Abstract: The used lodging resistance index is lodging score, with 0 as most resistant and 4 as most sensitive. In breeding for lodging resistance, an index more precise than lodging score and independent from the cultivation conditions is expected. In the present study, four kinds of lodging resistance indices, i.e. fresh matter moment (plant height × above ground fresh weight, PF), dry matter moment (plant height × above ground dry weight, PD), fresh weight moment per unit of stem broken strength (PFS), and dry weight moment per unit of stem broken strength (PDS), were designed in two experiments, one with 32 diverse cultivars and one with the RIL population NJRIKY including 184 recombinant inbred lines of the cross (Kefeng 1 × Nannong 1138-2) in 2005 and 2006. Among the four indices, fresh weight moment (PF) designated as lodging potential performed with higher correlation with lodging score, more relevant physical meaning, easier operation of measurement, better stability in various environments and more common QTLs with lodging score than those of the other indices, therefore PF was the best candidate of lodging resistance index to replace lodging score. On the basis of the results, QTL analysis was performed for lodging score and lodging potential. Seven QTLs for lodging score on linkage groups A2, C2, D2, and G explaining 6%–12% of phenotypic variation, but no common one between the two years, were detected. There were seven QTLs for lodging potential on linkage groups B1, C2, and O, explaining 5%-12% phenotypic variation, with the same QTL qPFC2-2 in two years. Between lodging score and lodging po-tential, two QTLs were with same flanking markers, i.e. GMKF059a–satt319 and satt286–A63_1T, and the lodging resistance alleles were mainly contributed from Kefeng 1. Between the two loci, qPFC2-2 was of larger contribution, so its flanking markers can be used in marker-assisted selection for lodging resistance in soybean.

Key words: Soybean, Lodging indix, Correlation, QTL analysis