Intercropping is the simultaneous cultivation of more than one crop species on the same piece of land and is regarded as the practical application of basic ecological principles such as diversity, competition and facilitation. Field experiments were carried out on a sandy loam soil and a sandy soil in Denmark over three consecutive cropping seasons including dual grain legume (pea, faba bean and lupin)-barley intercropping as compared to the respective sole crops (SC). Yield stability of intercrops (IC) was not greater than that of grain legume SC, with the exception of the IC containing faba bean. Faba bean and lupin had lower yield stability than pea and fertilized barley. However, the different IC used environmental resources for plant growth up to 50% (LER = 0.91-1.51) more effectively as compared to the respective SC, but with considerable variation over location, years and crops. The SC performance supported the interspecific interactions within the IC stand. On the sandy loam 13% greater grain yield of pea cv. Agadir (520 g m -2 ) was observed as compared to cv. Bohatyr. Faba bean and lupin yielded similarly (340 g m -2 ) in the sandy loam soil, with decreasing yields on the sandy soil (320-270 g m -2 ). Nitrogen fixation was very constant in grain legume SC over species and location, varying from 13.2 to 15.8 g N m -2 , being lowest in peas and highest in faba bean and lupin. The intercropped grain legumes increased the proportion of plant N derived from N 2 -fixation by on average 10-15% compared to the corresponding SC. However, especially lupin was suppressed when intercropping, with a reduced N 2 -fixation from 15 to 5-6 g N m -2 . The IC were particularly effective at suppressing weeds, capturing a greater share of available resources than SC. Weed infestation in the different crops was comparable; however, it tended to be the highest in sole cropped faba bean, lupin and unfertilized barley, where the application of urea to barley reduced the weed infestation by around 50%. Reduction in disease was observed in all IC systems compared to the corresponding SC, with a general disease reduction in the range of 20-40%. For one disease in particular (brown spot on lupin) disease reduction was almost 80% in the IC. Intercropping practices offer many advantages but improved understanding of the ecological mechanisms associated with planned spatial diversity, including additional benefits with associated diversity, is needed to enhance the benefits achieved.

The fungal pathogen Blumeria graminis f. sp. hordei develops on the barley leaf via distinct, morphologically well-defined stages. After landing on a host plant, the conidia rapidly germinate to form a primary germ tube. Subsequently, an appressorial germ tube emerges from the conidium and differentiates an appressorium from which penetration of the host cell wall is attempted. We have used serial analysis of gene expression to provide a measurement of messenger RNA contents in ungerminated conidia, during conidial germination, and during appressorium formation. The resulting data provide a resource for the characterization of changes in transcript accumulation during early development of B. graminis.

Development of conidia of barley powdery mildew involves the formation of a primary germ tube (PGT), an appressorial germ tube (AGT), and an appressorium. Previously, it was found that cyclic AMP (cAMP) was involved in these developmental processes. Comparison of development on the host surface with two types of cellulose membrane revealed that frequency of PGT emergence was surface independent. On one type of cellulose, where the frequencies of both AGT and appressorial differentiation were similar to that on the host surface, cAMP levels and protein kinase A (PKA) activities had a biphasic pattern with peaks at 15 min and 4 h after inoculation (prior to PGT and AGT emergence, respectively). The effect of manipulating cAMP levels was tested on another type of cellulose membrane, which stimulated a lower degree of AGT and appressorial formation than the host surface. Cholera toxin and forskolin, activators of adenylyl cyclase, significantly increased PGT emergence, but cAMP did not. Cholera toxin, forskolin, and cAMP increased the frequency of AGT and appressorial formation, but in a time-dependent manner.

The effect of barley-legume intercrop in an organic farming system on disease incidence was investigated. The legumes<br />were lupin, faba bean and pea. Diseases were detected on pea and barley. On pea, only ascochyta blight (Ascochyta pisi)<br />was observed. When either pea variety was intercropped with barley, the level of ascochyta blight was reduced. Net<br />blotch (Pyrenophora teres), brown rust (Puccinia recondita) and powdery mildew (Blumeria graminis f.sp. hordei) (in<br />order of incidence) were monitored on barley between flag leaf emergence and heading. The levels of all three diseases<br />were reduced in every intercrop treatment compared to the barley monocrop. However, this reduction was only statistically<br />significant in the pea treatments for net blotch.

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