الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 121 |  |  |
| | | from | 121 | | |
Abstract
Phosphorus is one of the major nutrients for plants. A grater part of soil phosphorus, approximately 95-99% is present in the form of insoluble phosphates and hence cannot be utilized by the plants. phosphatic fertilizer, such as costly chemical fertilizers that contain large amounts of soluble phosphorus, have been applied to the agricultural fields to maximize production. However, a large proportion of fertilizer phosphorus after application is quickly transformed to the insoluble form. Therefore, very little percentage of the applied phosphorus is available to plants, making continuous application necessary.
Phosphate solubilizing microorganisms (PSMs) play an important role in supplementing phosphorus to the plants, allowing a sustainable use of phosphate fertilizers. Application of PSMs in the field has been reported to increase crop yield. Accordingly, it was interesting to perform this investigation which has the following objectives:
1. Isolation of natural yeasts from different geographical regions in Egypt collected from soils and crops of banana, guava, and sugarcane.
2. Determination of P-solubilization potential using yeast isolates.
3. Quantitative measurement of P-solubilization by yeast isolates.
4. Determination of variation between these isolates by using RAPD-PCR analysis with six different primers.
5. Evaluation of the Isolates for their thermotolerance.
6. Selection of two isolates (the best solubilizers yeast strains) and using them as a bio-fertilizer for wheat.
a. Effects of inoculation with yeast strains on p-uptake and growth of wheat.
7. Identification of yeast isolates based on sequence analysis of D1/D2 of large subunit (LSU) 26S rRNA gene.
The results showed that:
1.a. Fifty six yeast isolates were collected from soils and crops of banana, guava, and sugarcane from different geographical regions in Egypt.
2.a. All isolates showed varied abilities to solubilize inorganic phosphates based on inducing clear zones around their colonies.
2.b. The isolates ranged in solubilizing index values between (1.1) for the isolates PY-7 (banana soil from Nga Hamady) and PY-47 (guava crop from Sohag) and (2.28) for the isolate PY-33 (banana crop from Tanta).
2.c. Six isolates showed good ability to solubilize inorganic phosphates were selected.
3. Amounts of phosphorus solubilized from tricalcium phosphate by the yeast isolates were determined. The maximum amount of P solubilized (49.66 μg/ml) was recorded for yeast isolate PY-33. and the lowest amount of P solubilized was recorded for yeast isolate PY-12 (21.33 μg/ml).
4. As for the used six primers, the results of the RAPD-PCR analysis showed that there were significant variations between the isolates of the yeast at the molecular level. Meanwhile, no specific band(s) associated with phosphorus solubilization.
5. There was a significant variation between these isolates in terms of their ability to tolerate thermal exposure. The results showed also that the isolate PY-29 showed the highest tolerance to heat where its viability percentage reached 98.26% at 52°C. However, the isolates PY-33 showed the lowest tolerant to heat where its viability percentage was 14.13% at 52°C.
6.a. Inoculating the wheat with yeast isolates PY-29 or/and PY-33caused a significant or non-significant increases in the fresh and dry shoot and root weights and P-uptake compared with the control (uninoculated plants) and the isolate PY-33 was more stimulative when compared with the isolate PY-29.
6.b. Co-inoculating yeast isolate PY-29 in a mixed with isolate PY-33 produced further promotive effects on the shoot and root fresh and dry weights and P-uptake in the shoots when compared with a single inoculation treatment with only one isolate.
6.c. The promotion effect of inoculating with yeast isolates PY-29 or/and PY-33 on the plant growth and P-uptake was more obvious at the fertilization level of 50 Kg P2O5/Feddan, whereas increasing the P-fertilization to 100 Kg P2O5/Feddan decrease the promotive effect of the inoculation.
7. BLAST analysis of the 26S rRNA gene sequence of the isolate PY-29, was revealed it to be a perfect match with Wickerhamomyces anomalus (Pichia anomala) with four base substitution (99% similarity), while PY-33 demonstrated 99% identity to Rhodotorula glutinis with one base substitution.
This research used phosphate solubilizing microorganisms due to its great importance from the practical side not only in reducing the high cost of phosphate fertilizer, but also in mobilizing the non-dissolved phosphorus in the soil in order to use it and hence solving many environmental problems.
This research focused particularly on yeast because of its ability to produce organic acids, especially citric acid, vitamins, and hormonal substances, in addition to the high rate of viability under hard soil conditions. Furthermore, yeast started to be used as plant bio-fertilizers as they provide safe nutrition for plants, and have a significant impact on plants growth and branching, increased shoot, and the quality of flowering.
It is also worth mentioning that the yeast offers all what’s needed for performing any genetic experiments.
It was necessary in this research to identify distinct strains of yeast, which will be tested as bio-fertilizers due to the importance of knowing the characteristics and significance of the species used. Through this, modern molecular techniques were used to identify the strains due to their easiness of application and high accurateness results.