Department of Plant and Animal Sciences, Department of Engineering, and Department of Business and SocialSciences, Nova Scotia Agricultural College, Truro, Nova Scotia, Canada

The Effect of Seed-Tuber Physiological Age and Cultivar on Early Potato Production

S. K. Asiedu, T. Astatkie and E. K. Yiridoe

Authors’ addresses: Dr S. K. Asiedu, Department of Plant and Animal Sciences, Dr T. Astatkie, Department of Engineering, andDr E. K. Yiridoe (corresponding author; e-mail: eyiridoe@nsac.ns.ca), Department of Business and Social Sciences, Nova ScotiaAgricultural College, PO Box 550, Truro, Nova Scotia B2N 5E3, Canada

With 7 tables

Received November 22, 2002; accepted January 8, 2003

Abstract

Enhancing physiological aging of seed-potatoes has thepotential to substantially affect production, especially forshort-season growing areas. This study analysed the effectof seed-tuber age and cultivar, jointly, to identify thecombination for optimum early crop production, based onfield experiments conducted at two locations in Nova Scotia,Canada. The potato cultivars Superior, AC-Novachip,Niska, and Yukon Gold were aged by exposing seedsstored at 4 �C to warming periods of 0, 242 (3 weeks), and484 (6 weeks) day-degrees, prior to planting. Cultivar andage levels were completely randomized within each locationand replicated four times. Harvest periods at 65, 80 and95 days after planting (DAP) were analysed as an unbal-anced split-plot factorial, with year as a random blockingfactor, location as a whole plot treatment, and cultivar andage crossed as subplot treatments. Total yield and market-able yield from Yukon Gold improved with physiologicalage when harvested early at 65 and 80 DAP, while thatfrom AC-Novachip improved when aged only 3 weeks.Niska was not affected by age. Overall, AC-Novachip wasconsistently better than the remaining cultivars, regardlessof age. The best treatment combination that maximizedmarketable yield was Yukon Gold aged 6 weeks planted ata commercial farm and harvested 95 DAP. For earlyharvest (65 DAP), however, AC-Novachip aged 3 weeksand Yukon Gold aged 6 weeks generated the highest yields.Niska and Superior generated lower yield and higher culls.

Key words: early marketable yield — physiologicalage — repeated measures analysis — seed-tuber — Solanum tuberosum L.

Introduction

The physiological condition of a seed-tuber thatrelates to its productivity defines the physiologicalage of the potato (Solanum tuberosum L.). Tem-perature exposure prior to planting is a key factorthat affects physiological age. Advancing the phy-

siological age of seed-tubers stimulates the growthhabit and performance of potatoes and thereforeprovides an opportunity for enhancing early potatoproduction and marketing, particularly for short-season regions. Besides generating earlier yields,physiologically older seed-potatoes can also gener-ate higher output (Perennec and Madec 1980,O’Brien et al. 1983, McKeown 1994). Increasingphysiological age modifies growth responsethrough a gradual loss of apical dominance (Iritaniet al. 1983) and, in turn, can promote vigoroussprouting from meristems (Knowles and Botar1991). Knowles and Botar (1991) reported that age-induced changes in sprouting can also be used toreasonably predict both yield level and quality.Early yields can also help reduce exposure of thepotato crop to adverse weather, pests and otherhazards that may limit yield and ⁄or lower thequality of tubers (Horton 1987, Reust et al. 2001).In addition, harvesting potatoes early can make theland available for other crops in a rotation.

In Atlantic Canada (and other potato-producingregions of North America), farmers receive asubstantial price premium for early-season pota-toes, compared to prices during the main cropseason (Horton 1987, Eastern Canada Soil &Water Conservation Centre 1993). A sharp dropin early-season potato price can substantially erodethe potential benefits of a bumper harvest andhence makes marketing a critical component ofthe production process. Thus, for short-seasongrowing areas, generating early yields has thepotential to help sustain profitability of farmbusinesses. Apart from price premium, early cropharvests can translate into substantial savings invariable cost through a reduction in farm labour

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and management, and other input (e.g. pesticideand fertilization) costs. Higher potato yields canalso translate into higher gross revenue and,ultimately, higher farm profits.

