Amer J of Potato Res (2006) 83:149-160 149

Growth-Room and Fie ld Studies with Seed Tubers Treated with Ethy lene and 1-methylcyc lopropene (1-MCP) During Storage

K. P r u s k i ~*, R. K. P r a n g e 2, B. J. D a n i e l s - L a k e 2, J. N o w a k 3, T. A s t a t k i e 4, a n d D. H. R o n i s ~

1Department of Plant and Animal Science, Nova Scotia Agricultural College, P.O. Box 550, 50 Pictou Rd., Truro, NS, B2N 5E3 Canada 2Atlantic Food and Horticulture Research Centre, Agriculture and Agri-Food Canada, 32 Main St., Kentville, NS, B4N 1J5 Canada

• ~Department of Horticulture, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061. USA 4Department of Engineering, Nova Scotia Agricultural College, P.O. Box 550, 50 Pictou Rd., Truro, NS, B2N 5E3 Canada

'~McCain Produce Inc., 317 Main St., Florenceville, NB, E71 3G6 Canada • Corresponding author: Tel: 902-893-6032; Fax: 902-897-9762; Email: kpruski@nsac.ns.ca

ABSTRACT

Based on e thy lene managemen t in po t a to s torage,

we hypothes ized tha t the appl ied t r e a t m e n t s would mod-

ify number o f sprouts pe r seed tuber. Thus, in combina-

t ion with in-row spacing (c lose r for seed, wider for

process ing) in the field t r e a t m e n t s will give e i the r (1) a

high number o f small t ube r s des t ined for seed use, o r (2)

a re la t ive ly smal ler number o f large, uni form tuber s

sui table for processing. A th ree -yea r s tudy (2001-2003),

conducted wi th two f rench fry process ing cult ivars, Rus-

se t Burbank (RB) and Shepody (SH), a imed a t the devel-

opment o f a novel modif ied a tmosphere seed t u b e r

s to rage t r ea tmen t . Seed tube r s were s to red a t 4 C f rom

October to May of each yea r in a cold room unde r f ive

modif ied a tmospher ic regimes: (1) a i r ven t i l a t ion only

(Cont rg l ) ; (2) 4 pl L -1 e thy lene appl ied cont inuous ly

beginning in November and (3) beginning in February;

(4) 1 Ill L -~ MCP (1-methylcyc lopropene) appl ied as a gas

for 48 h only in ear ly December fol lowed by con t inuous

4 p l L -I e thy lene and (5) MCP alone appl ied as above.

Each year, once a mon th (mid-January unt i l end o f

April) , a number o f seed tube r s was t aken f rom each

s torage t r e a t men t , p lan ted to pots and grown for 4 wk in

a growth-room. In these studies, shoo t emergence f rom

the e thy lene - t r ea t ed seeds o f both cul t ivars occur red

s ignif icant ly earlier, giving h igher number o f s tems per

tube r and s to lons per s t em than Con t ro l and MCP t rea t -

ments . Moreover , the t ime to emergence a f te r p lant ing

Accepted for publication 29 September 2005. ADDITIONAL KEY WORDS: apical dominance, Solanum tuberosum L, seed spacing, tuber size control, tuber size distribution

dec reased with the increased length o f s torage. Fie ld

s tudies t ha t were conduc ted f rom the end o f May (plant-

ing) unt i l Oc tober each year, p roduced s imilar t r ends

(a l though no t s ignif icant a t P _< 0.05) and r e su l t ed in a

higher number o f tube r s pe r s tem. In RB at the c loser in

row spacing (30 cm) used for seed produc t ion , e thy lene

enhanced yield o f smal le r tubers in the 30- to 115-g and

115- to 300-g categor ies . The e thy lene s to rage t rea t -

men t s also increased t u b e r number per plant , but no t

the to ta l mass o f ha rves t ed po ta toes . The MCP t rea t -

ment , in combina t ion with the wider in-row spacing ( 4 0

cm) used for the p roduc t ion o f p rocess ing tubers , signif-

icant ly inc reased the pe rcen t age o f large tube r s (>300

g). In SH, con t ra ry to RB, the e thy lene t r e a t m e n t s did

no t a l t e r t ube r size d i s t r ibu t ion and the appl ica t ion o f

MCP reduced t ube r size r a t h e r than increas ing it.

Resul t s f rom this s tudy suggest t ha t bo th e thy lene and

MCP can be used in seed po t a to s torage to inf luence the

t ube r size d i s t r ibu t ion o f the crop from tha t seed.

RESUMEN

Basado en el mane jo de e t i l eno para el almace-

namien to de papa, hemos asumido la h ip6tes is de que los

t r a t a m i e n t o s ap l i cados m o d i f i c a r i a n el n d m e r o de

b ro tes por tub6rculo semilla, asi en combinaci6n con el

e spac iamien to en el campo (co r to para semil la y largo

pa ra p rocesamien to ) nos dar~i ya sea (1) un gran ndmero

de tub6rculos pequef ios des t inados a semi l la o (2) un

ndmero r e l a t i vamen te pequefio de tub4rculos g randes y

un i formes adecuados para p rocesamien to . Se real iz6 un

es tud io de t res afios (2001 a 2003) con dos cu l t ivares

pa ra p rocesamien to de papa fr i ta , Russe t Burbank (RB)

