Qurban Ali Panhwar

Isolation and characterization of phosphate-solubilizing bacteria from aerobic rice

Phosphate-solubilizing bacteria are frequently used as plant growth promoters. A study was conducted to isolate phosphate-solubilizing bacteria (PSB) from aerobic rice grown in Penang Malaysia and to determine some biochemical properties of the isolates such as, organic acids, enzymes, indoleacetic acid (IAA), siderophore production and its antagonistic effect against pathogen Rhizoctonia solani. Selective media used for the isolation were; Pseudomonas aeruginosa (PA), national botanical research institutes phosphate growth medium (NBRIP), Pikovskaya and Pseudomonas spp. (PS). Organic acid production was determined using high performance liquid chromatography (HPLC). The PSB populations were higher in rhizosphere than non-rhizospheric soil and the highest population was found in PS and Pikovskaya, while the lowest was found in PA media plates. The highest P solubilizing activity (69.58%) was found in PSB9 strain grown in NBRIP plate. Isolated PSB were able to produce different organic acids and growth hormone such as IAA. A number of PSB isolates belong to the Bacillus sp. and proved for the antagonistic effect against R. solani (sheath blight) even though most of the isolated strains can grow in nitrogen, free semi-solid medium and able to produce siderophore. PSB inoculants with their beneficial traits would be considered as potential biofertilizer for the sustainable aerobic rice cultivation system.

Biochemical and molecular characterization of potential phosphate-solubilizing bacteria in acid sulfate soils and their beneficial effects on rice growth.

A study was conducted to determine the total microbial population, the occurrence of growth promoting bacteria and their beneficial traits in acid sulfate soils. The mechanisms by which the bacteria enhance rice seedlings grown under high Al and low pH stress were investigated. Soils and rice root samples were randomly collected from four sites in the study area (Kelantan, Malaysia). The topsoil pH and exchangeable Al ranged from 3.3 to 4.7 and 1.24 to 4.25 cmolc kg−1, respectively, which are considered unsuitable for rice production. Total bacterial and actinomycetes population in the acidic soils were found to be higher than fungal populations. A total of 21 phosphate-solubilizing bacteria (PSB) including 19 N2-fixing strains were isolated from the acid sulfate soil. Using 16S rRNA gene sequence analysis, three potential PSB strains based on their beneficial characteristics were identified (Burkholderia thailandensis, Sphingomonas pituitosa and Burkholderia seminalis). The isolated strains were capable of producing indoleacetic acid (IAA) and organic acids that were able to reduce Al availability via a chelation process. These PSB isolates solubilized P (43.65%) existing in the growth media within 72 hours of incubation. Seedling of rice variety, MR 219, grown at pH 4, and with different concentrations of Al (0, 50 and 100 µM) was inoculated with these PSB strains. Results showed that the bacteria increased the pH with a concomitant reduction in Al concentration, which translated into better rice growth. The improved root volume and seedling dry weight of the inoculated plants indicated the potential of these isolates to be used in a bio-fertilizer formulation for rice cultivation on acid sulfate soils.

Application of potential phosphate-solubilizing bacteria and organic acids on phosphate solubilization from phosphate rock in aerobic rice.

A study was conducted at Universiti Putra Malaysia to determine the effect of phosphate-solubilizing bacteria (PSB) and organic acids (oxalic & malic) on phosphate (P) solubilization from phosphate rock (PR) and growth of aerobic rice. Four rates of each organic acid (0, 10, 20, and 30 mM), and PSB strain (Bacillus sp.) were applied to aerobic rice. Total bacterial populations, amount of P solubilization, P uptake, soil pH, and root morphology were determined. The results of the study showed significantly high P solubilization in PSB with organic acid treatments. Among the two organic acids, oxalic acid was found more effective compared to malic acid. Application of oxalic acid at 20 mM along with PSB16 significantly increased soluble soil P (28.39 mg kg−1), plant P uptake (0.78 P pot−1), and plant biomass (33.26 mg). Addition of organic acids with PSB and PR had no influence on soil pH during the planting period. A higher bacterial population was found in rhizosphere (8.78 log10 cfu g−1) compared to the nonrhizosphere and endosphere regions. The application of organic acids along with PSB enhanced soluble P in the soil solution, improved root growth, and increased plant biomass of aerobic rice seedlings without affecting soil pH.