Although there is a growing literature on thephysiological age of seed-tubers, the application forpotato management is currently imprecise. Ingeneral, advancing seed-potato age affects cropyield, but the actual effect depends not only on thecultivar (Van der Zaag and Van Loon 1987), butalso on the field conditions (Knowles and Botar1991, Caldiz et al. 1998), cropping systems(Karalus and Rauber 1997), and managerial skills.Although the Atlantic region is a dominant potato-producing region in Canada, it has a relativelyshort growing season. Productivity gains andproduction cost savings can therefore help sustaina competitive market share for the region. Theearly maturation of a seed crop as a consequence ofphysiological age manipulation is useful in short-season growing areas where virus-infested aphidsare absent in the first part of the growing season(Struik and Wiersema 1999). Thus, knowledge ofthe effects of advancing seed-potato age on pro-duction has the potential to greatly benefit thepotato industry in the area. Yet, there is limitedinformation on the effect of physiological aging ofpotato seed-tubers for short-season growing areas(Knowles and Botar 1992), especially for AtlanticCanada.

The purpose of this study was to developproduction technology for advancing earliness inselected potato cultivars for Nova Scotia condi-tions. The specific objectives were: (i) to assess theefficacy of utilizing physiologically aged seed-tubersto enhance earliness in the development and yieldof potatoes grown for early fresh and processingmarkets, and (ii) to evaluate the effect of selectedpotato cultivars of various physiological ages ontotal yield and marketable yield. An analysis ofseed age and cultivar, jointly, will help identify thecombination for optimum early crop production.

Materials and Methods

Description of cropping systems

The experiment was conducted at the Nova Scotia Agri-cultural College (NSAC) research farm in Truro, NS, andat a commercial farm in Canning, NS, during 1995 and1996. Elite IV seed potato cultivars (Superior, AC-Nova-chip, and Niska) that had been stored at 3 to 4 �C wereobtained from �Boyen’s Seed Potato Farm�, Canning, NS,Canada, a reputable seed-potato farm in 1995. AC-Nova-

chip and Niska are chip processing varieties that are mid-season in maturity. Seeds were obtained from the samesource in 1996; however, Niska was replaced with YukonGold because of lack of seed-tubers from the same source.Superior (early to mid-season maturity) and Yukon Gold(mid-season maturity) are major table stock varieties inNorth America. The tubers were aged by exposing them to15 to 20 �C in a controlled chamber where the relativehumidity was maintained between 85 and 90 %. Seed ages0, 242, and 484 day-degrees (DD), which correspond to 0,3, and 6 weeks of aging, were obtained by calculating theday-degrees above 4 �C (Van der Zaag and Van Loon1987), from the time when dormancy was broken. The threephysiological ages studied represent control (not aged),intermediate, and old seed. After the aging process, seed-tubers were held at 4 �C until they were ready for plantingin May of each year. Based on soil test recommendations,17-17-17 fertilizer was band-applied at 780 kg ha)1 for theTruro location, while 14-28-14 fertilizer was banded at1000 kg ha)1 at the Canning site.

Pre-warmed seeds were cut at least 3 days prior toplanting on 16 May at the Truro location, and on 23 Mayat Canning in 1995. In 1996, the treated seeds were plantedon 17 and 20 May at the Truro site and on 24 May atCanning. Seed-tubers aged 3 and 6 weeks had sprouted,while the 0-week-old seeds had no sprouts. The cultivar andage levels were completely randomized within each loca-tion, and replicated four times. A post-planting herbicide,Sencor 500F (metribuzin), was applied at 1.5 l ha)1 at theTruro site, while Lorox (Linuron) was applied at2.2 kg ha)1 at Canning, 1 week after planting. Threeresponse variables, namely total yield, marketable yield(38.1 to 114.3 mm), and culls (<38.1 mm and >114.3 mm)(Government of Canada 1981), were measured at 65, 80and 95 days after planting (DAP), in tonnes ha)1.

