Thermal and photothermal effects on the growth and development of diverse grain sorghum genotypes

Abstract

A study was conducted to determine if thermal or photothermal models (indices) could be developed to accurately predict phenological development of these diverse genotypes grown in different climatic regimes. Growth analysis of the genotypes was conducted at College Station, Texas during 1978 to ascertain the differences in growth habit between tropically adapted and temperate genotypes. Serial sowings of the five genotypes, NB505, RS610 (temperately adapted hybrids), ATx623 x RTx430 (tropically adapted hybrid), RTx430 and BTx623 (tropically adapted lines) were conducted at Weslaco, College Station and Lubbock, Texas, and at Isabela, Puerto Rico in 1978 and 1979. Phenological observations were taken for all genotypes at all planting times. Maximum and minimum temperatures were obtained for each experimental site. From the temperature data, known solar occurrences and the 1978 phenological data thermal and photothermal indices were constructed. The indices with the lowest coefficients of variability were used to predict the phenology of the 1979 plantings utilizing normalized temperature data. All genotypes had a similar photoperiod response with a critical photoperiod of approximately 12 hours. For thermal and photothermal indices developed for the entire growth period of the plant there were no significant effects due to location; there were significant effects due to planting time at each location except for HS5 (a modified GDD index). For the indices used to predict stage to stage phenological development, there were significant location and planting time effects. There was a marked decrease in the variability of the indices while the plants remained vegetative (Growth Stage 1). Regardless of the index of growth used all genotypes spent approximately one-third of their life cycle in each of 3 growth stages (GS1 - planting to floral initiation; GS2 - floral initiation to 50% anthesis; GS3 - 50% anthesis to black layer at the base of panicle). Growth indices developed from the 1978 serial sowings were used to predict the development of the 1979 plantings, utilizing 25 year temperature averages as the temperature inputs to the indices...