Planta (2014) 239:1243–1263 DOI 10.1007/s00425-014-2048-8
Original Article
In‑season heat stress compromises postharvest quality and low‑temperature sweetening resistance in potato (Solanum tuberosum L.) Daniel H. Zommick · Lisa O. Knowles · Mark J. Pavek · N. Richard Knowles
Received: 19 December 2013 / Accepted: 18 February 2014 / Published online: 11 March 2014 © Springer-Verlag Berlin Heidelberg 2014
Abstract Key message High soil temperature during bulking and maturation of potatoes alters postharvest carbohy‑ drate metabolism to attenuate genotypic resistance to cold-induced sweetening and accelerate loss of process quality. Abstract The effects of soil temperature during tuber development on physiological processes affecting retention of postharvest quality in low-temperature sweetening (LTS) resistant and susceptible potato cultivars were investigated. ‘Premier Russet’ (LTS resistant), AO02183-2 (LTS resistant) and ‘Ranger Russet’ (LTS susceptible) tubers were grown at 16 (ambient), 23 and 29 °C during bulking (111–164 DAP) and maturation (151–180 DAP). Bulking at 29 °C virtually eliminated yield despite vigorous vine growth. Tuber specific gravity decreased as soil temperature increased during bulking, but was not affected by temperature during maturation. Bulking at 23 °C and maturation at 29 °C induced higher reducing sugar levels in the proximal (basal) ends of tubers, resulting in non-uniform fry color at harvest, and abolished the LTS-resistant phenotype of ‘Premier Russet’ tubers. AO02183-2 tubers were more tolerant of heat for retention of LTS resistance. Higher bulking and maturation temperatures also accelerated LTS and loss of process quality of ‘Ranger Russet’ tubers, consistent with increased invertase and lower invertase inhibitor activities. During LTS, tuber respiration fell rapidly to a minimum as temperature decreased from 9 to 4 °C, followed by an increase to a maximum as tubers
D. H. Zommick · L. O. Knowles · M. J. Pavek · N. R. Knowles (*) Postharvest Physiology and Biochemistry Laboratory, Department of Horticulture, Washington State University, P.O. Box 646414, Pullman, WA 99164‑6414, USA e-mail: [email protected]
acclimated to 4 °C; respiration then declined over the remaining storage period. The magnitude of this cold-induced acclimation response correlated directly with the extent of buildup in sugars over the 24-day LTS period and thus reflected the effects of in-season heat stress on propensity of tubers to sweeten and lose process quality at 4 °C. While morphologically indistinguishable from control tubers, tubers grown at elevated temperature had different basal metabolic (respiration) rates at harvest and during cold acclimation, reduced dormancy during storage, greater increases in sucrose and reducing sugars and associated loss of process quality during LTS, and reduced ability to improve process quality through reconditioning. Breeding for retention of postharvest quality and LTS resistance should consider strategies for incorporating more robust tolerance to in-season heat stress. Keywords Solanum tuberosum · Heat stress · Low-temperature sweetening · Cold-induced sweetening · Reducing sugars · Reconditioning · Respiration · Respiratory acclimation response · Invertase Abbreviations DAH Days after harvest DAP Days after planting DNS Dinitrosalicylic acid Fru Fructose Glc Glucose INV Acid invertase LTS Low-temperature sweetening NWPVD Northwest Potato Variety Development PM Physiological maturity PNW Pacific Northwest RAR Respiratory acclimation response REC Reconditioning period RS Reducing sugars
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SG Specific gravity SP Starch phosphorylase (L and H) SPS Sucrose-6-phosphate synthase TEA Triethanolamine WH Wound-healing
Introduction The Pacific Northwest (PNW; Washington, Idaho and Oregon) produced 63 % of the nation’s fall potato crop in 2011, with 7.4 million metric tons utilized in processing value-added products, such as frozen French fries (NASS 2012). Strict processing standards necessitate potatoes with low reducing sugars (RS; glc and fru) and moderately high specific gravity (SG; starch and dry matter content). High RS content darkens finished fry color (Shallenberger et al. 1959) and enhances the formation of acrylamide (Amrein et al. 2003), resulting in unacceptable processed product. Temperatures during crop development and storage can be critical in dictating tuber RS