1. Introduction
Fusarium solani KMZW-1, is a well-recognized entomopathogenic fungus belonging to the family Tuberculariaceae; order Hypocreales. Recently, biological control has garnered increased attention for managing agricultural insect pests, due to its environmental friendliness. Biocontrol agents such as
F. solani KMZW-1, have become a focal point for experts seeking sustainable pest management solutions.
Bactrocera dorsalis (Diptera; Tephritidae), commonly known as the oriental fruit fly, is a significantly destructive and persistent pest affecting over 250 host plants as documented [
1]. Effective control of
B. dorsalis is crucial for minimizing crop damage and financial losses.
Previous researches have showed the insecticidal potential of biocontrol agents. For example Methoxyfenozide and
Beauveria bassiana (Hypocreales; Cordycipitaceae) have demonstrated promising results in controlling
B. dorsalis. Chandramohan et al., (2016) reported mortality rates of 67.5%, 65.0% and 63.5% for Methoxyfenozide and 60.0%, for
B. bassiana [
1]. Similarly, Li et al. (2024) screened six strains of
B. bassiana and found mortality rate of 90.67% for adults of oriental fruit fly with most active strain B4 [
2]. These studies provide a theoretical basis for exploring new biocontrol agents against
B. dorsalis high-lighting the need for further research into the pathogenicity of
F. solani KMZW-1.
In recent years, advancement in biotechnology have provided new insights into the success of biological control. Genomic sequencing and comparative genomics analyses have become focal points in studying biocontrol potential of entomopathogenic fungi, offering crucial insights about their biological characteristics and potential applications [
3]. For instance, genetic data based fungal co-expression network analysis of the entomopathogenic fungus
B. bassiana have revealed the infection associated modules and host pathogen interaction related to its biocontrol potential against insect pests [
4]. These findings offers deep understanding of the genetic characteristics, pathogenic mechanisms, and biocontrol potential of entomopathogenic fungus.
Whole genome sequencing has emerged as a powerful tool for understanding the genetic basis of biological traits and behaviors in various organisms. The complete genome analysis of
L. attenuatum Strain Lec8 revealed the genome size of 32.38 Mb, containing 9,531 genes, including those encoding proteins related to biosynthetic pathways which suggested strong entomopathogenic potential [
5]. Similarly, The genome sequencing of
F. solani-melongenae (CRI 24-3) revealed 49.6 Mb chromosome-level draft genome containing 15,374 putative coding genes, Contigs N50, 4,496,268 (bp) and GC content was 50.7%, it also showed relatively high numbers of virulence factors such as carbohydrate-active enzymes (CAZymes), pathogen host interaction (PHI) proteins, and terpene synthases (TSs) [
6]. These findings provide significant insights on the molecular basis of fungus though further research is needed for exploring its pathogenic potential. Whole genome sequencing may explore the genetic basis of
F. solani KMZW-1 as a biocontrol agent.
Fruit flies poses a major threat to a wide range of fruits and vegetables globally from tropical to subtropical environments due to their polyphagous nature [
7,
8].
B. dorsalis, in particular is a significant threat to horticultural crops in China and neighboring regions. Biological control of many insect pests including fruit flies, frequently employs entomopathogenic microorganisms [
9,
10,
11,
12]. This study aims to explore the entomopathogenic potential of
F. solani KMZW-1 against
B. dorsalis by utilizing complete genome sequencing and comparative genomics. Additionally, we compared its pathogenicity potential against different sex of
