Productivity of single cross maize hybrids under varying plant densities and agro-ecological conditions

Abstract

Maize (Zea mays) is an important crop globally as food, feed, fodder biofuel and industrial crop, and is making a significant contribution to the economy of Uganda. However, there is scarcity of hybrid maize seed in Uganda due to use of inappropriate plant densities/spacing by seed companies producing seed, resulting in low seed yields (1.5 - 3.0 MT/ha) instead of at least 5.0 MT/ha. There is scanty information as to the best plant density/spacing that can optimize maize seed yields. Thus this study investigated the effect of plant population density/spacing on the growth characteristics, yield performance and stability of single cross maize hybrids under different agro-ecological conditions. Sixteen single crosses were constituted from inbred lines of heterotic groups A and B using diallel mating design. The evaluation of single cross hybrids together with two checks was carried out in NaCRRI, Bulindi, NaSAARI and Ngetta. Four plant spacing treatments/plant densities used were 60 x 20 cm (83,333 plants/ha), 75 x 20 cm (66,666 plants/ha), 75 x 25 cm (53,666 plants/ha) and 75 x 30 cm (44,444 plant/ha). The experimental design was randomized complete block design (RCBD). The data was collected on days to anthesis and to silking, plant height, root and stem lodging, number of ears/plot, number of rows/cob, number of kernels/row, 1000 grain weight and seed yield. The results indicated that plant spacing and hybrid had significant (P<0.05) effect on the number of days to anthesis (AD), plant height, root and stem lodging, number of ears/plot, number of kernels/row and seed yield. At high plant densities (60 x 20 cm) and for heterotic group B, hybrids 3 and 9 took longer (P<0.05) than the control and other hybrids to reach the AD (71.3 days), while hybrid 8 took fewer days (65.8 days) though this was not different (P>0.05) from those of hybrids 1, 2, 4, 5, 6, 7 and 11. At low densities (75 x 30 cm), hybrid 3 took longer (72.1 days) to reach AD than the rest apart from hybrids 1, 4 and 9. At high plant densities (60 x 20 cm), apart from hybrids 3 and 4 all the hybrids had similar heights, and were taller (P<0.05) than the control. At low plant densities (75 x 25 cm), plant heights of all the hybrids were similar (P>0.05) to that of the control. Generally, mean heights of plants at high plant densities (201.4 and 207.7 cm for 60 x 20 and 75 x 20 cm respectively) were greater (P<0.05) than those of plants at low densities (198.7 and 197.2 cm for 75 x 25 and 75 x 30 cm respectively). Root lodging was greater at high plant densities (10.5 and 10.3% for 60 x 20 and 75 x 20 cm respectively) than at lower plant densities (5.7 and 3.4% for 75 x 25 and 75 x 30 cm, respectively). Low plant density (75 x 30 cm) resulted in lower number of ears/plot (18.3) than the other spacing treatments, which produced 20.2, 23.2 and 22.8 number of ears/plot for 60 x 20, 75 x 20 and 75 x 25 cm, respectively. The mean number of kernels/row for the spacing of 75 x 25 cm (40.2) was greater than those of the other spacing treatments that had 34.3, 38.9 and 38.1 kernels/row for 60 x 20, 75 x 20 and 75 x 30 cm, respectively. The mean seed yield gradually decreased from 5.6 MT/ha as the spacing increased (plant density decreased), becoming significantly lower at 75 x 30 cm, which yielded 3.9 MT/ha. Furthermore, the results on the effect of genotype and genotype-by-environment interaction biplots showed that hybrids 6, 11, 2 and 5 were the most stable and can be used in the production of three-way cross hybrids, or can as well be released as hybrids. The biplot analysis also revealed Namulonge as a discriminating environment because it had the longest vector and NaSAARI as the representative environment of all because it had the smallest angle from the Average Environment Coordinate. In conclusion, planting single cross maize hybrids at 75 x 25 and 75 x 30 cm minimizes plant heights and consequently reduces lodging of plants. In addition, the spacing of 75 x 25 optimizes the number of ears/plot, number of kernels/row and consequently maximizes seed yield. Therefore, single cross maize hybrids should be planted at 75 x 25 cm to reduce plant heights and lodging of plants, and in turn optimize the numbers of ears/plot and numbers of kernels/row, which consequently optimizes seed yield.