Consumption of processed potatoes is increasing in Brazil. However, little information is available on the effect of nitrogen (N) rates on performance of potato cultivars developed in Brazil. The objective of this work was to evaluate yield and quality of tubers of potato processing cultivars, submitted to N rates at planting. Three field trials with eight treatments were conducted: two cultivars (Atlantic and BRSIPR Bel) and four N rates (0, 75, 150, and 225 kg/ha). Yield and quality of tubers were evaluated, as well as the post-frying absorbed oil content. Cultivar BRSIPR Bel showed higher total tuber yield (18% more) and commercial tuber yield (15% more) due to the production of higher number of tubers (29% more) compared to the cultivar Atlantic. On the other hand, Atlantic cultivar produced tubers with higher dry weight (22%) and lower oil absorption (38%). For both cultivars, the estimated N rate of 151 kg/ha resulted in the highest commercial tuber yield (diameter larger than 45 mm): 34.0 t/ha. For all studied variables there was no interaction between cultivar and N rate, concluding that the cultivars in this study (American and Brazilian origin) respond similarly to N rates.

The results from humic substances (HS) application in varied crops and conditions are controversial, and the experiments with the potato crop in Brazil are scarce. The objective of this study was to evaluate the effects of HS doses on the growth and yield of two potato cultivars. Four doses of HS were tested: 0, 5.05, 10.10, and 15.15 L ha-1, applied in the planting furrows of cvs. Agata and BRS F63 Camila, in Guarapuava-PR, in the 2015 and 2016 crop seasons, between October and February. The experiment was carried out using a randomized complete block design, in a factorial scheme (crop season x dose x cultivar), with four replications. Plant samplings were performed at tuber initiation, flowering, tuber bulking, and plant maturation growth stages. After shoot senescence, the total and commercial tuber yields were evaluated. Cultivars responded similarly to HS application, with no significant interaction between HS and cultivars, for most assessed variables. At tuber initiation, there was a negative linear effect of HS doses on leaf area index, number of formed tubers, and tuber and total plant dry weight. In the other evaluations, the effect of HS application was not observed regarding the assessed variables. Likewise, no effects were detected on the number and fresh weight of tubers in total and commercial yields. We concluded that HS application affected both cultivars similarly, hampering initial plant growth and not increasing potato yield.

In vitro propagation and tissue culture technique is an alternative for obtaining healthy potato seeds. However, data found in the literature differ on the optimal consistency of the culture medium to be used in vitro. The aim in this research was to look at the adaptation of potato cultivars to medium with different agar concentrations. The experimental design was entirely randomized in a factorial scheme. The experiment tested the effect of 3 agar medium concentrations (solid, semisolid and liquid) on 6 cultivars (Agata, Bel, Camila, Catucha, Clara and Eliza), with 5 repetitions. We quantified from the plantlets, fresh and dry mass of roots and shoot, the number of nodes, the multiplication capacity and vigor. The study showed that potato cultivars respond significantly to different concentrations of agar and their best response was in the semisolid medium.