Analysis of seed and ware potato production systems and yield constraints in Argentina

The aim of this thesis is to analyze the seed and ware potato production systems in Argentina and their possible yield constraints in order to develop specific strategies to increase seed quality and tuber yield.This thesis starts with a survey of the actual potato production systems in Argentina carried out during 1994/95 and updated in 1999. Argentina currently produces well over 2 million tonnes of potatoes per annum on just over 100,000 ha. The survey also describes the acreage and production in different areas, agro-ecological conditions in each of these areas, yield constraints and perspectives for yield improvement. It also presents data on area, production and yield for each growing season and characterizes the seed and ware production systems in these areas in terms of weather based on long-term meteorological data and soils based on digitized soil maps for the whole country. In each of these areas yield determining, yield limiting and yield reducing factors are identified. High temperatures during planting and harvest time are the main yield determining factors as they affect crop growth and/or seed and ware quality. Also high temperatures during storage may be detrimental to the quality of stored seed or ware. Water and nutrient supply and physiological age of the seed are the main yield limiting factors in different seed and ware potato areas. Virus diseases, early ( Alternaria solani ) and late ( Phytophthora infestans ) blight are the main yield reducing factors in some areas. Strategies to solve problems of improper physiological age and virus infection are analyzed later in this thesis in order to obtain further improvements in yield and quality.A simulation study at national and regional levels (1) characterizes agro-ecological zones for potato production; (2) establishes potential growing seasons; (3) estimates the potential yields of the crop in these zones and seasons, and, at a regional level, also for different planting dates; and (4) discusses how these results match with reality and how they can be used for the benefit of the potato industry.Two models are used in these studies; the SUBSTOR-POTATO model for yield prediction and the LINTUL-POTATO model for a yield gap analysis.The SUBSTOR-POTATO model is calibrated and validated using Argentinian data sets from experimental results from different sites and years. Cultivar-specific coefficients are obtained during calibration and validation is based on several independent sets of field data, including cvs Huinkul, Kennebec, Mailén and Spunta. The observed and simulated values show good agreement within normal ranges of tuber yields. The particular behaviour of the input parameter maturity date is also considered, in order to properly assess tuber yield. A genetic coefficient for the duration of tuber bulking needs to be included in the model in order to obtain proper yield values under Argentinian conditions.A yield gap analysis is carried out with data from five different agro-ecological potato growing zones by comparing potential yield data obtained with the LINTUL-POTATO simulation model with the actual and attainable yields. This analysis is used to identify the possible factors determining, limiting or reducing yield in each of the areas considered and to analyse options for further yield improvement. Special emphasis is put on the yield limiting effect of the physiological age of seed tubers, water and nutrient management, and the quality and yield reducing effects of virus diseases. Results show, for the regions studied, that the actual yield is still far below the attainable and potential yields, due to suboptimal light interception by the foliage, poor seed quality, and lack of early ( Alternaria solani ) and late blight ( Phytophthora infestans ) control.Based on these results a physiological age index (PAI) that combines both the effect of chronological and physiological age of seed tubers is developed. PAI calculation is based on different key-dates of the life cycle of a seed tuber, which are easy to assess, i.e. the haulm killing date of the seed crop (T 0 ) and the end of the incubation period of seed tubers, measured under standard conditons. The PAI is: T 1 /T 2 , where T 1 is the time from haulm killing date (T 0 ) to possible planting date and T 2 the time from T 0 to the end of the incubation period. The PAI expresses physiological ageing of seed potato tubers within a range from 0 for physiologically young to 1 for old tubers. To test the PAI, existing data are re-evaluated and re-elaborated and specific experiments on the effects of seed origin and storage conditions for different cultivars have been performed during 1994/99. The effects of seed origin, seed supply and seed flow are also analyzed in terms of the effects of the physiological age of seed tubers on subsequent crop performance and yield. A survey on seed supply and seed flow evaluates the effects of different origins and storage systems upon crop growth and yield under practical conditions. The effects of physiological age on yield can be mainly attributed to improved light interception. PAI correlates well with the proportion of potential yield attained in different planting seasons.Different strategies may help to overcome the effect of yield limiting and quality and yield reducing factors, such as the physiological age of seed tubers and virus diseases. Application of plant growth regulators such as gibberellic acid and benzyl aminopurine modifies the effect of the physiological age of seed tubers on the progeny crops. Especially benzyl aminopurine is promising in overcoming the negative effect of old seed tubers on crop growth and yield. The development of a seed production system on the isolated island of Tierra del Fuego in the southern part of the country proves to be a sound strategy to multiply basic seed or to carry out initial multiplications in breeding programmes. Presence of nematodes, aphids and virus proves to be very low and growing and storage conditions allow the production of young seed. Seed yields and physiological quality are acceptable, and the seed is very healthy, with virtually no viral, fungal or bacterial infections.The study shows how a highly complex potato production system, like the Argentinian one, can be surveyed and analyzed. The survey work is complemented with the use of a Geographic Information System and simulation model approaches which improve our understanding of the possibilities for increasing future crop production by expanding the area cropped with potatoes and/or yield. The use of a yield gap analysis is also a useful and comprehensive tool to identify and rank yield defining, yield limiting and yield reducing factors for those agro-ecological zones where the potato is currently grown. With these procedures, the physiological age of seed tubers and virus diseases are identified as the most relevant factors limiting and reducing yield. Specific strategies are developed to counteract their limiting and reducing effects upon seed quality and tuber yield.The approach of this thesis does not only applied for the specific situation of the potato crop in Argentina, but this framework could be successfully applied to other crops or production systems elsewhere.