English abstract
For decades, conventional farming has played a vital role in producing food and
reducing starvation in developed and developing countries. However, its negative impacts
on human health, animals, plants, and the environment, especially soil, are becoming
increasingly evident. Climate change is also exacerbating these impacts, including
drought and soil salinity. Organic farming, on the other hand, seeks to address and
mitigate these issues through various practices, particularly by maintaining the
biodiversity of soil microorganisms and the addition of beneficial microorganisms such
as arbuscular mycorrhizal fungi (AMF) in crop production. AMF are ubiquitous in the
plant kingdom, with more than 80% of terrestrial plants forming symbiotic relationships
with them. Known benefits include providing nutrition and protecting against biotic and
abiotic stresses for the host plant. This research investigated the impact of conventional
and organic farming practices on AMF biodiversity in both systems and isolated some
quick-colonizing AMF species to test their effects on cucumber plants under salinity and
drought stress.
The overall research was divided into three parts: the first part’s objective was to
investigate the impact of organic and conventional farming systems on the diversity of
AMF in the rhizosphere soils of mango, citrus and cucumber. The objective of second
part was to evaluate and compare the efficacy of native inoculation, obtained through a
quick colonizing method, and a commercially available AMF product in enhancing the
physiological responses of two cucumber varieties ‘Diva’ and ‘Safaa’ under four salinity
stress conditions. The third study’s objective was to investigate the potential of enhancing
drought tolerance in cucumber plants through a combination of a native quick root
colonizer AMF, a commercial AMF, and potassium silicate (PS).
The first study investigated the impact of organic and conventional farming
practices on AMF diversity in the rhizosphere soils of mango, citrus, and cucumber from
16 sites. Spore morphological analysis and internal transcribed spacers (ITS) RNA
analysis were employed for AMF identification. Additionally, some AMF species were
isolated by using the quick colonizer method, and they were identified morphology and
molecular techniques by using AMF primers. Spore morphological analysis identified 9
families, 20 genera, and 36 species, with higher diversity observed in samples from
organic farming. ITS sequencing analysis detected 6 families and 12 genera, and, once
again, greater diversity in terms of taxa and the Shannon H index was observed in organic
farming samples. The families Diversisporaceae and Glomeraceae were found to be the
most abundant across all treatments. A higher mycorrhizal inoculum potential for
cucumber was observed in organic soils, and higher root colonization percentages were
recorded for citrus in organic soils. Furthermore, two AMF species, Rhizoglomus
intraradices and Septoglomus viscosum, were identified as quick colonizers with potential
for cucumber production in Oman. These results contribute to the understanding of AMF
diversity in different farming systems and support the development of sustainable
agriculture in semi-arid and arid region.
The second study compared the effects of native inoculation obtained through the
quick colonizing method, a commercial AMF product, and control treatments on plant
physiological response of two cucumber varieties; ‘Diva’ and ‘Safaa’. Salinity stress was
induced by irrigating with saline water at various levels (0.64 dS m-1
as control, 2, 4, and
6 dS m-1
). The mycorrhizae treatments included native AMF quick root colonizer and a
commercial inoculum containing 5 species of Glomeraceae, Glomerales. The study found
that salinity stress led to a significant reduction in plant growth, disrupted ion homeostasis
(K/Na ratio), decreased mycorrhizal root colonization percentage, and increased levels of
proline, chlorophyll content (SPAD), leaf chlorophyll fluorescence, Na concentration in
leaves, and malondialdehyde (MDA) content. The two AMF inoculants improved plant
growth, including plant height, biomass, potassium (K), and phosphorus (P) uptake. They
also enhanced the K/Na ratio and optimized nutrient availability under saline conditions.
AMF inoculation resulted in improved SPAD and photosynthetic efficiency, increased
proline accumulation, and enhanced catalase activity. Notably, native AMF exhibited
higher root colonization percentages compared to the commercial AMF product. These
findings underscore the complex interplay between plant and fungal genotypes in
regulating salinity tolerance. The study suggests that the use of native AMF species, better
suited to the region's soil and climate, can partially benefit cucumber plants under salinity
stress, offering potential integration into sustainable farming practices to improve
vegetable production in high-salinity conditions.
The third investigated the impact of combined AMF and potassium silicate on
drought tolerance in cucumber plants in a greenhouse experiment. Cucumber plants were
grown under two watering regimes: drought-stressed 60% water holding capacity
(WHC)and unstressed 80%WHC, and three mycorrhizal inoculation treatments (control,
native AMF: quick root colonizer species, and commercial AMF) with or without
potassium silicate application. Drought stress significantly reduced plant height, biomass,
and photosystem II efficiency, while it increased the content of leaf glycine betaine and
catalase activity. Generally, AMF inoculation significantly improved plant growth,
SPAD, photosystem II efficiency, concentration of proline, glycine betaine, and catalase
activity, and the native species exhibited comparable effects to commercial species for
most variables studied. Contrary to our expectations, PS application alone did not improve
plant growth, except for increased photosystem II efficiency, but root fresh and dry
weights were reduced. Under drought stress, combination of PS and AMF significantly
improved plant height, shoot fresh weight, chlorophyll content (SPAD), glycine betaine,
and catalase activity compared to PS alone. Our results highlight that the combined
application of PS and AMF inoculants can protect cucumber seedlings from drought
stress; however, further research is needed to optimize the PS application method and
dosage and to investigate the long-term effects on plant growth and yield under field
conditions.
