IMPACT OF PREVIOUS CROPS AND TILLAGE SYSTEMS ON HEALTH STATUS OF WINTER WHEAT

Zuzanna Sawinska, Irena Małecka, Andrzej Blecharczyk
Department of Plant and Soil Cultivation, Agricultural University of Poznan, Poland

ABSTRACT

The paper presents results of 3-year experiment (2001-2003) on the effect of different previous crops (winter wheat, pea, spring barley) and tillage systems (conventional tillage and direct drilling) on the incidence of fungal diseases of leaves, ear, stem base and roots of winter wheat. The highest infection percentage and index for the take-all and brown foot rot diseases were found when winter wheat was sown directly into the stubble. Significantly higher infection with the stem base and root diseases occurred after cereals (spring barley, winter wheat) than after pea. The conventional tillage increased the incidence of leaf and ear diseases of winter wheat as compared with direct drilling, except for the dry year. The occurrence and severity of wheat diseases depended on the previous crops and environmental conditions.

Key words: winter wheat, stem base and root diseases, leaf and ear diseases, previous crop, tillage system.

INTRODUCTION

Recent changes in agricultural practices towards conservation tillage cause us to wonder if farming is entering a new era of disease problems [3]. Tillage practices in combination wits the crop residue may physically, biologically and structurally alter the local field environment by affecting soil temperature and moisture, competition among microorganisms [18]. In no-till systems, the post-harvest residues left on the field surface become a direct source of fungal diseases, especially those which infect roots [2,3,5,12,17,18]. The investigations into the impact of the direct seeding on the occurrence of stem base diseases in winter wheat have given no clear-cut results. The effect of tillage systems on subsequent disease severity depends heavily on the previous crop. The crop selection affects the quantity and the quality of plant residue left on the surface or in the soil which can influence pathogen development, sporulation and survival rate through a release of fungicidal and fungistatic substances during the process of residue decomposition, or alternatively by providing substrates for specific pathogens to feed on. The relationship between the pathogen development and the kind of crop residue may be also modified by environmental conditions [3,5]. Alternative crops such as pea used to diversify cereal grain cropping systems play a valuable role to breaking the life cycle of fungal diseases [8,9,10,14,20,23].

The working hypothesis has assumed that in the direct seeding sysem the crop residue on the soil surface has a direct impact on the crop health status. However, the risk of diseases of direct-seeding winter wheat can be lower by eliminating monoculture and improving the diversity of crops in the rotation.

The aim of this paper was to determine the impact of previous crops and soil tillage systems on the occurrence of leaves, ears and stem base as well as root fungal diseases of winter wheat.

MATERIAL AND METHODS

The studies carried out over 2001-2003 involved a static field experiment established in 1995 at the Brody Research Station of the Agricultural University in Poznań. The soil of the experimental fields is classified as Albic Luvisols developed on loamy sands overlying loamy material. ‘Sakwa’ winter wheat was grown after various previous crops (winter wheat, pea, spring barley) using conventional tillage (skimming + pre-sow ploughing) or direct drilling into the stubble with a disc coulter drill of the Great Plains Company. The fertilizer rates were applied at 26 kg P·ha^-1, 81 kg K·ha^-1 and 120 kg N·ha^-1 doses. The herbicide program for tillage systems used pre-plant and post-emergence applications. Before planting 3 dm³·ha^-1 of glyphosate herbicide was applied on all plots with direct drilling to control perennial weed and forecrop volunteers. For weed control during the growing season post-emergence Huzar 05 WG (jodosulphuron) was applied at the rate of 0.2 kg·ha^-1. The seeds were dressed with Raxil Extra 060 FS fungicide (60 ml per 100 kg seed) containing thiuram and tebuconazol. For diseases control Alert 375 SC fungicide (flusilazole and carbendazime) at the rate of 1 dm³·ha^-1 was applied on all plots at GS 31 growth stage.

The assessment of the winter wheat infection with the stem base and root diseases was carried out at four growth stages [25]: shooting (GS 31), beginning of heading (GS 51), beginning of milk stage (GS 73) and at full maturity (GS 92). Crop infection with the stem base and root diseases was evaluated visually at the lower parts of culms and roots with characteristic spots, discolorations and necroses. For each of the diseases there were calculated the percentage of plants with such symptoms, irrespective of their severity, as well as the infection index. The degree of infection with the take-all was assessed on the roots of plants with the 5-grade scale based on the CEB – Commission des Essais Biologiques de I’Association Nationale de Protection des Plantes [6], while the severity of the brown foot rot on the culm according to the 3-degree scale [24]. The infection of winter wheat plants with leaf and ear pathogens was assessed at the milk stage (GS 73) by determining the percentage of total leaf and ear area with disease symptoms using a graphic key for the determination of diseases developed by EPPO.