Bio-Fertilizer, Ground Magnesium Limestone and Basalt Applications May Improve Chemical Properties of Malaysian Acid Sulfate Soils and Rice Growth

Acid sulfate soils are normally not suitable for crop production unless they are appropriately ameliorated. An experiment was conducted in a glasshouse to enhance the growth of rice, variety MR219, planted on an acid sulfate soil using various soil amendments. The soil was collected from Semerak, Kelantan, Malaysia. Ground magnesium limestone (GML), bio-fertilizer, and basalt (each 4 t ha−1) were added either alone or in combinations into the soil in pots 15 d before transplanting. Nitrogen, P and potash were applied at 150, 30, and 60 kg ha−1, respectively. Three seven-day-old rice seedlings were transplanted into each pot. The soil had a pH of 3.8 and contained organic C of 21 g kg−1, N of 1.2 g kg−1, available P of 192 mg kg−1, exchangeable K of 0.05 cmolc kg−1, and exchangeable Al of 4.30 cmolc kg−1, with low amounts of exchangeable Ca and Mg (0.60 and 0.70 cmolc kg−1). Bio-fertilizer treatment in combination with GML resulted in the highest pH of 5.4. The presence of high Al or Fe concentrations in the control soil without amendment severely affected the growth of rice. At 60 d of growth, higher plant heights, tiller numbers and leaf chlorophyll contents were obtained when the bio-fertilizer was applied individually or in combination with GML compared to the control. The presence of beneficial bacteria in bio-fertilizer might produce phytohormones and organic acids that could enhance plant growth and subsequently increase nutrient uptake by rice. Hence, it can be concluded that addition of bio-fertilizer and GML improved rice growth by increasing soil pH which consequently eliminated Al and/or Fe toxicity prevalent in the acid sulfate soil.

Eliminating aluminum toxicity in an acid sulfate soil for rice cultivation using plant growth promoting bacteria.

Aluminum toxicity is widely considered as the most important limiting factor for plants growing in acid sulfate soils. A study was conducted in laboratory and in field to ameliorate Al toxicity using plant growth promoting bacteria (PGPB), ground magnesium limestone (GML) and ground basalt. Five-day-old rice seedlings were inoculated by Bacillus sp., Stenotrophomonas maltophila, Burkholderia thailandensis and Burkholderia seminalis and grown for 21 days in Hoagland solution (pH 4.0) at various Al concentrations (0, 50 and 100 μM). Toxicity symptoms in root and leaf were studied using scanning electron microscope. In the field, biofertilizer (PGPB), GML and basalt were applied (4 t·ha−1 each). Results showed that Al severely affected the growth of rice. At high concentrations, the root surface was ruptured, leading to cell collapse; however, no damages were observed in the PGPB inoculated seedlings. After 21 days of inoculation, solution pH increased to >6.0, while the control treatment remained same. Field study showed that the highest rice growth and yield were obtained in the bio-fertilizer and GML treatments. This study showed that Al toxicity was reduced by PGPB via production of organic acids that were able to chelate the Al and the production of polysaccharides that increased solution pH. The release of phytohormones further enhanced rice growth that resulted in yield increase.

Phosphate-Solubilizing Bacteria Improves Nutrient Uptake in Aerobic Rice

Phosphate-solubilizing bacteria (PSB) are frequently used in agriculture as plant growth promoters because they provide soluble P to growing plants by solubilizing complex soil inorganic phosphates like Al-P, Fe-P, and Ca-P. Several PSB strains isolated from local aerobic rice are able to solubilize P from insoluble P through production of organic acids, for example, oxalic, malic, succinic, and propionic acids. Hence, the application of PSB plays a vital role in supplying P to growing plants. The application of PSB strains in this study solubilized higher P from the soil and significantly enhanced plant uptake in aerobic rice. Besides possessing P-solubilizing activity, PSB has greater potential to produce phytohormones, for example, indoleacetic acid, and enzymes like phosphatase and phytases. The continuous supply of soluble P to soil P pool and phytohormones in the root environment have resulted in the increased P uptake and consequently improved the growth of aerobic rice. The impact of PSB on aerobic rice is highlighted in this chapter.

Biomolecular Characterization of Diazotrophs Isolated from the Tropical Soil in Malaysia

This study was conducted to evaluate selected biomolecular characteristics of rice root-associated diazotrophs isolated from the Tanjong Karang rice irrigation project area of Malaysia. Soil and rice plant samples were collected from seven soil series belonging to order Inceptisol (USDA soil taxonomy). A total of 38 diazotrophs were isolated using a nitrogen-free medium. The biochemical properties of the isolated bacteria, such as nitrogenase activity, indoleacetic acid (IAA) production and sugar utilization, were measured. According to a cluster analysis of Jaccard’s similarity coefficients, the genetic similarities among the isolated diazotrophs ranged from 10% to 100%. A dendogram constructed using the unweighted pair-group method with arithmetic mean (UPGMA) showed that the isolated diazotrophs clustered into 12 groups. The genomic DNA rep-PCR data were subjected to a principal component analysis, and the first four principal components (PC) accounted for 52.46% of the total variation among the 38 diazotrophs. The 10 diazotrophs that tested highly positive in the acetylene reduction assay (ARA) were identified as Bacillus spp. (9 diazotrophs) and Burkholderia sp. (Sb16) using the partial 16S rRNA gene sequence analysis. In the analysis of the biochemical characteristics, three principal components were accounted for approximately 85% of the total variation among the identified diazotrophs. The examination of root colonization using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) proved that two of the isolated diazotrophs (Sb16 and Sb26) were able to colonize the surface and interior of rice roots and fixed 22%–24% of the total tissue nitrogen from the atmosphere. In general, the tropical soils (Inceptisols) of the Tanjong Karang rice irrigation project area in Malaysia harbor a diverse group of diazotrophs that exhibit a large variation of biomolecular characteristics.

