INTERACTION OF 2 SUGARY-1 ALLELES (SU1 AND SU1(ST)) WITH SUGARY-2 (SU2) ON CHARACTERISTICS OF MAIZE STARCH

Two recessive alleles at the maize (Zea mays L.) sugary-1 locus, sugar y-1 reference (su1) and sugary-1 starchy (su1(st)), were examined. Ker nels homozygous for the su1 allele result in a wrinkled/glassy phenoty pe while su1(st) kernels were nearly normal in appearance. Both sugary -1 alleles, however, result in the wrinkled/glassy phenotype when in a double-mutant combination with the recessive sugary-2 (su2) gene. Our objectives were to investigate the interaction between su2 and the tw o sugary-1 alleles (su1 and su1(st)) by examining starch thermal prope rties by Differential Scanning Calorimetry (DSC) and starch granule si ze using a laser-based particle size analyzer. A dosage study was also conducted between su2 and the two sugary-1 alleles in order to provid e additional genetic information regarding these gene interactions. Th e double-mutant genotypes su1(st) su2 and su1 su2 produced starches ha ving low gelatinization enthalpy (Delta H) values (2.2 and 0.8J/g, res pectively) compared to normal (12.1J/g), su2 (5.2J/g), su1(st) (10.9J/ g) and su1 (9.2J/g). In contrast to previous studies based on birefrin gence end-point temperature (BEPT), our DSC data demonstrated that su2 rather than su1 is epistatic with respect to gelatinization temperatu re. Dosage studies revealed that gelatinization onset (To), peak (Tp) and Delta H decreased upon increasing doses of the recessive su2 allel e. A similar dosage effect for su2 was observed in a su1 and su1(st) b ackground. A dosage effect was also seen for su1 on the Delta H value when the su2 gene was homozygous. No significant dosage effect occurre d with respect to stach granule diameter mean or mode. A trend was obs erved, however, in which a slight increase in starch granule mean and mode was associated with increasing doses of the su1 allele.