Broomrape (Orobanche cumana Wallr.) can Influence the Microbial Cenosis in Sunflower Rhizosphere

Abstract The bacterial and micromycete complexes in the rhizosphere of sunflower plants non-infected and infected with broomrape (Orobanche cumana Wallr.) have been compared. The investigations were carried out in the conditions of a stationary infectious field which was annually enriched with infected plant residues and broomrape seeds collected in different regions of Ukraine. Soil is leached, low-humic chernozem with acidic pH. The soil samples selected at the end of vegetation from the rhizosphere of healthy and infected with broomrape plants of sunflower breeding samples. The total number of bacteria found in the rhizosphere of sunflower plants infected by the parasite did not differ significantly from the control and was 11.7 and 12.1 million CFU / g of soil, respectively. The numbers of ammonifiers as well as bacterial microflora, using for its life mineral nitrogen, and pedotrophs and oligotrophs in the compared soil samples did not differ significantly, and generally corresponded to this type of soil. Although in general, both tested samples of soil were characterized by a low content of bacteria of the genus Azotobacter, the number of representatives of this genus in the rhizosphere of parasite-infected plants was somewhat less than in control (35 % and 21 %, respectively). However, unlike most bacteria, the number of micromycetes detected on Czapek-Dox and starch-ammonia agar media, in the rhizosphere of plants infected by broomrape almost twice exceeded the number of these microorganisms in the rhizosphere of healthy plants. Analysis of the generic and species composition of microscopic fungi showed that in the rhizosphere of sunflower plants infected by the parasite a very specific mycocenosis was formed that differ from a mycocenosis of healthy plants. This mycocenosis was characterized by a much smaller number of genera and species of micromycetes. At the same time for the structure of the fungal cenosis of diseased plants there was a characteristic increase in the proportion of toxin-forming fungi of the Aspergillus and Penicillium genera with active conidiogenesis. The obtained data testify not only to the differences in the microbial complexes in the rhizosphere of sunflower plants non-infected and infected by broomrape, but also indicate the direction of action of this parasite.