Pavel MATUSINSKY − Renata MIKOLASOVA − Tomas SPITZER
Cultivars of winter wheat (Sulamit, Ebi, Drifter and Bill), farming practices (organic and conventional), soil management (ploughing compared to min- and no-tillage) and the preceding crop (cereal, maize and oilseed rape) were studied as factors affecting the incidence of stem-base pathogens. The stem-base diseases were assessed by molecular methods (PCR) at four growth stages. The dynamics of the stem base colonization by these fungi over the growing season were observed, and the association between individual pathogenic fungi was also evaluated. In addition, the fungal leaf sheaths penetration, which can cause physical disturbance, was assessed. The asymptomatic presence of fungal DNA in wheat tissue was confirmed. Microdochium nivale was found on the stem bases most frequently. Other fungi, such as Oculimacula spp., Rhizoctonia cerealis and Fusarium spp., were presented considerable less frequently. The statistical significant association was confirmed only between M. nivale var. nivale and M. nivale var. majus. Out of these, M. nivale tended to decrease in summer season, the frequency of occurrence of Oculimacula spp. and R. cerealis increased at later growth stages. Along with this, these species infected only plants previously colonized by M. nivale. The comparison of organic and conventional farming practices did not result in large differences in the relative incidence of stem-base pest species over the period of this study; nevertheless, a higher frequency of positive detection was recorded for three organisms (O. acuformis, O. yallundae and M. nivale var. nivale) under conventional farming. Other factors had none or only partial effects. Soil management didn’t affect the stem- base pathogens incidence significantly. The preceding crop maize reduced the incidence of M. nivale var. majus.
Key words: brown foot rot, eyespot, PCR diagnostics, sharp eyespot
Introduction
Complex of wheat stem base diseases includes fungal species Oculimacula yallundae and O. acuformis (anamorph: Pseudocercosporella herpotrichoides), Ceratobasidium cerealis (anamorph: Rhizoctonia cerealis), two varieties of Monographella nivalis (anamorphs: Microdochium nivale var. nivale and M. nivale var. majus) and species of the genera Gibberellaand Fusarium. The first three pathogens cause diseases with symptoms of distinct lesions on the stem base just above the crown. When they are severe, the plants are killed or break down at the base. A complex of several species of the fungi Gibberella, Fusarium and Monographella attack wheat plants causing foot and crown rot, by growing from crop residue. The fungus continues to grow into the crown tissue, rotting the crown and destroying the plant tissues responsible for transporting water from the roots to the above-ground parts of the plant (DRAPER et al., 2000). This study is aimed at the dynamics of colonizing wheat stem bases by species of phytopathogenic fungi and associations among these species. Winter wheat cultivars and farming practice was evaluated as a factor affecting incidence of stem-base diseases. Likewise, the other factors such as soil management and preceding crop were studied.
Materials and method
Four winter wheat cultivars (Sulamit, Ebi, Drifter and Bill) were conventionally cultivated after a cereal crop in small-plot field experiments. Certified seed, chemically treated with Vitavax 2000 (Carboxin 200 g l-1 and Thiram
200 g l-1), was used for sowing. Mineral fertilizers (regeneration and production rates of 30 kg N ha-1 each in the
form of ammonium nitrate with limestone) were applied to the stands. Treatment with herbicides was carried out in the autumn. A system of fungicidal treatments against leaf and ear diseases was applied (stem-base diseases were not chemically controlled). The same method of growing, i.e. conventional farming practice, was used to lay out experiments - always with one winter wheat cultivar (Sulamit) preceded by maize and oilseed rape. In addition to this, experiments under various practices of soil tillage were conducted: medium (22 cm), shallow (15 cm), and no-tillage. This soil management experiment was conducted under conventional farming practice.
In the system of organic farming, small-plot experiments were conducted with four winter wheat cultivars (Sulamit, Ebi, Drifter and Bill) in eight-course crop rotation after the preceding crop red clover according to IFOAM guidelines. The field in which the experiments were laid out has been maintained using the system of organic farming since 1991, i.e. for more than 15 years.
All plots (2 x 5 m) were arranged in randomized blocks and four replications. The cultivars chosen had different susceptibilities to eyespot according to the Central Institute for Supervising and Testing in Agriculture of the Czech Republic (CISTA) resistance ratings. These were Drifter and Bill with low resistance to stem-base diseases and Sulamit and Ebi with moderate resistance. There are no fully resistant cultivars in the Czech Republic.
