Of the five characteristics evaluated, only TFD and LFD showed significant variation in all environments. AFM showed significant variation in three environments, and NFP and SSC in two environments. Considering that four accessions were common in all experiments, we believe that excessive environmental variance was the main cause of not finding significant difference between the accession for AFM, NFP and SSC in some environments. Thus, there is potential for genetic improvement, but it is necessary to better control the environment, through improved cultural treatments, irrigation system and control of pests and diseases. Furthermore, the addition of new accessions from different origins can increase the genetic variability.
Fruits that present larger size and mass are more favored by commerce (Melo et al. 2017). Oliveira et al. (2011), evaluating physical, physicochemical characteristics and technological potential of camapu fruits, found mean values of 4.33 g, 21.7 mm and 18.6 mm, respectively, for the characteristics fruit weight, length and width. Tanan et al. (2018) found for P. angulata the average of 16.3 mm for transverse diameter and 15.4 mm longitudinal diameter. In the present study, mean values of close to 13 mm (TFD and LFD) and 1.4–1.8 g (AFM) were found in the experimental field, and value close to 12 mm (TFD and LFD) and 1.2 g (AFM) were found in the greenhouse. The differences found between these values in the all environments may be due to the environmental variation found in these locations, including attacks by powdery mildew on the plants in Exp1-GH, as well as the possible effect of the genotype x environment interaction.
Working with the same species in the same location, Silva et al. (2008) found an average of 8.5 mm (TFD), 8.6 mm (LFD) and 0.38 g (AFM), with coefficient of variation of 15.18%, 15.09% and 40.77%, respectively. However, Rufato et al. (2013) reported that the ripe fruit of P. angulata has an average diameter up to 15 mm, values higher than those found in the experiments of this study. Evaluating the fruits of P. peruviana, Rodrigues et al. (2014) found mean values of transverse and longitudinal diameters of 16.89 mm and 18.17 mm, respectively, in addition to a mean fruit mass of 2.843 g. It is notable that the fruit size of P. peruviana is larger than P. angulata.
Working on diallel analysis for morphoagronomic descriptors of P. angulata hybrids, Farias et al. (2022) found no significant genetic variance for weight of fruits per plant and NFP traits, but found genetic variation for plant height and SSC traits. The authors suggested that genetic variation within accessions and environmental variation may have been the reason for high residual variation in NFP. In the present work, NFP showed significant genetic variation in the greenhouse in both experiments, with a higher mean in Exp2. One of the factors that may have led to a better result in our study is the number and composition of the experimental plots. In the present study, the experiments were carried out with 24 repetitions with one plant per experimental plot, while Farias et al. (2022) used three repetitions with four plants per experimental plot. Our results suggest that is better to invest in a greater number of repetitions than experimental plots with more plants.
It can be seen that the AFM trait showed significant variation at 1% of probability in both experiments in the field. On the other hand, in the greenhouse, there was significant variation only in Exp2. This result indicates the possibility of selection among the evaluated accessions to advance the improvement of the species, based on this characteristic, although considerable residual variation is observed in some situations.
The average SSC character in this study varied from 9.23 ºBrix (Exp2-GH) to 13.58 °Brix (Exp1-EF), according to Tables 2 and 3. However, there was no significant variation in Exp2. These results can be explained, besides the high variation in the locations of the experiments, in part, due to the way of storing P. angulata fruits before the evaluation of this characteristic in the second experiment, when the fruits were frozen and stored in freezer. In Exp1, the fruits were stored in refrigerator (without being frozen).
According to Lima et al. (2009), for the commercialization of physalis (P. peruviana) fruits, the minimum value should be 14º Brix. Evaluating P. angulata fruits, Farias et al. (2022) found SSC values ranging from 10.73 to 12.90 ºBrix, while Sadyah et al. (2020) found values between 9.06 to 11.66 ºBrix, and Golubkina et al. (2018) found values between 4.9 and 9.7 ºBrix. Considering these studies, the average value of 13.58 ºBrix found in Exp1-EF was the closest to 14 ºBrix, indicating that the P. angulata species has the potential to reach the minimum SSC value required for P. peruviana commercialization, since several fruits presented values above 14 ºBrix. It is noteworthy that the accession BAAN-04 showed an average of 15.21 ºBrix in Exp1-EF, exceeding the minimum threshold for the market.
In breeding programs, the traits that have higher heritability coefficients are interesting and provide greater chance of gain by selection (Londero et al. 2006; Ramalho et al. 2012). However, the most important traits for the crop can be of low heritability. In this work, a high heritability in experimental field was found in Exp2 for the characters TFD (91.9%) and AFM (91.44%). In the greenhouse, LFD (78.44%) Epx2 and NFP (75.66%) showed the highest heritability (Exp1). The highest heritability values were found, in general, in the field experiments. Considering that these are probably quantitative traits, the values found in our study indicate great chances of gain with selection.
