Zbornik Matice srpske za prirodne nauke / Proc. Nat. Sci, Matica Srpska Novi Sad, ¥110, 103—108, 2006
UDC 633.63:632.4(497.113)
V e r a B. S t o j š i n1, F e r e n c F. B a g i1, S t e v a n M. J a s n i ã2, F e r e n c F. B a l a ÿ1, D r a g a n a B. B u d a k o v1
1 Faculty of Agriculture, Department of Plant and Environmental Protection Dositeja Obradoviãa 8, 21000 Novi Sad, Serbia and Montenegro
2 Scientific Institut of Field and Vegetable Crops,
Maksima Gorkog 30, 21000 Novi Sad, Serbia and Montenegro
RHIZOCTONIA ROOT ROT (
RHIZOCTONIA SOLANI
K Ü H N.) OF SUGAR BEET IN PROVINCE VOJVODINA*
ABSTRACT: Sugar beet root rot appears regularly each year, but its intensity de-pends on agro ecological conditions. The predominant causers of root rot in Vojvodina are fungi fromFusariumgenus and speciesMacrophomina phaseolina. Over the last couple of years, more intense occurrence of Rhizoctonia root rot has been observed.
Rhizoctonia solani, the causal agent of root rot is present in sugar beet fields. During 2000—2005, on the territory of Vojvodina, the frequency ofRhizoctonia solaniin phytopat-hological isolations from rotted sugar beet roots was between 0,0—18,2%. The intensity of the disease depends on localities, agro ecological conditions and genotypes.
Symptoms ofRhizoctoniaroot rot were registered at some localities in all regions of Vojvodina: Srem, Banat and Baåka. The disease appearance is above all local. It occurs in small patches, on heavy, non-structured soil and on depressed, wet parts of plots. Individual diseased plants can be found during July. Brown rot appears on sugar beet roots, with dried tissue on surface, which is present on the tail as well as on the middle part and the head of root. Tissues with described symptoms are deeper regarding the healthy part of root. On vertical root section, the necrotic changes are clearly visible comparing to tissue section without symptoms. The heavily infected tissue forms fissures on roots in most cases. Besi-des the above-mentioned symptoms on roots, the plant wilting and leaf handle necrosis as well as leaf dying are also observed. When rot spreads to the whole root head, plants quickly die.
KEY WORDS: distribution, aetiology,Rhizoctoniaroot rot,Rhizoctonia solani, sugar beet, Vojvodina
INTRODUCTION
Various types of rot on sugar beet root have become more and more frequent in the last couple of years and have caused economically significant losses in our country (S t o j š i n, 2003, M a r i ã and S t o j š i n, 2004).
There are a lot of available data on parasites that cause root rot. The first noteworthy occurrence and greater losses were registered during 1960s in Ba-nat and the north part of Baåka (M a r i ã et al., 1970). Later, in the last deca-de of 20thand at the beginning of 21stcentury, root rot occurred, usually in dry years, when it caused economically significant losses which manifested in dec-rease of yield and digestion. According to many authors (M a r i ã et al., 1970, S t o j š i n et al. 2001, J a s n i ã et al., 2001, J a s n i ã et al., 2004, P e j o -v i ã et al., 2003, M a r i ã and S t o j š i n, 2004, S t o j š i n, 2003), Fusa-rium root rot is the most important root disease in our country. This one, to-gether with charcoal root rot (Macrophomina phaseolina) causes huge dama-ges on sugar beet, especially in dry years (M a r i ã et al., 1970, S t o j š i n, 1993, S t o j š i n, et al., 1999). Other species like Thanatephorus cucumeris (anamorphic Rhizoctonia solani) — Rhizoctonia root rot, Erwinia carotovora — causal agent of bacterial soft rot, Streptomyces scabies — the causal agent of scab root, Pleospora bjoerlingii (anamorphic Phoma betae) — seedling damping-off, etc. appear from time to time on individual plots or isolated plants and they are not harmful to sugar beet in Vojvodina (M a r i ã and S t o j š i n, 2004). Nevertheless, some authors claim that Rhizoctonia root rot (Rhizoctonia solani) is spread in Vojvodina and that it can cause significant losses in some years, especially in Srem (V i c o et al., 2004).
MATERIAL AND METHODS
Collecting root samples
Root rot was evidenced in more localities in Vojvodina and was being followed during vegetative periods in years from 2000 to 2005. In order to di-agnose and identify the cause of root rot and to examine symptoms of decay, sample roots with symptoms of the rot were collected from different localities. The roots were selected randomly and the part of roots with typical symptoms was used for isolation and determination of parasites that cause rot.
Isolation
Phytopathological isolations were done by standard procedure, which me-ans isolation on Potato Dextrose Agar (PDA) medium, in Petri dishes and in-cubation in thermostat at 25°C. After the colony development, isolates were transferred in order to get pure cultures and to determine the fungus.
Determination
THE RESULTS AND DISCUSSION
Phytopathological isolations
During experimental period,Fusarium species were predominant pathoge-nes which caused sugar beet root rot in Vojvodina (40,8%). Species like Mac-rophomina phaseolina (2,86%), Rhizoctonia solani (8,94%) and other fungi genera were registered in lower percentage (19,76%) (Table 1).
