HUSK LEAVES OF EARLY DENT MAIZE: BREEDING BEHAVIOR AND CONTRIBUTION TO GRAIN YIELD

Leaves that extend from the modified leaf sheaths or husks enclosing the ear of maize (Zea mays L.) are referred to as husk leaves and they may significantly add to the photosynthetic area of the husks. The husk leaves may have the potential to compensate for leaf area lost during mechanical detasseling of hybrid seed corn production fields.;Differences in mean husk leaf area of F1's and F2's between locations suggested that environmental effects, especially plant population, may be important. Midparent heterosis for husk leaf area averaged 254% of St. Paul and 169% at Rosemount, Minn. for the high x high F1's; but few of the high x low and none of the low x low F1's displayed significant heterosis, which suggested that epistasis may have been involved. Husk leaf expression of inbreds per se and general combining ability effects satisfactorily predicted the husk leaf area of the hybrids. Broad-sense heritability values of husk leaf area on an individual F2 plant basis averaged 49% at St. Paul and 69% at Rosemount. Relative frequency distributions of visual husk leaf ratings on F2 plants indicated that alleles favoring low husk leaf area appeared to be at least partially dominant to alleles favoring high husk leaf area and that several loci control the trait. Husk leaf area of the materials I studied should be regarded as a quantitative trait that could be modified by standard maize breeding procedures.;I also investigated the contribution of husk leaves to grain yield under normal conditions and stress induced by partial defoliation prior to anthesis in four inbreds and two hybrids of early Corn Belt dent maize with high husk leaf area. Treatments consisted of a check, removal of the tassel plus the top two leaves prior to anthesis, and removal of all tissue above the uppermost ear prior to anthesis. Also, the husk leaves were either left intact (check) or removed when they were fully extended. Six replications in each of three year-locations were used.;Reduction in grain yield due to the removal of only the tassel and the top two leaves averaged 9.2% over all genotypes. Removal of all tissue above the uppermost ear caused an average yield loss of 50.2%. Both treatments resulted in a significant reduction in grain moisture at harvest that varied with genotype. The decrease in grain yield due to complete husk leaf removal was significant for 4 of the 6 genotypes and the average reduction was 2.6% (1.2 q/ha). The contribution of the husk leaves to grain yield was similar across the various detasseling treatments. Therefore, selection of seed parent inbreds with husk leaf areas similar to those we studied would not greatly offset yield reductions caused by mechanical detasseling.;The inbred parents, F1's, and F2's from an eight-parent diallel were examined to determine the breeding behavior of husk leaves in Corn Belt dent maize. Four inbreds with high husk leaf area and four with no husk leaves were used in the diallel. Husk leaf area was measured with a leaf area meter and visual ratings for husk leaf area given to individual plants.