The cultivation knowledge about the Cerrado native fruits is incipient. These plants are found in wild conditions and its fruits are obtained through extraction, as the case of araticum (Annona crassiflora Mart.), which is a species with the great economic potential. This plant propagation by grafting, among other methods, has proved problematic. Possible incompatibility causes were investigated using histochemical and anatomical studies. Transverse and longitudinal stems sections were analyzed in the araticum grafting area on rootstocks of araticum-de-terra-fria (Annona emarginata (Schltdl.) H. Rainer “Terra-fria”), biribá (Annona mucosa (Jacq.) Baill), and soursop (Annona muricata L.). Araticum graft survival rate was low with these rootstocks, which seems to be associated with anatomical and histochemical factors. The periderm and pith are more developed in araticum than in the other plants, which affects the alignment and juxtaposition of the cambium and vascular bundles in the graft area, hindering a successful graft. The histochemical reactions for phenolic compounds detection were very strong in cortical parenchyma, pith and xylem fibers of araticum (A. crassiflora). The presence of phenolic compounds is increased depending on the cut for grafting and the formation of these compounds is evidenced as an important limiting factor for successful grafting. It is recommended practices for reducing these compounds and a larger diameter of the graft, as a mean to overcome these anatomical difficulties.
The Cerrado region covers 204 million hectares, mainly distributed in the states of Minas Gerais, Goiás, Mato Grosso, Mato Grosso do Sul, Tocantins, Bahia, Piaui, Maranhao, and the Federal District, corresponding to approximately 22% of Brazil’s territory [
According to [
Araticum has a low germination rate of seeds and, according to [
The grafting compatibility is understood as one in which the union is successful and that has the satisfactory development forming a single plant composition. When that does not happen, we have a graft incompatibility [
Affinity includes the plant’s morphological and physiological aspects. The morphological and anatomical affinities as well as tissue formation affinities refer to the two plants’ conductive vessels which are compatible for showing similar diameters and in aproximately equal number. The physiological affinity is related to the quantity and composition of the sap [
This study aims to evaluate the graft incompatibility in propagation of araticum (A. crassiflora Mart.) on three rootstocks: araticum-de-terra-fria (Annona emarginata (Schltdl.) H. Rainer “Terra-fria”), biribá (Annona mucosa (Jacq.) Baill) and soursop (Annona muricata L.), all belonging to Annonaceae.
The graft’s anatomical and histochemical analysis were performed in the Laboratory of Plant Anatomy, in the Department of Botany, Faculty of Biology, University of Brasília.
The rootstocks remained in a nursery with 50% shade screen and sprinkler irrigation once a day, suspending it on rainy days. The cuts were made with carbon steel blades sharpened and cleaned with soap and water. The cuts were made quickly and accurately, uniting the graft and rootstock with plastic tape. The araticum’s scion collected had a diameter similar to the rootstock, for better juxtaposition of the cambium tissue, and were cut into sections containing about 4 buds and wrapped in paraffin film for subsequent use in grafting. The grafted plants were covered with transparent plastic bags, measuring 30 cm long by 5 cm wide. Plants were always inspected for weed control and pests and diseases monitoring. Spraying with insecticides, acaricides or fungicides were not necessary during the experiment conduction and plants were not fertilized after grafting.
Slides with sections were obtained by microtome table. The grafting union area was underwent to anatomical histochemical analysis. Anatomical characterization was carried out using transverse and longitudinal sections of stem in area of grafting, performed in microtome table and clarified for 30 minutes in a solution of 50%. sodium hypochlorite. The sections were dyed for 1 min with 1% safranin and alcian blue in 5:1 ratio with water. The sections were placed on glass slide and coverslip with water.
For histochemical tests, samples of stem in the graft area were fixed in formaldehyde, acetic acid and ethyl- alcohol (FAA) 50% and stored in a 50% alcohol solution for later use in testing [
For these parameters analysis, boards were made with pictures taken from slides observed under a optic microscope.
