The critical value of soil Olsen-P (mg Olsen-P kg-1) is the value of soil Olsen-P above which the probability of crop response to P fertilization is small or null. The aim of the present study was to determine the critical value of soil Olsen-P for potato tuber yield in volcanic soils. The data used in this study were taken from 41 experiments of P fertilization conducted in southern Chile from 1977 to 2015 by the National Potato Center at the Instituto de Investigaciones Agropecuarias (INIA). To identify the critical values of soil Olsen-P, relationships between relative yields and initial soil P-Olsen were assessed using three models (linear-plateau, boundary and Mitscherlich function). Across experiments, the average fresh tuber yield was 41.9 Mg ha-1 and varied between 4 and 89 Mg ha-1. Fresh tuber yield decreased up to 92% by P deficiency; however, yield reduction was concentrated between 20 and 40%. The critical Olsen P values determined were 41, 33 and 11 mg Olsen-P kg-1 obtained (P < 0.01) with linear-plateau, boundary function and Mitscherlich function, respectively. However, linear-plateau and Mitscherlich functions showed lower coefficient of determinations (R 2 = 0.23-0.31) than the boundary function (R 2 = 0.97). Therefore, we suggest that the critical Olsen-P value of 33 mg P kg-1 determined with the boundary function is more appropriate for potato growers than the critical value determined with the other models. This information will be valuable for optimizing strategies for P fertilizer management in potato production systems aimed at achieving optimal crop yield and minimizing potential environmental risk.

The Potato virus Y (PVY) is distributed worldwide and is one of the most damaging viruses in terms of yield reduction in the potato (Solanum tuberosum L.) crop with losses sometimes reaching 80%. To reduce its impact, there is great interest in obtaining varieties carrying the Ryadg gene that provides extreme resistance to this virus. This could be facilitated with SCAR (sequence characterized amplified region) RYSC3 by molecular marker-assisted selection (MAS). This study compared the effectiveness of the RYSC3 marker in the detection of the Ryadg gene vs. biological tests on populations of the Potato Breeding Program of the Instituto de Investigaciones Agropecuarias (INIA), Chile. Within the group of 71 progenitors, 30 plants had some kind of resistance to the virus, of which 17 were carriers of the RYSC3 marker. These genotypes came from Cornell University, Centro Internacional de la Papa (CIP), Peru, and INIA. The analysis of 460 progenies which came from three different crosses showed that 299 individuals amplified the RYSC3 marker and had the resistant phenotype, with the exception of one plant. Within the group of non-RYSC3 carrier plants, a significant percentage (22.5%) showed a resistant phenotype, indicating that these progenies segregate other R genes (e.g., hypersensitivity) that reduce biological test effectiveness. This high effectiveness (99.7%) in the detection of the Ryadg gene in both parents and segregating progenies, showed that this marker is appropriate in assisting selection of genotypes with extreme PVY-resistance in the potato breeding programs.

The critical value of soil exchangeable potassium (K) (mg K kg −1) is a valuable tool for an efficient K fertilization management in potato production systems. The aim of the present study was to determine the critical value of soil exchangeable K for potato crops grown in different environments and differing availabilities of initial exchangeable K. The data used in this study were taken from 34 experiments on K fertilization conducted in southern Chile from 1977 to 2017 by the National Potato Center at the Instituto de Investigaciones Agropecuarias (INIA). Yield responses to K fertilization rates were assessed with linear-plateau and Mitscherlich models in order to determine the critical soil exchangeable K across environments. Across experiments, the average fresh tuber yield ranged between 18 and 91 Mg ha −1. Fresh tuber yields decreased by up to 70% when no K fertilization was applied. Yield reduction was concentrated around 25% in response to K deficiency. Relative yields were described as significant by both linear-plateau and Mitscherlich models. However, relative yields were better described by the linear-plateau model (p < 0.01, R 2 = 0.62; SEE = 0.11). The critical soil exchangeable K value identified with the linear-plateau model was 224 mg K kg −1. This critical K value will be useful for potato farmers that produce their crops in volcanic soils, such as Andisols. Moreover, this critical K value will help to increase K use efficiency through better K fertilization management strategies aimed at building and/or maintaining K levels in soils.

Evaluación de la calidad de semilla sexual de papa (SSP) híbrida (Solanum tuberosum L.) para su uso en producción comercial y alimentación humanaEvaluation of the quality of hybrid true potato seed (TPS) (Solanum tuberosum L.