Endophytic actinomycetes from spontaneous plants of Algerian Sahara: indole-3-acetic acid production and tomato plants growth promoting activity

Twenty-seven endophytic actinomycete strains were isolated from five spontaneous plants well adapted to the poor sandy soil and arid climatic conditions of the Algerian Sahara. Morphological and chemotaxonomical analysis indicated that twenty-two isolates belonged to the Streptomyces genus and the remaining five were non- Streptomyces. All endophytic strains were screened for their ability to produce indole-3-acetic acid (IAA) in vitro on a chemically defined medium. Eighteen strains were able to produce IAA and the maximum production occurred with the Streptomyces sp. PT2 strain. The IAA produced was further extracted, partially purified and confirmed by thin layer chromatography (TLC) analysis. The 16S rDNA sequence analysis and phylogenetic studies indicated that strain PT2 was closely related to Streptomyces enissocaecilis NRRL B 16365T, Streptomyces rochei NBRC 12908T and Streptomyces plicatus NBRC 13071T, with 99.52 % similarity. The production of IAA was affected by cultural conditions such as temperature, pH, incubation period and L-tryptophan concentration. The highest level of IAA production (127 lg/ml) was obtained by cultivating the Streptomyces sp. PT2 strain in yeast extract-tryptone broth supplemented with 5 mg L-tryptophan/ ml at pH 7 and incubated on a rotary shaker (200 rpm) at 30°C for 5 days. Twenty-four-hour treatment of tomato cv. Marmande seeds with the supernatant culture of Streptomyces sp. PT2 that contained the crude IAA showed the maximum effect in promoting seed germination and root elongation

Plant growth-promoting actinobacteria: a new strategy for enhancing sustainable production and protection of grain legumes

Grain legumes are a cost-effective alternative for the animal protein in improving the diets of the poor in South-East Asia and Africa. Legumes, through symbiotic nitrogen fixation, meet a major part of their own N demand and partially benefit the following crops of the system by enriching soil. In realization of this sustainability advantage and to promote pulse production, United Nations had declared 2016 as the “International Year of pulses”. Grain legumes are frequently subjected to both abiotic and biotic stresses resulting in severe yield losses. Global yields of legumes have been stagnant for the past five decades in spite of adopting various conventional and molecular breeding approaches. Furthermore, the increasing costs and negative effects of pesticides and fertilizers for crop production necessitate the use of biological options of crop production and protection. The use of plant growth-promoting (PGP) bacteria for improving soil and plant health has become one of the attractive strategies for developing sustainable agricultural systems due to their eco-friendliness, low production cost and minimizing consumption of non-renewable resources. This review emphasizes on how the PGP actinobacteria and their metabolites can be used effectively in enhancing the yield and controlling the pests and pathogens of grain legumes

Management of Soil-Borne Diseases of Grain Legumes Through Broad-Spectrum Actinomycetes Having Plant Growth-Promoting and Biocontrol Traits

Chickpea (Cicer arietinum L.) and pigeonpea (Cajanus cajan L.) are the two important grain legumes grown extensively in the semiarid tropics (SAT) of the world, where soils are poor in nutrients and receive inadequate/erratic rainfall. SAT regions are commonly found in Africa, Australia, and South Asia. Chickpea and pigeonpea suffer from about 38 pathogens that cause soil-borne diseases including wilt, collar rot, dry root rot, damping off, stem canker, and Ascochyta/Phytophthora blight, and of which three of them, wilt, collar rot, and dry root rot, are important in SAT regions. Management of these soil-borne diseases are hard, as no one control measure is completely effective. Advanced/delayed sowing date, solarization of soil, and use of fungicides are some of the control measures usually employed for these diseases but with little success. The use of disease-resistant cultivar is the best efficient and economical control measure, but it is not available for most of the soil-borne diseases. Biocontrol of soil-borne plant pathogens has been managed using antagonistic actinobacteria, bacteria, and fungi. Actinobacterial strains of Streptomyces, Amycolatopsis, Micromonospora, Frankia, and Nocardia were reported to exert effective control on soil-borne pathogens and help the host plants to mobilize and acquire macro- and micronutrients. Such novel actinomycetes with wide range of plant growth-promoting (PGP) and antagonistic traits need to be exploited for sustainable agriculture. This chapter gives a comprehensive analysis of important soil-borne diseases of chickpea and pigeonpea and how broad-spectrum actinomycetes, particularly Streptomyces spp., could be exploited for managing them