Investigating planting environment and seed physiological age interaction on potato crop growth

Seed tuber physiological age is known to influence a range of important growth processes in potato including early vigour of the plant, stem number per plant, hence tuber size distribution, time to emergence and the rate and duration of canopy cover rate of the plant. There is also an indication in published evidence to suggest that the expression of the seed tuber physiological age effects is modified by planting environment and varies with genotype. Furthermore, current process-based potato models do not capture the effect of the seed tuber physiological age and the interaction with planting environment. This reflects the lack of understanding and quantification of the effect of physiological age on potato growth. This thesis reports on physiology studies to investigate the effect of seed tuber physiological age and planting environment on stem number and component processes of pre-emergent growth and canopy development for important commercial cultivars of potato. The resultant findings are incorporated into a process-based potato model. Investigation of a production dataset collected from commercial potato paddocks in northern Tasmania showed that tuber size distribution was correlated with stem number per plant. The investigation also showed that planting environment (i.e. location, sowing date and soil type) varied with stem number. A follow-up controlled-environment trial provided further confirmation of the interaction between seed tuber physiological age and planting environment and that the response varies with genotype. Currently, the lack of any reliable measure of physiological seed age makes it difficult to develop response functions that can be incorporated into process-based models. With this in mind, a study was conducted to explore the possibility of using mitotic index as an indicator for tuber sprouting pattern as affected by seed tuber physiological age. Physiologically older tubers were found to have a higher mitotic index than younger tubers. However, mitotic index of the eye bud cannot be used to explain the sprouting pattern of the seed tuber having different physiological ages. Sprouting pattern was controlled by a correlative inhibition and availability of soil water. Pre-emergent growth of sprouts after planting was characterised by an initial period of slow growth (lag phase) followed by rapid linear growth. The duration of the lag phase was strongly influenced by temperature. Linear growth of the longest sprout was significantly affected by the interaction between temperature and water potential and varied significantly between cultivars. Physiological age of the seed tubers was found to have a significant influence on the canopy development of potato. Plants grown from physiologically older tubers were characterized by more branching on the main stem nodes and smaller individual leaf size. Leaf appearance rate was affected significantly by seed physiological age with the response varying with cultivar. In Russet Burbank, leaves generated from physiologically older seed appeared at a faster rate (39.5 °Cd per leaf or 0.025 leaves per day degree) than leaves from physiologically younger seed tubers (51.2 °Cd per leaf or 0.02 leaves per day degree). No significant difference was found between treatments for Atlantic although the first leaf in plants from older seed reached full size earlier ( 46.9 °Cd) than plants from younger seed tuber (75.9 °Cd). Seed tuber physiological age did not significantly affect the leaf senescence rate. However, senescence commenced earlier in plants derived from older seed tubers. The results from the physiology studies were incorporated into a new process-based growth and development model for potato for use within the APSIM modeling framework. A conceptual model was developed for the relationship between seed physiological age, soil moisture and temperature conditions at sowing and stem number. The complete potato model (APSIM Potato) was calibrated for leaf and stem biomass, tuber yield and phenology against a dataset collected from commercial paddocks in northern Tasmania and then validated against a larger independent dataset (48 paddocks) covering a wide range of growing environments. The model was found to adequately predict tuber yield (R2 = 80% for 48 observed vs predicted plot).