Currently the conservation of endangered species is becoming more important due to the accelerated degree of ecosystem deterioration. There are collections of these species through seed banks where they germination capacity and viability of the seed have been tested as part of the conservation process by knowing the biology of these species
(Godefroid et al., 2010).
Scarification
There are several ways that the seeds can germinate, where scarification or stratification treatments are highlighted to accelerate and break the dormancy of the seeds. Through scarification it has been possible to make way for embryos to contact air and water and to germinate. The results in this work show that the mechanical scarification in the greenhouse was the best treatment form germination of seed, starting at 27 DAS. However, scarified seeds in germination chamber, obtained only the 50% of the germinated seeds (p<0.05) (Fig 2). Germination of seeds with scarification was higher than other treatments (p = 0.02). Therefore it would be deduced that
A. deceptrix has limitations for its reproduction and hence to secure their presence in the ecosystems. There are other factors that can restrict germination, such as heat and the amount of light, factors that affect other threatened species as
Asterolasia buxifolia (Collette and Ooi, 2017).
Our results resemble those of
Patel et al., (2019) who obtained the maximum germination of seeds of
A. squamosa when it was scarified and did not undergo any chemical treatment. Presumably because seed scarification reduces the seed coat size and facilitates its rupture. For example,
A. squamosa seed germination occurs in two separate and consecutive phases: 1) the rupture of the seed coat and 2) the rupture of the endosperm (
Martínez-Maldonado et al., 2013). Also, scarification is related to reducing the resistance of the seed coat so that the radicle can exit faster (
Baskin and Baskin 2004). As a result,
A. deceptrix scarified seed germinated faster than the others did. Our findings are similar to the high germination percentage in seeds of
A. muricata (84% GP) (
Ledo and Cabanelas, 1997) and
A. squamosa (80% GP)
(Adeniji et al., 2014) with mechanical scarification
.
However, in species such as
A. muricata, mechanical scarification with sandpaper or stones was not positive for germination
(Dada et al., 2019). In this case, chemical scarification with 50% sulfuric acid for 5 minutes was an efficient treatment to break dormancy in
A. muricata seeds, presenting 60% germination and soak the seeds in coconut water for 15 minutes, represented with 39% germination
(Dada et al., 2019).
Maximum germination value (2.5 germinated seeds per day) and germination energy (45%) were higher in the scarified seeds in greenhouse conditions (Table 2). Pre-germination treatments in germination chamber shown values close to zero, the germination capacity of seeds were less than 40% (Fig 3).
Imbibition in gibberellic acid and water
In this study gibberellic acid (GA
3) had not effect on seed germination; moreover, treatments with doses higher than 700 ppm of GA
3 (treatments three and four) had lower GP than the control treatment (Fig 2).
In contrast to our results seed germination in other Annona species have shown favorable results with GA
3. For instance, good results were obtained using low concentrations
in vitro conditions with 3 mg GA
3 in
A. reticulata and
A. cherimola (86 and 82% GP respectively)
(Kudikala et al., 2018; Padilla and Encina, 2003), 50 and 100 mg GA
3 + mechanical scarification in
Annona squamosa L. and
Annona cherimola Mill. x
Annona squamosa L. (75 and 44% GP respectively)
(Stenzel et al., 2005); 600 mg GA
3 in
Annona squamosa L. (95% GP) up to 800 mg GA
3 in
Annona cherimola L. and
Annona muricata L. (83 and 62% GP respectively)
(Lobo et al., 2007), these results are the opposite of the result of this study. The lowest germination capacity (35%) was observed in seeds in T4 (800 mg L
-1 of GA
3) under greenhouse conditions and 25% in treatments T2, T3, T4 (600,700,800 mg L
-1 of GA
3) germination chamber conditions.
These results show that concentrations above 600 ppm can cause germination problems and the best results in different species of Annona are in low concentrations of gibberellic acids, a condition that is similar to
A. squamosa species
(Jain et al., 2017).
In this case, many times the embryo in the seeds is covered by an impermeable membrane and the micropyle is the only entrance through which water enters, as happens in
A. cherimola (
De Smet et al., 1999).
Seed imbibitions in water for 48 hours showed the lowest germination capacity (20%) in the germination chamber,
Ledo and Cabanelas (1997) also found the lowest result (7%) in the imbibition of
A. muricata seeds in water for 24 hours, half our study.
Low germination of Annonas
Low germination of
A. deceptrix in natural conditions coincides with the available literature of
Annonas spp., e.g. seeds of
A. cherimola Mill. X
A. squamosa L. without pre-germination treatments had 1% GP
(Stenzel et al., 2005) and
A. reticulata 8.8% GP
(Kudikala et al., 2018). These results showed that these species struggle to maintain a high population in natural conditions. The time it takes for the seeds to germinate is also another limitation and species such as
A. crassiflora can take up to 150 days to germinate (
Da Silva et al., 2007). In this study, the seeds with the lowest germination percentage (20%) were those imbibed in water for 48 hours in the germination chamber and the ones that took longer to germinate (34 DAS) were the control seeds in greenhouse conditions.
There are other factors that affect the germination of the Annona seed, such as the position inside of the fruit and the presence of a micropylar woody plug in the case of
A. macroprophyllata (
González-Esquinca et al., 2015)
.
Endangered species should receive special treatment, since there are no major basic studies about them. Currently, the references available related to Annonaceae family or genus, they are in commercial species, but there are no major reports in endangered species. Due to this, it becomes necessary to study on reproductive aspects of the species and determine the type of dormancy present in they, as in this case,
Ribes echinellum, threatened species located in Southeastern US it has morphophysiological dormancy, which indicates that it needs hormonal treatments for germination (
Negrón-Ortiz, 2018).
This study highlight that germination capacity of
A. deceptrix depends on some factor that breaks the dormancy of the seed and if in natural conditions it does not find any factor that promotes this process; the species permanence of this species in ecosystems is at risk. Likewise, this seed possess a high germination capacity but it needs to break seed dormancy in a short time. In addition, it has been observed that there are insects that perforate the ripe fruits and damage the embryo. This situation further increases the low seed germination rate by decreasing the number of viable seeds.
Our result confirms that A. deceptrix is a species that deserves special attention, as well as with other threatened species;
A. deceptrix is forgotten and underutilized because it does not have an economic value, yet that is why
in-situ and
ex-situ conservation strategies
(Kour et al., 2018) are vital until species domestication program could be achieved
(Sakthivel et al., 2019).