content and thus process quality. For example, high temperatures can reduce SG and increase free sugars at harvest (Krauss and Marshner 1984; Geigenberger et al. 1998; Yamaguchi et al. 1964; Epstein et al. 1966). Following harvest, low-temperature storage (e.g., 4–7 °C) can prolong dormancy, reduce disease pressure and extend marketability. However, storage at less than 9 °C induces starch breakdown and low-temperature sweetening (LTS), a reversible accumulation of RS (Sowokinos 2001). A major goal of potato breeding programs is to develop varieties with LTS resistance. Though considerable research has been conducted to identify key traits associated with LTS resistance (reviewed in Sowokinos 2001; Blenkinsop et al. 2004), and LTS-resistant cultivars have recently been developed, the influence of in-season heat stress on retention of LTS-resistant phenotype and postharvest processing quality is unknown. Environmental and cultural conditions during growth interact to affect postharvest quality and storability of potatoes and isolating the effects of in-season abiotic stressors (e.g., heat) on subsequent retention of postharvest quality can be challenging. Indirect evidence from the PNW Potato Variety Development (NWPVD) program, along with results from recent management studies on newly released cultivars, have suggested that growing location and harvest timing affect heat-unit accumulation by tubers, which in turn can compromise storability. Decades of research from the NWPVD program have shown that genotypes grown in warmer areas of the southern Columbia Basin (ca. 45.6–46.7°N Lat, −118.5° to −120.2°W Long) consistently exhibit reduced process quality at harvest, reduced storability and greater incidence of physiological disorders (e.g., sugar ends, mottling and senescent sweetening) than the same genotypes grown in cooler areas of the Columbia Basin and southern Idaho (Pavek and
13
Planta (2014) 239:1243–1263
Knowles 2004–2012). Furthermore, management studies conducted on newly released NWPVD cultivars have shown that over-maturation under dead vines can undermine harvest quality and storability (Knowles et al. 2008, 2013). Tubers appear to be most sensitive to high temperature-induced accelerated aging during maturation under senesced vines and into early storage (Driskill et al. 2007; Blauer et al. 2013a). Previous studies to assess the impact of heat stress on crop growth and development and tuber quality have relied on modifying soil temperatures in controlled environments with heated water (Epstein 1966; Reynolds and Ewing 1989; Ingram and McCloud 1984; Yamaguchi et al. 1964), air temperature in growth chambers or greenhouses (Lafta and Lorenzen 1995; Timlin et al. 2006), or involved correlative studies comparing crop performance at different altitudes (Manrique and Bartholomew 1991) or between growing regions (Sarquis et al. 1996; Temmerman et al. 2002). Such correlative studies, while useful, are confounded by complex interactions among climatic, edaphic and agronomic variables. Moreover, tubers grown in controlled environments are often developmentally and physiologically different than fully mature tubers grown under field conditions and this affects their postharvest behavior and storability. Here, we present results on the impact of elevated soil temperatures at two phases of crop development (bulking and maturation) on retention of postharvest quality (tuber specific gravity, RS content, respiration, dormancy length, and LTS resistance) for LTS-resistant and susceptible cultivars. Three genotypes were selected based on extremes in LTS resistance; ‘Premier Russet’ and AO02183-2 are resistant to LTS while ‘Ranger Russet’ is susceptible. The numbered clone AO02183-2 has exhibited excellent retention of process quality regardless of growing location across the PNW (Pavek and Knowles 2004–2012) and was thus included to evaluate its potential tolerance of heat stress. Embedded soil-warming cables were used to increase soil temperatures by ca. 7 and 13 °C above ambient during tuber bulking and maturation in 2011 and 2012. Physiological differences among morphologically indistinguishable tubers from the high heat and control plots were characterized. High temperatures during bulking and maturation compromised retention of postharvest quality, resulting in loss of LTS resistance in ‘Premier Russet’ and to a lesser extent AO02183-2, and exacerbated LTS in ‘Ranger Russet’.