The results were subjected to variance analysis for randomized complete block design. The results were compared using Fisher-Snedecor’s test and verified with the Tukey test at P ≤ 0.05.

The weather conditions varied considerably over the experimental period. The mean air temperature during the spring vegetation period of winter wheat was above the multi-year mean, except for June 2001. Growing season precipitation from 2001 to 2003 (from sowing to harvest) was 447, 450 and 470 mm, respectively. Greater variations in precipitation occurred April through June and ranged from 148 mm in 2001 to 76 mm in 2003, whereas in 2002 amounted to 135 mm. To conclude, the weather conditions were more favorable to the development of wheat diseases in 2001 and 2002 than in 2003.

RESULTS

The dominant pathogens identified in the experiment were: Gaeumannomyces graminis (Sacc.) v. Arx et Olivier causing take-all and Fusarium spp. inflicting brown foot rot, Mycosphaerella graminicola (Fuck.) Schrot. – wheat leaf spot, Pyrenophora tritici-repentis (Died.) Drechs.– leaf blotch and Blumeria graminis DC – powdery mildew. The stem base and root diseases severity increased from GS 31 to GS 92 (Table 1), which was seen from both the percentage and index of root infection in respective years. In 2001 and 2002 the percentage of plants infected with take-all at the successive evaluation dates was higher than in 2003 which coincided with the weather conditions unfavorable to the development. Before harvest, disease symptoms were recorded on 61.7% plants in the first year of the experiment, on 67.3% – in the second and on 36.7% – in the last year of the investigations. The extent of winter wheat infection with take-all expressed by the index of root infection also varied in the successive years of the experiment. In early spring the value of the infection index was higher in 2003 than in 2001 and 2002, although none of the values recorded exceeded mild infection levels. Towards the end of the vegetation period of winter wheat, this parameter increased and reached strong infection in 2001 (37.3) and in 2002 (31.6) and moderate infection in the last year of the studies (14.7).

The degree of culm infection with brown foot rot was significantly higher in the first two years than in 2003, as expected from different weather conditions. During the period of heading (GS 51), the percentage of culms with symptoms of brown foot rot in 2001 and 2002 accounted for 34.4% and 33.8%, respectively, while in 2003 – for 20.4%. During the vegetation period, the percentage of infected culms increased and before harvest it reached the value of 82.0% in 2002, 73.7% in 2001 and 41.9% in the last year of the experiment. In all the experimental years, the calculated infection index for brown foot rot during the heading period (GS 51) was low and it did not exceed the range assumed for healthy plants, while at full maturity (GS 92), it increased to the level of medium infection in 2001 and 2002 and low infection in 2003.

Both the infection index and the percentage of plants with symptoms of take-all depended on the previous crop and tillage systems (Figs 1 and 2). Winter wheat grown after pea was less affected by take-all than after spring barley and winter wheat. When wheat was grown after pea, the percentage of plants with symptoms of take-all ranged from 8.8% in early spring to 28.3% before harvest (mean for the three years of the experiment). In comparison with the conventional tillage, at all evaluation dates, there was observed a significantly higher infection of winter wheat with Gaeumannomyces graminis where direct drilling was applied. At the shooting phase (GS 31), the share of plants with symptoms of take-all for the conventional tillage was 17.3%, whereas for direct drilling – 22.1%. Before harvest, the share of infected plants increased to 49.0 and 61.4% for conventional tillage and direct drilling, respectively.

The occurrence of brown foot rot in winter wheat also depended on the experimental factors (Figs 3 and 4). Regardless of the evaluation date, the lowest infection of winter wheat with brown foot rot was observed where wheat was grown after pea. On the other hand, conditions favorable to the disease development occurred when either winter wheat or spring barley constituted the previous crop. During the heading period (GS 51), the percentage of winter wheat plants infected with Fusariun spp. accounted for 27.6% after pea, 31.2% after winter wheat and 29.5% after spring barley. At full maturity, the percentage of culms with symptoms of the infection increased by 61.3, 65.3 and 71.0% after pea, winter wheat and spring barley, respectively. The infection index at the first evaluation date was low and ranged from 42.0 to 66.1, whereas at the end of the vegetation period, it increased to mild infection after pea and moderate – after winter wheat and spring barley. As compared with the conventional soil tillage, the percentage of culms with symptoms of brown foot rot and the infection index were significantly higher when direct drilling was performed.

