Environmental effects on growth and development of cassava (Manihot esculenta Crantz.) III. Assimilate distribution and storage organ yield

Assimilate distribution and storage organ (storage roots plus swollen planting piece) yield of serial plantings of the cassava cultivar M Aus 10, made throughout a year, and grown for one year duration were studied with sequential harvests in S.E. Queensland (latitude 27° 37′S), Australia. Seasonal differences in the proportion of total dry matter assimilation partitioned to storage organs over a given time period (referred to as distribution ratio, DR) were observed with low DR over the mid-summer (January to March) period (0.1 to 0.3) when crop growth rate (CGR) was at a maximum compared with 0.4 to 0.5 in November to December and 0.5 to 1.0 in late autumn to winter (April to July). This period of low DR restricted storage organ yields which were generally lower (6-9 t DW ha-1 year-1) than those reported for adapted germplasm at lower latitudes. Multiple regression models were developed which accounted for much of the variation in DR in terms of mean air temperature or photoperiod and leaf area index (R2 = 0.73). High temperatures, long photoperiods and high leaf area indices were associated with reduced DR. Mean air temperature and photoperiod are highly correlated in this environment and their separate effects on DR could not be distinguished. This model of distribution ratio was combined with earlier published models of CGR, and storage organ growth rate predicted