150 AMERICAN JOURNAL OF POTATO RESEARCH Vol. 83

y Shepody (SH), des t inado al desarrol lo de un novedoso

t r a t amien to de a tm6sfera modificada para el almace-

namien to de tub~rculos semilla. Los tub~rculos semilla

fueron a lmacenados a 4 C de oc tubre a mayo de cada afio

en un ambien te frlo bajo cinco reglmenes atmosf~ricos

modificados: (1) so lamente ventf lac i6n de aire (Tes-

tigo); (2) 4 Llq de l e t i leno aplicado con t i nuamen t e a

par t i r de noviembre y (3) comenzando en febrero; (4) 1

Llq de 1 MCP (1-met i lc loropropeno) aplicado como gas

por 48 horas so lamente a pr inc ip ios de dic iembre

seguido de 4 Llq de 1-eti leno y (5) MCP solo aplicado en

la forma anterior . Cada afio, una vez al mes (mediados

de enero has ta f ines de abri l ) , se tomaron unos cuantos

tub~rculos semilla de cada t r a t amien to de almacenaje ,

fueron sembrados en macetas y l levados a la cdmara de

crec imiento por 4 semanas. En es tos estudios, la emer-

gencia de bro tes de las semillas t r a t adas con e t i leno se

realiz6 en ambos cul t ivares mucho mils antes , con un

ndmero mayor de tal los por tub~rculo y es to lones por

tal lo q u e e n el test igo y los t r a t amien tos con MCP. Mils

adn, el t iempo de emergencia despu~s de la s iembra dis-

minuy6 con u n mayor t iempo de a lmacenamiento . Los

es tudios de campo que se rea l izaron desde f ines de mayo

( s iembra) has ta oc tubre de cada afio mos t r a ron t enden-

cias s imilares ( aunque no significativas a P -< 0.05) y

dieron un mayor ndmero de tub6rctflos por tallo. En RB

a menor espaciamiento (30 cm) usado para la produc-

ci6n de semilla, el e t i leno elev6 el r end imien to de tub~r-

culos mils pequefios en las categorias de 30-115 g y

115-300 g. Los t r a t amien tos de a lmacenamien to con

etf leno tambi~n i nc r emen ta ron el ndmero de tub~rctflos

por planta , pero no la masa to ta l de papa cosechada. E1

t r a t amien to con MCP, en combinaci6n con un mayor

espaciamiento en t re p lan tas (40 cm) usado para la pro-

ducci6n de papa para procesamiento inc remen t6 signi-

f ica t ivamente el porcenta je de tub~rculos mds grandes

(>300 g). En SH, con t r a r i amen te a RB, los t r a t amien tos

con e t i leno no a l t e ra ron la d is t r ibuci6n de tamafio y la

aplicaci6n de MCP redujo el tamafio del tub~rculo en

lugar de incrementar lo . Los resu l tados de este es tudio

sugieren que t an to el e t i leno como el MCP pueden

usarse en a lmacenamien to para inf luenciar la dis tr ibu-

ci6n de tamafio del tub6rctflo del cult ivo a diferencia de

lo que se quiere para semiIla.

INTRODUCTION

Potato tubers (Solarium tuberosum L.) are grown for a

variety of markets, including baker, pre-pack, table, french fry,

potato chip, canned, and seed. Failure to achieve the correct

size range of tubers for these specific markets can cause eco-

nomic losses to producers, distributors, and the processing

industry (Marshall and Young 2004). In the U.K., for example,

the cost of not meeting size specifications has been estimated

at £ 24 million per year (British Potato Council 1999).

Although specialized potato markets require specific

tuber sizes, field production practices generally target seed,

table, or processing use and are adjusted accordingly. In

Canada, the major challenges regarding tuber size and yield

manipulation are focused on 'Russet Burbank' and 'Shepody',

two major french fry cultivars that constitute approximately

90°/5 of the processed market. The cultivars have quite different

maturities, Shepody being used for the early crop and Russet

Burbank for the late crop and long-terra storage. Russet Bur-

bank tends to produce a relatively large number of tubers of

various sizes, many of which are too small for table stock or

processing. Shepody, on the other hand, tends to produce a

small number of large sized tubers, consequently giving a low

yield of seed tubers (New Brunswick Department of Agricul-

ture and Rural Development 1997). Tuber size variation

requires additional grading, resulting in a high number of

unmarketable culls. The methods currently used by growers to

control tuber size are only partially effective. They are based

predominantly on manipulation of in-row spacing and delay of

planting until late spring when the soil temperature is warm

and uniform. Development of seed tuber storage treatments

and field production practices to specifically favor either seed

or processing use of the harvested crop could reduce sorting

cost and increase the proportion of marketable tubers, thus

increasing growers' profits.

Tuberization in potato is a complex physiological and

metabolic phenomenon determined by genotype and environ-

mental stimuli (Ewing and Struik 1992; Xu et al. 1998; Han-

napel et al. 2004; Vreugdenhil 2004). The number and size of

tubers produced by each plant depends to a great extent on

the number of stems produced by the seed tuber and the num-

ber of stolons formed on each stem. Many factors affect tuber-

ization, including carbohydrate supply, nitrogen status,

carbon/nitrogen (C/N) ratio, day-length, temperature, cultivar,

growth regulators, and molecular controls (Ewing and Struik

2006 PRUSKI et al.: EFFECTS OF ETHYLENE AND MCP ON SEED POTATOES 151

1992; Harris 1992; Machackova et al. 1998; Hannapel et al.

2004). Tuberization is closely linked to dormancy and physio-

logical age of the mother tuber (Claassens and Vreugdenhil

2000; Suttle 2004). Dormancy of tubers in storage can be bro-

ken by various methods including the artificial depletion of

endogenous ABA (Suttle 1995, 2004) or an exogenous supple-

ment of gibberellins (Mikitzel 1993; van Ittersum and Scholte

1993). Exogenous ethylene releases potato bud dormancy

(Suttle 2004) and significantly shortens the duration of the rest

period (Kader 1985). Continuous ethylene exposure during

storage can suppress tuber sprouting by inhibiting sprout elon-

gation (Prange et al. 1998). Such a treatment also reduces api-

cal dominance and causes more uniform sprouting (Prange et

al. 1998, 2005a; Pruski and Daniels-Lake 2003; Pruski et al.