Statistical model and analysis

The statistical model for a given harvest day is anunbalanced split-plot factorial (Montgomery 2001) withyear (two levels: 1995 and 1996) as a random blockingfactor, location (two levels: Truro and Canning) as a wholeplot treatment, and cultivar (four levels: Superior, AC-Novachip, Niska and Yukon Gold) and age (three levels: 0,3 and 6 weeks) crossed as subplot treatments. The design isunbalanced because all four cultivars were not used in bothyears. Year is a random effect because the inferencesregarding the other effects are intended to be for these aswell as other years. Location is regarded as a fixed factorbecause any differences between the two sites can beattributed to differences in weather, and farm managementsystems. The Truro location is an educational researchfarm whereas the Canning location is a commercial farm.The remaining two factors, cultivar and age, are consideredfixed factors.

The analysis was performed for each harvest day and forall harvest days jointly as repeated measures. The MixedProcedure in SAS (Littell et al. 1996) was used for bothanalyses. For this study, the Mixed Procedure is more

Enhancing Earliness in Potato Production 177

appropriate than the GLM Procedure because it allows oneto consider year as a random effect both in the univariate(each harvest day) and in the repeated measures settings,and to use appropriate error structure in the repeatedmeasures analysis (Littell et al. 1996, Littell and Henry1998). A preliminary analysis indicated that variability intotal yield as well as marketable yield increased with harvestday. Thus, the analysis was performed using heterogeneousvariance by harvest day. Since the design is unbalanced, aleast square (LS) means comparison was conducted toseparate the means of significant fixed effects. The residualswere examined to check for a constant variance and normaldistribution of the experimental errors, which are requiredfor validity of the statistical tests. The validities of constantvariance (within each harvest day) and normal distributionof the error terms were verified using the methods describedin Montgomery (2001).

Results and Discussion

The first phase of the statistical analysis involveddetermining whether the main and ⁄or interactioneffects of the fixed factors were significant. Furtheranalysis was conducted to compare the LS means ofthe treatment combinations of significant interac-tions. The results for total yield are followed by thosefor marketable yield, and then culled potatoes.

Total yield comparison

For total yield harvested 65 days after planting(DAP), the main effects of cultivar and age weresignificant, implying that at least one of thecultivars and the age groups were different(Table 1). There was also a significant interactioneffect between location and age, and betweencultivar and age. Consequently, a further analysisinvolving separation of LS means of the treatmentcombinations out of the interactions was conduc-ted (Table 2).

Similarly, for total yield harvested 80 DAP, themain effects of cultivar and age were significant. Inaddition, there were significant interaction effectsbetween location and cultivar, and cultivar andage. A separation of the LS means is summarized inTable 2. In contrast to the findings for harvest 65and 80 DAP, there was no significant difference intotal yield for potatoes harvested 95 DAP. Theinteraction effect between cultivar and harvest daywas also significant and the corresponding meansseparations are presented in Table 2.

It was observed that potatoes harvested fromphysiologically older seed-tubers developed lessfoliage and showed earlier senescence. For harveston 65 DAP, separation of the LS means of locationand age (Table 2) indicated that the Canning sitegenerated higher yield than the Truro site forpotatoes from seed-tubers aged 0 and 3 weeks.However, for potatoes aged 6 weeks, the twolocations generated similar yields. For physiologi-cal ages 0 and 3 weeks, separation of the LS meansby cultivar and age indicated that AC-Novachipgenerated the highest total yield, followed by Niska(for age 0 weeks), and Niska, Superior and YukonGold (for seed-tubers aged 3 weeks). For seed-potatoes aged 6 weeks, AC-Novachip and YukonGold generated the highest total yields, while Niskaand Superior ranked the next highest. The resultsalso suggested that, if harvested early on 65 DAP,total yield for Yukon Gold improved with physio-logical age.

Total yield harvested at 80 DAP was analysed byseparating the LS means of location and cultivar(Table 2). As was found for harvest at 65 DAP,AC-Novachip generated the highest total yield atboth experimental sites, of all the cultivars studied.The other cultivars ranked the same as thoseharvested at 65 DAP, except that all four cultivars

Table 1: P-values for testing the fixed effects on total yield response at eachharvest day, and the interaction of these effects with harvest date

Source of variation

Harvest date (DAP)Interaction with

harvest date65 80 95

Harvest date 0.001Location (L) 0.294 0.591 0.844 0.199Cultivar (C) 0.001 0.001 0.768 0.001L · C 0.638 0.032 0.685 0.211Physiological age (A) 0.001 0.038 0.587 0.270L · A 0.018 0.714 0.388 0.902C · A 0.001 0.001 0.749 0.867L · C · A 0.215 0.294 0.981 0.999Residual variance 6.82 10.91 41.86 22.17

178 Asiedu et al.

generated similar total yields when aged 6 weeks.The lowest total yield was obtained from Superiorand Yukon Gold at the Truro site, while at

Canning, Niska and Superior generated the nexthighest actual total yields.

