Breeding against mycorrhizal symbiosis: Modern cotton (Gossypium hirsutum L.) varieties perform more poorly than older varieties except at very high phosphorus supply levels

Cotton (Gossypium hirsutum L.) is an important fiber cash crop, but its root traits, including mycorrhizal related to phosphorus (P) acquisition have been poorly understood. Eight cotton varieties bred in northwestern China that were released between 1950 and 2013 grown pots with or without one arbuscular fungal (AMF) species (Funneliformis mosseae) at three P supply levels (0, 50 300 mg as KH2PO4 kg-1). Eleven traits measured calculated after seven weeks of growth. More recent accessions had smaller diameters, acquired less obtained biomass, indicating (inadvertent) varietal selection for thinner roots provided cortical space AMF, which then increased the need high fertilizer. At two lower levels, plants more produced biomass than non-mycorrhizal (3.2 vs. 0.9 plant-1; 1.8 g plant-1 P0; 14.5 1.7 4.7 1.6 plant-1at P50). highest level, (18.8 13.4 plant-1), there was no difference (6.2 6.3 plant-1). intermediate diameter significantly positively correlated shoot concentration content plants. Our study supports importance outsourcing model economics framework. Inadvertent last decades, resulting a benefit from has caused productivity moderate (when mycorrhizal, average older 5.0 plant-1vs. newer 4.4 rethink breeding efforts order achieve yields very input. One feasible way solve problem inadvertent be aware trade-offs do-it-yourself strategy towards AMF include both morphological when varieties.