2004). 1-methylcyclopropene (MCP) has anti-ethylene effects

and blocks the ethylene binding sites in plant cells (Blanken-

ship and Dole 2003; Prange and DeLong 2003). It is applied as

a gas treatment on stored product for 24 to 48 h, and it has

been approved for commercial use on some products, for

example, apples in the USA and other countries. 1-MCP has

been tested on a large number of fruit, vegetables, and orna-

mentals (Blankenship and Dole 2003), but its effects on potato

tubers were tested with regards to fry color only (Prange et al.

2005a). We hypothesized that an application of 1-MCP to

stored tubers would block sprout-promoting ethylene effects

by reducing number of sprouts that in effect would give a

lower number of stems with a lower number or large size

tubers.

The objective of this study was to develop a novel modi-

fied-atmosphere seed tuber storage treatment, based on man-

agement of ethylene and an anti-ethylene compound, 1-MCP,

which in combination with the known agronomic practices

(i.e., in-row spacing) can give either (1) a high number of small

tubers destined for seed use or (2) relatively large, uniform

tubers suitable for processing.

MATERIALS AND METHODS

Elite I seed tubers (35-45 mm, approx. 50 g each, Elite

Seed Potato Farm, Alberton, IMnce Edward Island, Canada) of

Russet Burbank (RB) and Shepody (SH), were subjected to the

storage treatments during three consecutive storage seasons,

from November to May, starting in 2000. Tuber storage experi-

ments and growth-room studies were done at the Atlantic

Food and Horticulture Research Centre (AFHRC)-Agriculture

and Agri-Food Canada, Kentville, NS, Canada. Field experi-

ments were also conducted over the three growing seasons, on

a sandy loam soil, at the Nova Scotia Agricultural College in

Truro, Nova Scotia, Canada. The crop received a total of 2602

corn heat units (CHU), and rainfall of 285 mm in 2001, 2636

CHU and 360 mm of rainfall in 2002, and 2550 CHU and 320

mm of rainfall in 2003. The corn heat unit system, now also

known as crop heat units (CHU), was developed in the 1960s

and is used to recommend corn hybrids and soybean varieties

that are best suited for production in specific CHU zones in

various regions of Canada (Bootsma et al. 1992).

Storage Treatments The tubers were stored in sealed 1.9-m:* chambers in a

temperature-controlled cold-room. The temperature was 13 C

until early December, when it was reduced 1 C per week until

it reached 4 C. The temperature remained at 4 C until early

May. Chambers were ventilated with ah, at 15 L min -~, for two

6-h periods, daily. Treatments in storage included (1) air venti-

lation only (Control); (2) 4 pl L -~ ethylene applied continuously

beginning in November (Eth Early); (3) 4 pl L -1 ethylene

applied continuously beginning in February (Eth Late); (4) 1 l]l

L -1 1-methylcyclopropene (MCP; SmartFreshTM--AgroFresh

Inc.) applied as a gas for 48 h only in early December followed

immediately by continuous 4 Ill L 1 ethylene (Eth + MCP); and

(5) MCP alone applied as above in early December (MCP).

Ethylene was added to the ventilation air stream in sufficient

quantity to maintain the desired concentration within the

chambers. The ethylene concentration was monitored regu-

larly by GC analysis of a sample of the chamber atmosphere.

About 2 wk prior to field planting (May 10-15 each year, after

approx. 200 days in storage), the temperature in the storage

room was increased to 10 C, and the ethylene application was

discontinued.

Growth-Room Studies Each year, at ca. 75 (mid-January), 110 (mid-February),

140 (end of March) and 175 (end of April) days after start of

the trial (mid-November), six tubers were removed from each

of the cultivar x storage treatment combinations, planted in

175-nml (7-in.) pots, one tuber per pot, filled with a soil-less

growing medium (AFHRC mix), and placed in a walk-in

growth-room (Econaire, V~rmnipeg, Manitoba, Canada) at 22/18

C day/night temperature with 16-h photoperiod for 1 month.

The pots were hand watered every other day. Tinm to emer-

152 AMERICAN JOURNAL OF POTATO RESEARCH Vol. 83

gence (days) and the number of stems and stolons produced

after 1 month were recorded.

F i e l d Studies The seed tubers were warmed to room temperature by

the day of planting. Storage treatments were superimposed on

the planting densities in the field. The planting dates were 28,

22, and 30 May, respectively, in 2001, 2002, and 2003. Plots con-

sisted of 10 rows, 90 cm apart and 5 m in length. Two guard

rows (red-skinned cultivar) were planted along each side of

the plot. Two guard plants were planted at each end of each

row in the plot. In-row spacings of 30 and 20 cm were used for

processing and seed, respectively, for SH and 40 and 30 cm for

RB. All plots were replicated four times. Emergence data were

collected every 3 to 4 days from 2 wk after planting until max-

imum emergence at 40 days. The average time of emergence

(ATE) was calculated using the standard formula:

ATE = dl - nl + d.~ .n.~ + ...... +dn " nn/n, where

dl .... dn- days after planting ; n~ .... nn - number emerged

at dl..., dn ; n - total number emerged per plot

Stems were counted 45 days after planting. Harvests were

mid-September for SH and early October for RB. Reglone ®

(diquat dibromide) at the rate of 2 L • ha -1 was applied 2 wk

prior to each cultivar's harvest to top-kill the haulms. A single-

row potato digger was used to harvest the tubers. Tubers were

bagged by hand and transported to the lab for measurements.

