Variables related to fruits and seeds can vary between plants of the same species, reproductive years, or even within the same plant (Lovatel et al. 2021). Seed size is one factor influencing seedling emergence through the quantity of reserves present in the seed (Pádua et al. 2010). Furthermore, fruit biometric variables also help in the plant breeding of several species, quantifying phenotypic divergence through quantitative and qualitative descriptors (Abud et al. 2018), and it is also possible to extract genotypic values from these attributes. Therefore, the genetic variability within and between tree populations can be characterized by fruit and seed biometry, and can also be related to environmental factors, helping conservation and genetic improvement programs of species (Silveira et al. 2019).
Genotypic variances (σ²g) smaller than the residual variances (σ²e), in all variables, result in low or intermediate levels of heritability. In other words, the effect of the environment (residual variance) was predominant in the genotypic effect of the progenies. Heritability is the parameter that determines phenotypic traits that well represent the genetic gain of progenies. The amount of phenotypic plasticity is a consequence of the genotype, and it is a reliable guide to use in genetic selection (Moraes et al. 2015; Silva et al. 2018).
The coefficients of determination of the matrix effects (c²parc) were low because there is a significant interaction between the sites in which each one is inserted (area, soil, pollen source, etc.), resulting in the high genetic variability of the progenies (Santos 2021). This result is expected because, in allogamous species, it is common for genetic diversity to be greater within than between populations, or in this case, seed trees (Golunski et al. 2015; Siqueira et al. 2021).
Seed biometry is an efficient criterion to verify genetic divergence among individuals (Lovatel et al. 2021). It should also be noted that the heritability coefficient, in the strict sense, reflects how much of the phenotypic variation, observed in a quantitative character, is heritable due to the additive gene effects transferred from parental individuals to their descendants (Costa et al. 2010). Due to lack of information on family structure, in this work, the heritability coefficient in the strict sense could not be calculated.
The collection of reproductive material from seed trees with better emergence rates and fruits with attractive characteristics, helps in the genetic improvement of forest restoration projects. The genetic quality of the sources of material is essential for the establishment, rapid growth, and sustainability of tree populations (Jansson et al. 2016; Mazhula et al. 2021). Kavaliauskas et al. (2021) recommends that seed collection evaluation should depend on attributes such as the number of viable and reproductive individuals, CBH, and height. They also highlight the importance of selecting material sources based on phenotypic characteristics and genetic diversity criteria.
Also, Kijowska-Oberc et al. (2020) brings up the issue of proper conservation of seed stocks in gene banks since phenotypic plasticity plays an essential role in plant adaptation to environmental changes. Reserves with greater genetic diversity, with populations grown in different locations, have a better chance of surviving under new climatic conditions. Given the importance of genotype selection and the rapid development of phenotyping technology, it is becoming increasingly important to know how additional phenotypic traits can improve the prediction accuracy for a target trait (Arouisse et al. 2021).
However, since forest restoration projects rarely consider the genetic diversity associated with seed quality for their development, there is a lack of market demand for native species that meet these needs. Thus, expanding knowledge about the diversity of high-quality native seed species is critical (Atkinson et al. 2021).
The G. americana population of the Saltinho Biological Reserve is a good source of reproductive material for the species since seed trees 1, 4, and 6, respectively, were genetically satisfactory to be designated for this purpose. However, it should be noted that it is not recommended to select only three seed trees for a restoration or conservation project with allogamous and dioecious species. Considering the assumptions of Nunes (2021), based on a mean of 441 seeds and a variance of 1,458, this work has an effective population size of 12 and a potential inbreeding for the restoration project of 4.16%. For this to occur, it is necessary, for the restoration project, for seedlings to be formed from all these seeds, implanted, and conducted, without any mortality.
Melo et al. (2021) found a low effective population size for G. americana of 2.69 and 3.27 in a natural population (NP) of Sergipe and progeny test (PT), respectively, due to the high outcrossing rate between related trees. The number of alleles for both populations ranged from 8 to 23, with 96 alleles and a mean of 13.7. Of these, 19 alleles were deprived of the NP population and 15 from the PT population. Therefore, the number of seed trees needed for the collection was 56 in NP and 46 in PT. From this, the authors recommend that the same number of male and female trees should be maintained in each progeny to maximize the effective population size of the parental population of G. americana for offspring production.
Manoel et al. (2015b) obtained a mean effective population size of 2.5 and a mean number of alleles of 23.5 in a population of G. americana in São Paulo. In this work, it was recommended to collect seeds from at least 60 seed trees. Ancestry must be reduced and effective sample variance increased for ex situ conservation and forest restoration. Collecting seeds from multiple trees helps achieve these parameters.