For harvest at 80 DAP, across all physiologicalages, separation of the LS means by cultivar andage resulted in AC-Novachip generating the high-est yield, followed by Niska. For age 0, total yieldsfrom Superior and Yukon Gold were similar, butlower compared to those from AC-Novachip andNiska. However, for seed-potatoes aged 3 weeks,both Superior and Yukon Gold generated similartotal yields to Niska. In contrast, and on average,total yields were similar for all four cultivars forpotatoes aged 6 weeks. All four cultivars gave theirhighest yield when aged 3 weeks, and aging AC-Novachip beyond 3 weeks showed an adverseeffect.

A repeated measures analysis indicated that, forall cultivars, total yield harvested 95 DAP wassignificantly higher than total yield harvested80 DAP, which in turn was significantly higherthan that at 65 DAP. Thus, based on total yieldalone, all the cultivars studied were similar ifharvested at or after 95 DAP. The importance ofthis finding is that choice of cultivar can greatlyaffect earliness in potato production. Total yieldfrom Yukon Gold, for example, tended to improvewith physiological age when harvested 65 and 80DAP, while AC-Novachip was consistently betterthan the other three cultivars, regardless of phy-siological age. Variations in dormancy of potatocultivars contribute to the aging response to plantemergence, and ultimately to yield. Knowles andBotar (1991, 1992) also reported that day-degreesaccumulate in dormant tubers, resulting in earlieremergence and yield.

In summary, all the cultivars studied generatedthe highest total yield when aged 3 weeks. Thiscould be attributable to earlier emergence, whichadvanced tuber initiation and bulking. However,when aged 6 weeks, there was a significant declinein yield for AC-Novachip. This decline cannot beattributed to post-emergence frost damage becausethere was no frost after emergence in June. Also, noother post-emergence damage was noticed in bothyears that could affect AC-Novachip only.

Marketable yield comparison

As was found for total yield, the main effects ofcultivar and age were significant for harvest at 65and 80 DAP, implying that at least one of thecultivars and the physiological ages are different(Table 3). However, there was no significant

Table 2: Least square means of total yield (t ha–1)broken by the significant interactions. (a) Harvest at65 DAP; (b) harvest at 80 DAP; (c) interaction betweenharvest date and cultivar (from repeated measuresanalysis)

(a)

Physiological age (weeks)

0 3 6

LocationTruro 10.35 b1 11.70 b 12.47 aCanning 12.20 a 15.08 a 12.58 aCultivarAC-Novachip B2 15.66 a A 17.73 a C 13.86 aNiska A 13.33 b A 11.45 b A 11.27 bSuperior B 7.92 c A 12.11 b A 11.34 bYukon Gold B 8.19 c A 12.25 b A 13.63 a

(b)

Cultivar

Location

Truro Canning

AC-Novachip 26.50 a 24.16 aNiska 22.82 b 21.32 bSuperior 20.36 c 21.39 bYukon Gold 21.16 bc 22.71 ab

Cultivar

Physiological age (weeks)

0 3 6

AC-Novachip A 26.57 a A 26.90 a B 22.51 aNiska A 22.16 b A 22.36 b A 21.69 aSuperior B 19.43 c A 21.96 b AB 21.23 aYukon Gold B 19.05 c A 23.13 b A 23.64 a

(c)

Cultivar

Harvest date (DAP)

65 80 95

AC-Novachip C 15.75 a B 25.33 a A 28.47 aNiska C 13.36 b B 22.71 b A 26.41 aSuperior C 10.46 c B 20.87 b A 28.24 aYukon Gold C 10.02 c B 21.30 b A 28.56 a

1 LSM within a column followed by the same (small)letter are not significantly different at the 5 % level.2 LSM within a row (cultivar) followed by the same(capital) letter are not significantly different at the 5 %level.