Yield and number of stems and tubers per plant were

recorded. The number of tubers per stem was calculated. Har-

vested tubers were grouped into four size categories: (i) <30 g

(1 oz) and culls, (ii) 30-115 g (1-4 oz), (iii) 115-300 g (4-10 oz),

and (iv) >300 g (10 oz). Data were converted into tons per ha.

Percentage of tubers in each size category was calculated by

weight and by number of tubers per ha.

Stat is t ical Analys i s For each eultivar, data from the three years of growth-

room experiments were analyzed together as a 4 x 5 factorial

with six replications in three blocks to determine the effect of

days in storage and storage treatment on (1) emergence, (2)

number of stems, and (3) number of stolons. The blocking fac-

tor was year.

Data from the field experfinents were also analyzed

together for each cultivar as a split-plot by combining the three

years and the four field plots (a total of 12 blocks) as random

blocks, two levels of spacing as whole plot treatments, and the

five storage treatments as sub-plot treatments. The responses

analyzed were (1) total yield per ha, (2) total number of tubers

per ha, (3) percentage of tubers <30 g + culls, (4) percentage

of tubers 30-115 g, (5) percentage of tubers 115-300 g, (6) per-

centage of tubers >300 g, (7) number of days to emergence, (8)

number of stems per plant, and (9) number of tubers per stem.

For each response, the validity of model assumptions was ver-

ified for each response variable by examining the residuals as

described in Montgomery (2001). The ANOVA analysis was

completed using the Proc Mixed (SAS Institute 1999) and the

least squares means were compared using a 5% level of signif-

icance. Unless noted otherwise, only results significant at P <

0.05 are discussed.

RESULTS

Growth-Room Studies Shoot emergence and stem and stolon number in both

cultivars were affected by both ethylene and MCP storage

treatments over the three consecutive years (Table 1). The

2001, 2002, and 2003 results were combined. Analysis of vari-

ance showed an interaction effect of storage length and stor-

age treatment on time to emergence (P = 0.018) and stem

number (P = 0.001), but not on number of stolons (P = 0.82) for

RB. On the other hand, for SH, the interaction effect was not

significant for time to emergence. Highly significant interac-

tion effects were observed in SH on both stem and stolon num-

ber (P = 0.001 andP = 0.002). The main effects on all responses

were significant (P = 0.001) and both cultivars responded in

similar manner. Under all storage treatments, the time from

planting to shoot emergence shortened as the duration of stor-

age progressed, and was shorter (3-6 days) in the ethylene-

treated tubers compared with MCP and control (Table 1).

Stem and stolon numbers were also higher in plants of both

cultivars from the ethylene-treated seed. The differences were

more pronounced with the increasing time of tuber storage:

from slightly above one stolon in both cultivars after 75 days in

storage to close to five in SH and more than seven stolons after

175 days in RB (Table 1). The same trends were observed in all

3 years. Plants from seed tubers stored with ethylene for 175

days also set tubers (data not shown).

F i e l d Studies Each of the three growing seasons had good growing con-

ditions and the crop received almost the same amount of CHU

2006 PRUSKI e t al.: E F F E C T S O F ETHYLENE AND MCP ON S E E D POTATOES 153

TABLE 1--Effects of length of storage and storage treatments on average time to emergence (ATE), number of stems and

stolons of Russet Burbank and Shepody grown in growth-room during three experimental periods 2001, 2002,

and 2003. : . . . . . . : : . . . . . . . : : - .

Russet Burbank Shepody Days in ATE t Stem --Stolon ATE ? - -S-tern ..... Stolon storage Treatment (days) Number Number (days) Number Number

75 Control 31.8 a 1.1 d 0.1 i 34.0 a 1.1 ef 0.4 defg Eth Early 27.0 bc 1.2 d 1.2 efgh 26.7 cde 1.0 f 1.7 bcd Eth Late 28.3 b 1.0 d 0.6 hi 30.2 bc 1.1 ef 1.0 cdef Eth+MCP 28.3 b 1.0 d 0.7 ghi 29.0 bcd 1.0 f 0.3 efg MCP 28.7 b 1.0 d 0.6 hi 30.9 ab 1.1 ef 0.4 defg

110 Control 24.5 cd 1.3 cd 0.7 ghi 23.1 efg 1.2 ef 0.2 fg Eth Early 18.8 fgh 1.2 d 3.1 cde 19.6 gh 1.6 bcde 1.9 bc Eth Late 21.6 ef 1.3 cd 2.5 cdef 20.7 fgh 1.4 cdef 0.4 defg Eth+MCP 22.9 de 1.6 bcd 1.6 defgh 22.6 efg 1.3 def 0.4 defg MCP 24.9 cd 1.3 cd 0.8 fghi 22.9 efg 1.2 ef 0.8 cdef

140 Control 21.3 ef 1.5 bcd 2.3 cdefg 25.5 def 1.4 cdef 1.6 bcde Eth Early 17.0 ghi 2.2 b 4.2 abc 20.4 fgh 2.5 a 2.95 ab Eth Late 17.0 ghi 1.4 bcd 3.9 bcd 19.2 gh 2.6 a 1.4 bcde Eth+MCP 19.8 fg 1.7 bcd 3.7 bcd 23.0 efg 2.0 abc 1.3 bcdef MCP 21.4 ef 1.3 cd 2.9 cde 22.7 efg 1.6 bcde 1.4 bcde

