruit plants, but these products were withdrawn due to the risks they posed to operators, their negative environmental impact, and the harmfulness of potential residues left on treated fruits.

[0006] Therefore, at present there are no products available to standardize bud break (or interrupt dormancy), precisely when this practice is becoming increasingly necessary due to global warming.Objects and summary of the invention

[0007] The present invention relates to the interruption of bud dormancy by means of biostimulant compositions comprising bacteria that progressively produce hydrocyanic acid(HCN).Brief description of the drawings

[0008] Fig. 1 is a diagram showing, on the ordinate axis, the percentage of bud break in kiwifruit compared to the Control (no treatment), treatment with Dormex®, and treatment with various strains of bacterial species producing HCN.

[0009] Fig. 2 is a graph showing the survival (expressed in days) of various HCN-producing bacterial strains once applied to the plant.Detailed description of an embodiment of the invention

[0010] The present invention makes it possible to solve the above-mentioned problems through biostimulant compositions comprising bacteria capable of producing HCN, to be used for field spraying on plants to be treated.

[0011] According to the invention, bacteria capable of producing HCN include, for example, bacteria belonging to the families Microbacteriaceae, Balillaceae, Morganellaceae, Oxalobacteriaceae, Pseudomonadaceae, Rhizobiaceae, Azospirillaceae, Enterobacteriaceae, and Xanthomonadaceae.

[0012] More specifically, according to the invention, bacteria capable of producing HCN include: Microbacterium sp., Bacillus pumilus, Providencia rettgeri, Massilia sp., Pseudomonas parafulva.

[0013] The TABLE below reports the results of metabolic tests carried out on pure cultures of the different bacteria, showing HCN production by various strains in their growth solution.TABLE

[0014] Among the bacteria indicated, only Pseudomonas parafulva B4 / 3 produces HCN as a gaseous compound, whereas the other strains produce it in the liquid phase.

[0015] The production of HCN in the liquid phase is particularly advantageous as it allows greater control of its release on the plant and a more localized application.

[0016] These strains can be used to promote bud break in fruit plants under mild winter conditions.

[0017] The compositions according to the invention may be in liquid form: solutions, suspensions (optionally frozen), or in solid form: powders, water-dispersible granules, frozen or microencapsulated granules.

[0018] The liquid compositions may contain bacteria in amounts typically ranging from 105to 107CFU mL-1, whereas the solid compositions preferably contain bacteria in amounts of 109CFU mL1.Experimental Section

[0019] The bacterial strains mentioned above were cultured, according to known techniques, for 24 hours at 27°C in LB (Lysogenic Broth) medium supplemented with glycine (4.4 g L-1) and maintained under constant agitation (150 rpm) until a high population was obtained (ca. 109CFU mL1). At the end of fermentation, the bacterial cells were separated from the culture medium by centrifugation and optionally frozen, dried, or lyophilized under a nitrogen stream according to known techniques. The solid compositions will preferably contain 109bacteria per gram.

[0020] If desired, the above-mentioned compositions may further comprise cryoprotectants (such as sucrose, trehalose, mannitol), osmoregulators (such as proline), sugars or amino acids commonly used to promote bacterial growth in the plant, and surfactants (such as pinophen or rapeseed oil) to facilitate adhesion to the plant and dispersion.

[0021] For field use, the compositions thus obtained are suspended in tap water (or sterilized deionized water) preferably at a concentration of 106CFU mL1; additionally, if desired, aqueous solutions of MgSC (preferably 10 mM) may be used for dilution.

[0022] In general, field spraying is carried out using aqueous suspensions of solid products: powders, water-dispersible granules, as well as frozen or microencapsulated formulations prepared to increase shelf life and extend expiration date.Field Treatment

[0023] The suspensions obtained as described above were applied to kiwifruit buds (Actinidia chinensis var. chinensis) with a manual sprayer until complete wetting. The bacteria were applied to the plants prior to bud break (early March), and efficacy, expressed as the percentage of buds opened, was monitored daily over the following 30 days. To verify the ability of these bacteria to colonize the plant, kiwifruit branches were treated after budbreak and, every 5 days, 3 leaves were collected. These leaves were agitated in MgSC (10 mM) to extract bacteria from the leaf lamina. The washes were serially diluted 1:10 and plated on solid growth medium (LBA) supplemented with cycloheximide 100 pg mL1to prevent fungal contamination. After 24 hours at 27°C, the colonies grown were counted. A similar experiment was also conducted on previously disinfected leaves to verify whether naturally resident microbial populations on the leaves influenced plant colonization.

[0024] Two controls were used: untreated and treated with Dormex® at 4% (positive control). The results are shown in Figure 1.

[0025] As can be seen, none of the untreated buds (control) opened because the chilling requirement had not been met. Dormex® induced bud break in 30% of the buds. The bacterium M29 (Massilia sp.), which produces the highest amount of HCN, induced bud break in nearly 60% of the buds.

[0026] Furthermore, as shown in the graph of Figure 2, these bacteria are able to survive for more than 20 days on the plant while maintaining a high population (ca. 108CFU ml_1). After 20 days, the population begins to decline.

[0027] It should be noted that the bacteria are able to colonize the plant in such a way as to gradually release the active principle without reaching concentrations hazardous to the operator.

[0028] A further advantage is that the bacterial populations are already naturally present on the plant and, to date, no accumulation of HCN in the fruits has been reported.

[0029] The invention therefore allows bud break in fruit plants in temperate zones to be promoted and made uniform even in cases where the chilling requirement has not been met.

Claims

CLAIMS1. Compositions for the interruption of fruit tree bud dormancy comprising bacteria that progressively produce hydrocyanic acid, wherein said bacteria are selected from the group comprising: Microbacterium sp., Bacillus pumilus, Providencia rettgeri, Massilia sp., Pseudomonas parafulva.

2. Compositions according to claim 1, wherein said compositions are in the form of suspensions or solutions, possibly frozen.

3. Compositions according to claim 1, wherein said compositions are in the form of powders, water-dispersible granules, or microencapsulated granules.

4. Compositions according to claim 2, wherein said compositions contain a bacterial concentration ranging from 105to 107CFU mL-1.

5. Compositions according to claim 3, wherein said compositions contain a bacterial concentration of 109per gram.

6. Compositions according to claim 3, wherein said compositions comprise cryoprotectants, osmoregulators, sugars or amino acids capable of promoting bacterial growth in the plant, and surfactants.

7. Compositions according to claims 1-6 for the treatment of Pomaceae, Drupaceae, and kiwifruit.

8. Process for promoting bud break in fruit plants, wherein compositions according to claims 1-6 are employed.

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