Potato Response to Drought Stress: Physiological and Growth Basis

Drought poses a major challenge to the production of potatoes worldwide. Climate change is predicted to further aggravate this challenge by intensifying potato crop exposure to increased drought severity and frequency. There is an ongoing effort to adapt our production systems of potatoes through the development of drought-tolerant cultivars that are appropriately engineered for the changing environment. The breeding of drought-tolerant cultivars can be approached through the identification of drought-related physiological and biochemical traits and their deployment in new potato cultivars. Thus, the main objective of this study was to develop a method to identify and characterize the drought-tolerant potato genotypes and the related key traits. To achieve this objective, first we studied 56 potato genotypes including 54 cultivars and 2 advanced breeding lines to assess drought tolerance in terms of tuber yield in the greenhouse experiment. Drought differentially reduced tuber yield in all genotypes. Based on their capacity to maintain percent tuber yield under drought relative to their well-watered controls, potato genotypes differed in their ability to tolerate drought. We then selected six genotypes, Bannock Russet, Nipigon, Onaway, Denali, Fundy, and Russet Norkotah, with distinct yield responses to drought to further examine the physiological and biochemical traits governing drought tolerance. The drought-induced reduction in tuber yield was only 15–20% for Bannock Russet and Nipigon, 44–47% for Onaway and Denali, and 83–91% for Fundy and Russet Norkotah. The tolerant genotypes, Bannock Russet and Nipigon, exhibited about a 2–3-fold increase in instantaneous water-use efficiency (WUE) under drought as compared with their well-watered controls. This stimulation was about 1.8–2-fold for moderately tolerant genotypes, Onaway and Denali, and only 1.5-fold for sensitive genotypes, Fundy, and Russet Norkotah. The differential stimulation of instantaneous WUE of tolerant and moderately tolerant genotypes vs. sensitive genotypes was accounted for by the differential suppression of the rates of photosynthesis, stomatal conductance, and transpiration rates across genotypes. Potato genotypes varied in their response to leaf protein content under drought. We suggest that the rates of photosynthesis, instantaneous WUE, and leaf protein content can be used as the selection criteria for the drought-tolerant potato genotypes.

The Effect of Field Heat Reduction Methods on Fresh and Processing Qualities of Red and Russet Potato Cultivars

The effect of three field heat reduction methods, including temperature lowering stepwise (TLS), temperature lowering gradually (TLG), and temperature lowering immediately (TLI), after harvesting on the quality of Russet Norkotah 3 and red skin numbered line CO 07102-1R potatoes were investigated. The tubers were analyzed at harvest (0 time), when they reached 3 °C, and after 6 months of storage at 3 °C for physiological weight loss, firmness, wound healing, total phenolics content, reducing sugars, and color of french fries. The results indicated that weight and firmness losses were lower under the TLS reduction method after 6 months of storage than TLG and TLI methods. The weight loss in TLS is 12%, TLG 14% and TLI 17% in CO 07102-1R whereas Russet Norkotah TLS is 4%, TLG 6%, and TLI 8% respectively. Wound healing was more effective using the TLS reduction method, especially in Russet Norkotah 3. French fry color was lighter at harvest (USDA grade 0), while there were no differences in the color of French fries prepared from tubers stored under the TLS and TLG methods (both had USDA grade 2). French fries were darker for tubers from the TLI method (USDA grade 4). The total phenolic content and reducing sugars were significantly increased in the TLI field heat reduction method. Keywords: Potato, Storage management, Wound healing, Weight loss, French fry

Prediction of the Leaf Primordia of Potato Tubers Using Sensor Fusion and Wavelength Selection

The sprouting of potato tubers during storage is a significant problem that suppresses obtaining high quality seeds or fried products. In this study, the potential of fusing data obtained from visible (VIS)/near-infrared (NIR) spectroscopic and hyperspectral imaging systems was investigated, to improve the prediction of primordial leaf count as a significant sign for tubers sprouting. Electronic and lab measurements were conducted on whole tubers of Frito Lay 1879 (FL1879) and Russet Norkotah (R.Norkotah) potato cultivars. The interval partial least squares (IPLS) technique was adopted to extract the most effective wavelengths for both systems. Linear regression was utilized using partial least squares regression (PLSR), and the best calibration model was chosen using four-fold cross-validation. Then the prediction models were obtained using separate test data sets. Prediction results were enhanced compared with those obtained from individual systems’ models. The values of the correlation coefficient (the ratio between performance to deviation, or r(RPD)) were 0.95(3.01) and 0.9s6(3.55) for FL1879 and R.Norkotah, respectively, which represented a feasible improvement by 6.7%(35.6%) and 24.7%(136.7%) for FL1879 and R.Norkotah, respectively. The proposed study shows the possibility of building a rapid, noninvasive, and accurate system or device that requires minimal or no sample preparation to track the sprouting activity of stored potato tubers.

