Effect ofBarchytic-2 Gene on Yield and Yield Components of Maize (Zea mays L.)

Abstract

A series of 4 experiments was conducted on the effects of the brachytic-2 and other dwarfing genes on grain yields and yield components of maize at Waimanalo Research Station of the University of Hawaii. The brachytic-2 gene has been used by breeder especially in Hawaii and Colombia to reduce the often excessive height of tropical corn. The primary interest in my study was to determine whether any loss of grain yield occurs when this gene is employed. It was of additional interest to determine how great the height reduction was in tropical inbreds and single cross hybrids, how great the loss of stover yield would be, whether the gene differentially affected the yield and yield components. Tests were also conducted to determine how these parameters were affected by temperate vs tropical day lengths, using 16 vs 12-hr day. The first experiment involved eleven dwarf mutant genes and one normal tall that were planted as a completely randomized design in February 1983. All mutants were isogenic to the tall inbred (Hi27). Filled ear length of brachytic-2 {br2) was 85% of the filled ear length of Hi27. Plant height and ear height of br2 were about 70% and 68% of Hi27, respectively. Internode lengths of br2 were 70% of Hi27, and leaf area per plant was 69% of that of Hi27. The internode elongation patterns of br2 was sigmoid. Correlations among plant height, ear height, internode length and typical internode length of all genotypes tested in this experiment were positive and highly significant. Based largely on this survey, the dwarfing gene br2 was chosen for all further studies. The second experiment involved 80 hybrids, made up of 40 isogenic pairs of br2 and normal, which were planted in two seasons (September 1983 and March 1984). These trials were laid out in a split-split plot design with 4 replications. Grain yield and filled ear length of br2 hybrids were not significantly different from their normal counterparts in the March planting and in combined analysis of September and March plantings. In individual analysis of September planting, grain yield and filled ear length of br2 were significantly below those of the normal by an average 7% and 11% respectively. Traits that were negatively affected by br2 included stover yields (-15%), ear height (39%), and plant height (-24%). Brachytic-2 silking dates were delayed 2.4 days (range l to 5 days) compared to those of the normals. Kernel weights and kernel depths were not affected by this gene. Grain yield was significantly correlated with filled ear length. Other highly significant correlations included those of ear height and plant height with stover yield. A third experiment involved extended daylengths on genetic dwarfs, carried out as a randomized complete block design with two replications in April 1983. Incandescent lights were used to extend daylengths, 4 hours each day. Filled ear lengths under extended light were shorter than those of the normal day length by an average 14%. Days to tasseling and silking under extended light compared to those under normal light were delayed 13.3 days and 16.5 days, respectively. Traits that were affected positively by extended daylength included plant height (+22.5%), and ear height (+37%). Typical internode length and patterns of internode elongations were not affected by extended daylength. The fourth experiment involved ten normal hybrids under 4 hrs extended daylength planted in April 1983. This experiment was carried out as a randomized complete block design with three replications. Grain yield was affected negatively by extended daylength (-21%) compared ·to_that under normal daylength. Filled ear length under extended daylength was not significantly different from that under normal daylength. Days to tasseling and silking under extended daylength were delayed 7.7 days and 11.1 days respectively, compared to those under normal light. Traits that were affected positively by extended daylength icluded ear height (+49%), and plant height (+29.1%). Typical internode length was not affected by extended daylength. The fifth experiment involved 20 pairs of the best hybrids from trial 3.2 were planted on 9/11/1984 in a split split plot design with 4 replications at Kohala on the Island of Hawaii. Main plots were with and without windbreak; sub plots were normal and brachytic. Brachytic-2 hybrids without windbreak produced grain yield of 0.48 Mg/ha or 36% lower than that with windbreak. Without windbreak the average grain yields of brachytic-2 hybrids were not different from the normal hybrids; but with windbreak br2 hybrids produced 0.36 Mg/ha or 361 higher than that of the normal. Brachytic-2 hybrids generally had bigger stem diameter than their normal counterparts, with a mean difference of 0.22 cm (121), significant at 51 level. The presence or absence of windbreak seemed to affect the stem diameter. A decrease in value was noted in plants grown with windbreak, which were found to be significantly different at 5% probability level from plant grown without windbreak.