Enhancing Earliness in Potato Production 179

difference among the locations, cultivars and agesfor marketable yield at 95 DAP. For harvest at65 DAP, there were significant interaction effectsbetween location and age, and between cultivar andage. Similarly, for potatoes harvested 80 DAP,there were significant interaction effects betweenlocation and cultivar, and cultivar and age, whilefor harvest at 95 DAP there was no significanteffect. Results of the separation of the LS meansfor the various harvest days are summarized inTable 4.

The LS means comparison for marketable yieldat 65 DAP indicated that the Canning site gener-ated higher yield for seed-potatoes of all physiolo-gical ages, compared to the Truro site (Table 4).Separation of the LS means by cultivar and agealso indicated that AC-Novachip generated signi-ficantly higher marketable yield, followed byYukon Gold, across all three physiological ages.Yukon Gold, a mid-season maturing variety, has ahigh demand in the table potato market. Conse-quently, it will command a price premium ifharvested early in the season. At age 0, Niskaand Yukon Gold generated similar marketableyields, but these were significantly lower than thatof AC-Novachip. Overall, average marketable yieldfor Superior was the lowest.

For seed-potatoes aged 3 weeks, there was nodifference in the marketable yields from Superiorand Niska, and these were lower compared toyields from Yukon Gold and AC-Novachip. Forpotatoes aged 6 weeks, average marketable yieldswere similar for AC-Novachip and Yukon Gold,but higher than the average for Niska and Superior(which generated similar marketable yields). Over-all, AC-Novachip generated the highest marketableyield, followed by Yukon Gold, for potatoesharvested early (65 DAP). In addition, as was

found for total yield, marketable yield for YukonGold improved considerably with physiologicalage. The positive response of physiological agingin enhancing earliness in Yukon Gold, after chit-ting seed-tubers, is consistent with the findings ofMcKeown (1994). Yukon Gold has excellent sto-rability with long dormancy, and therefore bene-fited substantially from physiological aging ofseeds. Given that Yukon Gold is a major mid-season North American yellow-flesh table potatovariety, even slight levels of enhanced earliness cansubstantially improve its profitability in the earlyseason market. Generating early yields implies thatearly top kill can be applied to minimize virusspread by aphids, and hence help to produce high-quality seed crops in short-season growing areas.

For harvest at 80 DAP, separation of the LSmeans of location and cultivar indicated that AC-Novachip generated significantly higher yield thanthe other cultivars at both locations, followed byYukon Gold (Table 4). Average marketable yieldsfor Superior and Niska were similar at bothexperimental sites, although actual yields werelower at Truro than at Canning. In addition,marketable yields for Superior and Niska were thelowest at both sites.

Separation of the LS means by cultivar and ageindicated that, for all physiological ages, AC-Novachip generated significantly higher market-able yield, followed by Yukon Gold. At age 0, therewas no difference in the marketable yields fromNiska, Superior and Yukon Gold, and the yieldsfor this group were significantly lower than that ofAC-Novachip. However, for seed-potatoes aged3 weeks, average marketable yield from YukonGold was the second highest, followed by those ofSuperior and Niska. For potatoes aged 6 weeks,AC-Novachip declined and Yukon Gold improved

Table 3: P-values for testing the fixed effects on marketable yield responseat each harvest day, and the interaction of these effects with harvest date

Source of variation

Harvest date (DAP)Interaction with

harvest date65 80 95

Harvest date 0.001Location (L) 0.001 0.563 0.853 0.151Cultivar (C) 0.001 0.001 0.998 0.001L · C 0.416 0.014 0.613 0.086Physiological age (A) 0.001 0.015 0.829 0.146L · A 0.022 0.652 0.302 0.897C · A 0.001 0.011 0.971 0.944L · C · A 0.218 0.678 0.994 0.998Residual variance 5.57 12.59 45.30 23.95

180 Asiedu et al.

and generated similar marketable yields, whilethose for Niska and Superior were lower.

