Vesicular-arbuscular mycorrhizae (VAM) improve phosphorus and zinc nutrition and growth of pigeonpea in a Vertisol

Abstract

In a glasshouse trial, pigeonpea (Cajanus cajan) was grown in a Vertisol from the Darling Downs, Qld. The experimental design included two rates of inoculation with vesicular-arbuscular mycorrhizal (VAM) fungi (nil and inoculated), three rates of phosphorus (P) application and two of zinc (Zn), and inoculation (nil and inoculated) with a recently discovered pathogen of pigeonpea, Phytophthora drechsleri Tucker (Pdr). lnoculation with the pathogen was included in the factorial design to investigate any effect of VAM on root rot. Plants responded to inoculation with VAM fungi, showing that the growth of pigeonpea is highly dependent upon mycorrhizal colonization of its root system. The mycorrhizal plants yielded, on average, 3.3 times the dry weight of the non-mycorrhizal plants. Shoot dry weight and Zn concentration of the shoots were both exponentially related to per cent VAM colonization of the root length ( R2 values of 0.904 and 0.644 respectively) and P concentration was linearly related to VAM colonization (R2 = 0.888). VAM increased P concentration, P uptake, Zn concentration, Zn uptake and P/Zn ratio, indicating enhanced growth through improved P and to a lesser extent Zn nutrition. Zinc fertilizer (15 mg kg-1 soil) without Phytophthora inoculation was fungitoxic to the mycorrhizae, decreasing per cent VAM colonization and depressing plant growth. lnoculation with Pdr did not result in infection and root rot symptoms. However, it did overcome the Zn toxicity, possibly through organic chelation effects, and thereby enhanced VAM colonization. Greatest VAM colonization and best plant nutrition and growth were obtained with the combination of VAM inoculation, Pdr inoculation, Zn (15 mg kg-1) and P (10 mg kg-1). Our results indicate the importance of maintaining adequate levels of VAM fungi in soil through appropriate agricultural practices in order to maximize pigeonpea growth.

The effect of ectomycorrhizal fungi on Zn uptake and distribution in seedlings of Pinus sylvestris L

“…This agrees with results of Wellings et al (1991) who examined different species of VAM fungi. Bowen et al (1974) concluded that the higher absorption of Zn by mycorrhizas was due first to a larger size of ectomycorrhizas compared with uninfected roots, and second to a larger absorbing power of the mycorrhiza surface.…”

“…As well as major nutrients, this involves the uptake of trace elements such as Zn, which can be increased by mycorrhizal associations (Wellings et al, 1991). Zn deficiency of nonmycorrhizal plants is caused by the low mobility of Zn in the soil and the development of depletion zones around the roots .…”

Mycorrhizal responsiveness of aerobic rice genotypes is negatively correlated with their zinc uptake when nonmycorrhizal

“…A beneficial effect of mycorrhizal colonization on Zn uptake has been shown for maize (Faber et al 1990;Liu et al 2000;Sharma et al 1992), pigneonpea (Wellings et al 1991), wheat (Khare et al 1998;Ryan and Angus 2003) and wetland rice (Purakayastha and Chhonkar 2001). Upon colonization, the mycelium of the AMF increases the nutrient absorbing surface area of the symbiosis, enhances exploration of a larger soil volume and thereby increases uptake, specifically of immobile nutrients such as P and Zn (Smith and Read 1997).…”

Improving zinc bioavailability in transition from flooded to aerobic rice. A review

“…A large number of studies demonstrate the beneficial effect of AM fungi on Zn uptake by the host plants, including lowland rice (Purakayastha and Chhonkar 2001), pigeon pea (Wellings et al 1991), wheat (Ryan and Angus 2003), and tomato (Cavagnaro et al 2010). The effects are mostly reported for plants grown in soils with low Zn availability.…”