Evaluating seed quality and performance of low and high phytic acid maize (Zea mays L.) under varying phosphorus rates and water regimes in dryland conditions.
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Abstract
Maize (Zea mays) being the staple crop for many communities in Sub-Saharan Africa and also
used for animal feeding, a considerable effort has been made to improve quality and yield. In recent
times plant breeders have focused on reducing phytic acid (PA) on maize seeds to improve grain
nutritional quality. Although studies of low phytic acid genes have been reported in temperate
maize, the current research was based on the tropical genetic background which was screened for
low phytic acid. This is the first report for applied breeding of the trait in the tropical maize. Little
is known on the agronomy and responses of tropical maize specifically to water stress and its
response to phosphorus application. No studies provided on the seed quality performance and
response of low phytic acid maize to water stress and phosphorus application. Reducing Phytic
acid of tropical maize could have negative effects on seed quality and yield. The primary objective
of this study was to compare the performance of low phytic acid (LPA) maize seeds of tropical
origin with three other varieties i.e. high phytic acid (HPA) of tropical origin, SC701 and LS8520
based on seed quality and water stress.
The study consisted of two maize synthetic populations differing in phytic acid (PA) content (from
the African Center of Crop Improvement (ACCI)); namely, LPA and HPA synthetic populations.
Both the LPA and HPA synthetic populations were derived from a tropical second generation (F2)
population and were selected based on their phytic acid (PA) content. They were produced at the
Ukulinga Research Farm, University of KwaZulu-Natal (29°40'05.7"S 30°24'20.9"E), in
Pietermaritzburg, South Africa. These two maize synthetic populations were compared with two
commercial maize varieties (from McDonald Seeds), white maize (SC701) and yellow maize LS
8520 R (484) which in this study was coded LS8520. All seeds used in this study were produced
under identical production conditions and in the same growing season, thereby ensuring that the
seeds were of the same physiological age.
The first experiment investigated the characterisation of LPA maize varieties for seed germination
and vigour. Seed quality was evaluated using the standard germination test and accelerate aging
test together with electric conductivity test (EC). The second experiment was conducted as a pot
trial to investigate the effect of exogenous phosphorus application on seed quality and yield of low
phytic acid maize varieties. In third experiment, a field study over two seasons (2015/2016 and
2016/2017) was conducted at Ukulinga Research Farm in Pietermaritzburg, under dryland
conditions. The objective of the experiment was to evaluate the newly produced ACCI’s two
genetically synthetic maize populations of LPA and HPA under dryland field condition and
compare them with the commercial white and yellow tropical maize varieties their germination,
growth, yield and yield components. Lastly, an experiment under controlled conditions on
photosynthetic efficiency and yield responses of LPA and HPA maize tropical lines to deficit
irrigation. The study was carried out under controlled environment conditions. The objective was
to evaluate the photosynthetic efficiency of low phytic acid (LPA) and high phytic acid (HPA)
tropical maize varieties grown under water-stressed conditions.
The results of the first experiment indicated that the performance of LPA varieties was comparable
to those of commercially produced varieties. This study suggests that the combination of LPA lines
of tropical origin used in this study was satisfactory to meet the minimum seed quality parameters
particularly seed germination and vigour. The results for phosphorus application showed that the
application of phosphorus improved the growth, flowering and yield of LPA and other varieties as
well. The mean germination time (MGT), germination vigour index (GVI), electrical conductivity
(EC) (μS g-1), root length, shoot length and the root-shoot ratio of the harvested seeds after
phosphorus application were also improved. When the LPA and HPA tropical maize exposed to
dryland environments the results revealed that the SC701 variety outperformed the other three
varietiess in growth and yield. It was concluded that the LPA maize performed lower under field
conditions. In the water stress trial, results showed that LPA maize varieties recorded higher values
of stomatal conductance (gs) and transpiration rate (T) compared to HPA and SC701 for both
normal and water stress conditions. HPA showed a significantly (P< 0.001) higher value of
photosynthetic rate (A) than LPA and SC701 for all the water stress treatments. HPA and SC701
were comparable in most of chlorophyll fluorescence parameters. With regard to yield, HPA
showed increased performance in terms of overall yield and seed weight, and this suggests that
HPA varieties are less sensitive to water stress than LPA maize varieties. The results from this
study have proven that LPA maize varieties are sensitive to limited conditions and further research
under a wide range of environmental conditions is required.
Overall, the results indicated that the seed germination of LPA was comparable to other varieties
but the yield remains low. There is a need to conduct more experiments to demonstrate the
performance of LPA under field conditions in response to phosphorus application and water stress.
These differences between the traits could help breed programs. The selection for LPA and HPA
tropical maize should be based on their physiological performance to be planted in temperate zones
to grant higher yield performance.
Description
Doctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.