B. dorsalis.
4. Discussion
In recent years, whole-genome sequencing emerged as important tool for elucidating the genetic characteristics and biological mechanisms of biocontrol fungal strains [
56]. Comparative analyses have revealed distinct genomic features among these strains including variations in GC content, numbers of coding genes, and specific gene clusters. In our study, whole genome sequencing revealed a genome size of 47,239,278 bp, comprising 27 contigs, with a GC content of 51.16%. The genome completeness was assessed as 97.93% us-ing BUSCO analysis, DFVF sequence identifier was
Fusarium 0G092560.1, AntiSMASH analysis identified 29 gene clusters associated with secondary metabolite biosynthesis providing insights into the genetic basis of its pathogenic mechanisms and biocontrol potential. Our findings align with previous whole genome sequencing studies on different organisms. For example, the whole genome sequence of entomopathogenic fungus
B. bassiana JEF-350 revealed a total of 34,655,292 Illumina reads (5,232,949,092 bases), 49.61% G1C content, 8 assembled contigs and 22,202,500 filtered Illumina reads. Annotation of protein coding genes and functional annotation showed that there were 28,999 and 17,771 exons and introns, respectively; while a total of 11,225 protein coding genes were predicted. Total genes annotated for transport and metabolism related to amino acids, nucleotides, coenzymes, carbohydrates, lipids, and inorganic ions in the eggNOG classification were 1,593 [
57]. A 49.6 mb chromosome-level draft genome containing 15,374 putatively coding genes was obtained with a GC content of 50.7% and 12 scaffolds by sequencing the pathogenic fungus
F. solani-melongenae (CRI 24-3) using third-generation and next-generation sequencing techniques [
5]. In another study by Lee et al. (2024), hybrid assembly approach was used to study the whole genome sequencing of
B. bassiana strain KNU-101. The genome analysis revealed comprehensive insights into its genetic makeup. The genome sequencing of strain KNU-101 showed a maximum scaffold length 10,066,884 bp with a GC content of 49.49%, 26 contigs and 1,822,896 reads (9,827,426,196 bp) with an N50 read length of 13,949 bp through nanopore sequencing [
58]. Similarly, the genome analysis of
B. pseudobassiana strain RGM 2184 resulted in 114 genes encoding for extracellular enzymes, four biosynthetic gene clusters reported as producers of insecticidal and bactericidal factors such as oosporein, beauvericin, desmethyl-bassianin, and beau-veriolide. Comparative genomic analysis revealed that 65–95% of these genes are
Beauveria genus-specific. Metabolic profiling of supernatant extracts from RGM 2184 cultures exhibited secondary metabolites such as beauveriolide, oosporein, inflatin C, and bassiatin, which were main factors involved in its insecticidal activity [
59].
This study performed comprehensive functional annotation of the genome of
F. solani KMZW-1, including annotations from GO, KEGG, KOG, and DVDF databases. The results showed 9994 GO annotations, 3775 KEGG annotations, 7059 KOG annotations, and 3054 DVDF annotations. In a similar study, Iwanicki et al., (2022) conducted genome sequencing of
Metarhizium humberi (Hypocreales; Clavicipitaceae) in order to get its genomic signatures and insights into host niche adaptation. In
M. humberi, 10633 genes were predicted by the genome annotation, of which 92.0% have putative functions assigned to them, and roughly 17% of the genome was marked as repetitive sequences. They discovered that 18.5% of the
M. humberi genome resembles proteins linked to pathogen host interaction; while the
M. humberi strain ESALQ1638 genome showed some distinct features that set it apart from the genomes of the other 8
Metarhizium species. These features included a greater number of genes functionally annotated as polyketide synthases (PKSs), over represended GO-terms linked to the transport of ions, organic matter, and amino ac-ids, a higher proportion of repetitive elements, and higher levels of RIP-induced point mutations [
60]. Similarly, Binneck et al., (2019) studied whole genome sequencing of
Metarhizium rileyi (Hypocreales; Clavicipitaceae), strain Cep018-CH2/ARSEF 7053. Results revealed as 31,808,756 bp was the total length of the final assembly, made up of 249 scaffolds, 240 of which were larger than 1,000 bp, and 1,044 contigs. The longest scaffold had a length of 2,535,063 bp while the N50 scaffold had a length of 815,204 bp while the L50 value was 10. There was 51.30% G+C content altogether. Gene prediction and annotation showed 8,945 protein-codings and 102 tRNA genes. antiSMASH analysis revealed 30 gene clusters that were involved in the biosynthesis of specialized metabolites and Functional annotation of the predicted proteins revealed key genes coding for peptidases, carbohydrate-active enzymes, secreted proteins, and transcription factors [
61]. Gene annotation in the KOG, GO, KEGG and DVDF databases yielded 7059, 9994, 3775 and 3054 genes, respectively.