Materials and methods Temperature treatments, plant material, field plot design and maintenance Postharvest studies were conducted to assess the effects of soil temperature during tuber bulking and maturation
Planta (2014) 239:1243–1263
on physiological processes affecting retention of process quality during storage. Tubers were grown in a Shano silt loam soil (Lenfesty 1967) at the Washington State University Irrigated Research and Extension Unit at Othello, WA (46.8°N Lat, −119.0°W Long) in 2011 and 2012. Treatments in 2011 consisted of two soil temperatures (23 and 29 °C; +7 °C and +13 °C above ambient, respectively) imposed during bulking (111–164 DAP; Aug. 4 to Sept. 26) and maturation (151–180 DAP; Sept. 13 to Oct. 12) plus the non-heated ambient (16 °C) control. Treatments in 2012 consisted of one soil temperature during bulking (21 °C; +6 °C above ambient; 114–155 DAP; Aug. 8 to Sept. 18) and two soil temperatures during maturation (21 °C and 28 °C +6 °C and +13 °C above ambient; 155–179 DAP; Sept. 18 to Oct. 12). Soil temperatures (and thus tuber temperatures) were manipulated with heating cables installed in-furrow at planting. Certified (G3) seed potatoes of cvs. Premier Russet and Ranger Russet were planted in 2011 with the inclusion of AO02183-2, a numbered clone from the NWPVD program, in 2012. Seed potatoes were acquired in October and stored at 4 °C (95 % RH) until planting on 15 April 2011 and 16 April 2012. Seed tubers were hand cut into 50- to 64-g seedpieces and suberized at 10 °C (95 % RH) for 2–4 days prior to planting. In 2011, five replicated plots per cultivar were planted with 24 seedpieces spaced 25 cm apart in each plot. In 2012, with the addition of AO02183-2, seed spacing was reduced to 20 cm and five replicated plots were planted for ‘Premier Russet’ and AO02183-2 while three replicated plots were planted for ‘Ranger Russet.’ Guard seedpieces (cv. All Blue) were planted at the beginning and ends of each plot to facilitate delineation of plots during mechanical harvest. Heated rows were separated by non-heated guard rows planted with the respective cultivar/ clone. Redi-Heat heavy duty heating cables (Wrap-On Company Inc., Bedford Park, IL, USA) were installed during planting. Rows were opened for placement of two 61-m cables positioned 20–25 cm apart at the bottom of each furrow at seed depth (20 cm after hilling). Seedpieces were then hand planted between the two cables and the furrow was filled to ground level by hand raking. Two additional cables were installed on top of the furrow parallel to each lower cable, and the upper cables were covered with soil during hilling (Fig. 1a). Non-heated control and guard rows were planted using a two-row assist-feed planter. Solid-set sprinkler irrigation maintained soil moisture at a minimum of 65 % of field capacity throughout the season. Pre-plant and in-season fertilizer applications were based on soil tests and petiole analyses, respectively, following standard practices for long-season russet potatoes in the Columbia Basin. Herbicides, insecticides and fungicides were applied as needed.
