Morpho-physiological parameters affecting iron deficiency chlorosis in soybean (Glycine max L.)

Iron deficiency chlorosis (IDC) leads to severe leaf chlorosis, low photosynthetic rates, and yield reductions of several million metric tonnes each year. In order to devise breeding and genetic transformation programs that aim at generating high-yielding and IDC-tolerant soybean lines, it is necessary to better understand the mechanisms that enable tolerant plants to survive under Fe-limiting conditions. An in silico analysis in the USDA soybean collection allowed the identification of a set of novel efficient and inefficient soybean cultivars which can be used in future studies concerning IDC response. Plants were grown in iron deficient and iron sufficient conditions using a bicarbonate system and several IDC-related aspects were studied. A new set of efficient and inefficient soybean lines were identified in silico, and their tolerance to IDC was confirmed under laboratorial conditions. New plant traits that are highly correlated to IDC scoring were identified: a negative correlation was found between SPAD values and stem weight, weight of the unifoliolates and iron concentration of the first unifoliolates was found; higher SPAD values were correlated with the amount of iron in the first trifoliate leaves. Our data also show that having higher concentrations of iron in the seeds provides increased resistance to IDC. No correlation was found between root iron reductase activity and chlorosis. Soybean differential chlorosis susceptibility between different accessions is linked to specific morpho-physiological parameters such as unifoliolate leaf size, stem weigh, concentration of iron in the seeds, and tissue iron partitioning.