1Department of Plant Protection, Faculty of Agriculture, Bu-Ali Sina University, Hamadan, Iran; 2Department of Agriculture, University of Reading, Earley Gate, Reading RG6 6AT, UK

Background and objectives
The current demand for methods of cereal production using reduced input levels and providing high quality grain has led to an increasing interest in alternative wheat cultivation techniques. An alternative reduced input method involves the intercropping of winter wheat in a permanent clover understorey [1]. Consideration of cultural practices as a means for the control of eyespot, caused by Pseudocercosporella herpotrichoides, has increased in recent years. The objective of this study was to investigate the effect of the presence of clover on spore production of P. herpotrichoides in clover-wheat bicrop systems. The impact of cereal-clover bicrop on the levels of spore production was compared with sole wheat monocrop during the growing seasons in 1994/95 and 1995/96.

Materials and methods
In an experiment at IACR-Long Ashton, a fine, firm seed bed was prepared incorporating 75 kg/ha P and K fertilizer. White clover seed was sown at 10 kg seed/ha, and the developing swards of clover were cut in early October. In late October, plots (13x60 m) were marked out for each treatment in three replicate blocks. Winter wheat cv. Hereward was direct drilled into clover understorey for bicrop plots using a Hunter rotaseeder, or directly into the soil, following chemical removal of the clover. During the seasons in 1994/95 and 1995/96, trash remaining on the surface of the three replicates in all different plots was collected on six sampling dates, and 10 g of stubble was washed in 100 ml sterile distilled water containing a small amount of surfactant to aid spore removal. The numbers of P. herpotrichoides spores per g stubble (based on five replicated counts from each replicate plot) were calculated for each of two treatments.

Results and conclusions
Results indicated that the reproduction of spores was significantly higher in bicrop plots relative to fungal spore production in monocrops. Within the wheat-clover bicrop plots the rate of wheat stubble loss was significantly lower than in the wheat monocrop. However, the total amount of wheat stubble in monocrop direct-drilled plots was greater than in bicrop plots. A number of mechanisms, including microclimatic changes, wheat stubble decomposition and wheat-stem nitrogen content were assessed for their efficacy in affecting spore production in the two cultural systems. From all the factors assessed, the more favourable relative humidity and air canopy temperature in bicrops seemed to be most directly responsible for spore production. This compares well with previous reports that pathogens such as P. herpotrichoides persist better on colonized plant debris in the soil than on debris aboye the soil surface, and that disease is suppressed in minimum tillage agriculture [2].

1. Jones L, Clements RO, 1993. Annals of Applied Biology 123, 417-25.
2. Doupnik B, Boosalis MG, 1980. Plant Disease 64, 31-35.