Furthermore, the analysis of variance showed an interaction of the previous crop and tillage system on the index of root infection with Gaeumannomyces graminis (Table 2). The infection index for winter wheat after pea was significantly lower, at all the evaluation dates, as compared with winter wheat grown after winter wheat or spring barley in both systems of soil tillage. In conventional tillage, a similar infection index of take-all after spring barley and winter wheat was recorded, whereas for direct drilling this parameter was significantly higher for winter wheat grown in monoculture than after spring barley.

When analyzing the occurrence of the diseases found on the second leaf of winter wheat, it can be stated that leaf blotch and leaf spot occurred with greater severity than powdery mildew (Table 3). The infection with pathogens was greater in 2002 than in the other years. The effect of the previous crop on the disease incidence depended on the pathogen and varied in successive years. In the first year, the incidence of Blumeria graminis and Pyrenophora tritici-repentis on the second flag leaves did not depend on the previous crop. However, in the following years a higher infection with Blumeria graminis was observed on the leaves of winter wheat grown after pea than after winter wheat and spring barley, in contrast to the occurrence of Pyrenophora tritici-repentis which was lower after pea than after cereals. The effect of the previous crop on the infection of the second flag leaves with Mycosphaerella graminicola was observed only in 2002 when pea, as the previous crop, intensified the occurrence of this pathogen. The occurrence of Septoria nodorum was significantly affected by the previous crop; the same pathogen was also recorded in the second year of the experiment when the infection was higher after spring barley than after pea and winter wheat. The incidence of winter wheat leaf and ear diseases was higher under conventional tillage than after direct drilling, except for last year which was dry.

DISCUSSION

A combination of monoculture and reduced tillage results in more post-harvest residue on the soil surface, which, in turn, may increase soil moisture and decrease soil temperature favorable to the occurrence of stem base and root diseases [2,3,5,18]. On the other hand, direct drilling plant residue left on the soil surface increases organic matter content in the topsoil and biological activity which can reduce pathogen populations in the soil [9]. For that reason the reports on the impact of soil tillage systems, especially direct drilling, on the occurrence of fungal diseases are quite inconsistent. Stem base and root diseases have been reported to be more intensive with reduced tillage [4,7,11,14,17], more intensive with conventional tillage [18,19] or similar whether the crop is grown with reduced or conventional tillage [15,16]. According to many researchers [1,4,7], the impact of tillage systems on fungal diseases is much smaller than the effect of environmental conditions (weather, soil), crop rotation, cultivars and seed dressing.

The results of the Brody investigation demonstrated that direct drilling increased the infection of winter wheat with stem base and root diseases as compared with the conventional soil tillage. Negative effects of reduced tillage on winter wheat can be alleviated by an appropriate crop rotation. Winter wheat, similarly as spring barley, is one of the most sensitive crops to stem base and root infection. Numerous authors [2,9,19] report on the effect of the previous crop on plant infection with pathogenic fungi being significantly higher than the effect of the soil tillage system.

A break crop in cereal rotation facilitates breaking the fungi life cycle in the soil [8,9,10,13,14,20,23]. Legumes in cereal grain rotations can reduce N mineral fertilization and decrease the incidence of stem base and root diseases [9,10,21,22]. The results of the present study coincide with the above reports. On average, the results of the three-year investigations showed a significantly higher infection of winter wheat with stem base and root diseases after cereal previous crops than after pea. The infection of winter wheat leaves and ears was low, except for leaf spot in 2002.

In some years a higher incidence of Blumeria graminis and Mycosphaerella graminicola was observed on the leaves of winter wheat grown after pea than after winter wheat and spring barley, in contrast to the occurrence of Pyrenophora tritici-repentis which was lower after pea than after cereal previous crops. Irrespective of tillage systems, for a majority of winter wheat leaf diseases, there was recorded a slightly higher infection for conventional than for reduced tillage, which could have been due to the specific development of this disease. Its severity is found higher in cereal rotations and in the fields exposed to reduced tillage which results in post-harvest residue on the soil surface [1,3,4].

CONCLUSIONS

1. Direct drilling into the cereal stubble increased the infection of winter wheat with Gaeumannomyces graminis and Fusarium spp., as compared with conventional tillage.

2. Pea included in the crop rotation, especially when exposed to direct drilling, minimized the impact of winter wheat on the occurrence of root diseases.

3. The conventional tillage increased the incidence of Blumeria graminis, Mycosphaerella graminicola and Pyrenophora tritici-repentis on the winter wheat leaves and Septoria nodorum on the ears, as compared with direct drilling, except for the dry year.

4. In most years the incidence of Blumeria graminis and Mycosphaerella graminicola was highest when winter wheat was sown after pea, while that of Pyrenophora tritici-repentis – after cereals.

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Accepted for print: 21.12.2006

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