Phosphites (Phi) are alkali metal salts of phosphorous acid, with the ability to protect plants against different pathogens. In this research, the effect of Phi applied to potato plants on severity of three important potato diseases in Argentina was assessed. Seed tubers and foliage of potato cvs Shepody and Kennebec were treated with Phi to assess effects on resistance against Phytophthora infestans, Fusarium solani and Rhizoctonia solani. Protection resulting from Phi treatment in seed tubers was high against P. infestans, intermediate against F. solani, and low against R. solani. In addition, seed tubers treated with calcium or potassium phosphites (CaPhi and KPhi, respectively) at 1% of commercial product emerged earlier than untreated ones. When Phi were foliarly applied two or four times at different doses, high levels of protection against P. infestans were achieved in both cultivars. Higher protection was observed in Kennebec when CaPhi was applied, while in Shepody this was true for KPhi. Expression of β-1,3-glucanases was induced at different times after treatment but no correlation between β-1,3-glucanases expression and foliar protection level was found. On the other hand, Phi positive protection effects did not produce negative effects in plant growth. Leaves from CaPhi-treated plants showed a darker green colour than leaves from control plants; also an increase in Rubisco protein and a delay in crop senescence was observed.

The utilization of phosphites (Phi) could be considered as another strategy to be included in integrated disease management programmes to reduce the intensive use of fungicides and production costs.

The mechanism involved in systemic acquired resistance (SAR) can be non-specifically induced in susceptible plants. In response to pathogens, plants' natural defence mechanisms include the production of lignin and phytoalexins and the induction of plant enzymes. The aim of this research was to study the induction of SAR mediated by the chemical activator DL-3-aminobutyric acid (BABA) and the fungicide fosetyl-aluminium in potato cultivars with different levels of resistance against Phytophthora infestans (Mont) de Bary. To study the chemical induction of the resistance, the foliage of several potato cultivars was sprayed with BABA, fosetyl-aluminium or water (as a control treatment). After 3 days the foliage was inoculated with P. infestans. Seven days after inoculation, development of disease symptoms in the foliage was assessed. In postharvest tuber samples, evidence for enhancement of the defence response was evaluated by measuring the protein content of several hydrolytic enzymes as well as the phenol and phytoalexin content. The highest level of protection against late blight was observed when the chemicals were applied at early stages of crop development. An increase in resistance to late blight was also detected in tubers after harvest. There was also an increase in the protein level of beta-1,3-glucanase and aspartic protease as well as in the phenol and phytoalexin content of potato tuber discs obtained from postharvest tubers of treated plants. Thus the protective effect seemed to persist throughout the whole crop cycle. This treatment may offer the possibility of controlling both foliage and tuber blight and could have a major impact in reducing over-winter survival of P. infestans in tubers.

No abstract

In 1994, LINTUL-POTATO was published, a comprehensive model of potato development and growth. The mechanistic model simulated early crop processes (emergence and leaf expansion) and light interception until extinction, through leaf layers. Photosynthesis and respiration in a previous crop growth model-SUCROSwere substituted by a temperature-dependent light use efficiency. Leaf senescence at initial crop stages was simulated by allowing a longevity per daily leaf class formed, and crop senescence started when all daily dry matter production was allocated to the tubers, leaving none for the foliage. The model performed well in, e.g., ideotyping studies. For other studies such as benchmarking production environments, agroecological zoning, climatic hazards, climate change, and yield gap analysis, the need was felt to develop from the original LINTUL-POTATO, a derivative LINTUL-POTATO-DSS with fewer equations-reducing the potential sources of error in calculations-and fewer parameters. This reduces the number of input parameters as well as the amount of data required that for many reasons are not available or not reliable. In LINTUL-POTATO-DSS calculating potential yields, initial crop development depends on a fixed temperature sum for ground cover development from 0% at emergence to 100%. Light use efficiency is temperature dependent. Dry matter distribution to the

In potato (Solanum tuberosum L.), the accumulated day-degrees (temperature sum, calculated by accumulating the daily temperatures) from dormancy break until seed tuber use has been suggested as an indicator of the physiological status of the seed. We tested whether similar temperature sums differing in timing of a short period of high temperatures gave similar seed performance. Four field experiments were performed in which seed was used that had been exposed to different storage temperature regimes, differing in total temperature sum or in timing or duration of a warm period. Emergence, number of stems, number of tubers, and early and mature tuber yield were assessed. During the storage period, the onset of sprouting was recorded. Cultivars with a high rate of physiological degeneration (''ageing'') were usually sensitive to warm storage during the second part of the storage period, especially if the first 12 to 18 wk of storage had also been warm. This was reflected in reduced emergence (#10%), low densities of stems (#0.5 stems m 22 ) and tubers (#5 tubers m 22 ), and low yields, especially with early harvesting (#20 g m 22 ). Specific phasing of the warm period could reduce yields to levels even below the yield of the seed tubers exposed to the highest accumulated temperature sum. A higher temperature sum after the end of dormancy advanced and accelerated the process of ageing of seed tubers. Cultivars with a high rate of ageing showed much greater difference between the same temperature sums built up over time in different ways than cultivars with a low rate of ageing. The resulting maximum differences in final fresh tuber yield between seed lots exposed to the same temperature sum could be 65 Mg ha 21 for Astarte (a cultivar with a high rate of ageing) compared with nil for Dé siré e (a cultivar with a low rate of ageing).

Phosphite (Phi) compounds are salts derived from phosphorous acid. These compounds have the ability to protect plants against different pathogens. The aim of the present research was to assess the effect of Phi compounds on components of potato tuber periderm and cortex and to assess their effects on pathogen resistance in the postharvest stage. In a series of field experiments, potassium phosphite (KPhi) was applied to seed potato tubers and foliage. After harvest, several variables were analyzed in tubers obtained from these plants. An increase in pectin content was observed in both periderm and cortex tissue in tubers originating from KPhi-treated plants. After wounding and infection with Fusarium solani, a higher amount of pectin accumulation in cortical tissues was observed in tubers following treatment with KPhi. The content and/or activity of polygalacturonase and proteinase inhibitor also increased in tubers from KPhi-treated plants. A new isoform of chitinase was detected in the tuber periderm of treated plants.These results suggest that KPhi applied to seed tuber and foliage induces defense responses in tuber periderm and cortex and that these reactions are associated with structural and biochemical changes in these tissues.

As in other crops, yield and quality in the potato is determined by the genotype×environment interaction; limited by seed, crop, and storage management; and reduced by weeds, pests, and diseases. Within the limiting factors, seed tuber quality is crucial, both in low-and high-input crops. If poor seed tubers are used in low-input crops, only low yields can be expected. If poor seed tubers are used in high-input crops, the crops will not take proper advantage of other inputs, such as water, fertilizers, and pesticides applied. At present, physical aspects, such as shape and presence of wounds, seed tuber size, health, and physiological age, are the main components of seed quality, impacting seed vigour. Physiological age is defined as the physiological status of a seed tuber at any time, determined by genotype, chronological age, and environmental conditions from tuber initiation until new plant emergence. This minireview summarizes the physiological age assessment methods and the effects of crop and storage environment and management on physiological age and future crop performance. Possible tactics to reverse physiological age effects are also discussed. More research is still needed to develop a reliable and predictable indicator or index which can relate physiological age to yielding potential.