Few studies estimating heritabilities for P. angulata fruits are found in the literature. Farias et al (2022) found broad-sense heritability values for plant height (53%) and SSC (41%), after evaluating eleven vegetative and productive traits. This SSC value was considerably lower than those found in this work in Exp1 in the field (77.06%) and greenhouse (65.19%), indicating that increasing the number of repetitions can lead to increased heritability for fruit traits. Working with P. peruviana, Kumar et al. (2017) found high heritability values for the characters fruit diameter (96.89%), fruit per plant (82.72%) and plant height (51.27%). High heritability in tomato plants for the trait fruit per plant (84–99.5%) was also found by Basavaraj et al. (2015).
The different values of the CV found in the experiments in the two locations justify the need to estimate the coefficient of repeatability. The values of CV found in both environments, greenhouse and experimental field, for all characteristics, can be explained by the possible genetic variability within the accessions and the influence of the environment, as previously commented. Moreover, these accessions are still in the domestication stage and have not undergone the improvement process. A recent study classified the species as being facultative autogamous (Figueiredo et al. 2020), occurring intense visitation by bees during cultivation, indicating the possibility that the accessions are not homozygous lines, but have some level of heterozygosity. In addition, because the species is tetraploid, the elimination of heterozygotes during generations of self-fecundation is slower compared to diploid species. These facts increase the chance of genetic variability within the accessions.
Resende (2009) classified the repeatability coefficients: values less than or equal to 0.3% are considered low, between 0.3% and 0.6% average, and greater than or equal to 0.6% are high. According to this standard, in our study, the repeatability coefficient was low for ANOVA and structural analysis, for all characters evaluated, and medium for estimation by principal components in the most traits and environments (Tables 4 and 5). For the SSC in Exp1-EF, the repeatability coefficient was 0.72, estimated by PC-cov method, being considered high. In the greenhouse, the values found for repeatability coefficients can be classified as average by the principal components, and the highest value was found in LFD (0.51 in Exp2), estimated by the PC-cov method.
NFP is an important trait controlled by several genes and severed influenced by the environment. The repeatability values of this characteristic do not exceed 0.40, according to Lira Junior et al. (2014) in Spondia purpurea. This agreed to the experiments in the greenhouse, for which we found 0.40 in Exp1 and 0.42 in Exp2. For the experiments in the field, this character did not show significant variation. Similar values of r were found for NFP in tomato, varying from 0.3 to 0.52 (Gonzalo et al. 2022).
Only one study about repeatability in Physalis fruits was found in the literature. Silva et al. (2008), using PC-cor method to estimate repeatability coefficient in P. angulata found values between 0.2826 and 0.3765, for the characteristics number of seeds per fruit and volume of the internal cavity, respectively. The authors also estimated r for SSC (0.2389), AFM (0.2893) TFD (0.3233) and LFD (0.3233). These values were low compared to those found in this work. Studies with tomato (Abreu et al. 2006) and pout pepper (Lucio et al. 2022) showed repeatability coefficients close to the founds in our study.
A major application of the repeatability coefficient is to allow the estimation of the number of measurements required to reach a level of reliability in estimating the value of a genotype. The higher the value of the repeatability coefficient, the better the actual value of the individual can be predicted with a small number of repeated measurements; however, a large number of measurements is necessary when this value is low. With a 95% reliability in mind, in the experimental field, 7 to 21 repetitions are needed in Exp1 and 18 to 38 repetitions in Exp2. In the greenhouse, 13 to 22 replicates are needed in Exp1 and 20 to 49 replicates in Exp2. With 99% reliability, in the field, 67 to 124 repetitions were needed in Exp1, and 95 to 255 repetitions in Exp2. In the greenhouse, 137 to 207 measurements were needed in Exp1 and 94 to 200 measurements in Exp2. Thus, reaching 99% reliability proves to be unfeasible, but reaching 95% reliability may be feasible for some characteristics in the experimental field, such as LFD (21), TFD (18), AFM (13), and SSC (7). In the greenhouse, with 90% confidence, the minimum number of measurements is around 14 (AFM, TFD, SSC), 12 (NFP) and 11 (SSC).
The high number of repetitions required according to our study may be due to the fact that the accessions have not yet been fully domesticated, the possibility of genetic variation within accessions, and the environmental variation, as previously discussed. Indeed, the plants suffered several attacks of pests and diseases, including African snail (Achatina fulica), slugs, whitefly (Bemisia tabaci), mites (Aceria anthocoptes), powdery mildew, and other environmental factors. This set of factors justifies the residual variation obtained in both environments. Estimating the minimum number of repetitions is an alternative to achieve good estimates of genetic parameters with the efficient use of plant genetic resources.
According to the results found for repeatability coefficient by principal component analysis, in view of the standardization of the number of repetitions in studies with P. angulata, we found higher results in the estimation of the number of repetitions based on this method than the others (ANOVA, and structural analysis). Taking all the experiments together, we considered that 20 measurements can provide about 95% reliability for field experiments and 90% reliability for greenhouse experiments for all traits. Further studies on repeatability in P. angulata are suggested to increase the efficiency of the selective process in the genetic improvement of the species.