Date of Award

10-2016

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Science

First Advisor

Dr. Khaled El-Tarabily

Second Advisor

Or. Abdulmajeed AIKhajeh

Third Advisor

Synan AbuQamaer

Abstract

In the present thesis, the ability of different plant growth promoting actinomycetes to promote the growth of tomato plants under saline conditions was examined using phosphorus solubilizing actinomycetes and/or plant growth regulates producing actinomycetes compared to tomato plants grown in soil not amended with any actinomycetes isolates. The overall aim of the present project was to determine whether enhanced phosphorus solubilization, as a result of soil inoculation with either phosphorus-solubilizing actinomycetes and/or with the production of plant growth regulators by plant growth promoting actinomycetes or the combination of both characteristics will results in the promotion of tomato plant growth.

To achieve this, 62 isolates of Streptomyces spp. obtained from rhizosphere saline soils in the United Arab Emirates (UAE) were initially tested for their ability to tolerate high NaCl concentration (25 g L-1). Out of these 62 Streptomyces spp. Only 47 were shown to be tolerant to NaCl at the rate of 25 g L-1. All these isolates were further tested for their abilities to solubilize insoluble forms of phosphorus. Only 25 isolates have been shown to be phosphorus solubilizes. Out of the 25 phosphorus-solubilizing actinomycetes only the strongest 15 isolates were tested for their abilities to colonize tomato roots in vitro and in the greenhouse and to show strong rhizosphere competence potential and also to produce auxins (indole-3-acetic acid)(IAA) and polyamines (putrescine, spermidine and spermine) in their culture filtrates.

In addition, out of the 22 non-phosphorus solubilizing isolates, only 10 isolates produced auxins and polyamines in their culture filtrates. These 10 isolates were also tested for their abilities to colonize tomato roots and to show rhizosphere competence potential. Only four isolates were able to colonize tomato roots. The three outstanding and most promising rhizosphere competent were identified as Streptomyces spp. Isolate # 6 (S. rochei) was a phosphorus solubilizing and auxins and polyamines producing isolate. Isolate # 33 (S. pactum) was a phosphorus solubilizing and not auxins and not polyamines producing isolate. Isolate # 49 (S. noursei) was a non-phosphorus solubilizing and auxins and polyamines producing isolate. These three outstanding and most promising actinomycetes in the present study that showed the strongest rhizosphere competence and root colonization potential were further selected for a greenhouse experiment to study their effects on tomato growth in saline soils. The application of isolate # 6 (S. rochei) enhanced the growth and development of tomato seedlings in the greenhouse experiment compared to other treatments.

In this treatment, there were significant (P<0.05) increases in the dry weight and length of roots and shoots, compared to the tomato plants treated with the isolate # 33 (S. pactum) or isolate # 49 (S. noursei).In the present study, tomato plants grown in soils inoculated with isolate # 6 had significantly (P<0.05) higher levels of endogenous plant nutrients in the roots and shoots than those plants grown in soils inoculated with isolate # 33 or with isolate # 49 or the control plants grown in soils not amended with any actinomycete isolates. Tomato plants in soils inoculated with isolate # 33 had significantly (P<0.05) higher levels of endogenous plant nutrients in the roots and shoots than those plants grown in soils inoculated with isolate # 49 or the control plants grown in soils not amended with any actinomycete isolates. In the present study, tomato plants grown in soils inoculated with isolate # 6 had significantly (P<0.05) higher levels of endogenous IAA and endogenous polyamines than those plants grown in soils inoculated with isolate # 33 or with isolate # 49 or the control plants grown in soils not amended with any actinomycetes isolate. However, tomato plants in soils inoculated with isolate # 49 had significantly (P<0.05) higher levels of endogenous IAA and polyamines than those plants grown in soils inoculated with isolate # 33 or the control plants. These three promising streptomycete actinomycetes is considered to have the potential to perform as biological inoculant to promote the growth of tomato plants in nutrient impoverished saline soils in arid coastal areas in the UAE. The present study is the first to demonstrate the potential of salt tolerant phosphorus solubilizing and auxins and polyamines producing actinomycetes to promote tomato growth under greenhouse conditions as all the work done to date (to the best of my knowledge) have been done using non salt tolerant actinomycetes isolates. It is also concluded that the application of environmentally friendly actinomycetes, which can increase the salt tolerance response in crop plants, can enhance plant growth and productivity in saline sandy soil such as those found in the UAE.

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