175 Control 18.5 ghi 1.5 bcd 4.2 abc 20.6 fgh 1.9 abcd 2.2 bc Eth Early 15.8 i 3.1 a 7.5 a 15.6 h 2.2 ab 4.2 a Eth Late 16.1 hi 2.1 bc 6.8 ab 18.4 gh 1.5 cdef 5.2 a Eth+MCP 18.5 ghi 1.7 bcd 5.0 abc 19.2 gh 2.1 ab 5.1 a MCP 18.5 ghi 1.7 bcd 4.4 abc 19.3 gh 1.8 abcd 3.1 ab

Significance p value 0.001 0.001 0.001 0.001 0.001 0.001

Values followed by the same letter within a given cultivar are not significantly different at P _< 0.01 level. Due to a large number of treatment combinations, a 1% level was used to control Type I experiment-wise error rate. tAverage time to emergence.

each year. Shoot emergence was 99°/5 for b o t h cult ivars in all

th ree growing seasons , a l though the re was some var ia t ion

obse rved b e t w e e n the th ree growing seasons regarding the

o the r m e a s u r e d responses . Due to lack of rainfall by the end of

the growing season in 2001, the yield was slightly r educed

compared to yields in 2002 and 2003; however, b o t h cul t ivars

r e sponded in s imilar way showing s imilar t r ends in all o the r

m e a s u r e d parameters . The ma in effects of in-row spacing and

s torage t r ea tmen t were signif icant (Tables 2, 3, and 4), wi th a

s ignif icant in te rac t ion only in the p ropor t ion of tube r s >300 g

in RB (Table 5). The lack of s ignif icant in terac t ion b e t w e e n

spac ing and t r e a t m e n t suggests t ha t the s torage t r ea tmen t ( s )

tha t were effective in improving tube r size for p rocess ing were

also benef ic ia l in the p roduc t ion of seed tubers .

Total yield in RB g rown for seed (30 cm) was 37 t/ha, i.e.,

13°/5 h igher t han the yield at the spac ing for p rocess ing (40 cm),

32.2 t /ha (Table 2). The to ta l n u m b e r of tube r s pe r h a and the

pe rcen tage of tube r s in the 30- to l15-g size ca tegory (by

weight and by n u m b e r of tube r s ) were h igher in the spac ing

for seed t han in the spac ing for p rocess ing in b o t h cul t ivars

(Table 2). In the spacing for seed, the re were a lmos t 22% and

7% more tube r s pe r h a in RB and SH, respec t ive ly c o m p a r e d

wi th the spacing for p rocess ing (Table 2). The pe rcen t age of

n u m b e r of t ube r s pe r h a in 115- to 300-g t u b e r ca tegory was

h igher in the spacing for p rocess ing in RB bu t no t in SH. In

b o t h RB and SH, ATE was no t af fected by spacing. The num-

b e r of tube r s pe r s t em was h igher in the spac ing for process-

ing t han in the spac ing for seed in SH only.

The tota l yield was no t significantly di f ferent b e t w e e n

s eed s torage t r e a t m e n t s in b o t h cul t ivars (Table 3), a l though in

SH it was lower f rom seed t r ea ted wi th MCP t h a n f rom any

o the r t r e a t m e n t (marginal s ignif icance of P = 0.087, Table 3).

The RB and SH p lan t s p roduced more tube r s pe r h a f rom seed

t r ea ted wi th e thy lene (all t h ree e thylene t r e a tmen t s ) t han f rom

the MCP or cont ro l p lan ts (Table 3), a l though in SH the differ-

ences were not significant.

154 A M E R I C A N J O U R N A L O F P O T A T O R E S E A R C H Vol. 83

TABLE 2--Effects of in-row spacing in the field on yield, number of tubers per hectare, percentage of tubers in size

categories (by weight and by number~ha), ATE, and number of tubers per stem of Russet Burbank and

Shepody. Least squares means are averaged over three growing seasons, 2001, 2002 and 2003.

Total Total

In-row Yield number Spacing (t/ha) tubers/ha

Russet Burbank 30 cm seed 37.0 a 319736 a 37.0 a

40 cm proc. 32.2 b 261043 b 31.5 b significance

p value 0.001 0.001 0.005

S h e p o d y 20 cm seed 29.7 a 175161 a 17.70 a

30 cm proc. 27.8 a 163516 b 13.79 b significance

p value ns 0.018 0.008

% tubers in size categories

3 0 - 1 i 5 g 30-115 g 115-300 g >300 g No. of by by by by ATE t tubers

weight/ha No./ha No.faa No./ha (days) pe r s tem

54.8a 37.5b +1 25.2a 2 .4a

5 l A b 41.3a + 25.3a 2 .5a

0.017 0.007 ns 2 ns

33.2a 56.7a 8 .0a 26.3a 1.2b

28.8b 58.4a l l . 0 a 26.0a 1.6a

0.034 ns ns ns 0.001

Values followed by the same let ter within a given cultivar are not significantly different at P _< 0.05 level.

tAverage t ime to emergence.

iInteraction effect be tween spacing and t reatment was significant and is shown in Table 5. 2No significant difference at P -< 0.05 level.

TABLE 3--Effects of storage treatments on yield, number of tubers per hectare, ATE, number of stems per plant, and

tubers per stem in Russet Burbank and Shepody. Least squares means are averaged over three

growing seasons, 2001, 2002, and 2003.