Management of Acid Sulfate Soils for Sustainable Rice Cultivation in Malaysia

Acid sulfate soils are an alternative aspect for the sustainable rice cultivation. Mostly these soils are not suitable for the crop production unless are effectively improved. Acid sulfate soils have toxicity due to the presence of high Aluminum (Al), and iron (Fe) with low pH (<4.0). Usually these types of soils have nutrient deficiency especially in phosphorus, which causes poor plant growth and development. The soils need to be improved with some soil amendments like application of basalt, ground magnesium limestone and organic materials (biofertilizer) that can increase the soil pH, improve soil nutrients and reduce the Al and Fe toxicity. The application of biofertilizer can enhance the rice plant growth, and yield by producing plant growth hormones (IAA) and organic acids that can chelate Al toxicity and solublize insoluble form of phosphorus in the soil. Hence, using ground magnesium limestone, basalt and biofertilizer, rice cultivated on acid sulfate soils can produce yield equivalent to that of the granary areas of Malaysia.

Biofertilizer as a Supplement of Chemical Fertilizer for Yield Maximization of Rice

Biofertilizer performs major role in crop production. A study was conducted to determine the effect of bio-organic fertilizer with reduced chemical fertilizer for rice yield maximization. The treatments were (i) control (without fertilizer), (ii) N, P, K at recommended rate i.e. 100% (120, 30, 60 kg ha -1 ), (iii) N and P (75%), and K (recommended rate) with biofertilizer (5 t ha -1 ) and (iv) N and P (50%), and K (recommended rate) with biofertilizer (10 t ha -1 ). Results showed that N and P (50%) with biofertilizer (10 t ha -1 ) increased the number of tillers (29), panicle length (28 cm), weight of 1000 grain (21.31 g), and produced the highest grain yield (7.26 t ha -1 ). There was no significant difference found among the N, P (75%) with biofertilizer (5 t ha -1 ) and N, P (50%) with biofertilizer (10 t ha -1 ) treatments for plant height, number of panicle plant -1 and harvest index (%). The application of biofertilizer with beneficial microbes improved the leaf chlorophyll, plant nutrient uptake and grain protein content in rice. Hence, the use of chemical N and P fertilizer can be minimized by 50 percent and improve rice yield with the supplement of 5 ton ha -1 of bio-organic fertilizer.

Soil Properties (Physical, Chemical, Biological, Mechanical)

Introduction ............................................................................................................ 104 Physical Properties of Malaysian Soils .................................................................. 105 Soil Physical Properties..................................................................................... 105 Chemical Properties of Malaysian Soil .................................................................. 112 Cation Exchange Capacity ................................................................................ 112 Soil Acidity........................................................................................................ 113 Processes of Acid Generation in Soils ................................................................... 113 Natural Ecosystems ................................................................................................ 113 Highly Weathered Soils ..................................................................................... 113 Acid Sulfate Soils .............................................................................................. 114 Peatland ............................................................................................................. 115 Ways to Overcome Soil Acidity ............................................................................. 117 Soil Organisms, Their Beneficial Activities, Habitat, and Diversity in the Soils of Malaysia .................................................................................................... 118 Introduction ....................................................................................................... 118 Soil Organisms ....................................................................................................... 118 Macroorganisms ................................................................................................ 119 Functions of the Macroorganisms ................................................................ 121 Soil Microorganisms ......................................................................................... 126 Functions and Beneficial Characters of the Soil Microorganisms ......................... 127 Releasing Nutrients from Organic Matter ......................................................... 127 Fixing Atmospheric Nitrogen ............................................................................ 127 Legumes ....................................................................................................... 127 Symbiotic Nitrogen Fixation ........................................................................ 128 Nonsymbiotic Nitrogen Fixation .................................................................. 128 Diazotrophs Associations in Rice ................................................................. 128 Increasing Phosphorus Availability ................................................................... 129 Phosphate-Solubilizing Bacteria .................................................................. 129