Table 1. Isolation from diseased sugar beet roots in different locations in Vojvodina (2000—2004)
Year of diseasedNumber roots
Isolated fungi (%)
Fusarium
spp. R. solani Macrophominaphaseolina
Others saprophytic
organisms
2000 99 68,8 0,0 2,5 6,0
2001 30 16,7 10,0 0,0 6,7
2002 60 26,3 4,7 4,7 48,3
2003 30 61,3 11,8 7,1 23,3
2004 55 30,9 18,2 0,0 14,5
Average 54,8 40,8 8,94 2,86 19,76
Symptoms of Rhizoctonia root rot
The first symptoms which could be noticed on diseased plants are sudden chlorosis and wilting of leaves. Black necrosis of leaf stems appear, especially on leaves close to the root head. Faded, wilted leaves quickly collapse and form brown to black rosette, which is present throughout the whole vegetative period. Root rot can be complete or partial. Brown to black parts of tissue ap-pear on diseased root. They can unify and capture one part or the whole root. Deep fissures are usually located near the head of the root. In humid conditi-ons, tissue can soften and symptoms of wet rot are present then. Another type of symptom is dry rot, which manifests itself in lesions which are light and dark brown, in the shape of concentric circles. Under the lesions, parasite mycelium is formed with clearly distinguished margins between healthy and diseased tissue.
DISCUSSION
Para-site causes greater losses when sugar beet is grown (B u d d e r m e y e r and P e t e r s e n, 2004) in monoculture (inadequate crop rotation) or in frequent breeding on one parcel only (M a r i ã, 1992, B u d d e r m e y e r and P e -t e r s e n, 2004, W e s -t e r d i j k e-t al., 2004). Therefore, concerning all -these reasons, it is necessary to use integrated control to fight Rhizoctonia root rot, caused by R. solani. These means that control should include improved culti-vation practice, then the use of fungicides as well as biological means of con-trol against the disease.
One of the most important measures concerning cultivation practice is crop rotation. On the parcels where sugar beet is grown in monoculture, the percentage of Rhizoctonia root rot is significantly higher, while on those par-cels with preceding cereal crops (wheat or barley) or grasses, the frequency of diseased plants is much lower (W e s t e r d i j k et al., 2004).
On compacted soil the intensity of the disease is higher. That is why soil impacting and compressing should be avoided. Soil for sugar beet breeding ne-eds to be loose and well-aerated.
Also, it is recommended to breed resistant sugar beet variants, since the resistant genotypes exist. However, environmental conditions and the amount of inoculum can effect the resistance degree. Seedlings of resistant sugar beet variants are usually very susceptible to the parasite (W e s t e r d i j k et al., 2004). With the purpose of seedling protection chemical measures are recom-mended. These measures include fungicide treatment of the seeds as well as chemical treatments of young plants. The treatment of young plants with the fungicides on the basis of strobilurin (active substance is azoxystrobin, com-mercial product Quadris) turned out to be a very successful one. According to the results of S t u m p and F r a n c (2003), the use of strobilurin decreases the appearance of root rot in 41—81% and increases yield 3—4 times compa-ring to non-treated control in the conditions of artificial inoculation of sugar beet in field. Seed treatment with protective fungicides (Maneb, Mankozeb and Tiram) is efficient in seedling protection.
Biological measures against damping-off and flattening of the seedlings, since they are non-resistant to R. solani are usually recommended and they in-clude seed treatment with spore suspension ofTrichoderma virens fungus. So-me of these isolates express high efficiency against seedling damping-off ( H a n s o n, 2003). It is well known that fungus from Trichoderma genus form antibiotics, which inhibit the development of other fungi species (H o -w e l l et al., 1993). T. harzianum manifests activity against Rhizoctonia root rot, but it does not affect damping-off and flattening of seedlings (R u p p e l et al., 1983).
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RHIZOCTONIA SOLANI K Ü H N. PROUZROKOVAÅ MRKE TRULEŸI
KORENA ŠEÃERNE REPE U VOJVODINI
Vera B. Stojšin1, Ferenc F. Bagi1, Stevan M. Jasniã2,
Ferenc F. Balaÿ1, Dragana B. Budakov1 1 Poqoprivredni fakultet, Trg D. Obradoviãa 8,
Novi Sad, Srbija i Crna Gora
2 Nauåni Institut za ratarstvo i povrtarstvo,
Maksima Gorkog 30, Novi Sad, Srbija i Crna Gora
Rezime
Truleÿ korena šeãerne repe javqa se svake godine u slabijem, ili jaåem intenzitetu, pre svega u zavisnosti od agroekoloških uslova. Dominantni pro-uzrokovaåi truleÿi korena šeãerne repe u našoj zemqi su gqive iz roda
Fusa-riumi Macrophomina phaseolina. Posledwih godina uoåena je intenzivnija
poja-va mrke truleÿi korena šeãerne repe prouzrokopoja-vane od straneRhizoctonia solani.
Rhizoctonia solani, prouzrokovaå mrke truleÿi korena, prisutna je na
poqi-ma pod šeãernom repom. U periodu 2000—2005. na teritoriji Vojvodine zastu-pqenost gqive Rhizoctonia solani u fitopatološkim izolacijama iz korena sa simptomima truleÿi bila je u intervalu 0,0—18,2%. Intenzitet pojave oboqe-wa zavisi od lokaliteta, vremenskih uslova i genotipa.
