Quantitative trait loci associated with lime-induced chlorosis in a recombinant inbred population of maize

Lime-induced chlorosis in maize is commonly associated with iron deficiency in high pH soils. Calcareous soils of this type are relatively common in the lower rainfall areas of the tropics and limit maize production especially in Mexico and the Middle East. Scientists at the International Maize and Wheat Improvement Center (CIMMYT) in Mexico have a breeding and physiological program for improving tolerance to such soils at their Tlaltizapan station in Morelos, Mexico. In 1997 we evaluated 100 recombinant inbred lines (RILs) derived from elite inbreds Hi31 (Hawaii/Iowa) and Ki14 (Thailand) in four replicated trials on iron-deficient soils at the Tlaltizapan station. Leaf chlorosis was evaluated by visual ratings and with a Minolta SPAD-502 Chlorophyll Meter during the first 8 weeks of growth. The parents differed significantly in all trials with Hi31 susceptible and Ki14 highly tolerant. RIL inbreds varied widely between the parental extremes with approximately one fourth in each of the parental classes. The RIL population had been genotyped previously with 127 RFLP markers, creating a well saturated linkage map (MING et al., 1997). Putative quantitative trait loci (QTLs) were analyzed through single-factor ANOVA and with MAP-MAKER\QTL interval mapping. QTLs significantly associated with lime-induced chlorosis occurred on chromosomes 2, 3, 4, 5, and 9. The QTL with largest effect was associated with RFLP locus umc26 on Chromosome 3, and explained 41% of the variation within the population. Two intervals on the long arm of chromosome 3 also gave the highest observed LOD scores for chlorosis. High LOD scores were also recorded for the interval between umc156 and umc200 on chromosome 4. These QTLs are believed to be good candidates for marker-assisted selection to overcome problems associated with cultivation of maize on iron-deficient soils.