A repeated measures analysis for marketableyield revealed that, for all cultivars, potatoesharvested at 95 DAP gave significantly higher

yields than those harvested at 80 DAP, which inturn gave significantly higher yields than thoseharvested at 65 DAP, as expected. However, forpotatoes harvested at 65 and 80 DAP, AC-Nova-chip generated the highest marketable yield.Although AC-Novachip consistently generatedhigher marketable yield than the other cultivarsfor all physiological ages, its response to agingdiminished beyond the age of 3 weeks. However,marketable yield for Yukon Gold improved withaging, making it the cultivar that responded best tophysiological aging of seed-tubers. This is a featurethat can be explored for early chip processing withAC-Novachip (aged 3 weeks), and early table usefor Yukon Gold (aged 6 weeks). For potatoesharvested at 95 DAP, AC-Novachip, Yukon Goldand Superior generated similar yields, on average,while Niska gave the lowest yield.

In summary, across harvest periods, AC-Novachip generated the highest marketable yield,while Niska generated the lowest. As with the totalyield results, all the cultivars generated the highestmarketable yield when aged 3 weeks, regardless ofthe DAP. Furthermore, for Superior and YukonGold, aging at 6 weeks did not adversely affectmarketable yield, as the yield was similar to that forseed-tubers aged 3 weeks.

Culled potato comparison

The main effect of cultivar was significant for cullson all harvest days, and the interaction betweencultivar and age was significant for culls frompotatoes harvested 65 and 80 DAP (Table 5).However, the interaction effect between locationand cultivar was significant for 80 DAP only(Table 5). The significant interaction effects promp-ted further analyses to separate the LS means(Table 6). Furthermore, there was a significantthree-way interaction amongst location, cultivarand harvest day, whose means separations arepresented in Table 7.

For culls harvested at 65 DAP, separation of theLS means by cultivar and age indicated that, for allphysiological ages, Niska generated significantlyhigher culls than the other cultivars (Table 6). Atage 0, Niska and AC-Novachip generated similarculls and, in turn, these were significantly higherthan that of Superior. Yukon Gold generated thelowest culls. However, for seed-potatoes aged 3 and6 weeks, culls from Superior and Niska weresimilar and ranked the highest. There was alsono difference in culls from Yukon Gold and

Table 4: Least square means of marketable yield (tha–1) broken by the significant interactions. (a) Harvestat 65 DAP; (b) harvest at 80 DAP; (c) interactionbetween harvest date and cultivar (from repeatedmeasures analysis)

(a)

Physiological age (weeks)

0 3 6

LocationTruro 3.82 b1 6.31 b 6.83 bCanning 7.43 a 10.43 a 8.26 aCultivarAC-Novachip B2 9.30 a A 13.55 a B 9.56 aNiska A 5.96 b A 5.63 c A 5.46 bSuperior B 2.64 c A 5.90 c A 5.16 bYukon Gold B 4.60 b A 8.41 b A 10.01 a

(b)

Cultivar

Location

Truro Canning

AC-Novachip 23.12 a 20.49 aNiska 15.67 c 17.47 bSuperior 14.94 c 16.95 bYukon Gold 19.01 b 20.72 a

Cultivar

Physiological age (weeks)

0 3 6

AC-Novachip A 22.11 a A 24.21 a B 19.10 aNiska A 16.73 b A 16.68 c A 16.30 bSuperior B 14.46 b A 17.03 c AB 16.36 bYukon Gold B 16.99 b A 21.27 b A 21.33 a

(c)

Cultivar

Harvest date (DAP)

65 80 95

AC-Novachip C 10.80 a B 21.80 a A 24.49 abNiska C 6.62 b B 17.56 bc A 22.52 bSuperior C 4.57 b B 15.95 c A 24.36 abYukon Gold C 6.74 b B 18.87 b A 26.00 a

1 LSM within a column followed by the same (small)letter are not significantly different at the 5 % level.2 LSM within a row (cultivar) followed by the same(capital) letter are not significantly different at the 5 %level.

Enhancing Earliness in Potato Production 181

AC-Novachip, and these ranked lower comparedto average culls from Superior and Niska. Overall,Yukon Gold generated the lowest culls, while AC-Novachip generated the second lowest culls forpotatoes aged 3 and 6 weeks and harvested early,at 65 DAP. Although Yukon Gold is a mid-seasonmaturing variety that sets low tubers, the enhancedearly development from physiological ageing ofseed-tubers resulted in rapid bulking and yield.

