4.1. Genetic Tolerance of Accessions to Ph and Asp
The high tolerance observed in certain accessions to
Ph aligns with the findings of Arafa et al. (2017) [
63], who reported resistance in the LA1777 accession. Similarly, the tolerance shown by NGB00699 and NHT0206a is consistent with the resistance levels reported for tomato accessions LA1352, LA2855, LA1347, LA1718, and LA1295. The moderate tolerance identified in other accessions correlates with accessions LA1269, LA1578, LA3152 (Ph-2), LA3151 (Ph-2), and LA4286 (Ph-3), which showed moderate resistance. The moderately susceptible accessions noted in this study are comparable to LA2196, while the susceptible accessions observed reflect patterns reported for accessions such as LA1252, LA1772, LA1223, LA1378, LA1367, LA1340, LA0716, LA1674, LA1478, LA1594, LA2646, and LA2009 (Ph-1).
Finally, the highly susceptible accessions correspond to the findings for accessions LA1303, LA1302, LA0751, LA1649, LA0443, LA1586, LA1561, LA0413, LA2147, LA1579, LA1617, LA1633, LA2391, LA3123, LA3161, LA1246, LA0375, LA0114, LA1237, LA1469, LA1256, LA1242, LA1343, LA1935, LA0446, LA2581, LA1333, and super strain B [
63]. The tolerance levels observed in various lines are consistent with the findings of Arafa et al. (2017) [
63] across similar accessions, confirming the validity of these accessions as benchmarks for tolerance studies. The variations observed in tolerance and susceptibility among the accessions can be attributed to genetic backgrounds. This highlights the significant role that genetic factors play in determining the response of accessions to pathogens, with tolerant accessions likely carrying specific genetic traits that confer tolerance, while susceptible ones may lack these protective genetic factors. Therefore, the genetic makeup of each accession is a critical determinant of its ability to cope with pathogen stress. The classification of tolerance and susceptibility provides a robust framework for identifying promising lines for further breeding programs. However, the variability in susceptibility highlights the importance of selecting tolerant accessions for environments prone to severe stress.
The high level of tolerance observed in
Asp-infected accessions aligns with the findings of Aguilar-Gonzalez et al. (2017) [
64], who reported a high level of tomato tolerance to
Asp under three treatments using essential oil. Similarly, the tolerance noted in certain accessions is consistent with results from a related study utilizing a 3/4M treatment, which revealed 8 out of 20 positive cases following
Asp inoculation. Furthermore, the moderately tolerant accessions observed in this study are in agreement with the same study, where a 1/2M concentration of essential oil treatment resulted in a 10 out of 20 infection rate after
Asp inoculation. Meanwhile, the susceptible accessions identified correspond with the findings of Sale et al. (2018) [
65], who reported susceptibility in
Siria and
UTC varieties of tomatoes (
Solanum lycopersicum). These findings underscore the effectiveness of certain treatments in enhancing tolerance and highlight the variability in response among tomato varieties and lines.
4.2. Chromosomal Deletions After Pathogen Infection
This study demonstrates that the deletion of chromosomes occurs in tomatoes during infection by
Phytophthora infestans (
Ph) and
Aspergillus (
Asp), indicating complex host–pathogen interactions and cytological effects. Pathogen infections are shown to induce genomic stress, leading to chromosomal alterations.
Ph infection causes the deletion of chromosomes, leading to the loss of host genes related to the genetic traits of resistance/tolerance and reactive oxygen species control, resulting in genomic changes, including deletions in chromosome number, particularly in susceptible tomato accessions [
66,
67]. Similarly,
Asp infections are associated with metabolic disruptions that destabilize genome integrity. Chromosomal instability, such as deletions leading to aneuploidy, may arise as a result of pathogen-induced genomic pressure, weakening the plant’s defense mechanisms [
41]. These findings highlight the cytogenetic consequences of pathogen infection and their potential role in modulating plant defense responses.
