Effects of field conditions, low nitrogen and drought on genetic parameters of protein and tryptophan concentrations in grain of quality protein maize

Quality Protein Maize (QPM) has about twice the amount of lysine and tryptophan of normal maize and hence represents an important tool of correcting its deficiency in protein quality. However, the effects of low nitrogen and drought on genetic parameters such as gene action and combining abilities of protein quantity and quality of QPM are not known. To study how these genetic parameters are affected by field conditions, low nitrogen and drought, eight inbred lines were acquired from Centro Internacional Del Mejoramiento de Maiz y Trigo (CIMMYT) and used to generate single cross hybrids with North Carolina Design II procedures. The single crosses were evaluated at Kiboko in Kenya in 2006 under optimum, low nitrogen and drought environments. Observations were performed on protein and tryptophan concentrations in grain. Results showed that, the gene action of protein concentration was predominantly of additive and maternal natures whereas that of tryptophan concentration was predominantly of non-additive nature. Field conditions, low nitrogen, and drought changed the proportions of genetic effects. Field conditions suppressed maternal effects for protein concentration, but induced non-additive effects for both traits. Low nitrogen reduced additive and maternal effects on protein concentration while it reduced non-additive effects on tryptophan concentration. Drought reduced non-additive effects on both protein and tryptophan concentrations in grain. By changing the proportion of genetic effects, environments changed magnitudes and directions of general (GCAs) and specific (SCAs) combining abilities.