Samples were taken from the small plots at four growth stages (GS): tillering (GS 21), jointing (GS 32), heading (GS 51), and waxy maturity (GS 85). Twenty-five plants per replication were taken from each plot, i.e. a sample of 100 plants per variant.
Results and discussion
Molecular diagnostic methods were employed for nine species and varieties of pathogenic fungi. In samples,
Oculimacula spp. DNA with balanced proportions of both species O. acuformis and O. yallundae was present
(2.21 % and 1.77 %, respectively). The most frequent positive detected species was M. nivale, at approximately balanced proportions of varieties, nivale and majus (50.88 % and 53.98 % samples, respectively). Further, samples contained DNA of R. cerealis (3.54 %) and in three cases also F. avenaceum. The species F.
graminearum, F. culmorum and F. poae were not detected at all in the samples from our experiments in 2006.
The two species of the eyespot fungus Oculimacula occurred in variants evaluating effects of the farming practice and preceding crop. They occurred at quite similar incidence. O. acuformis was detected at the last two times of assessment (GS 51 and GS 85) and O. yallundae at GS 85 only. Both of them were detected only under conventional farming, not under organic.
The sharp eyespot fungus R. cerealis was detected in samples at a relatively low level. In the variant of soil management; this species was found only on the final assessment (GS 85).
The predominant foot rot-causing species was M. nivale. Both varieties showed a significant time effect in the variant of soil management where the positive detection frequency of M. nivale var. majus was higher at GS 51 and GS 85 compared with the first two assessments (GS 21 and GS 32) and the detection frequency of M.
nivale var. nivale was the highest at GS 51, whereas it declined at the following assessment time (GS 85). The
incidence of the variety nivale was also influenced by the wheat cultivar and farming practice. Cv. Sulamit was infected by M. nivale var. nivale more frequently. Under conventional farming, the incidence of this variety was more frequent than under organic. The frequency of M. nivale var. majus detection in samples was significantly lower after the preceding crop maize than after cereal and oilseed rape.
According to the dynamics of colonization of wheat stem bases, we can divide the mentioned species into those which were present throughout the whole growing season at relatively high levels and those that colonize stem bases with successive ageing process of host. In the first group mentioned, there are two varieties of M.
nivale, whose frequency of incidence gave prevalence over other species at all terms of assessment. Other species
- namely Oculimacula spp. and R. cerealis, can be put into the second group. The moderate decrease of incidence of M. nivale at last term of assessment can be caused by competitive species from the second group. The statistical significant association was confirmed only between two varieties of M. nivale. No relationship was confirmed between other species studied.
Relatively high amount of samples contained no DNA from any of the studied species. The highest number of samples contained DNA of one and two pathogens and only several of them contained DNA of three pathogens. No samples containing DNA of more than three of the examined species were found. If two pathogenic organisms occurred on a stem base, these were mostly M. nivale var. nivale and M. nivale var. majus. The occurrence of this pathogen with Oculimacula spp. was sporadic only. In the case that three organisms were present on one stem base, these were always M. nivale vars majus and nivale plus the third species that was either
F. avenaceum, R. cerealis or species of Oculimacula.
Leaf sheaths enclosing the stem at the height of about 1-5 cm above ground examined 220 days after sowing (16 May 2006) contained only DNA of M. nivale var. nivale and M. nivale var. majus. DNA of both varieties was also detected, even though at less extent, in the stem without leaf sheaths.
DNA of both varieties of M. nivale was found in a relatively high amount of samples without any visual infection symptoms (brown discoloration, spots, etc.). However, the frequency of the samples with the pathogen DNA content that simultaneously exhibited symptoms was significantly higher than in asymptomatic occurrence. There was a significant relationship between visual infection symptoms and the incidence of M. nivale vars
nivale and majus. No significant relationship was found between the DNA presence in other examined species
and stem-base disease symptoms.
Acknowledgements
This work was supported by GACR project no. 522/06/P103.
References
DRAPER, M. A. − STYMEIST, C. − JIN, Y. 2000: Common root and crown rots of wheat in South Dakota. SDSU Extension Extra. 2 pp.
____________________________ Adresa autora:
Pavel MATUSINSKY, Renata MIKOLASOVA, Tomas SPITZER, Agricultural Research Institute Kromeriz, Havlickova 2787, 767 01 Kromeriz, email: [email protected]