Suzana Kristek

Inoculation of Sugar Beet Seed with Bacteria P. fluorescens, B. subtilis and B. megaterium – Chemical Fungicides Alternative

Seed inoculation with the bacteria showing antagonistic activity against pathogenic fungi such as Rhizoctonia solani, Pythium ultimum, P. debarianum, Phoma betae and Aphanomyces cochlioides account for an alternative to chemical fungicides and an option of solving problem of disease control, not only in sugar beet, but in other, mainly vegetable crops.

The influence of mycorrhizae on pea yield and quality in drought caused stress conditions

Mycorrhizas are associates of fungi, representatives of Zygomyceta, Basidiomyceta and Ascomyceta living on the higher plant roots. Mycorrhizal fungi fossil residues were found on the roots of the first vascular plants derived from the Devon period approx. 400 mil. years B. C. Botanists think that this symbiotic association played an essential role in developing and spreading vascular plants on the earth. However, regardless of their effect on vascular plants development of mycorrhizal fungi affected soil development. They produce humous components and an organic sticky substance (extra-cellular polysaharides) that hold soil into aggregates resulting in a well structured soil of good porosity and a large mycorrhizas intake in the total microbial bio-mass. These fungi colonize roots in about 90% of the vascular plants. The symbiotic association between higher plants and mycorrhizal fungi is highly-interrelated whereby plants benefit from their symbiont whereas fungi gets photosynthesis-formed carbon compounds. Owing to a dense hyphas network that interweaves large soil volume, an effective root absorption zone increases via hyphas. However, the mycorrhizal fungi also extracts chemical agents, thereby, making available elements such as phosphorus, iron, zinc, copper, boron, otherwise presented in low concentrations in a soluble form. Mycorrhizas produce antibiotics protecting plants from parasitic fungi and nematodes whereas owing to hypha network around a root, a plant is protected against parasites. Mycorrhized plants are more resistant to a drought-caused stress, have better and more adequate root system and vascular tissue development. Due to the aforesaid, dry conditions are characterized by plants having higher survival percent and higher yield elements compared to non-mycorrhized ones. Thanks to the traits of this symbiosis and all benefits possessed by mycorrhized plants compared to non-mycorrhized, an agricultural production does not rely only on the indigenous strains of these fungi but inoculation of seedling seed and root is done by a compatible strain of mycorrhizal fungi. Inoculation is done by a dry treatment or wet one in a way that the inoculum suspended is water prior to inoculation (similar to legume seed inoculation with bio-preparations of the nodule bacteria). This procedure is capable for ensuring effective symbiosis and reducing mineral fertilizer and pesticide requirements being very important from economical and ecological aspect.

Use of the bacteria Pseudomonas fluorescens in the control of sugar beet root decay agent — Rhizoctonia solani

In Republic of Croatia sugar beet is grown on approximately 30 000 ha, with an average yield of 37 t/ha and sugar content of 14, 4% Reasons for such a low production results after the Patriotic War are found in inadequate soil management, devastated soil structure, and climatic conditions. The result of the stated is high degree of disease development. Apart from beet leaf spot (C. beticola) and the disease induced by Rhyzomanie virus, the most serious issue is root rot of beet induced by pathogenic fungi (P. betae, P. ultimum, P. debarianum, R. solani, Fusarium spp., and A. cochlioides). Depending on the soil and climatic conditions, 10-50% of plants have been decaying being attacked by the pathogenic fungi. Growth of the surviving plants is slowed significantly giving them no possibility to reach normal size, which finally reflects on yield and sugar content values. Major measure in the control of sugar beet root decay agent is application of fungicides in the course of seed processing. However, though chemical fungicides prevent development of the fungi to some degree, they are at a disadvantage affecting human health and environment (being exposed to washing out, they give rise to underground water eutrophication). Moreover, pathogenic fungi have ability to rapidly develop resistance to the fungicides applied. Acceptable alternative to the application of chemical pesticides is seed inoculation with the bacteria P. fluorescens and T. harzianum that express antagonism against pathogenic fungi. Since the benefit bacteria do not express sensitivity to the low fungicide doses, on the soils heavily infected with the fungi – the root decay agents on sugar beet, positive effect was accomplished by combining seed inoculation with the bacterium P. fluorescens and the seed treatment with low doses of fungicides. Pathogenic fungi R. solani is found to be the most serious issue, so the influence of the bacterium P. fluorescens to the pathogenic fungi – the root decay agent of sugar beet, has been investigated.