Biotic and Abiotic Stresses of Major Fruit Crops in Oman: A Review

Oman is located in an arid region of the world that is characterized by adverse climatic conditions, including heat and drought. In recent years, it has also been affected by climate turbulence and the occurrence of severe weather, such as cyclones and heat/cold waves affecting large agricultural areas of the country. Fruit cultivation area represents 31% of the total cultivated area (97,239.58 ha) in the country. However, the production share is only 17% of the total crop production in the country (2.6 million tons). About 90% of the fruit cultivation area is dominated by date palm, banana, lime, and mango. In addition to the abiotic stresses, such as drought, heat, and salinity, major fruit crops have declined in recent years due to various biotic stressors, primarily insect pests, and diseases. For several decades, the date palm has suffered from the Dubas bug and in recent years from Red Palm Weevil. Lime has been infected with Witch’s Broom Disease of Lime (WBDL) caused by ‘Candidatus Phytoplasma aurantifolia’ that has led to the decline of production to 25% from its peak in the nineties. Banana is Oman`s second-largest fruit crop in production and export. It has also been the subject of studies due to losses incurred by farmers during pre-and post-harvest stages, in addition to several pests and diseases that affect bananas in Oman. Mango is another major fruit crop that is primarily cultivated in northern Oman. Severe infection with mango decline has led to the eradication of mango orchards from many regions of Oman, particularly in Batinah Coast, where increased salinity has led to a decline in mango yield. Research conducted in Oman has investigated several aspects of these challenges. This review paper summarizes the outcome from studies conducted in the country and proposes directions towards resolving current and future challenges to the fruit industry

Aspergillus terreus Inhibits Growth and Induces Morphological Abnormalities in Pythium aphanidermatum and Suppresses Pythium-Induced Damping-Off of Cucumber

The study investigated the efficacy of two isolates of Aspergillus terreus (65P and 9F) on the growth, morphology and pathogenicity of Pythium aphanidermatum on cucumber. In vitro tests showed that the two isolates inhibited the growth of P. aphanidermatum in culture. Investigating P. aphanidermatum hyphae close to the inhibition zone showed that the hyphae showed abnormal growth and loss of internal content. Treating P. aphanidermatum with the culture filtrate (CF) of A. terreus resulted in significant rise in cellular leakage of P. aphanidermatum mycelium. Testing glucanase enzyme activity by both A. terreus isolates showed a significant increase in glucanase activity. This suggests that the cell walls of Pythium, which consist of glucan, are affected by the glucanase enzyme produced by A. terreus. In addition, Aspergillus isolates produced siderephore, which is suggested to be involved in inhibition of Pythium growth. Also, the CFs of 65P and 9F isolates significantly reduced spore production by P. aphanidermatum compared to the control (P < 0.05). In bioassay tests, the two isolates of A. terreus increased the survival rate of cucumber seedlings from 10 to 20% in the control seedlings treated with P. aphanidermatum to 38–39% when the biocontrol agents were used. No disease symptoms were observed on cucumber seedlings only treated with the isolates 65P and 9F of A. terreus. In addition, the A. terreus isolates did not have any negative effects on the growth of cucumber seedlings. This study shows that isolates of A. terreus can help suppress Pythium-induced damping-off of cucumber, which is suggested to be through the effect of A. terreus and its glucanase enzyme on P. aphanidermatum mycelium

Classification of a new phytoplasmas subgroup 16SrII-W associated with Crotalaria witches’ broom diseases in Oman based on multigene sequence analysis