In araticum, the presence of phenolic compounds is increased by cutting and these compounds formation is the main limiting factor of grafting success. Phenolic compounds are associated with plant defense against pathogens and herbivores [
. Ocurrence of phenolic componds in the stem tissues of Annona crassiflora, Annona muricata, Annona mucosa, and Annona emarginata var. terra fria evaluated by the potassium dichromate test and Iron (III) chloride. (+) presence; (−) absence; (+/−) weak reaction Legend: Iron (III) chloride = ICIII; PD = potassium dichromate
Tissues/structures | Annona crassiflora | Annona muricata | Annona mucosa | Annona emarginata var. terra fria | |||||
---|---|---|---|---|---|---|---|---|---|
Phenolic compounds | |||||||||
ICIII | PD | ICIII | PD | ICIII | PD | ICIII | PD | ||
Periderm | + | + | + | + | +/− | +/− | + | + | |
Phloem | Cortical parenchyma | + | +/− | + | + | − | − | − | − |
Fibers | − | − | − | − | − | − | − | − | |
Sieve tube element | − | − | − | − | − | − | − | − | |
Radial parenchyma | − | − | +/− | − | − | − | − | − | |
Phloem ray | − | − | + | + | − | − | − | − | |
Cambium | − | − | − | − | − | − | − | − | |
Xylem | Axial parenchyma | − | − | − | − | − | − | − | − |
Radial parenchyma | − | − | +/− | − | − | − | − | − | |
Vessel element | − | − | − | − | − | − | − | − | |
Fibers | − | − | − | − | − | − | − | − | |
Inner phloem | − | − | − | − | − | − | − | − | |
Pith, parenchyma, fibers | + | + | − | − | − | − | − | − |
zone. The biriba rootstock showed weak responses on the phloem sieve tube with Iron (III) chloride. In biribá rootstock, there were positive reactions to the Iron (III) chloride, showing formation of phenolic compounds in the periderm and phloem fibers.
Due to the low araticum grafting survival rate on rootstocks, we proceeded the anatomical and histochemical study in the grafting area, to assist in addressing the causes of these low rates. Histochemical tests revealed the presence of phenolic compounds in parenchyma cells of the grafting area, being very pronounced in araticum tissues. During the development of the experiment, the rootstocks sprouted in the area below the graft because apical dominance breaking by grafting methods. This fact shows that the rootstocks were seen to be stronger and able to develop. Most grafts that did not work, presented bud necrosis, dry-looking, with little time after grafting. Two grafts showed buds swelling at 45 days after grafting, but a graft, with the English method showed a little development of the bud and then immediately died. The other graft, with the method simple English, was able to develop, but with little vigor.
According to [
It was noted differentiated araticum anatomy in relation to rootstocks, because it shows larger periderm and pith with the same diameter shoots, affecting the juxtaposition of cambium and vascular bundles and making the successful grafting difficult (Figures 1(A)-(D)). It was observed that the grafting area had no evidence of callus formation, except in a case of araticum grafting on the araticum-de-terra-fria rootstock and according to [
The presence of tyloses was also described by [
Since phenolic compounds are essential to the lignin synthesis, they represent an important cell walls component whose structure varies depending on constitution of phenolic compound type, between plant species and between cell types [
In the araticum grafting on araticum-de-terra-fria rootstock it was noticeable that the union was not complete and only a part of the grafting area formed a differentiated callus. Even 12 months after the procedure, the grafted plant showed little vigour and swelling in the area above grafting area, typical symptoms of morphological incompatibility. According to [
It can be observed in
Transverse section of the stem. (A)-(D) Anatomical differences between species. (A) Annona crassiflora Mart.; (B) Annona emarginata (Schltdl.) H. Raine; (C) Annona mucosa (Jacq.) Baill.; (D) Annona muricata L.; (E) Stem in secon- dary growth of A. crassiflora grafting region on A. emarginata; (F) Absence of callus on the grafting of A. crassiflora on (A) muricata region; (G) (H) Phenolic compounds in A. crassiflora on A. mucosa (orange colour: potassium dichromate, black: Iron (III) chloride
to be more efficient and rapid on grafted coffee. The long period of domestication and grafting in orange is not comparable with the little knowledge we have about araticum, where there seems to be a requirement to align the cambium, such as with coffee.
The cambium is a meristematic area, therefore able to divide, which is important for the new tissues formation such as xylem and phloem, which are responsible for crude and elaborated saps transportation, respectively [
In the araticum grafting on the soursop rotstock, it was observed that the grafting region showed no hint of callus formation, suggesting that there was incompatibility localized and immediate. Araticum presents different anatomy in relation to soursop, with more developed pith and periderm compared to soursop, making the juxtaposition of parenchymatous tissue and cambium difficult. There was a phloem reaction to Iron (III) chloride and in the araticum cut surface, besides the presence of tyloses in soursop, both identifiable by the reaction to ferric chloride and with potassium dichromate (
In the araticum grafting on the biribá rootstock, the phenolic compounds formation were found near the grafting area, in the secondary phloem and secondary xylem of both species (
According to [
An incompatibility in Uapaca kirkiniana Müell Arg. was studied by [
Araticum grafting on rootstocks of soursop, biribá, araticum-de-terra-fria proved to be unfeasible due to incompatibility with the rootstocks tested. Phenolic compounds were identified in the region of grafting, especially in parenchymatic cells in araticum stems.