Genetic variation and parameters
Nine of the twenty descriptors evaluated show no variation between the experimental plots (CC, CS, CSC, GH, LAS, LBS, LLS, LMS, SC) and were discarded from the statistical analysis. The descriptors evaluated in this study were adapted from P. peruviana (González et al. 2008), once there is no official descriptors list for P. angulata. Despite the similarities and phylogenetic proximity between P. peruviana and P. angulata, this could be the cause of the lack of variation of these descriptors. Between the eleven descriptors submitted to Deviance Analysis, PH and TSS showed significant genetic variability at 1% and 5% of probability, respectively (Table 1), indicating that these traits have potential for genetic breeding.
The relative high values of residual variance found in many of the descriptors evaluated in this study (Table 1) could be due to high environmental interference, including for PH and TSS. There was observed considerable variance within plots and this can be explained due to the species had not yet undergone genetic improvement and there is still no well-established crop system. Moreover, despite P. angulata is considered a self-pollinated species (Menzel 1951; Saavedra et al. 2019; Sadiyah et al. 2021), a recent study of reproductive biology classified the species as a facultative self-pollinated (Figueiredo et al. 2020), indicating that the accessions may not be homozygous lines, with genetic variation within and between plots of the same treatment.
We found an average TSS of 11.75 ºBrix, varying from 10.73 to 12.90 ºBrix, with plots reaching 13.77 ºBrix. These values are higher than those found by Sadyah et al. (2020) (9.06-11.66 ºBrix) and Golubkina et al. (2018) (4.9-9.7 ºBrix), evaluating P. angulata in Est Java-Indonesia and Moscow-Russia, respectively. High SSC are desirable because its associated with the sweetness of the fruits, a factor that influence the consumer choice (Curi et al. 2018), although the high SSC can be harmful for the storage time, since it favors the fermentation and deterioration processes of the fruits (Silva et al. 2013). According to Rodrigues et al. (2012), P. peruviana fruits reach about 14.21 ºBrix in their physiological maturation stage. Our results showed that P. angulata fruits can almost reach the SSC values of P. peruviana, even that the accessions of this study did not pass through genetic improvement.
Although there was no significant genetic variation for NFP and WFP, two important traits related to fruit yield, there were a high phenotypic variation between treatments. NFP varied from 90.55 to 316.53 and WFP varied from 107.57 g to 483.16 g. Considering the row spacing used in this study, we could estimate yields varying from 2151 kg.ha-1 to 9663 kg.ha-1.
Information about crop systems in P. angulata are still incipient and the absence of good control of the environment can elevate the residual variance. Besides that, the species has not yet been domesticated (Souza et al. 2016), and the possibility that the accessions may not be homozygous can also increase residual variance. So, we believe that there is genetic variance between the accessions but new experiments need to be proceeded for evaluate this variation.
High genetic variation for yield traits have been found in P. peruviana (Herrera et al. 2011; Kumar et al. 2017), indicating a potential to produce more than 15 t.ha-1 (Herrera et al. 2011). Using the maximum value of WFP found in our studies, we found that some plots reached potential yields of 16 t.ha-1 of fruits, with the hybrid Can x Laj reaching 9.3 t.ha-1, on average, reinforcing the potential of P. angulata to be a Brazilian crop. It is important to mention that to reach those high yields in crop conditions, not only genetic breeding but the establishment of the ideal crop system for the culture is necessary.
We found broad-sense heritabilities 0.53 and 0.41 for PH and TSS, respectively (Table 1). Kumar et al. (2017) found a similar heritability for PH (0.51) in P. peruviana, and Leiva-Brondo et al. (2001) found heritabilities of 0.53 and 0.87 for TSS in P. peruviana evaluated in glasshouse and outdoors, respectively. The heritability coefficients are measures that vary depending on the genetic variability in the genotypes, the environment conditions and the nature of the trait. Both PH and TSS are considered quantitative traits (Silva et al. 2019), but we believe that as the crop system of P. angulata is being developed, higher heritability coefficients will be found in future experiments.
Correlations
There were observed negative phenotypic correlations between PH and SD (-0.266), FPP (-0.236), WFP (-0.247), LFL (-0.331) and TFL (-0.371) (Table 2), indicating that plants with lower plant height at 45 days had more fruits, with bigger size and higher weight. Saavedra et al. (2019) evaluated wild and weedy populations of P. angulata in Mexico and found similar correlations between height of the plant at 90 days and number of fruits per plant and average fruit weight. Observing the plants in the experimental field, it was observed that smaller size plants showed more ramifications and consequently more fruiting branches. According to Santiaguillo et al. (1998) and Peña-Lomelí et al. (2008), the number of branches is an important yield compound in Physalis. This way, PH shows perspectives to be used in indirect selection for yield traits.