The chromosomal deletions observed in certain accessions that were treated with
Ph differed from the findings of Bal and Abak (2007) [
68] and El-Mansy et al. (2021) [
69], who reported a diploid chromosome number of 2n = 2x = 24 in untreated tomato roots. These deletions were specifically observed under pathogen stress, indicating that these accessions, unlike the untreated ones, were susceptible to the pathogen. This suggests that
Ph may induce chromosomal deletions as part of its infection strategy. Furthermore, the highest chromosome number of 2n = 2x = 26, reported by Bal and Abak (2007) [
68] and El-Mansy et al. (2021) [
69], was not observed in certain accessions and the control that showed tolerance, which retained the standard diploid chromosome number of 2n = 2x = 24. The discrepancies between the current study and previous findings can likely be attributed to differences in experimental treatments and conditions. However, the presence of the diploid chromosome number in
Ph-tolerant accessions is consistent with the findings of Wang et al. (2006) [
54], Song et al. (2012) [
70], Gerszberg et al. (2015) [
71], Singh et al. (2015) [
72], Mesquita et al. (2019) [
73], and Waiba et al. (2021) [
21], supporting the stability of the chromosomal state under normal conditions.
Chromosomal deletions were observed in certain accessions, indicating susceptibility, while other accessions and the control accessions retained a diploid state of 2n = 2x = 24 chromosomes in
Asp-treated plants, indicating tolerance. These findings suggest that
Asp treatment induces chromosomal deletions in susceptible tomato accessions. The observed chromosomal deletions contrast with reports by Bal and Abak (2007) [
68] and El-Mansy et al. (2021) [
69], who documented a diploid state of 2n = 2x = 26 chromosomes in tomato. This discrepancy may result from differences in experimental treatments or plant genotypes used across studies. The genomic instability induced by pathogen–host interactions appears to underlie the chromosomal deletions observed in this study, as infections likely disrupt cellular processes critical for maintaining genomic integrity. Conversely, the diploid state observed in tolerant accessions aligns with findings from Brasileiro-Vidal et al. (2009) [
74], Pavan et al. (2009) [
75], Bhala and Verma (2018) [
76], and Brake et al. (2022) [
22]. These consistent results reinforce the hypothesis that genomic responses to stressors, including
Asp treatment, are accession-specific and highlight the role of
Asp in genomic destabilization within susceptible tomato genotypes.
4.3. Variance Components, Heritability, and Genetic Advance of Growth Characteristics
The analysis of growth traits under
Ph treatment revealed a strong environmental influence, as indicated by the higher PV and EV compared to GV. This suggests that the growth traits are highly susceptible to pathogen attacks, with environmental factors playing a more prominent role than genetic factors in shaping phenotypic variation. The high ECV further supports this, demonstrating the substantial impact of environmental factors, particularly the pathogen, on the traits studied. The heritability values for these traits were low, reinforcing the conclusion that genetic contributions are minimal, and most of the observed variation was due to the pathogens and the environmental conditions. The low GA across all traits, along with moderate to high GAM for some traits like NL, suggests limited potential for genetic improvement in these growth traits under pathogen stress. This is consistent with findings from Meena et al. (2018) [
77], who reported similarly low GA values for PH under pathogen stress. The moderate to high GAM for certain traits further emphasizes the role of environmental effects, suggesting that these traits may respond more readily to environmental manipulations rather than selective breeding for genetic resistance.
Contrastingly, studies like those of Pooja et al. (2022) [
78] and Phom et al. (2016) [
79] have reported differing levels of genetic contribution to traits such as PH and NL, which may reflect differences in genotypes and treatment conditions across different geographic regions. These discrepancies underscore the complexity of genotype–environment interactions and highlight the challenges of improving these traits genetically under pathogen stress. The high PCV observed in this study for traits like NL and LL, coupled with moderate GCV, contrasts with the results of studies like Yadav et al. (2017) [
80], where lower GCV and PCV values were observed. These differences may be due to variations in experimental conditions, such as genotype or pathogen strains, and emphasize the role of environmental factors in shaping trait expression.
This study also revealed the strong environmental effect on traits like LW and SG, which showed a low genetic contribution, as evidenced by the low GV and high PV for these traits. This aligns with the findings of Tripura et al. (2016) [
81], who similarly observed a high environmental influence on SG. However, the heritability values for these traits indicated susceptibility to pathogen attacks, in contrast to other studies where genetic resistance was the dominant influence, such as those by Yadav et al. (2017) [
80], where LW was predominantly under genetic control. These differences again highlight the importance of considering genotype–environment interactions when assessing the impact of pathogens on phenotypic traits. In summary, the dominance of environmental factors, particularly pathogen treatment, over genetic factors in determining the growth traits studied suggests that improving resistance to pathogens in these traits may require strategies beyond traditional genetic selection. These may include optimizing environmental conditions or breeding to gain increased tolerance to environmental stress. The discrepancies observed between this study and previous research also highlight the influence of experimental variables such as pathogen strains, genotypic diversity, and environmental conditions on phenotypic outcomes.