1245
Soil temperatures were controlled by adjustable thermostats (Wrap-On Company Inc., Bedford Park, IL, USA) connected to the cables and the temperature at a depth of 13 cm was recorded hourly from 48 to 180 DAP with Watchdog temperature probes (Spectrum Technologies Inc., Aurora, IL, USA) in each row. Soil temperature profiles (heat maps) of each treatment row were generated using a 30.5-cm-long temperature probe (Oakton Instruments, Vernon Hills, IL, USA) with measurements taken in a grid pattern every 8.9 cm across the 62-cm-wide hill and every 5 cm deep from the top of the hill to a final depth of 23 cm (n = 40). Vines were chemically desiccated (Diquat) at 157 and 155 days after planting (DAP) in 2011 and 2012, respectively. Tubers were harvested with a single-row mechanical harvester 181 DAP in 2011 and 180 DAP in 2012. Tubers were washed, weighed, counted, and sorted into the following categories: 397 g, and culls. Total yield included the combined weights of all categories and US number one yield was equal to the sum of all categories except cull and undersize (
Original Article
In‑season heat stress compromises postharvest quality and low‑temperature sweetening resistance in potato (Solanum tuberosum L.) Daniel H. Zommick · Lisa O. Knowles · Mark J. Pavek · N. Richard Knowles
Received: 19 December 2013 / Accepted: 18 February 2014 / Published online: 11 March 2014 © Springer-Verlag Berlin Heidelberg 2014
Abstract Key message High soil temperature during bulking and maturation of potatoes alters postharvest carbohy‑ drate metabolism to attenuate genotypic resistance to cold-induced sweetening and accelerate loss of process quality. Abstract The effects of soil temperature during tuber development on physiological processes affecting retention of postharvest quality in low-temperature sweetening (LTS) resistant and susceptible potato cultivars were investigated. ‘Premier Russet’ (LTS resistant), AO02183-2 (LTS resistant) and ‘Ranger Russet’ (LTS susceptible) tubers were grown at 16 (ambient), 23 and 29 °C during bulking (111–164 DAP) and maturation (151–180 DAP). Bulking at 29 °C virtually eliminated yield despite vigorous vine growth. Tuber specific gravity decreased as soil temperature increased during bulking, but was not affected by temperature during maturation. Bulking at 23 °C and maturation at 29 °C induced higher reducing sugar levels in the proximal (basal) ends of tubers, resulting in non-uniform fry color at harvest, and abolished the LTS-resistant phenotype of ‘Premier Russet’ tubers. AO02183-2 tubers were more tolerant of heat for retention of LTS resistance. Higher bulking and maturation temperatures also accelerated LTS and loss of process quality of ‘Ranger Russet’ tubers, consistent with increased invertase and lower invertase inhibitor activities. During LTS, tuber respiration fell rapidly to a minimum as temperature decreased from 9 to 4 °C, followed by an increase to a maximum as tubers
D. H. Zommick · L. O. Knowles · M. J. Pavek · N. R. Knowles (*) Postharvest Physiology and Biochemistry Laboratory, Department of Horticulture, Washington State University, P.O. Box 646414, Pullman, WA 99164‑6414, USA e-mail: [email protected]
acclimated to 4 °C; respiration then declined over the remaining storage period. The magnitude of this cold-induced acclimation response correlated directly with the extent of buildup in sugars over the 24-day LTS period and thus reflected the effects of in-season heat stress on propensity of tubers to sweeten and lose process quality at 4 °C. While morphologically indistinguishable from control tubers, tubers grown at elevated temperature had different basal metabolic (respiration) rates at harvest and during cold acclimation, reduced dormancy during storage, greater increases in sucrose and reducing sugars and associated loss of process quality during LTS, and reduced ability to improve process quality through reconditioning. Breeding for retention of postharvest quality and LTS resistance should consider strategies for incorporating more robust tolerance to in-season heat stress. Keywords Solanum tuberosum · Heat stress · Low-temperature sweetening · Cold-induced sweetening · Reducing sugars · Reconditioning · Respiration · Respiratory acclimation response · Invertase Abbreviations DAH Days after harvest DAP Days after planting DNS Dinitrosalicylic acid Fru Fructose Glc Glucose INV Acid invertase LTS Low-temperature sweetening NWPVD Northwest Potato Variety Development PM Physiological maturity PNW Pacific Northwest RAR Respiratory acclimation response REC Reconditioning period RS Reducing sugars
13
1244
SG Specific gravity SP Starch phosphorylase (L and H) SPS Sucrose-6-phosphate synthase TEA Triethanolamine WH Wound-healing
