The impact of haulm killing on yield and quality of potato (Solanum tuberosum L.)

Disease-free and superior quality seed tubers could be obtained by haulm (vine) killing, which also reduces weight loss during storage. Higher resistance during storage ensures that seed tubers will be at the desired physiological age at the time of planting. The use of healthy seed tubers of appropriate physiological age will have positive impact on yield and quality. This study aimed to investigate the effects of haulm killing on seed potato yield and yield components (total tuber yield, average tuber yield/plant, number of tubers and average tuber weight) under semi-arid climate of Artova district in Tokat province, Turkey. The field studies were carried out during potato growing seasons of 2017 and 2018. The experiment consisted of two factors, i.e., potato cultivars and haulm killing. Five different potato cultivars, i.e., ‘Agria’, ‘Marabel’, ‘Hermes’, ‘Marfona’ and Madeleine were included in the study. The haulm killing treatments were ‘haulm killing’ and ‘no haulm killing’. Haulm killing positively affected the number of tubers per plant and average tuber weight, which are directly related to the tuber yield. Tuber seed yield in the first and second year with haulm killing treatment was 40.78 and 44.05 tons/ha, respectively. The yield without haulm killing in the first and second years was 37.78 and 38.76 tons/ha, respectively. The dry matter ratio of tubers with haulm killing was 21.89% in 2017 and 22.35% during 2018. The dry matter ratio of tubers without haulm killing was 20.57% in 2016 and 21.03% during 2017. The results revealed haulm killing had positive impact on yield, yield-related parameters and dry matter content of seed tubers. Therefore, haulm killing is recommended for higher yield and better quality of seed tubers.

Effects of Physical, Mechanical and Hormonal Treatments of Seed-Tubers on Bud Dormancy and Plant Productivity

The aim of this study was to develop a technique easy to apply in order to induce seed-tuber dormancy breakage. Over a two-year study, more than seven dormancy-breaking treatments were tested through evaluating different temperature effects alone or combined with gibberellins application, cutting in half of seed-tubers, and early haulm killing. Three varieties per year were considered: Spunta and Monalisa (medium and long dormancy) in both years, Europa during the first year and Arinda during the second year (both characterized by a short dormancy period). We found firstly that Europa and Arinda promptly responded to thermal treatments, and secondly to the same thermal treatments in combination with the application of gibberellins. Although not easily applicable, especially when a large volume of seed-tubers has to be handled (seed-tuber producers), the cutting in half of the seed-tubers also had a satisfactory result. Notwithstanding that treatments did not perfectly overlap between the two experiments, results were qualitatively similar. Therefore, these findings allow us to conclude that treatment with post-harvest storage at 20 °C, followed by a treatment with gibberellic acid at 38 days from harvesting, is the most efficient in releasing dormancy, in ensuring a good vegetative growth and productive performance at field-level irrespective of the variety.

Influence of Timing of Harvest in Relation to Haulm Killing and Planting Date on Potato Tuber Rot Caused by Phytophthora infestans

Killing potato haulms 2 to 3 weeks prior to harvesting tubers is recommended for the management of potato late blight to eliminate the foliage as a source of tuber blight inoculum. Some potato growers in the Columbia Basin of Washington and Oregon, however, harvest tubers within days of killing potato haulms or harvest tubers without killing potato haulms. The susceptibility of potato tubers harvested from green haulms to late blight is unknown. From 1996 to 1998, Russet Burbank and Ranger Russet seed tuber pieces were planted on three different dates and then harvested simultaneously to obtain daughter tubers at different levels of maturity as determined by physiological degree day (P-day) accumulation. Tubers from two trials in 1996 were harvested within 1 to 4 days of haulm killing, tubers from a single trial in 1997 were harvested 16 days after haulm killing, and tubers from two trials in 1998 were harvested 1 and 21 days after haulm killing. Tubers from each plot were divided into two samples; one sample was inoculated the day after harvest and the other sample was inoculated 6 months after harvest on the buds and periderm tissue with a US-8 isolate of Phytophthora infestans. Severity of tuber blight on tuber surfaces and internal tuber tissue was highly correlated. When tubers were harvested within 1 to 4 days after haulm kill, the youngest tubers had the highest percentage of skinning and the lowest percentage of tuber blight. These tests, however, were not designed to test the hypothesis that increased tuber skinning resulted in increased tuber rot. Severity of tuber blight was greater for Ranger Russet tubers than for Russet Burbank tubers. The correlation between the severity of tuber blight at harvest and after 6 months in storage was significant. In some cases, differences in susceptibility to tuber blight due to planting date were observed after 6 months in storage. When tubers were harvested within 1 to 4 days after vine killing, tubers from plants that had been growing longer were more susceptible to late blight tuber rot than tubers from plants that had been growing for a shorter period of time.