Calculated Total Total average

Yield number weight of ATE t

Treatment (t/ha) of tubers one tuber (g) (days)

Russet Burbank Control 32.75 a 266402 b 122 26.5 a Eth Early 34.62 a 310316 a l l l 24.5 c

Eth Late 34.97 a 301367 a 116 24.9 c

Eth+MCP 35.96 a 321306 a 112 24.7 c MCP 34.66 a 277557 b 125 25.6 b

significance

p value ns 1 0.001 - - 0.001

Shepody Control 28.78 a 170198 a 169 27.3 a Eth Early 29.91 a 178392 a 167 25.2 d

Eth Late 29.51 a 174411 a 169 25.6cd Eth+MCP 30.20 a 175882 a 171 26.7 b

MCP 25.77 b 172809 a 149 26.0 c significance

p value 0.087 ns - - O.001

Values followed by the same letter within a given cultivar are not significantly different at P <_ 0.05 level.

tAverage t ime to emergence. 1No significant difference at P -< 0.05 level.

Number Number

of s tems of tubers per plant per s tem

3.60 c 2.33 a 4.26 a 2.32 a

3.97 b 2.50 a 4.02ab 2.52 a

3.66 c 2.40 a

0.001 ns

2.70 b 1.30 a 2.87ab 1.40 a

3.00 a 1.33 a

2.66 b 1.46 a 2.79ab 1.39 a

0.061 ns

2006 PRUSKI et al.: E F F E C T S OF ETHYLENE AND MCP ON S E E D POTATOES 155

TABLE 4--Effects of storage treatments on percentage of tubers in different size categories by weight and by

number in Russet Burbank and Shepody. Least squares means are averaged over three growing seasons,

2001, 2002, and 2003.

% tubers in size categories % tubers in size categories by weight/ha by number/ha

Treatment 30-115 g 115-300 g >300 g 30M15 g 115-300 g >300 g

R u s s e t B u r b a n k Control 32.5 bc 55.4 a +1 51.4 bc 39.7 ab +1 Eth Early 38.3 a 56.2 a + 56.2 a 36.8 b + Eth Late 34,9 ab 58.6 a + 53.5 ab 40.5 ab + Eth+MCP 35,8 ab 56,6 a + 55.7 a 36,9 b + MCP 29,7 c 59.9 a + 48.0 c 43.1 a + significance p value 0.002 as2 _ _ 0.001 0.028 - -

Shepody Control 15.0 b 62.4 ab 22.2 ab 30.3 a 56.5 a 10.6 a Eth Early 16.5 ab 58.0 b 25.0 a 31.9 a 53.5 a 12.0 a Eth Late 14.1 b 64.1 ab 21,6 ab 28.4 a 58.7 a 11.1 a Eth+MCP 13.7 b 67.5 a 18.3 bc 28.5 a 61.3 a 8.8 a MCP 19.4 a 68.2 a 12.2 c 35.9 a 57.6 a 5.0 b significance p value 0.092 0.041 0.011 ns ns 0.007

Values followed by the same letter within a given cultivar are not significantly different at P _< 0.05 level. qnteraction effect between spacing and treatment was significant and is shown in Table 5. 2No significant difference at P _< 0.05 level.

Storage t reatment had no effect on the percentage of

tubers <30 g in either of the two cultivars (data not shown).

Comparing tuber size distribution by weight in RB (Table 3),

the Eth Early t reatment had a higher proport ion and MCP a

lower proport ion of 30- to l15-g tubers, compared with the

control treatment. In SH the storage t reatment effect was not

significant at P = 0.05 (P = 0.092, Table 4). When comparing on

a tuber number basis in RB, both Eth Early and Eth + MCP

treatments produced higher tubers numbers in the 30- to 115-

g category than the control (Table 4). Again, there were no sig-

nificant differences in SH (Table 4).

The proport ion of 115- to 300-g tubers in RB was unaf-

fected by the storage t reatments ff compared by weight, i.e.,

about 55% to 60°/6 of total yield in all t reatments (Table 4). How-

eve~; there was a t rea tment effect on this size category in RB,

on a tuber number basis (Table 4). Compared with the control

t reatment (39.70/6), the Eth Late (40.5%) and MCP (43.1%) treat-

ments produced higher tuber numbers in this size and the Eth

Early (36.8%) and Eth + MCP (36.9°/6) produced lower tuber

numbers (Table 5). In SH, the proport ion of 115- to 300-g

tubers was affected on a weight basis with the Eth Early pro-

ducing less weight and the o ther three t reatments (MCP, Eth

Late and Eth + MCP) producing progressively more weight of

tubers pe r ha (Table 4).

In the largest tuber size category (>300 g), SH was

affected by storage treatment, in both weight and tuber num-

ber (Table 4). Surprisingly, the MCP t rea tment had the lowest

proport ion and the Eth Early had the highest propor t ion of SH

tubers >300 g. In RB the propor t ion of tubers >300 g was

affected by an interact ion be tween spacing and storage treat-

ment (Table 5). In RB planted at the processing spacing (40

cm), the highest proport ion (by weight and by tuber number)

of tubers >300 g was from MCP-treated seed, while plants f rom

the ethylene t reatments (Eth Early and Eth Late) had lower

percentage of tubers >300 g (Table 5). In RB planted at the

seed spacing (30 cm), the propor t ion o f tubers >300 g, by both

weight and by tuber number, was the lowest in Eth Early, while

the proport ion of tubers >300 g f rom the other three treat-

ments (Eth Late, Eth + MCP, and MCP) did not differ signifi-

cantly from the control (Table 5).

ATE was about 2 days shorter in plants grown from the

Eth Early t reatment than f rom the controls in both cultivars

(Table 3). Seed t reated with ethylene in both cultivars pro-

duced plants with higher number of s tems than the controls,

156 A M E R I C A N J O U R N A L O F P O T A T O R E S E A R C H Vol. 83

TABLE 5---Percentage of tubers larger than 300 g in yield of Russet

Burbank. Least squares means are for spacing >( treatment

interaction averaged over three growing seasons, 2001, 2002, and

2003.