F. parceramosum and
F. aff. solani with a bootstrap support of 48, and
F. vanettenii with 32, indicating a close evolutionary relationship among these species. Additionally,
F. solani KMZW-1 forms a clade with
F. falciforme, and
F. coffeatum are with a bootstrap support of 28.2116 and 19.3965 respectively, highlighting its phylogenetic associations. The similar findings revealed the taxonomic and evolutionary position of
M. anisopliae var. anisopliae [
62]. OrthoFinder analysis revealed that
F. solani KMZW-1 possesses 269 unique genes and shares 142 genes with
F. solani, while sharing fewer genes with other strains, indicating varying degrees of genetic divergence. All strains share a core genome of 8728 genes, representing fundamental conserved functions. These reports aligned with Guo et al., (2023), who reported the structure and specific gene categories in the
P. herquei genome, and then comprehensively compared with those of the two well-studied
Penicillium species,
P. decumbens and
P. chrysogenum, using OrthoFinder [
63]. Additionally, the collinearity analysis between the genomes of
F. solani KMZW-1 and
F. solani-melongenae exhibited a high degree of synteny. Most of the contigs of
F. solani KMZW-1 correspond to the contigs of
F. solani-melongenae. These findings provide important evidence for understanding the evolutionary relationships and ecological characteristics of
F. solani KMZW-1.
Due to high damaging potential of B. dorsalis, its control often involves multiple tactics including the use of etomopathogenic fungus. In this study, B. dorsalis adult females and males were treated with different conidial suspensions of F. solani KMZW-1 strain at different concentrations (1×107, 1×106, 1×105, 1×104 conidia/mL). After 12 days of treatment, the cumulative average mortality rates of B. dorsalis adults were recorded as follows: 56.67% (68.89%), 52.22% (58.89%), 44.44% (53.33%), and 34.44% (46.67%) for females (males), respectively, compared to a survival rate of 85.56% (80%) in the control group. The calculated LogLC50 for F. solani KMZW-1 against female and male B. dorsalis adults were 5.662 and 4.486, respectively. Furthermore, after treatment with high concentrations (1×1011, 1×1010, 1×109, 1×108 conidia/mL) of F. solani KMZW-1, the cumulative average mortality rates of B. dorsalis adults were significantly higher than the control 14.44% (20%) after 12 days, reaching 67.78% (75.56%), 67.78% (75.56%), 65.56% (77.78%), and 58.89% (76.67%), respectively.
These findings are consistent with the results of many other researchers assessing the pathogenicity of different entomopathogenic fungus against
B. dorsalis. For example, Cherry and Moore, (2006) extensively observed the infection of
M. anisopliae on
B. dorsalis and found that approximately 70% of the treated fruit fly larvae were heavily infected, with a survival rate of only 30% [
64]. These results indicated that
M. anisopliae has high pathogenicity against
B. dorsalis similar to the pathogenic potential observed with the
F. solani KMZW-1 in this study. Similarly, seven different
Fusarium species were tested against
Helicoverpa armigera for their insecticidal potential. In field conditions, all of the collected fungi were insecticidal, however, some were severely lethal to
H. armigera larvae. After nine days mortality reached to 91% at concentration 1×108 conidia/mL. While
F. solani isolate displayed the highest toxicity against
H. armigera larvae [
65].
Jackson and Dunlap, (2012) found that
Isaria fumosorosea (Hypocreales; Cordycipita-ceae) treatment significantly reduced the survival rate of
B. dorsalis larvae upto 40% with an infection rate of 90% [
66]. Similarly, Murtaza et al., (2022) tested the efficacy of three entompathogenic fungi including
M. anisopliae,
B. bassiana and
V. lecanii, against
Bactrocera zonata ((Diptera: Tephritidae) stages under different laboratory conditions. They found that
B. bassiana and
M. anisopliae were more pathogenic to all stages of the fruit fly as compared to
V. lecanii. Following exposure to concentrations of 1 × 1010 conidia/ml of
B. bassiana, the highest rates of mortality were observed for the 3rd larval instar and the pupal stage, with 68.67% and 89.67%, respectively; while adults were most susceptible to all three fungus. However, at 1 × 1010 conidial concentration,
M. anisopliae was more virulent against adult
B. zonata flies as compared to
B. bassiana and
V. lecanii [
67]. In our studies,
F. solani KMZW-1 exhibited a concentration-dependent effect on both male and female adults of
B. dorsalis with a markedly higher impact on male adults. This suggests the strong potential of
F. solani KMZW-1 for use in integrated pest management programs targeting
B. dorsalis.