Mycorrhizal etiology of favorable proteoid rhizogenesis, nodulation, and nitrogenase of lupines

Abstract

Lupine (Lupinus albus L.) has been cultivated as a food‐grain legume for more than 3,000 years. Persistent productivity occurs on low fertility soils within regions of drought and unfavorable temperature extremes. Distinctive rhizosphere characteristics of Proteaceae genera include development of determinate rootlet clusters termed proteoids. This unique morphology contributes to adaptive tolerance with soil‐climate duress prohibitive to most food Leguminosae. Objectives of this study were to determine tripartite components for mycorrhizal colonization and effective Rhizobium symbiosis with proteoid nodulation governing productivity, nitrogenase activity and subsequent nitrogen (N) fixation of Lupine. Highest nitrogenase activity levels with largest top growth, nodulation and seed yield resulted with mycorrhizal colonization plus calcium (Ca) treatments. Mycorrhizal colonization without soil fertility amendments resulted in higher yields and nodulation than all phosphorus (P), Ca, and potassium (K) soil fertility treatment combinations without mycorrhizae. Phosphorus+Ca soil additions were greater than either plant nutrient used separately without mycorrhizal colonization. Nodule histological determinants were highly correlated with governing cytosol enzyme activity levels. Nitrate reductase (NR)was significantly lower and phosphoenol‐pyruvate carboxylase (PEPC) was significantly higher with mycorrhizal colonization. Differences were not significant for cytosol components of amine‐amide N, aspartate transaminase (AST), glutamate dehydrogenase (GDH), glutamine syn‐thetase (GS) and glutamate oxoglutarate transaminase (GOGAT).