Postharvest Development of ‘Candidatus Liberibacter solanacearum’ in Late-Season Infected Potato Tubers under Commercial Storage Conditions

Zebra chip (ZC) disease of potato is associated with the putative pathogen ‘Candidatus Liberibacter solanacearum’, which is transmitted by the potato psyllid Bactericera cockerelli (Hem., Triozidae). The present study was initiated to investigate ‘Ca. L. solanacearum’ development during and following typical commercial storage practices. Using bacteriliferous psyllids, Russet Norkotah potato tubers were infested in field cages 14, 10, and 4 days before harvest. Changes in ‘Ca. L. solanacearum’ detection rate, ‘Ca. L. solanacearum’ titer, and concentrations of phenolic compounds were documented throughout storage. ‘Ca. L. solanacearum’ titer continued to increase during storage. Although significant increases in the frequency of ‘Ca. L. solanacearum’ detection were observed in all infestation treatments, the impact of ‘Ca. L. solanacearum’ infection on tuber quality remained comparatively low in plants infected 4 days before harvest, because the majority of the tubers remained asymptomatic. Minimizing storage and retail chain movement durations would help to limit ‘Ca. L. solanacearum’ impact on tuber quality in tubers infected 14 and 10 days before harvest. This study also demonstrated that ‘Ca. L. solanacearum’ can relocate from a newly infected leaf to a tuber in as little as 4 days. Psyllid management is recommended until at least 4 days before green harvest, when psyllid pressure is high in fields in which tubers are destined for commercial storage.

Responses of Aphid Vectors of Potato leaf roll virus to Potato Varieties

Potato leaf roll virus (PLRV) can reduce tuber yield and quality in potato. Green peach aphid (Myzus persicae [Sulzer]) and potato aphid (Macrosiphum euphorbiae [Thomas]) are the two most important potato-colonizing PLRV vectors in the Pacific Northwest. We compared My. persicae and Ma. euphorbiae densities and PLRV incidences among potato varieties in the field to clarify the relationships between aphid abundance and PLRV incidence in plants. Aphids were sampled weekly over three years in the potato varieties Russet Burbank, Ranger Russet, and Russet Norkotah in a replicated field trial. In all years, My. persicae was more abundant than Ma. euphorbiae, representing at least 97% of samples. My. persicae densities did not differ among potato varieties across years; very low numbers of Ma. euphorbiae precluded such statistical comparisons for this species. PLRV infection did not differ significantly among potato varieties, although the percent of PLRV-infected plants differed among years when all varieties were combined (46% in 2013, 29% in 2011, 13% in 2012). For Ranger Russet and Russet Norkotah, PLRV incidence was positively correlated with aphid abundance as well as proportion of PLRV-positive aphids. In Russet Burbank, only aphid abundance was positively correlated with PLRV infection. Our results suggest that the three most commonly grown potato varieties in our region do not differ in their susceptibility to PLRV infection, and that aphid density was a consistent indicator of the risk of infection by this virus across varieties. Both of these findings can be used to hone PLRV monitoring and modeling efforts.

Evaluation of Solanum sisymbriifolium as a Potential Inoculum Source of Verticillium dahliae and Colletotrichum coccodes

Solanum sisymbriifolium, the litchi tomato, is a perennial herbaceous plant from South America that is used as a trap crop to reduce soilborne populations of the pale cyst nematode Globodera pallida, an important potato pathogen. Possible interactions of soilborne potato pathogens Verticillium dahliae and Colletotrichum coccodes with litchi tomato are unknown, yet important for potato production if litchi tomato is to be planted as a trap crop. The goal of this research was to quantitatively assess if litchi tomato is a potential inoculum source for C. coccodes and V. dahliae by comparing colony forming units (CFU) observed in litchi tomato to susceptible and resistant potato cultivars. The potato cvs. Alturas (P = 0.0003), Ranger Russet (P = 0.0193), and Russet Norkotah (P = 0.0022) produced more CFUs of the potato pathotype of V. dahliae than litchi tomato the first of two years of greenhouse trials. Significantly more CFUs of the potato pathotype of V. dahliae were quantified from stems and roots of only cv. Russet Norkotah compared with litchi tomato (P = 0.0001) in the second year. The CFUs for C. coccodes varied between litchi tomato and the potato cvs., perhaps due to varying levels of resistance since litchi tomato is from a selected intermated seed source. Based on these data, the effect of litchi tomato in rotation with potato is likely to have limited effect on the proliferation of V. dahliae or C. coccodes populations in the soil when compared with a susceptible potato cultivar.

Variations in Zebra Chip Disease Expression and Tuber Biochemistry in Response to Vector Density

Zebra chip (ZC) disease, caused by ‘Candidatus Liberibacter solanacearum’, which is transmitted by the potato psyllid, has negatively affected potato production in the United States for over a decade. The present study was conducted to evaluate the affect of the number of bacteriliferous psyllids on ‘Ca. L. solanacearum’ titer, levels of amino acids, carbohydrates, phenolics, and, subsequently, symptom severity in potato tubers. ‘Red La Soda’ and ‘Russet Norkotah’ potato were planted in the field and later inoculated with ‘Ca. L. solanacearum’ using 5, 10, and 30 bacteriliferous potato psyllids. In both cultivars, the increase in the number of psyllids resulted in elevated ‘Ca. L. solanacearum’ titer and symptom severity. In the cases of amino acids and reducing sugars, responses to vector density appeared to be cultivar specific. Overall, phenolic compounds showed a consistent increase following infection, a response that, in most cases, was positively correlated with the number of infective psyllids. Results quantified the impact of the number of infective psyllids on ‘Ca. L. solanacearum’ titer and biochemical content of infected tubers previously shown to be correlated with the degree of symptom expression. Managing vector numbers is currently the only effective approach for minimizing losses to ZC in grower’s fields. However, our findings on physiological responses to vector density suggest that, in combination with chemical control, development of more tolerant or resistant potato genotypes, with emphasis on interrupting pathways that are associated with increased phenolic activity levels, may lead to more sustainable management of ZC in the future.