Stability of rice grain and whole kernel milling yield is affected by cultivar and date of planting
The objectives of this study were to evaluate rice (Oryza sativa L.) cultivar stability and to characterize different planting dates for their consistency in grain yield and milling. Eight rice cultivars and seven planting dates were evaluated from 2003 to 2005 for a total of 19 yr x planting date environments. The coefficient of variation of cultivars and planting dates, a measure of relative variation that approximates stability, were compared along with mean performance to demonstrate a new method for interaction between the genotype x environment (GEI) evaluation of multi-environment datasets. Planting date was the most significant component of the total variation in grain yield due to environment while year, as a source of variation, was more significant for whole kernel milling yield. ‘Jupiter,’ a medium-grain type, was the highest yielding cultivar in the study but was also one of the least stable as evidenced by a large coefficient of variation. ‘Cypress’ and ‘CL161’ were among the most stable cultivars and exhibited high grain and whole kernel milling yields suggesting that they would be ideal cultivar selections for planting at less than optimum times or when abnormal conditions occur for rice planted during the recommended timeframe. Based on high grain and milling yields and consistent performance across years and cultivars, the optimum date for planting rice at this location was PD4. The methods and statistics we demonstrated in this study do not require expensive commercial software packages, are simple to compute and easily interpreted, and should have widespread applicability across most crops and locations.