No abstract

Yield and quality of potato depend on nutrient availability in soil, especially regarding nitrogen. Nitrogen (N) is a very dynamic plant nutrient and its uncontrolled application can considerably raise the price of agricultural production. If N is insufficiently utilised by plants environmental pollution can occur. The aim of the study was to investigate efficiency of nitrogen fertiliser use by potato. The field trials were carried out at the State Priekuïi Plant Breeding Institute from 2009 till 2012. Nine fertilisation variants were applied: no fertilisation; PK dose to provide potato yield of 40 t ha-1; and the remaining seven variants with a PK dose plus plus increasing N amount from 30 to 210 kg ha-1. The results of the four-year experiment years indicated that an increase in nitrogen fertilizer rate up to N120 kg ha-1 increased the potato yield. Nitrogen fertilizer rates should be applied depending on potato variety and planned use of the grown potato crop. Tuber nitrogen content increased with nitrogen fertilizer level from 1.09% in the treatment N0PK up to 1.53% in treatment N120, and practically remained at that level in treatments with higher N application levels. Nitrogen content in potato foliage was twice as high as that in tubers and continuously increased with the N amount applied, and particularly with higher nitrogen fertilizer rates of N150-210. In regard only to tuber yield, the N utilization coefficient at a nitrogen fertilizer rate up to N120 was on average 0.60. A further increase in nitrogen rate reduced the N utilization coefficient with each successive step.

Potato crop losses can be substantial when conditions for late blight (Phytophthora infestans) development and spread are favourable. In this study, drivers of differences between the P. infestans population structures in Latvia and Lithuania, two neighbouring countries with similar potato-growing traditions, were investigated. Genotypes of P. infestans and population genetic diversity were analysed using a 12-plex simple sequence repeat (SSR) marker assay. High genetic diversity was demonstrated in both populations, with population diversity being higher in Latvia. It would appear that local populations established from soilborne oospores early in the season are well adapted to the conditions in the region. However, somewhat greater spread and survival of local clones was detected in Lithuania, suggesting that potato cropping there is more vulnerable to clonal invasion than in Latvia. For effective disease management, current strategies should be adjusted according to the specific pathogen populations in the region, considering the reproduction and survival of the pathogen. Potato growers should implement late blight preventive measures such as longer field rotation to prevent oospore infections, especially in Latvia, and should use more disease resistant cultivars and high-quality seed potatoes.

Abstract-Many of the compounds present in potato are important because of their beneficial effects on health, therefore, are highly desirable in the human diet. The orange and yellow colour of the tuber flesh is due to carotenoids. The aim of this research was to determine the content of total phenolic content and carotenoids in relationship with the colour of organically and conventionally cultivated potato varieties before and after period of storage. In the research 31 potato samples of 12 potato varieties were analyzed on total carotenoid, total phenolic content and colour. Obtained results show that there was significant influence on carotenoid content between different cultivation environments (p<0.05) and between varieties (p<0.05). Total phenolic content significantly varies both per variety (p<0.001) and storage conditions (p<0.001).

Potato late blight, caused by the oomycete Phytophthora infestans (Mont.) de Bary, is one of the most serious potato (Solanum tuberosum L.) diseases, causing considerable yield loss in potato production worldwide, including Latvia. At present, the data on the population characteristics of P. infestans in Latvia is sparse. Therefore, the main aim of this study was to collect new data on Latvian isolates of P. infestans, to determine the main characteristics of the pathogen, particularly mating types, metalaxyl resistance and virulence with Black's differential set of potato genotypes containing resistance (R) genes R1-R11. During 2010-2012, 181 isolates of P. infestans were collected from 23 potato fields, from 13 locations in Latvia. Out of 181 isolates tested, 52.5% were A1, 43.1% -A2 and 4.4% -self-fertile mating type. Of 116 isolates screened for resistance to metalaxyl, 25.9% were resistant, 19.8% -intermediate and 54.3% -sensitive. More than 80% of isolates were virulent to R1, R3, R4, R7, R10 and R11, while 33% or fewer isolates were virulent to R5, R8 and R9. The least frequent was virulence against R9 in 24% of isolates. Our study revealed that the Latvian population of P. infestans is diverse. The proportion of mating types and the occurrence of both A1 and A2 in the same field indicate the possibility of sexual recombination in Latvian fields. Thus, it is very important to keep the crop rotation system, to prevent soil contamination with long-living oospores. The Latvian population of P. infestans shares many similarities with other European populations, which suggests gene flow between populations.