Introduction The Pacific Northwest (PNW; Washington, Idaho and Oregon) produced 63 % of the nation’s fall potato crop in 2011, with 7.4 million metric tons utilized in processing value-added products, such as frozen French fries (NASS 2012). Strict processing standards necessitate potatoes with low reducing sugars (RS; glc and fru) and moderately high specific gravity (SG; starch and dry matter content). High RS content darkens finished fry color (Shallenberger et al. 1959) and enhances the formation of acrylamide (Amrein et al. 2003), resulting in unacceptable processed product. Temperatures during crop development and storage can be critical in dictating tuber RS content and thus process quality. For example, high temperatures can reduce SG and increase free sugars at harvest (Krauss and Marshner 1984; Geigenberger et al. 1998; Yamaguchi et al. 1964; Epstein et al. 1966). Following harvest, low-temperature storage (e.g., 4–7 °C) can prolong dormancy, reduce disease pressure and extend marketability. However, storage at less than 9 °C induces starch breakdown and low-temperature sweetening (LTS), a reversible accumulation of RS (Sowokinos 2001). A major goal of potato breeding programs is to develop varieties with LTS resistance. Though considerable research has been conducted to identify key traits associated with LTS resistance (reviewed in Sowokinos 2001; Blenkinsop et al. 2004), and LTS-resistant cultivars have recently been developed, the influence of in-season heat stress on retention of LTS-resistant phenotype and postharvest processing quality is unknown. Environmental and cultural conditions during growth interact to affect postharvest quality and storability of potatoes and isolating the effects of in-season abiotic stressors (e.g., heat) on subsequent retention of postharvest quality can be challenging. Indirect evidence from the PNW Potato Variety Development (NWPVD) program, along with results from recent management studies on newly released cultivars, have suggested that growing location and harvest timing affect heat-unit accumulation by tubers, which in turn can compromise storability. Decades of research from the NWPVD program have shown that genotypes grown in warmer areas of the southern Columbia Basin (ca. 45.6–46.7°N Lat, −118.5° to −120.2°W Long) consistently exhibit reduced process quality at harvest, reduced storability and greater incidence of physiological disorders (e.g., sugar ends, mottling and senescent sweetening) than the same genotypes grown in cooler areas of the Columbia Basin and southern Idaho (Pavek and
13
Planta (2014) 239:1243–1263
Knowles 2004–2012). Furthermore, management studies conducted on newly released NWPVD cultivars have shown that over-maturation under dead vines can undermine harvest quality and storability (Knowles et al. 2008, 2013). Tubers appear to be most sensitive to high temperature-induced accelerated aging during maturation under senesced vines and into early storage (Driskill et al. 2007; Blauer et al. 2013a). Previous studies to assess the impact of heat stress on crop growth and development and tuber quality have relied on modifying soil temperatures in controlled environments with heated water (Epstein 1966; Reynolds and Ewing 1989; Ingram and McCloud 1984; Yamaguchi et al. 1964), air temperature in growth chambers or greenhouses (Lafta and Lorenzen 1995; Timlin et al. 2006), or involved correlative studies comparing crop performance at different altitudes (Manrique and Bartholomew 1991) or between growing regions (Sarquis et al. 1996; Temmerman et al. 2002). Such correlative studies, while useful, are confounded by complex interactions among climatic, edaphic and agronomic variables. Moreover, tubers grown in controlled environments are often developmentally and physiologically different than fully mature tubers grown under field conditions and this affects their postharvest behavior and storability. Here, we present results on the impact of elevated soil temperatures at two phases of crop development (bulking and maturation) on retention of postharvest quality (tuber specific gravity, RS content, respiration, dormancy length, and LTS resistance) for LTS-resistant and susceptible cultivars. Three genotypes were selected based on extremes in LTS resistance; ‘Premier Russet’ and AO02183-2 are resistant to LTS while ‘Ranger Russet’ is susceptible. The numbered clone AO02183-2 has exhibited excellent retention of process quality regardless of growing location across the PNW (Pavek and Knowles 2004–2012) and was thus included to evaluate its potential tolerance of heat stress. Embedded soil-warming cables were used to increase soil temperatures by ca. 7 and 13 °C above ambient during tuber bulking and maturation in 2011 and 2012. Physiological differences among morphologically indistinguishable tubers from the high heat and control plots were characterized. High temperatures during bulking and maturation compromised retention of postharvest quality, resulting in loss of LTS resistance in ‘Premier Russet’ and to a lesser extent AO02183-2, and exacerbated LTS in ‘Ranger Russet’.
