Abstract

Crop monoculture is successfull in obtaining maximum yield in high-input agriculture under near-optimal enviromental conditions. Monoculture of modern cereal crops is popular due to the technical and organizational reasons. A negative consequence of genetic uniformity is an increase in genetic vulnerability to diseases. Experimentally and practically it has been proved that cultivar and species mixtures can constitute an alternative to cultivar growing in pure stands. Cultivar mixtures can provide functional diversity that limits pathogen exspansion and that makes use of knowledge about interactions between hosts and their pathogens to direct pathogen evolution. Is has been found that in mixtures operate different epidemiological and ecological factors, which lead to considerable disease reduction, pest and weed control, which finally result in higher and more stable grain yields than in barley varietes grown in pure stands. The results of two years field experiment designed to evaluate epidemiological and economical effects of winter barley cultivar mixtures are presented. The impact of reduced dosages of fungicidies on disease incidence and grain yield in the mixtures were also evaluated.

Introduction

Appropriate mixtures of winter barley cultivars can considerably restrict the development of powdery mildew (Blumeria graminis f. sp. hordei) and to some extent other airborne diseases (Gacek et al., 1996). Cultivar mixtures can provide functional diversity that limits pathogen and pest expansion, and which makes use of knowledge about interactions between hosts and their pests and pathogens to direct pathogen evolution. Indeed, one of the most powerful ways to reduce risk of resistance break-down and to still make use of defeated resistance genes is to use cereal variety and species mixtures. (Finckh et al., 1999; Finckh et al., 2000).

The results of two years field experiment designed to evaluate epidemiological and economical effects of winter barley cultivar mixtures are presented. The aim of the studies was to evaluate the possibility of reduction of powdery mildew (B. graminis f. sp. hordei) and its effect on grain yield in winter barley, both through growing cultivar mixtures and various combination of fungicide timing and doses.

Materials and Methods

In the growing seasons 2001/2, two experiments with winter barley cultivar mixtures combined with different treatments of fungicides were carried out at two sites, namely in Experimental Station for Variety Testing Slupia Wielka (Wielkopolska District) and in the "Plant Breeding Smolice" Baków Division (Opole District). There two sites were 300 km away from each other, and had different soil and meteorological conditions.

During the 2002/3 growing season the studies were carried out in one place - Experimental Station for Variety Testing Slupia Wielka. The experiment in "Plant Breeding Smolice" Baków Division was completely destroyed by late frost in spring (March). In the experiment at Slupia Wlk., because of frost, 25% of plots were destroyed so no statistical analyses were carried out on these data.

In the experiments, four different winter barley cultivars and their two- and three-component mixtures were tested on 10m² plots in four replicates. There were following winter barley cultivars used in the experiment: Bombay, Gil, Gregor and Bazant, and the following mixtures: Bombay/Gil, Bombay/Gregor, Gil/Gregor/Bazant.

On the experimental plots different treatments with fungicides were used, namely:
- untreated plots (control)
- one treatment with 0,25 recommended dosage of fungicides
- one treatment with 0,5 recommended dosage of fungicides
- one treatment with full recommended dosage of fungicides
- two treatments with 0,25 recommended dosages of fungicides
- two treatments with 0,5 recommended dosages of fungicides
- two treatments with full recommended dosages of fungicides
The grain yield from all the experimental plots was measured and statistically evaluated.

During the vegetation season powdery mildew observations were done 3-5 times using 1-9 scale (where 9 - fully resistant, 1 - fully susceptible). In order to compare the disease occurrence levels on different cultivars in pure stands and on their mixtures combined with different fungicide treatments, the Area Under Disease Progress Curve (AUDPC) was evaluated (Shanner & Finney, 1977). The results were statistically evaluated. In the variance analysis the site effect was treated as the random effect. T-Student test (p=0,95) was used for multiple comparing.

Results and Discussion

In the vegetation periods 2001/02 and 2002/03, due to adverse weather conditions, generally low incidence of powdery mildew was observed. Nevertheless, there were seen some differences between cultivars and their mixtures (Table 1 and Table 2). In general, cultivar mixtures were less affected by the disease, than pure stands both on plots without - and with fungicide control. In 2001/02 cultivar Gil was the most severely infected, whereas cultivar Gregor was the least infected in both sites. In 2002/03 cultivar Bazant was the most severely infected, whereas cultivar Gregor was the least infected.

The development of powdery mildew in different treatments was analysed on the basis of the Area Under Disease Progress Curve (AUDPC) (Table 1 and Table 2).
The reduction of powdery mildew in the mixtures occurred due to epidemiological and ecological factors functioning in mixed stands (Wolfe and Schwarzbach 1975) were also evaluated (Table 3 and Table 4). The biggest and most frequently occurring disease reduction was observed in three-component mixture (Gil + Gregor + Bazant) in 2001/02. In the growing season 2002/03 disease reduction was observed in two-component mixtures.

As far as the grain yield is concerned, yield increase wa observed in the mixtures compared with pure stands (mixing effect). Futhermore yield increase was also observed between treated - and untreated plots (chemical control effects) (Table 5 and Table 6).

Conclusions

1. Winter barley cultivar mixtures were less infected by powdery mildew (B. graminis f. sp. hordei) than cultivars grown in pure stands.
2. Wheather conditions in growing seasons had an overriding influence on experiment results.
3. In the 2001/02 growing season the highest reductions of powdery mildew were observed in three-component mixture (Gil + Gregor + Bazant).
4. Whereas in the 2002/03 growing season the highest reductions of powdery mildew were observed in two-component mixtures.
5. A positive effect of combination of genetical disease control (cultivar mixtures) with chemical disease control (reduced doses) was found.
6. Cultivar mixtures combined with reduced fungicide treatments apart of their influence on powdery mildew reduction at the same time had a positive effect on grain yield in winter barley cultivars, and especially in their mixtures.
7. The results of the study show that the combination of cultivar mixtures with reduced use of fungicides can be regarded as a low - input and enviroment - friendly method of winter barley growing.

References

Finckh MR, Gacek ES, Czembor HJ, Wolfe MS, 1999. Host frequency and density effects on powdery mildew and yield in mixtures of barley cultivars. Plant Pathology 48, 807-816.

Finckh MR, Gacek ES, Goyeau H, Lannou C, Merz U, Mundt CC, Munk L, Nadziak J, Newton AC, de Vallavieille-Pope C, Wolfe MS, 2000. Cereal variety and species mixtures in practice, with emphasis on disease resistance. Agronomie 20, 813-837.

Gacek E, Czembor H, Nadziak J, 1996. Disease restriction, grain yield and its stability in winter barley cultivar mixtures. Proceedings of the Third Workshop on Integrated Control of Cereal Mildews Across Europe, 1994. Kappel a Albis, Switzerland, 185-190.

Shaner G, Finney RE, 1977.The effect of nitrogen fertilization on the expression of slow-mildewing resistance in Knox wheat. Phytopathology 67, 1051-1056.

Wolfe MS, Schwarzbach E, 1975. The use of virulence analysis in cereal mildews. Phytopathology 82, 297-307.