The results of this study highlight the dominant influence of environmental factors, specifically
Asp, on the phenotypic variation in growth traits, particularly PH, NL, LL, LW, and SG. The higher PV compared to GV, along with the high EV and relatively low genetic variance, indicates a stronger environmental influence, consistent with previous studies such as Shah et al. (2022) [
82] and Saini et al. (2018) [
83]. The high ECV further supports this conclusion, demonstrating that pathogen exposure has a significant impact on the traits observed. For PH and NL, the low GA and moderate GAM observed reinforce the conclusion that these traits are largely influenced by the pathogen treatment rather than genetic factors. The low GA values are consistent with findings by Shah et al. (2022) [
82], who also reported minimal genetic contributions to the variation in PH. This suggests that improving these traits through traditional genetic selection may be challenging, as they are more susceptible to environmental factors, particularly pathogens.
Saini et al. (2018) [
83] reported the similar dominant impact of environmental factors on NL and LL, where the high PV and EV, coupled with higher PCV than GCV, indicate that the pathogen’s effect predominated. However, there were discrepancies in the genetic influence, as Saini et al. (2018) [
83] observed a higher genetic contribution than this study. These differences can likely be attributed to variations in accessions, genotypes, and experimental conditions. The trait LL, in particular, showed a similar trend, with higher PV and EV than GV, indicating that pathogen treatment had the strongest impact on phenotypic variation. While Saini et al. (2018) [
83] found a stronger genetic influence on LL, this study’s results point to a more substantial environmental effect, as evidenced by higher PCV relative to GCV and low heritability, suggesting that the majority of the phenotypic variance was attributable to
Asp treatment.
For traits like LW and SG, the environmental influence remained dominant, but the genetic contribution was relatively stronger for LW, with GA values reflecting this dominance. This finding is consistent with the results of Saini et al. (2018) [
83], who also found genetic factors to be more influential in LW, whereas SG was largely influenced by environmental factors. The discrepancies observed between this study and those of Saini et al. (2018) [
83], and Tripura et al. (2016) [
81] regarding SG and LW are likely due to differences in the experimental setups, accessions, and pathogen strains used, emphasizing the role of genotype–environment interactions in shaping phenotypic expression. These variations across traits highlight the complexity of genetic–environmental interactions, with pathogen exposure exerting a stronger influence on some traits, while genetic factors play a more prominent role in others. This suggests that the improvement of resistance to pathogens in some traits may require environmental management strategies or breeding for tolerance to environmental stress, rather than focusing solely on genetic selection for resistance genes.
4.4. Variance Components, Heritability, and Genetic Advance of Agronomic Characteristics
The findings from this study highlight the varying contributions of genetic and environmental factors to the phenotypic variation of different traits in response to
Ph. infection. For SL, PL, and STL, the results revealed a higher PV compared to GV, alongside substantial EV. This pattern suggests that
Ph. had a dominant environmental effect on these traits. The higher PCV compared to GCV, coupled with the high ECV, further supports the conclusion that the pathogen played a significant role in shaping phenotypic outcomes. The low GA and moderate GAM for these traits suggest that genetic improvement for these traits under
Ph stress may be limited. Heritability estimates confirmed that the bulk of the phenotypic variation in SL, PL, and STL was driven by the treatment effect rather than genetic factors, consistent with studies highlighting the strong influence of environmental treatments under pathogen stress [
46,
82].
On the other hand, NDFF and NI exhibited higher genetic variance than environmental variance. The lower EV observed, combined with the higher GV, suggests that these traits were more influenced by genetic factors. The consistent trends of low environmental contributions and high genetic variance emphasize that genetic factors primarily govern the variation observed in these traits. Heritability values indicated that most of the phenotypic variation in NDFF and NI was occurred genetic control, highlighting the role of tolerance genes in shaping these traits. This finding aligns with the work of Singh et al. (2015) [
72], who that found genetic factors to play a dominant role in the determination of NDFF under stress conditions, suggesting genetic resilience in these traits.