Total soluble solids were positive correlated with SD (0.355), FPP (0.426), WFP (0.397), LFL (0.199) and TFL (0.249), indicating that plants which have good yield traits tend to have also more soluble solids in the fruits, a good scenery for the genetic improvement of the species. Correlations between TSS and weight of five ripe fruits (Silva et al. 2019), number of fruits (Pellizzaro et al. 2020) and weight of the fruit with calyx (Herrera et al. 2011) were also previous reported for Physalis species.
Positive phenotypic correlations were also observed between NFP and LFL (0.595), TFL (0.591) and WFP (0.973), indicating that plants that had the highest number of fruits tend to have bigger fruits with greater weight. These founds show good perspectives to genetic breeding since indicates that is possible to select for both increase the number, size and weight of the fruits. Silva et al. (2019) also found positive correlations between NFP and fruit longitudinal and transversal lengths.
Heterosis and heterobeltiosis, combining abilities and selection index
Heterosis and Heterobeltiosis were observed for PH and TSS in both ways (increasing and decreasing) (Table 3). Hybrids Pi x G53 (5.91%), Can x Pi (1.30%) and Can x LG (1.14%) showed heterobeltiosis for increasing TSS, while hybrids G53 x Laj (-8.83%), Pi x Can (-8.62%), G53 x Can (-6.22%), Laj x Pi (-4.75%), Laj x G53 (-3.91%), Can x Laj (-2.29%) and Pi x Laj (-2.29%) showed negative heterobeltiosis. Regarding PH, negative heterobeltiosis was observed in hybrids G53 x LG (-21.57%), Pi x Laj (-12.82%), and Can x Laj (-4,02%), while hybrids LG x Can (18.31%), LG x G53 (15.19%), Laj x LG (12.10%), Can x LG (9.13%). G53 x Can (7.55%), LG x Laj (2.79%) and G53 x Pi (2.00%) showed positive values.
The occurrence of heterosis and heterobeltiosis indicates the presence of non-additive effects controlling PH and TSS in P. angulata. The species has been considered a self-pollinated species (Menzel 1951; Saavedra et al. 2019; Sadiyah et al. 2021), but Figueiredo et al. (2020) suggested that the species is a facultative autogamous. Despite heterosis and heterobeltiosis are phenomena associated with cross-pollinated plants, they were observed in many traits in autogamous plants. However, studies evaluating heterosis, heterobeltiosis and combining ability in Physalis traits are incipient. Lagos et al. (2007) and Montejo et al. (2015) found heterosis effects for TSS in cape gooseberry (P. peruviana) and tomatillo (P. ixocarpa) hybrids, respectively. Regarding plant height, Sahagún-Castellanos et al. (1999) found heterosis effects evaluating tomatillo hybrids.
Evaluating GCA and SCA, we considered negative values to be ideal for PH, since this descriptor was negative correlated with yield traits. Accessions LG, Can and G53 showed negative GCA for PH, and seven hybrids showed negative SCA (Table 4). Regarding to TSS, we considered positive values to be ideal, since high TSS values are associated to the sweetness of the fruits, a trait which best suits the fruit market. Accessions Can, Pi and G53 showed positive GCA for TSS, and ten hybrids showed positive SCA. The accessions Can and G53 showed negative GCA for PH and positive GCA for TSS, so they can be considered the best parents for crossings. Five hybrids showed both negative SCA for PH and positive GCA for TSS (LG x G53, Can x Laj, Can x Pi, Can x G53 and Pi x Laj).
Higher GCA effects indicate a greater role of additive effects controlling the traits, while higher SCA effects point to the importance of non-additive effects controlling the characteristics (Zhao et al. 2014). The presence of additive and non-additive effects controlling fruit traits indicates that the development of both homozygous lines and hybrids must be considered in P. angulata breeding programs. Additive and non-additive effects was also observed in traits of P. peruviana (Lagos et al. 2007) and P. ixocarpa (Montejo et al. 2015).
Using Additive and Mulamba-Rank indexes for PH and TSS, hybrids Can x G53, Can x LG, Pi x G53, Can x Pi and G53 x Pi were selected as the best P. angulata hybrids for both PH and TSS (Table 5). These hybrids had good performance and are from at least one of the parents with higher GCA, agreeing with the proposed by Cruz et al. (2012). It is expected that crossings using genitors with higher GCA lead to populations with higher means and crossings with higher SCA lead to populations with more variability (Mendonça et al. 2002). Considering this, hybrid Can x G53 have the higher potential to develop P. angulata populations with high mean and variability.
The occurrence of heterosis and heterobeltiosis in our study suggests that the use of hybrids in P. angulata must be considered aiming to increase yield and quality fruit traits. Additionally, the best hybrids can be used to produce segregating populations which can be applied to proceed genetic breeding or to make genetic studies. This is the first report of diallel analysis and occurrence of additive and non-additive effects in P. angulata traits. Further studies are needed to find the best conditions for evaluating P. angulata germplasm, especially for fruit traits.