430 AJCS 6(3):430-435 (2012) ISSN:1835-2707 The effect of field pea (Pisum sativum L.) as companion crop on leaf histological parameters of lucerne (Medicago sativa L.) L. Zorić 1 , Dj. Krstić 2 , B. Ćupina 2* , A. Mikić 3 , S. Antanasović 2 , J. Luković 1 , Lj. Merkulov 1 1 University of Novi Sad, Faculty of Sciences, Department of Biology and Ecology, Novi Sad, Serbia 2 University of Novi Sad, Faculty of Agriculture, Novi Sad, Serbia 3 Institute of Field and Vegetable Crops, Novi Sad, Serbia * Corresponding author: cupinab@polj.uns.ac.rs Abstract In this work, structural modifications of lucerne lamina were examined using light microscopy, in order to evaluate the effect of cover crop pea cultivar and sowing density on lamina anatomy. The plants were grown under companion cropping conditions with two field pea cultivars (Jezero - afila type, and Javor – type with small leaflets), at three cover crop sowing densities (30, 60 and 90 plants/m 2 ). The results showed that companion cropping did not significantly affect the lamina structure, proportion of lamina tissues or the size of the cells. All treatments showed low variability of measured parameters and high level of homogeneity, which was confirmed by PCA analysis. Heliomorphic parameters, such as higher palisade/spongy tissue ratio, larger palisade cells and thicker epidermis, were more expressed in control group plants and those grown under lower cover crop density. As both cover crop cultivars, at three applied sowing densities, transmitted sufficient sunlight to lucerne, companion growing did not negatively affect the leaf photosynthetic tissue. Our anatomical results indicate a potential for development of a new, reliable and environmentally friendly method of the lucerne establishment, without negative effect on the process of photosynthesis. Keywords: intercropping, leaf anatomy, lucerne, pea, photosynthetic tissue. Abbreviations: MDA – Multivariate Discriminant Function Analysis, PCA – Principal Component Analysis, SE – standard errors. Introduction The companion cropping with perennial legumes is deemed an effective method of agricultural and, more specifically, forage production, as it offers increased yield stability, higher yields, reduced weed competition, increased protein content within a mixed diet and higher land-use efficiency (Anil et al., 1998). Despite its advantages, the agricultural intensification in terms of plant breeding, mechanization, fertilizer and pesticide use experienced during the last 50 years has led to elimination of intercropping from many farming systems. The success of companion cropping depends on the capacity of the undersown crop to develop in the shade of the cover crop, as the competition for light, nutrients, and water may reduce the yield and resistance of the undersown crop, in particular when the grains used for planting are small (Tan et al., 2004). In the West Balkan Countries and beyond, however, it is small grains — primarily oats and barley — that are traditionally intercropped with perennial legumes. Given that these species tend to be too fast-growing, they are typically too competitive for the legume component to thrive. Information on alternative companion crops is limited (Sule, 1993). Field pea (Pisum sativum L.) could be suitable for intercropping with lucerne (Medicago sativa L.) because N 2 fixation is improved, the crop can be harvested quickly and the canopy structure is not overly dense to cause suppressive shading (Cupina et al., 2011; Makoi and Ndakidemi, 2011). Modern field pea cultivars differ in morphology, primarily in leaf structure and plant height. The pea cultivars with short stems and leaflets reduced into tendrils — known as semi- leafless or afila type — are important for intercropping, as light penetration is much better, providing better conditions for the initial growth of the undersown crop (Koivisto, 2002). According to Simmons et al. (1995), the light intensity at the level of the perennial legume within the semi-dwarf companion crop canopy was consistently higher, compared to the conditions provided by conventional-stature companion crops. Moreover, the semi-leafless pea cultivars are able to convert solar radiation into dry matter more effectively than normal-leafed cultivars can (Heath and Hebblethwaite, 1985). In addition to the selection of a suitable field pea cultivar as the companion crop, an appropriate production technology also needs to be developed. To mitigate the effect of competition among the intercropped plants, reduction to the normal seeding rate of the companion crop is recommended. Hence the optimum stand density — i.e., the number of plants of the companion crop per unit area —needs to be determined (Vough et al., 1995; Cupina et al. 2010). Of all plant organs, the leaf is the most susceptible to the environmental factors, especially to the level of illumination and the amount of available water. Within the same individual plant, leaves developed in bright light conditions (sun leaves) tend to be smaller and thicker, with increased mesophyll tissue area, stronger, better developed mechanical tissue, and higher density of stomata and veins, compared to the leaves exposed to shade (shade leaves) (Dickison, 2000). It has been suggested that the strong light induces the