For NF, the higher PV, along with the relatively high EV, indicates that the pathogen’s environmental influence was stronger than the impact of genetic contributions. The high PCV compared to GCV and the higher ECV observed here also point to the dominant effect of
Ph on NF phenotypic variation, which aligns with the findings of Pandey et al. (2018) [
46], who similarly reported that environmental factors were the dominant contributor to flower number under pathogen stress. The low heritability and high GAM for NF further suggest that environmental treatments, especially pathogen exposure, had a significant impact on this trait, overshadowing the genetic contributions.
Overall, the contrasting roles of genetic and environmental factors observed across traits reflect the complex interplay between genetics and pathogen-induced stress. For traits like NDFF and NI, genetic factors played a stronger role, while traits such as SL, PL, STL, and NF were more strongly influenced by the pathogen. These findings are consistent with previous studies that emphasized the importance of considering both genetic and environmental components when breeding for disease resistance and tolerance. The variations observed also underscore the influence of experimental conditions, such as pathogen strains, genotypic diversity, and environmental settings, which can modulate the genetic–environmental interactions responsible for phenotypic expression.
In this study, the PV for SL, PL, STL, NDFFB, NI, and NF was predominantly influenced by
Asp treatment rather than genetic factors, as indicated by the higher PV compared to GV and the relatively high EV. This suggests that the environmental impact of the pathogen on these traits was stronger than the genetic contributions. For SL and PL, the higher phenotypic coefficients of variation (PCVs) compared to GCVs, along with high ECVs, further emphasized the dominance of the pathogen treatment. Heritability estimates revealed that a large portion of the observed variation in both SL and PL was due to
Asp treatment rather than genetic factors, corroborating findings from previous studies on pathogen-induced phenotypic changes under stress conditions [
46,
82]. The low GA and moderate GAM for these traits reinforced the conclusion that
Asp had a stronger influence than genetic factors. These trends are in line with reports that highlight the significant role of environmental factors in modulating phenotypic traits, particularly under pathogen stress.
Similarly, for STL, the higher PV, along with the higher PCV compared to GCV and the relatively high ECV, indicated that the treatment had a more pronounced effect on stamen length than genetic factors. The low heritability for STL suggested that the observed variation was largely driven by the environmental effects of
Asp treatment, rather than genetic components. This is consistent with the general understanding of how pathogens can alter plant traits, as also noted by Saini et al. (2018) [
83]. Conversely, NDFFB exhibited greater genetic influence, as indicated by lower EV and higher GV. The high heritability for NDFFB indicated that genetic factors were primarily responsible for the variation observed, while treatment effects had a lesser contribution. This supports findings from Singh et al. (2015) [
72], who suggested that genetic factors, especially tolerance genes, could dominate in determining flowering time under controlled conditions.
For NI and NF, higher PV relative to GV, along with substantial EV, suggested a stronger environmental impact. The higher PCV and ECV further confirmed the dominant impact of
Asp treatment on these traits, with heritability values indicating that a larger proportion of the variance in both traits was environmentally driven. These results align with studies like that of Pandey et al. (2018) [
46], which also found that pathogen-induced stress strongly influenced flower development traits in plants. The low GA and high GAM for both NI and NF further supported the notion that
Asp treatment had a dominant effect, as genetic improvement under these conditions was limited.
The findings underscore the complex interaction between genetic and environmental factors in shaping plant traits under pathogen stress. While some traits like NDFFB exhibited stronger genetic control, others, such as SL, PL, STL, NI, and NF, were predominantly shaped by the environmental influence of
Asp treatment. This highlights the critical role of environmental factors in modulating phenotypic expression, particularly in the context of pathogen interactions, as demonstrated in this study and supported by similar research in the field [
46,
82,
83]. The variation in the impact of genetic and environmental factors across traits emphasizes the need for a multifaceted approach when breeding for pathogen resistance, considering both genetic resilience and environmental conditions.
4.5. Variance Components, Heritability and Genetic Advance of Yield Characteristics
In this study, most of the yield traits were predominantly influenced by
Ph treatment rather than genetic factors. This was evidenced by higher PV relative to GV and the consistently high EV. The PCV observed was also greater than the GCV, with ECV being similarly elevated, underscoring the strong environmental influence on these traits. Heritability estimates further confirmed that a larger proportion of the observed variance was attributable to the pathogen treatment rather than genetic factors, reinforcing the conclusion that external environmental influences played a dominant role in driving phenotypic variation. The low GA for these traits further supports the finding that genetic factors contributed minimally to the observed phenotypic differences under pathogen stress, consistent with earlier research highlighting the significant impact of external treatments under stress conditions [
46,
84].