Materials and methods Temperature treatments, plant material, field plot design and maintenance Postharvest studies were conducted to assess the effects of soil temperature during tuber bulking and maturation
Planta (2014) 239:1243–1263
on physiological processes affecting retention of process quality during storage. Tubers were grown in a Shano silt loam soil (Lenfesty 1967) at the Washington State University Irrigated Research and Extension Unit at Othello, WA (46.8°N Lat, −119.0°W Long) in 2011 and 2012. Treatments in 2011 consisted of two soil temperatures (23 and 29 °C; +7 °C and +13 °C above ambient, respectively) imposed during bulking (111–164 DAP; Aug. 4 to Sept. 26) and maturation (151–180 DAP; Sept. 13 to Oct. 12) plus the non-heated ambient (16 °C) control. Treatments in 2012 consisted of one soil temperature during bulking (21 °C; +6 °C above ambient; 114–155 DAP; Aug. 8 to Sept. 18) and two soil temperatures during maturation (21 °C and 28 °C +6 °C and +13 °C above ambient; 155–179 DAP; Sept. 18 to Oct. 12). Soil temperatures (and thus tuber temperatures) were manipulated with heating cables installed in-furrow at planting. Certified (G3) seed potatoes of cvs. Premier Russet and Ranger Russet were planted in 2011 with the inclusion of AO02183-2, a numbered clone from the NWPVD program, in 2012. Seed potatoes were acquired in October and stored at 4 °C (95 % RH) until planting on 15 April 2011 and 16 April 2012. Seed tubers were hand cut into 50- to 64-g seedpieces and suberized at 10 °C (95 % RH) for 2–4 days prior to planting. In 2011, five replicated plots per cultivar were planted with 24 seedpieces spaced 25 cm apart in each plot. In 2012, with the addition of AO02183-2, seed spacing was reduced to 20 cm and five replicated plots were planted for ‘Premier Russet’ and AO02183-2 while three replicated plots were planted for ‘Ranger Russet.’ Guard seedpieces (cv. All Blue) were planted at the beginning and ends of each plot to facilitate delineation of plots during mechanical harvest. Heated rows were separated by non-heated guard rows planted with the respective cultivar/ clone. Redi-Heat heavy duty heating cables (Wrap-On Company Inc., Bedford Park, IL, USA) were installed during planting. Rows were opened for placement of two 61-m cables positioned 20–25 cm apart at the bottom of each furrow at seed depth (20 cm after hilling). Seedpieces were then hand planted between the two cables and the furrow was filled to ground level by hand raking. Two additional cables were installed on top of the furrow parallel to each lower cable, and the upper cables were covered with soil during hilling (Fig. 1a). Non-heated control and guard rows were planted using a two-row assist-feed planter. Solid-set sprinkler irrigation maintained soil moisture at a minimum of 65 % of field capacity throughout the season. Pre-plant and in-season fertilizer applications were based on soil tests and petiole analyses, respectively, following standard practices for long-season russet potatoes in the Columbia Basin. Herbicides, insecticides and fungicides were applied as needed.
1245
Soil temperatures were controlled by adjustable thermostats (Wrap-On Company Inc., Bedford Park, IL, USA) connected to the cables and the temperature at a depth of 13 cm was recorded hourly from 48 to 180 DAP with Watchdog temperature probes (Spectrum Technologies Inc., Aurora, IL, USA) in each row. Soil temperature profiles (heat maps) of each treatment row were generated using a 30.5-cm-long temperature probe (Oakton Instruments, Vernon Hills, IL, USA) with measurements taken in a grid pattern every 8.9 cm across the 62-cm-wide hill and every 5 cm deep from the top of the hill to a final depth of 23 cm (n = 40). Vines were chemically desiccated (Diquat) at 157 and 155 days after planting (DAP) in 2011 and 2012, respectively. Tubers were harvested with a single-row mechanical harvester 181 DAP in 2011 and 180 DAP in 2012. Tubers were washed, weighed, counted, and sorted into the following categories: 397 g, and culls. Total yield included the combined weights of all categories and US number one yield was equal to the sum of all categories except cull and undersize (