% tubers >300 g by weight/ha % tubers >300 g by number /ha

Seed Processing Seed Processing Treatment spacing 30 cm spacing 40 cm spacing 30 cm spacing 40 cm

Control 7.2 a t 9.4 ab 2.6 a 3.0 ab E thEar ly B t t 1.1b A 8.0ab 0 .4b 2 .8ab Eth Late 4.8 a 4.7 b 1.5 a 1.6 b Eth+MCP 6.1 a 4.6 b 1.9 a 1.6 b MCP B 4.7 a A 10.6 a 1.6 a 3.9 a significance p value 0.048 0.046

Values followed by the same letter are not significantly different P _< 0.05 level. tSmall letters are within the spacing. t tCapi ta l letters are between the spacings (when significant).

R t m s e t B u r b a n k

1(]0-

80

E ~v 41

• : : •

. :: •

• , , •

• • . J *

• k , •

: •

[ ] < 3 o

30-11.5 115-300 >300

FIGURE 1. Effects of seed storage treatments on percentages tubers of different s ize categories by weight (g) in yield o f field grown Russet Burbank and Shepody. Values are the averages calculated for each cultivar from both in-row spacings over the three growing seasons 2001, 2002, and 2003.

2006 PRUSKI et al.: EFFECTS OF ETHYLENE AND MCP ON SEED POTATOES 157

>300g 115-300g 30-115g <30g >300g 115-300g 30-115g <30g

>300g 115-300g 30-115g <30g+ culls >300g 115-300g 30-115g <30g

FIGURE 2. Illustration of tuber size distribution in plants field grown from: (A) control (air-treated) Russet Burbank seed, (B) ethy- lene early-treated RB seed, (C) control (air-treated) Shepody seed, and (D) ethylene early-treated SH seed. Each photo- graph represents tubers harvested from 10 plants.

although in RB this occurred in the Eth Early treatment, but in

SH it was in the Eth Late treatment (Table 3). Interestingly, no

significant differences between any of the storage treatments

in number of tubers per stem were observed in either cultivar

(Table 3). However, RB had almost twice as many tubers per

stem as SH.

The calculated average weight of one tuber for each treat-

merit (Table 3) shows that the mass of a single tuber in RB was

visibly reduced in plants grown from ethylene-treated seed

(111-116 g) compared with control and MCP-treated seed (122

and 125 g, respectively). MCP-treated seed produced slightly

larger tubers than control. In SH no such differences were

observed, except for the tubers grown from MCP-treated seed

that were considerably smaller (149 g) compared with an aver-

age tuber from other treatments and the control (167-171 g)

(Table 3).

The two cultivars responded differently to the seed stor-

age treatments in regard to the proportion of total yield that

fell into the various size categories (Figure 1). In RB, the ethy-

lene seed treatments (Eth Early and Eth Late) reduced the pro-

portion of large tubers (>300 g) and increased the proportion

of small tubers (30-115 g) compared with the control treat-

ment. In SH, these ethylene treatments Increased the propor-

tion of large tubers compared with the control treatment,

whereas the proportion of small tubers was not affected.

Among plants grown from MCP-treated seed, the proportion of

large tubers in SH was reduced and in RB unchanged com-

pared with the control treatment (Figure 1). Figure 2 illus-

158 AMERICAN JOURNAL OF POTATO RESEARCH Vol. 83

trates the tuber size distribution in plants of both cultivars that

were field grown from ethylene early and air-treated seed.

DISCUSSION

This study was conducted to develop a new management

system to control potato tuber size and to enhance tuber uni-

formity by manipulating seed storage conditions and in-row

spacing in the field. The growth-room results showed highly

significant effects of storage treatments on emergence .and

stem and stolon numbers in both cultivars. Although the

responses to storage treatments were less pronounced in the

field trials than in the growth-room studies, similar trends

were observed. For convenience and clarity, the growth-room

and field results are discussed separately.

The growth-room studies indicated beneficial effects of

both ethylene early and late treatments of stored seed on a

number of sprouts per tuber, shoot emergence, number of

stems and stolons. Independently of the cultivar, plants

emerged 3 to 6 days earlier from the both ethylene treatments

than from the MCP and control treatments (Table 1). As the

storage period progressed, the time to emergence decreased

from 27 days after 75 days of storage to 15 days when the seed

was stored in the presence of ethylene for 175 days. This phe-

nomenon could be linked to the increase in tuber ethylene pro-

duction once it breaks dormancy and begins sprouting (Suttle

2003) and may also explain the observed tuber set after 4 wk

of growth in the growth room in plants derived from seeds

stored with ethylene for 175 days (data not shown). Although

the seed was physiologically and chronologically older with

the longer storage duration and the observed increase in emer-

gence and stem numbers has been previously documented

(Burton et al. 1992; Struik and Wiersema 1999), ethylene treat-

ments significantly enhanced these responses. The higher

number of stems produced in plants grown from ethylene-

treated seeds was likely due to the loss of apical dominance.

Both the higher number of stems and stolons per plant recorded

in the growth-room trials suggested that this treatment could

increase the production of seed size tubers in the field.

Although the year-to-year variability observed in the field

studies was attributable to growing season differences, shoot

emergence of 99% was consistent in all three years in all treat-

ments, indicating that the treatments did not affect viability of

seed tubers. In both cultivars, ethylene treatments stimulated

earlier emergence by ca. 2 days (Table 3).