Conversely, traits such as FL, SC, and NC were primarily influenced by genetic factors, as indicated by higher GV compared to EV and greater GCV relative to ECV. These traits exhibited higher heritability values, suggesting that genetic factors played a larger role in the trait’s expression. The moderate GA observed for SC and low GA seen for FL and NC further emphasized the importance of genetic control over these traits. These findings are consistent with those of Pooja et al. (2022) [
78], who also reported a strong genetic influence on FL, highlighting the variability in genetic contributions across different traits.
On the other hand, traits such as NFS, CFW, NS, and NLS were more strongly influenced by the pathogen treatment, as evidenced by low heritability values and higher contributions from environmental variance. This contrasts with findings from Bhandari et al. (2017) [
85], who reported a stronger genetic influence on these traits. These discrepancies likely arise from differences in genotypes, accessions, and treatments across the studies, indicating the context-dependent nature of genotype–environment interactions in phenotypic expression. Similarly, FDM, TP, and NLS showed dominant treatment effects in this study, diverging from the conclusions of Pooja et al. (2022) [
78], who found genetic factors to be more influential. Likewise, in this study, FW was driven by treatment effects, contrasting with the findings of Somraj et al. (2017) [
86], who reported stronger genetic control over this trait. These discrepancies underscore the significant role of experimental conditions, genotypic diversity, and treatment protocols in shaping phenotypic outcomes.
In conclusion, this study highlights the complex interaction between genetic and environmental factors in determining phenotypic traits under pathogen stress. While some traits like FL, SC, and NC were predominantly genetically driven, others such as NDFR, NFS, and NS were more strongly influenced by the pathogen (Ph). These results align with previous research but also reveal how experimental conditions, accessions, and environmental stress can modulate the relative contributions of genetic and treatment effects to shaping plant phenotypes.
In this study, certain traits were predominantly influenced by
Asp treatment, as evidenced by higher PV and EV compared to GV. The consistently higher PCV relative to GCV, alongside the higher ECV, further supported the dominance of treatment effects. Additionally, heritability values revealed that a significant portion of phenotypic variation for these traits was driven by the pathogen treatment, with a minimal contribution from genetic factors. The low GA for these traits further corroborated the limited genetic contribution, emphasizing the stronger influence of environmental factors, particularly the pathogen stress, on phenotypic expression. Traits such as NDFR, CFW, NRC, PL, and PLAL also exhibited GAM, which reinforced the conclusion that
Asp played a dominant role in determining phenotypic variation. These findings align with previous studies on genotype–environment interactions under pathogen stress, highlighting the pivotal role of environmental conditions in shaping phenotypic outcomes [
46,
84].
In contrast, traits like FL were strongly influenced by genetic factors, as indicated by the higher GV compared to EV and greater GCV relative to ECV. The heritability of FL further confirmed the predominant genetic influence over this trait, contrasting with other traits that were more strongly affected by pathogen treatment. These observations emphasize the variability in the contributions of genetic and environmental factors across traits. In this study, traits such as NLS were strongly influenced by the pathogen treatment, differs from the findings of Rasheed et al. (2023) [
87], who reported genetic dominance. Similarly, traits like TP and CFW showed a higher environmental influence in this study, diverging from findings by Meena et al. (2018) [
77], where these traits were attributed to genetic factors. Such differences may arise due to variations in experimental conditions, accessions, and treatments between studies.
The discrepancies in the observed genetic and environmental influences on traits such as NC, FDM, NF, and NS reflect the dynamic interaction between treatment and genetic factors. In this study, these traits were predominantly influenced by pathogen effects, while studies by Meena et al. (2018) [
77] and Singh et al. (2015) [
72] reported genetic control over traits like NC and NF. Similarly, Aralikatti et al. (2018) [
88] found genetic factors to be the primary drivers of NS. These variations underscore the importance of experimental conditions, treatment protocols, and genotype–environment interactions in determining the phenotypic expression of traits under pathogen stress.
In summary, this study demonstrates the significant influence of Asp treatment on most traits, with a few exceptions where genetic factors exerted a stronger influence, such as for FL. The contrasting results with previous studies highlight the complex interplay between genetic and environmental factors, emphasizing the role of experimental context in modulating phenotypic outcomes.