Genetic analysis of maize growth and flowering response to phosphorus deficiency, and the evaluation of six mycorrhizal isolates for their ability to promote growth of maize genotypes under phosphorus deficiency

Optimization of P use efficiency in maize hybrid production is important to improve interactions between agricultural production systems and the environment, to improve the stability of world food supplies, and to optimize resource utilization in areas of intensive farming. Enhancing genetic characteristics of maize hybrids and manipulating mycorrhizal populations in association with maize can be beneficial in improving P use efficiency. The objectives of this dissertation were to (1) compare the B73 X Mo17 RIL shoot weight response to added P in the field with the response previously measured in the glasshouse, (2) characterize the genetic effect of low P on phenotypic expression of seedling emergence, flowering date, and plant height, and (3) to determine the relative growth benefit of six mycorrhizal isolates on maize inbreds grown under P deficiency. Phenotypic and rank correlations between shoot weight response to added P in the field and glasshouse experiments were not significant and near zero, proving that measurements made in the glasshouse are not predictive of field performance for this trait. Phenotypic correlations between growing degree days to anthesis and shoot weights under high and low P were significant and negative. A QTL was detected for growing degree days to flower with a greater allelic effect under low P than high P. This region has previously been identified for shoot weight response to added P and for flowering time in other populations, suggesting that a relationship between nutrient efficiency and flowering may exist with earlier flowering genotypes being more P efficient than later genotypes. While significant maize genotype by mycorrhizal interactions were found, the effect of mycorrhizal isolate was greater than the maize genotype effect. Mycorrhizal isolates in the Glomus genus provided the greatest benefit to shoot weight under low P and have the greatest potential for use under a wide range of maize inbreds. Our results indicate that a combination of cultivar development and management of mycorrhizal populations by inoculation or crop rotation will contribute to optimal maize productivity in reduced input systems.