The Potential of Cell-free Cultures of Rhizobium leguminosarum, Azotobacter chroococcum and Compost Tea as Biocontrol Agents for Faba Bean Broomrape (Orobanche crenata Forsk.)

Yasser El-Halmouch

doi:10.4172/2157-7471.1000205

Abstract

In the present study, cell-free cultures of four isolates of Rhizobium leguminosarum, an isolate of Azotobacter chroococcum and compost tea were investigated for their biocontrol potential against the root parasitic weed Orobanche crenata. Individual cell-free cultures of Azotobacter chroococcum or Rhizobium sp., dual and mixture of cell-free cultures of Rhizobium spp. or compost tea were applied to infested pots in greenhouse conditions. The treatments showed variable effects on many developmental parameters of both faba bean and broomrape. Significant decrease in the number of broomrape attachments, dry weight of the attached tubercles on faba bean roots and the reduction in percentage of broomrape seed germination were recorded. Compost tea, individual and mixture of R. leguminosarum isolates were more reducing on broomrape germination and growth than A. chroococcum alone did; being the former treatment is the best. The reduction in broomrape incidence by compost tea was due to certain phenotypic mechanisms, which acted alone or in combination. These mechanisms included negative effect of natural stimulant broomrape on seed germination, prevention of radical penetration inside the host roots, parasite yield reduction, and thus increasing the growth and vitality of faba bean. In vitro experiment indicated that seed germination percentage of broomrape was also negatively affected by the combination of root-exudates and compost tea. Radical apexes of the germinated seeds were distorted. These distortions may prevent the radicals to follow up the infestation. In conclusion, the study presents the potential of R. leguminosarum isolates and compost tea in biocontrol of broomrape. More investigations should be carried out with viable bacterial cells on the parasite plant before use in sustainable agricultural systems.

Highlights

Phytoparasitic weeds are known as destructive parasites on many agricultural crops in the Mediterranean region, Eastern Europe and North Africa [1,2]
Due to the scarce of information about the control of Orobanche by free living and symbiotic nitrogen fixing bacteria, this study aimed to evaluate the potential of individual and mixture of R. leguminosarum isolates, A. chroococcum and compost tea to control faba bean infection by O. crenata
In the two pot experiments, many parameters were used to evaluate the resistance of faba bean cultivars to O. crenata; two specific for the parasite, and six specific for the host

Summary

Introduction

Phytoparasitic weeds are known as destructive parasites on many agricultural crops in the Mediterranean region, Eastern Europe and North Africa [1,2]. Orobanche crenata is the most dangerous and the most widespread Orobanche species in the Mediterranean region and Western Asia. It is a major constraint for faba beans, field peas, lentils, vetches and various forage legumes [3]. The main impact of the biocontrol agent is the reduction of the seed germination [6,7], germ tube-host attachment or seed production, resulting in the prevention of supplementary infestation and seed dissemination, and leading to a reduction of the seed bank in the soil [8]. Toxins from soil-borne pathogens that inhibit Orobanche seed germination could prevent attachment of the parasite. The most common soil-borne pathogens isolated from diseased Orobanche plants belong to the genus Fusarium [10]

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Conclusion