Abstract Background Crotalaria aegyptiaca, a low shrub is commonly observed in the sandy soils of wadis desert and is found throughout all regions in Oman. A survey for phytoplasma diseases was conducted. During a survey in a wild area in the northern regions of Oman in 2015, typical symptoms of phytoplasma infection were observed on C. aegyptiaca plants. The infected plants showed an excessive proliferation of their shoots and small leaves. Results The presence of phytoplasma in the phloem tissue of symptomatic C. aegyptiaca leaf samples was confirmed by using Transmission Electron Microscopy (TEM). In addition the extracted DNA from symptomatic C. aegyptiaca leaf samples and Orosius sp. leafhoppers were tested by PCR using phytoplasma specific primers for the 16S rDNA, secA, tuf and imp, and SAP11 genes. The PCR amplifications from all samples yielded the expected products, but not from asymptomatic plant samples. Sequence similarity and phylogenetic tree analyses of four genes (16S rDNA, secA, tuf and imp) showed that Crotalaria witches’ broom phytoplasmas from Oman is placed with the clade of Peanut WB (16SrII) close to Fava bean phyllody (16SrII-C), Cotton phyllody and phytoplasmas (16SrII-F), and Candidatus Phytoplasma aurantifolia’ (16SrII-B). However, the Crotalaria’s phytoplasma was in a separate sub-clade from all the other phytoplasmas belonging to Peanut WB group. The combination of specific primers for the SAP11 gene of 16SrII-A, −B, and -D subgroup pytoplasmas were tested against Crotalaria witches’ broom phytoplasmas and no PCR product was amplified, which suggests that the SAP11 of Crotalaria phytoplasma is different from the SAP11 of the other phytoplasmas. Conclusion We propose to assign the Crotalaria witches’ broom from Oman in a new lineage 16SrII-W subgroup depending on the sequences analysis of 16S rRNA, secA, imp, tuf, and SAP11 genes. To our knowledge, this is the first report of phytoplasmas of the 16SrII group infecting C. aegyptiaca worldwide

Endophytic bacterial diversity of Avicennia marina helps to confer resistance against salinity stress in Solanum lycopersicum

The current study aimed to explore the endophytic bacterial diversity of Avicennia marina and the potential roles of these endophytes in counteracting saline conditions in tomato plants. Molecular analysis revealed strains from Paenibacillus, Bacillus, Microbacterium, Citrobacter, Lysinibacillus, Halomonas, Virgibacillus, Exiguobacterium, and Vibrio. However, Bacillus pumilus AM11 and Exiguobacterium sp. AM25 showed significantly higher growth in saline media. In response to salinity stress, tomato plants treated with AM11 and AM25 showed significantly higher (∼15–23%) biomass, photosynthetic rate and pigment accumulation compared to controls. Salinity-exposed plants had significantly reduced growth and increased (three-fold) lipid peroxidation, whilst glutathione, catalase, and peroxidase activities were significantly reduced. In contrast, AM11, AM25, and methionine improved these physiochemical attributes. The study concludes that the application of bacterial endophytes from plants growing in saline conditions can offer other plants similar stress-resistance potential. Such halophytic bacterial strains can be used to improve plant growth in saline conditions

Genome-wide analysis and expression profiling of CalS genes in Glycine max revealed their role in development and salt stress

Abiotic stress affects plants' growth and development. Soybean is an important crop of the world, however, its production is affected by abiotic stresses. Callose Synthase is the most crucial enzyme response to environmental and developmental signals. However, in soybean, information on the callose synthase genes is limited. In this study, we analyzed the callose synthase gene family of soybean at the genome-wide scale. We also studied the genes positions, gene structure, evolutionary relations, miRNAs target sites, and expression of CalS genes. Resultantly 24 CalS genes were found in soybean, with diverse chromosomal locations, cis-acting elements, conserved motifs, and gene structures. Further, GmCalS genes were divided into four phylogenetic classes. The evolutionary classification of CalSs was supported by the motif and gene structure analyses. Phytohormones, abiotic stresses, and growth-responsive elements were identified in the promoter of GmCalSs. In addition, the GmCalS genes higher expression in roots, leaves, flowers, and nodules tissues provided their significance in development. Furthermore, the higher expression of GmCalS17 and GmCalS19 genes in response to salt stress indicated their importance against salt stress. These findings will be helpful for further investigation of the CalS genes in other crops