For culls harvested 80 DAP, separation of theLS means of location and cultivar indicated thatthe lowest culls at both locations were from YukonGold. In contrast, the culls were highest for Niskaat the Truro site, and for Superior and Niska atCanning (Table 6). As was found for culls harves-ted 65 DAP, a separation of the LS means bycultivar and age across all physiological agesrevealed that Yukon Gold consistently generatedthe lowest culls, followed by AC-Novachip. Incontrast, culls from Niska and Superior weresimilarly high for all physiological ages.

Results from the separation of the LS means ofcultivar for harvest at 95 DAP were similar to theranking for culls for harvest at 80 DAP. YukonGold generated the lowest culls, followed by AC-Novachip. In contrast, culls were highest fromNiska, followed by Superior. As there was nosignificant interaction effect between cultivar andthe other factors for culls harvested 95 DAP, thesecomparisons are valid for both locations and allphysiological ages.

A repeated measures analysis for the Trurolocation indicated that culls for Yukon Gold werenot different across all harvest periods, and werealso the lowest of the cultivars studied (Table 7).However, average culls from AC-Novachip weresimilar to Yukon Gold culls, for harvest at 80 and

95 DAP. In contrast, average culls from Niska andSuperior were similar and ranked the highest,followed by AC-Novachip. Culls from Niskadecreased slightly for harvest at 95 DAP, whileculls from Superior showed a significant reductionwith harvest day.

At the Canning location, Yukon Gold consis-tently generated the lowest culls for all harvestdays, as was found for the Truro site. Average cullsfor AC-Novachip were lower compared to Niskaand Superior for harvest at 65 and 80 DAP, butthere was no difference in culls among the threecultivars when harvested 95 DAP. In contrast tothe finding for the Truro location, the relativeranking for Superior and Niska changed, withthese two cultivars generating similar culls onproduce harvested 80 and 95 DAP. The high cullat early harvest was mainly of undersized andimmature tubers, which would increase in size withgrowing period.

Conclusions

Enhancing earliness in potato production cantranslate into farm management and financialbenefits to producers. Field experiments wereconducted at two locations, at an educationalresearch farm and at a commercial farm, in NovaScotia, Canada to evaluate the effect of advancingseed-potato age and cultivar on yields. Total yield,marketable yield and culls were compared at 65, 80and 95 DAP.

Three of the four cultivars (AC-Novachip,Niska, and Yukon Gold) are mid-season matur-ing, while the fourth (Superior) is an early tomid-season cultivar. Advancing the physiologicalage of seed-potatoes by up to 3 weeks enhanced

Table 5: P-values for testing the fixed effects on cull response at each harvest date, andthe interaction of these effects with harvest date

Source of variation

Harvest date (DAP)Interaction with

harvest date65 80 95

Harvest date 0.001Location (L) 0.330 0.357 0.894 0.003Cultivar (C) 0.001 0.001 0.001 0.001L · C 0.202 0.001 0.304 0.008Physiological age (A) 0.050 0.172 0.537 0.448L · A 0.245 0.664 0.406 0.852C · A 0.001 0.021 0.595 0.091L · C · A 0.117 0.220 0.813 0.451Residual variance 1.97 1.15 1.73 1.74

182 Asiedu et al.

early yields as a result, in part, of earlyemergence which, in turn, advanced tuber initi-ation and bulking, but the actual effect dependedon the cultivar studied. In addition, the effecttended to decrease for growing periods above80 days.

All the cultivars generated the highest total andmarketable yields, regardless of harvest day, whenaged 3 weeks. However, when aged 6 weeks, AC-Novachip generated significantly lower marketableyield than the control (0 week) when harvested at

80 DAP, and significantly lower total yield whenharvested at 65 DAP. This suggests that aging AC-Novachip for more than 3 weeks is not to berecommended. However, aging Superior andYukon Gold for 6 weeks did not adversely affecttotal and marketable yields. Yet, given that yieldsat 6 weeks were similar to yields at 3 weeks, otherfactors such as the additional financial implicationsshould be taken into account in enhancing agingfor these two cultivars beyond 3 weeks. In general,enhancing aging did not affect yield for Niska.

