Soil acidity is a major limiting factor for upland crops. Arbuscular mycorrhizal fungi (AMF) help improve soil fertility through a fallow enriching tree, Macaranga denticulata, and directly enhance growth of many crops, but its benefit to legumes in acid soil are not known. Three experiments evaluated the benefits from AMF on legumes growing on acidic, low phosphorus soil (pH 5, 11 mg P kg-1by Bray II). In Experiment 1, root zone soil and root fragments of M. denticulata significantly increased cowpea (Vigna unguiculata) growth and P uptake. In experiment 2, CMU22 - a strain of Acaulospora morrowiae propagated from a single spore in the rhizosphere of mimosa (Mimosa invisa) - growing in soil with pH 5 and 11 mg P kg-1was as effective as soil from the root zone of M. denticulata on cowpea and mimosa growth. In experiment 3, cowpea growing in soil with pH 5 and 11 mg P kg-1was inoculated with varying rates of mimosa root zone soil containing CMU22 and CMU22 spores. Both types of inoculum promoted cowpea growth, but at a low rate of 100 spores plant-1. Root zone soil that contained infected root fragments and hyphae, as well as spores, was more effective. Arbuscular mycorrhizal fungi adapted to acidic, low P soils have been shown to be effective in alleviating acid soil stress in legumes, with CMU22, an Acaulospora morrowiae, especially well adapted to acid soil.
This study examined the distribution of iron (Fe) and zinc (Zn) along the grain length of seven rice varieties. The experiment was conducted in a completely randomized design with two factors (variety and grain fraction) and three independent replications. Samples of brown and white rice of six common Thai rice varieties and a high Fe and Zn variety, IR68144, were transversely cut into three fractions per grain (basal, middle, and distal) with approximately the same length in each fraction. The concentration of Fe and Zn was determined by the dry ashing method and quantified using atomic absorption spectrometry. The middle grain fraction of brown rice was found to have the lowest Fe and Zn with greater concentration of Fe and Zn in the basal (embryo end) than the other fractions. The rice varieties differed in the amount of Fe and Zn allocated to different fractions of the endosperm (white rice). The potential for loss of Fe and Zn during milling due to their uneven distribution along the grain length will become more significant when higher nutrient concentrations are involved, such as those achieved by biofortification efforts. Micronutrient distribution needs to be taken into consideration to ensure that rice consumers benefit from Fe and Zn biofortification.