Genome-Wide Analysis and Expression Profiling of <i>DUF668</i> Genes in <i>Glycine max</i> under Salt Stress

The DUF668 gene performs a critical role in mitigating the impact of abiotic stress factors. In this study, we identified 30 DUF668 genes in a soybean genome, distributed across fifteen chromosomes. The phylogenetic analysis classified the DUF668 genes into three groups (group I, group II, and group III). Interestingly, gene structure analysis illustrated that several GmDUF668 genes were without introns. Furthermore, the subcellular localization results suggested that GmDUF668 proteins were present in the nucleus, mitochondria, cytoplasm, and plasma membrane. GmDUF668 promoters were analyzed in silico to gain insight into the presence of regulatory sequences for TFs binding. The expression profiling illustrated that GmDUF668 genes showed expression in leaves, roots, nodules, and flowers. To investigate their response to salt stress, we utilized the RNA sequencing data of GmDUF668 genes. The results unveiled that GmDUF668-8, GmDUF668-20, and GmDUF668-30 genes were upregulated against salt stress treatment. We further validated these findings using qRT-PCR analysis. These findings provide a scientific basis to explore the functions of GmDUF668 genes against different stress conditions

Expression profiling of DUF599 genes revealed their role in regulating abiotic stress response in solanum tuberosum

The proteins containing the domain of unknown functions (DUFs) have significant roles in stress response and the growth of plants. A comprehensive genome-wide analysis and expression profiling of DUF599 was conducted to identify their roles in potato growth and response to stressed conditions. A total of nine DUF599 genes were identified, located on five chromosomes in the potato genome. The phylogenetic analysis divided StDUF599 genes into three groups in accordance with gene conserved motifs and gene structure distribution patterns. The StDUF599 promoters comprised several cis-acting factors responsive to plant hormones and abiotic stresses. The present study revealed that StDUF599 genes also possessed MBS, LTR, ABRE, and anaerobic induction responsive elements, indicating their importance in coping with abiotic stresses. StDUF599 genes were the target of several families of micro-RNAs also identified in this study. Purifying selection pressures lead to the duplication of the StDUF599 genes. Expression analysis of StDUF599-6 and StDUF599-9 in various tissues illustrated their vital role in developmental processes. It was found that StDUF599-7 and StDUF599-9 were highly expressed against heat and salt stresses. Expression profiling revealed that the StDUF599-8 gene has a significant role against GA3 and IAA. Lastly, this article forecasted that the DUF599 genes could enhance plant tolerance against several abiotic stresses

Endophytic bacterial diversity of <i>Avicennia marina</i> helps to confer resistance against salinity stress in <i>Solanum lycopersicum</i>

<p>The current study aimed to explore the endophytic bacterial diversity of <i>Avicennia marina</i> and the potential roles of these endophytes in counteracting saline conditions in tomato plants. Molecular analysis revealed strains from <i>Paenibacillus, Bacillus, Microbacterium</i>, <i>Citrobacter</i>, <i>Lysinibacillus, Halomonas, Virgibacillus</i>, <i>Exiguobacterium</i>, and <i>Vibrio</i>. However, <i>Bacillus pumilus</i> AM11 and <i>Exiguobacterium</i> sp<i>.</i> AM25 showed significantly higher growth in saline media. In response to salinity stress, tomato plants treated with AM11 and AM25 showed significantly higher (∼15–23%) biomass, photosynthetic rate and pigment accumulation compared to controls. Salinity-exposed plants had significantly reduced growth and increased (three-fold) lipid peroxidation, whilst glutathione, catalase, and peroxidase activities were significantly reduced. In contrast, AM11, AM25, and methionine improved these physiochemical attributes. The study concludes that the application of bacterial endophytes from plants growing in saline conditions can offer other plants similar stress-resistance potential. Such halophytic bacterial strains can be used to improve plant growth in saline conditions.</p