Phosphorous fertilizer efficiency and mycorrhizal infection in corn genotypes

In a world of limited resources and inexorable pressure to produce food for burgeoning populations, innovative approaches are needed to exploit these resources in a sustainable manner. Phosphorous (P) fertilizers are used extensively throughout the world for commercial crop production, and are a major factor in global food security. Yet, in developing countries, limited or no P fertilizer is used, often because of cost and infrastructure constraints, and this is therefore an impediment to sustainable production. The challenge facing soil scientists involved with soil and fertilizer P research is to produce adequate crops on inadequately fertilized soils in poorer countries and, at the same time, improve the efficiency of P use where excessive amounts are used, thus avoiding negative environmental impacts. Soil-plant fungi, especially arbuscular mycorrhizae (AM), may have a role in solving both horns of the P-use dilemma, since such associations have been shown to vary with plant species, and indeed genotypes within species, and to enhance crop utilization and uptake of P from soils low in soluble or available P. Therefore, as corn is an important feed and food crop in the Mediterranean coastal area of Turkey, we conducted two greenhouse studies to assess the P efficiency of a range of widely grown local corn genotypes and to establish the possible role of mycorrhizae in determining differences in observed P efficiency. The nine genotypes were grown with low to high P fertilizer rates (25-200 mg kg(-1)) and assessed for P efficiency, based on visual observations, dry matter yield, and tissue P concentration. Two efficient and two inefficient genotypes were then grown with and without P fertilizer and added mycorrhizae. The experimental bulk soil had natural mycorrhizal colonization. The genotypes XL 72AA, DK 626 and LG 60, LG 2777 responded differently to both P and mycorrhizal infection. The efficient genotypes were more dependent on added P (twofold yield increase) and mycorrhizae than the inefficient ones. Thus, while mycorrhizal colonization is not a substitute for fertilizer use, it is complementary to it. While difficulties still remain for AM inoculation of crops in the field, more attention to mycorrhizae should be given by plant breeders in the process of crop improvement.