In Russet Burbank, the closer spacing for seed production

enhanced both yield and number of smaller tubers (30-115 g),

which are desirable as seed. In-row spacing alterations have

been recently reported by Long et al. (2004) to significantly

influence tuber size distribution in several Michigan process-

ing cultivars. Seed potato growers often use closer seed spac-

ing to enhance the number of smaller tubers, but may sacrifice

total yield in so doing. In our study, the ethylene storage treat-

ments increased the tuber number without affecting the total

mass of harvested potatoes, i.e., the mean tuber size was

reduced while the numbers increased and the harvested mass

did not decline, in comparison to controls. This can be

attributed to the higher number of stems per plant due to loss

of apical dominance in ethylene-treated seed, resulting in a

shift to smaller daughter tubers. For example, a larger propor-

tion of the harvest was in the 30- to l15-g category from ethy-

lene-treated seed than from control or MCP-treated seed.

It is not surprising that the effects of the Eth Early and Eth

Late tream~ents produced similar results, as both involved

long-term exposure of dormant tubers to ethylene. Within the

Eth + MCP treatment, it appears that the ethylene-blocldng

activity of the single early application of MCP declined with

time, as was observed by Prange et al. (2005a). This may be

attributable to production of new ethylene-binding sites in the

tuber cells. Recent genetic and biochemical studies revealed

that the ethylene receptors function as negative regulators of

ethylene responses and that ethylene binding inactivates them

(Guo and Ecker 2004). With a continued exposure to ethylene,

the Eth + MCP treatment may essentially have functioned the

same as the Eth Late treatment (Jeong et al. 2002).

These observations reconfirm that close in-row spacing is

beneficial for production of RB tubers for seed purposes and

suggest that continuous ethylene exposure of seed tubers from

at least February appears to also be beneficial. In contrast,

ethylene exposure particularly at the wider processing spacing

appeared to be detrimental to the production of large tubers

for processing purposes in RB. This was reflected in the aver-

age mass per tuber for each treatment where the daughter

tubers coming from plants grown from ethylene-treated seed

were the smallest (Table 3).

The response of SH was different from that of RB. The

total yield did not differ between in-row spacings, although

higher numbers of tubers were harvested and more of them

were in the 30- to l15-g size (desirable for seed) at the seed

spacing than at the processing spacing. This reflects the higher

2006 PRUSKI e t al.: E F F E C T S O F ETHYLENE AND MCP ON S E E D POTATOES 159

n u m b e r of t ube r s pe r s t em at the s eed spacing c o m p a r e d wi th

the p rocess ing spacing. It also suggests t ha t g rowers of Shep-

ody seed will no t sacrif ice yield by efforts to p roduce more

smal l tube r s for seed.

In SH, which usually p roduces a smal l n u m b e r of r a the r

large tubers , t he e thy lene t r e a t m e n t s did no t a l ter the n u m b e r

of s tems, the n u m b e r of tubers , or the size d is t r ibut ion at har-

vest. On the contrary, the MCP t r e a t m e n t was more effect ive

t han e thylene in th is regard. The average weight of ha rves ted

tube r s was lowes t In the MCP t r e a t m e n t (Table 3). This was

also appa ren t in the lower p ropor t ion of the ha rves t In the

>300-g category, and a poss ib le Increase in the 30- to 115-g cat-

egory In the MCP t rea tment , c o m p a r e d wi th the cont ro l treat-

ment . The r e a s o n for th is size shif t is unclear, bu t it suggests

tha t MCP may have had an effect o the r t han b locking of ethy-

lene receptors , and which pers i s t ed for a m u c h longer per iod

of t ime (Prange et al. 2005b). Fu r t he r invest igat ion into th is

may be war ran ted , as it cou ld provide a useful tool for improv-

ing seed- tuber p roduc t ion f rom Shepody potatoes .

The resul t s of our 3-year s tudy sugges t tha t b o t h e thylene

and MCP can be used in seed po ta to s torage to inf luence the

t u b e r size d is t r ibut ion of the c rop f rom tha t seed; however, a

careful tai loring of the t r e a t m e n t s to each cul t ivar is necessary.

In the g rowth- room studies, RB and SH r e s p o n d e d in a very

s imilar fashion, whe rea s in the field these cul t ivars r e s p o n d e d

s o m e w h a t differently. This suggests tha t u n d e r ideal condi-

t ions ( such as a g rowth- room) the s torage t r ea tmen t s may

have more un i fo rm effects on r e sponses in different cultivars,

whe rea s in field p roduc t ion the resul t s may b e differentially

in f luenced by env i ronmen ta l condi t ions , making the effects of

e thylene and MCP cul t ivar<iependent . The s torage t r e a t m e n t

of seed did no t pract ical ly a l ter the total yields in the field

(wi th one excep t ion in SH wi th MCP-treated seed), a l though

the t ube r size d is t r ibut ion was shif ted towards smal ler daugh-

te r t ube r s f rom e thylene- t rea ted seed. Fu r the r s tudies are in

progress to e n h a n c e ou r knowledge a b o u t the use of e thylene

in seed po ta to s torage to cont ro l t ube r size in the field.

ACKNOWLEDGMENT

The f inancial ass i s tance of McCaln Produce Inc. and Nova

Scotia Agricultural College (NSAC) is gratefully acknowl-

edged. Authors t h a n k Kim Hiltz, Valerie S immons and D o n n a

Dean of AAFC, Kentville, and Doug MacDonald and his c rew

of NSAC, Truro for t echnica l ass is tance, da ta collection, and

da ta entry. Atlant ic Food and Hor t icu l ture Resea rch Centre-

AAFC, KentviUe NS p rov ided suppo r t by a l locat ing fully con-

t rol led s torage facilit ies and g rowth rooms.

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