Of the cultivars studied, AC-Novachip generatedthe highest total as well as marketable yields at allharvest times. However, total and marketableyields for Yukon Gold improved with physiologicalage at early harvest, and for aging for 6 weeks,Yukon Gold generated the same total and market-able yields as AC-Novachip. The enhanced earlyyields of AC-Novachip and Yukon Gold can beexplored for chip processing, particularly for theearly-season market. Yukon Gold is a popularyellow-flesh table market potato in North America.Thus, any slight improvements in earliness can

Table 6: Least square means of culls (t ha–1) broken bythe significant interactions. (a) Culls at 65 DAP; (b)culls at 80 DAP; (c) culls at 95 DAP

(a)

Physiological age (weeks)

0 3 6

AC-Novachip A1 6.36 a2 B 4.18 b B 4.30 bNiska A 7.45 a B 5.90 a B 5.89 aSuperior B 5.28 b A 6.22 a A 6.18 aYukon Gold A 3.51 c A 3.76 b A 3.53 b

(b)

Cultivar

Location

Truro Canning

AC-Novachip 3.38 c 3.67 bNiska 6.66 a 4.34 abSuperior 5.42 b 4.43 aYukon Gold 2.65 c 1.50 c

Cultivar

Physiological age (weeks)

0 3 6

AC-Novachip A 4.46 b C 2.69 b B 3.41 bNiska A 5.43 a A 5.68 a A 5.39 aSuperior A 4.97 ab A 4.93 a A 4.88 aYukon Gold A 2.06 c A 1.86 b A 2.31 c

(c)

Cultivar LSM

AC-Novachip 3.34 bNiska 4.33 aSuperior 3.72 abYukon Gold 2.12 c

1 LSM within a row (cultivar) followed by the same(capital) letter are not significantly different at the 5 %level.2 LSM within a column followed by the same (small)letter are not significantly different at the 5 % level.

Table 7: Least square means of culls (t ha–1) broken bythe three-way interaction amongst location, harvest dateand cultivar. (a) Interaction between harvest date andcultivar at Truro (from repeated measures analysis); (b)interaction between harvest date and cultivar at Can-ning (from repeated measures analysis)

(a)

Cultivar

Harvest date (DAP)

65 80 95

AC-Novachip A1 5.75 b2 B 3.38 c B 3.16 bcNiska A 7.17 a A 6.43 a B 4.38 aSuperior A 6.84 a B 5.42 b C 3.73 abYukon Gold A 3.64 c A 2.88 c A 2.62 c

(b)

Cultivar

Harvest date (DAP)

65 80 95

AC-Novachip A 4.13 c A 3.67 b A 3.53 aNiska A 6.61 a B 4.17 ab B 3.70 aSuperior A 4.94 b A 4.43 a B 3.74 aYukon Gold A 2.61 d A 1.67 c A 2.19 b

1 LSM within a row (cultivar) followed the same(capital) letter are not significantly different at the 5 %level.2 LSM within a column followed the same (small) letterare not significantly different at the 5 % level.

Enhancing Earliness in Potato Production 183

translate into substantial financial returns to pro-ducers involved in the table potato market.

Analysis of culled potato revealed that YukonGold consistently generated the lowest culls acrossharvest days at both locations. This gave a slightedge to Yukon Gold, over AC-Novachip, withrespect to marketable yield. The other two culti-vars, Niska and Superior, generated lower totaland marketable yields and higher culls, whenharvested early. All the cultivars gave the highestculls when not aged, and lower culls when aged for3 weeks, except for Superior harvested early at65 DAP.

In conclusion, for early harvest, the optimumaging for all four cultivars studied was 3 weeks.The best treatment combination to maximizemarketable yield was Yukon Gold aged 6 weeksplanted at the commercial farm and harvested95 DAP. For early harvest (65 DAP), however,AC-Novachip and Yukon Gold, both aged6 weeks, generated the highest yields.

Acknowledgements

Financial support was provided by the Nova ScotiaAgricultural Development Program of the Nova ScotiaDepartment of Agriculture and Marketing, under theTechnology Development Program Project No. DEV 52.The authors thank an anonymous reviewer for helpfulsuggestions.

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