Growth and development of potato (Solanum tuberosum L.) crops after different cool season storage

Growth and development of potato (Solanum tuberosum L.) crops after different cool season storage. Tuber yield variation has been attributed to seed potato physiological age in numerous studies on potato. Seed potato physiological age has been defined as the developmental stage of a seed potato, or physiological state which influences production capacity and causes major impacts on potato yields. Physiological age is reportedly determined by genotype, chronological age and environmental conditions (especially temperature) during the storage phase. The temperature sum (or thermal-time) accumulated by the seed potato during the storage period can been used as a measure of physiological age. Manipulating seed potato physiological age may be an effective method to alter tuber yield and yield distribution for many cultivars. One important way to manipulate physiological age is to expose the seed potatoes to different temperature regimes during the storage phase. Therefore, an assumption of this study is that physiological age can be measured through quantification of accumulated thermal-time through development processes, from harvest to planting. These, in turn, are then expected to impact potato yield and size (or the grade size of each potato, which determines the yield size distribution). The rationale of the research is that contrasting seed potato storage regimes will provide different physiological ages at the time of planting. This may affect crop growth and development in the field and potentially affect tuber yield and yield distribution for different cultivars. The hypothesis to do this is; if seed potato physiological age is an important source of yield variation it must impact on at least one of the parameters of yield; i.e. cumulative amount of radiation intercepted by the canopy (Rcum), radiation use efficiency (RUE) or partitioning (harvest index; HI). First, a field experiment (Experiment 1, or Benchmark experiment) under non-limiting growth conditions benchmarked the mechanisms of potato growth, development, yield and yield distribution for three commercial cultivars (‘Bondi’, ‘Fraser’ and ‘Russet Burbank’). In New Zealand, ‘Bondi’ has high yield ability, which interests growers. However tubers may be too long, which is a complaint of processors. ‘Fraser’ has excellent long-term storage attributes with resistance to cool temperature sweetening. However, the difficulty of getting high tuber yields is seen as a disadvantage by the potato growers. ‘Russet Burbank’ was included in Experiment 1 to benchmark results internationally because is used worldwide as the standard for French fries and consequently there is extensive scientific literature about this cultivar. The objective of Experiment 2 was to generate ‘Bondi’ and ‘Fraser’ seed potatoes of different physiological ages from contrasting storage regimes (treatments). At the end of storage the seed potatoes from the different treatments had accumulated 972 and 2249 °Cd and their sprouting patterns were assessed for differences. Half of the potatoes of each treatment had any developing sprouts removed before planting, which added two agronomic treatments; (i) seed potatoes planted with sprouts (‘Sprouts on’) and (ii) de-sprouted potatoes (‘Sprouts off’). A second field experiment (Experiment 3) assessed crop growth and development from these seed potatoes. To formalise the effects of physiological age on the establishment phase of ‘Bondi’ and ‘Fraser’, and quantify the effects of seed potato physiological age on seed potato “vigour” a wider range of storage temperature was artificially produced in Experiments 4 and 5. These potatoes were then planted at a constant temperature environment on six different dates (Experiment 4) and in a single late field planting (Experiment 5). In Experiment 1 ‘Bondi’ had the largest tuber fresh weight yield (66 t ha-1), which was 20% higher than ‘Fraser’. Yield differences among cultivars were explained by differences in radiation use efficiency (RUE), because the spatial and temporal patterns of canopy development were similar for all cultivars. This resulted in similar amounts of radiation intercepted at the time of 95% final tuber yield (~1400 °Cd from emergence). ‘Fraser’ had the lowest rate of canopy senescence, lowest harvest index (HI), produced thicker leaves (lowest specific leaf area) and maintained higher leaf DM at the end of the season. This cultivar also grew longer stolons on the below-ground stem nodes and had the latest tuber initiation and bulking. The storage treatments applied in Experiment 2 resulted in seed potatoes with different sprouting patterns (physiological ages) at the end of the storage period. The potatoes from a three month warm up sprouted earlier, produced longer sprouts with more nodes and higher sprout dry matter than a one month warm up. In Experiment 3 total tuber yield and number were unaffected by any of the storage or de-sprouting treatments applied in Experiment 2. The lack of any yield differences reflected a stable pattern of R/Ro, RUE and HI found for ‘Bondi’ and ‘Fraser’. However, the seed potatoes planted with ‘Sprouts on’ shifted the yield distribution towards larger grades. Measurements of individual leaves on the main stems of ‘Bondi’ and ‘Fraser’ indicated that the rate of leaf appearance was not constant during canopy expansion and was controlled by competition with the below-ground tubers. Experiment 4 showed that prolonged storage of tubers at 20 °C temperatures reduced the seed potato “vigour” of late plantings. Nevertheless, for the October planting (commercial planting time in Canterbury, New Zealand) crop establishment was unaffected regardless of whether tubers had accumulated 200 °Cd or 2000 °Cd during storage. The late field planting in ‘Experiment 5’ confirmed the plasticity in storability of ‘Bondi’ and ‘Fraser’ seed potatoes. It is concluded that seed potato physiological age produced from different thermal regimes during the storage phase, was unimportant for the production of ‘Bondi’ and ‘Fraser’ in Canterbury. Tuber yield and yield distribution were unaffected by the seed potato physiological age and this reflected a similar pattern of Rcum, RUE and HI among the different age treatments. This represents an opportunity for grower to choose more economical ways of storing seed potatoes in temperate areas. Under non limiting conditions for crop growth, RUE was identified as crucial component of potato yield among different cultivars and may be included as breeding criteria for higher tuber yields and calibrated on a cultivar basis in potato simulation models.