Amer J of Potato Res (1999) 76:317-319 317

Evaluation o f Various Potato Cultivars for Resistance to Wireworms (Coleoptera : E l a t e r i d a e )

Min K w o n ~, Y. I. H a h m 1, K. Y. Shin 1, a n d Y. J. A h n 2

~Division of Potato, National Alpine Agricultural Experiment Station, Rural Development Administration, Pyongchang, Kangwon Province, 232-950, Republic of Korea.

2Department of Applied Entomology, College of Agriculture and Life Science, Seoul National University, Suwon, 441-190, Republic of Korea.

ABSTRACT

Fifty po ta to cultivars, 11 early-maturing, 11 mid- maturing and 28 late-maturing cultivars, w e r e evalu- ated in the field for res i s tance to wireworms, using the equat ion injury rate (%) = (No. o f damaged tubers/No. o f total tubers ) x 100. In pre l iminary field tes ts , four wireworm species were found in the experimental site: Selatosomus puncticollis ( M o t s c h u l s k y ) , Melanotus legatus Cand~ze, Agrypnus argiUaceus ( S o l s k y ) , and A. binodulus coreanus Kishii. Larvae o f S . puncticoUis were dominant (over 95% occurrence) .

Significant differences for resistance were observed among the 50 cultivars. Of 11 early-maturing cultivars, high levels o f res i s tance to wireworms were obta ined ficom cvs Anco and Irish Cobbler. Among the 11 mid- maturing cultivars, the Amer ican cultivar Alamo and the Japanese cultivar Shinyuseo exhibited high resis- tance to wireworms. Of 28 late-maturing cultivars, cvs Whitu, Siegl inde, Spunta, and S o m e Miore w e r e very res i s tant to wireworms , whereas high leve ls o f resis- tance were observed in the cvs Cardinal, Norin No. 2, Ojiro and Rosa. T h e s e r e s i s t a n t cul t ivars shou ld be useful in future breeding programs.

INTRODUCTION

Potato, S o l a n u m tuberosum L., is an important crop in

Korea, its cultivation occurred on approximately 32,040 ha in 1996. Among the 51 species of arthropod pests of potato reported in Korea, wireworms are one of the most damaging

soft-dwelling insect pests. If not properly managed during the early growth stage of the crop, wireworms may adversely

Accepted for publication May 14, 1999. ADDITIONAL KEY WORDS: Potato, wireworms, Selatosomus puncti- col]is, resistant cultivar.

affect quantity and quality of yield due to immature stages

feeding excessively on the developing potato tubers, and indirectly by increasing the susceptibility to diseases such as blackleg and soft rot. Losses by wireworms were estimated

to be more than 50°/6 of the total harvest in certain plantings.

Current control of the wireworm population in Korea is primarily dependent upon repeated application of organo-

phosphate soil insecticides such as ethoprophos, fonofos, phoxim, and terbufos. However, their continued use on

potato for several decades has disrupted biological control by natural enemies and led to resurgences of wireworm pop_ ulations, and the development of widespread resistance to

various types of insecticides. In addition to these problems, factors such as higher labor costs, pesticide application costs, safety, and adverse effects on the environment make potato cultivation difficult. This economic consideration, and

the decreasing efficacy and increasing concern over adverse environmental effects of the early generation insecticides

have brought about the need for the development of new types of selective control alternatives or alternative control methods without or with reduced use of synthetic insecti- cides. We recognize that development of resistant varieties

could be the first defensive step in the control of insect pests,

especially wireworms. In the field studies described herein, we assessed the

resistance of 50 potato cultivars to wireworms including

seven recommended cultivars for Korea.

MATERIALS AND METHODS

P o t a t o C u l t i v a r s

Fifty potato cultivars, 11 early-maturing, 11 mid-matur- ing and 28 late-maturing cultivars were used in this study.

There are seven recommended potato cultivars in Korea, five of which belong to the early-maturing types, and two to the

late-maturing type. All the cultivars tested were stored in a cold room (at 4 C) of the National Alpine Agricultural Exper-

318 AMERICAN JOURNAL OF POTATO RESEARCH Vol. 76

iment Station (NAAES), Rural Development Administration,

Korea, and were subcult ivated when required.

Agronomic Practice and Field Design

This s tudy was c o n d u c t e d in the open f ie ld at the

NAAES located 800 meters above sea level. To choose the

appropriate test sites, we surveyed the density of wireworms

in the soil at three locat ions (area in all, 8,300 m'-') by using a

s a m p l i n g m e t h o d for w i r e w o r m s p r e v i o u s l y d e s c r i b e d

(Kwon et al., 1996). A tota l of 40 po t a to seed p i ece s (ca.

60g/piece) per site were buried at a 15 cm soil depth, at spac-

ing of 5 x 5 m apart. The baits were checked after 10 days,

and wireworms were col lected from the baits and counted.

Based on the result of this experiment, we selected the plots

with high ~ r e w o r m densities.

Seed pieces were pre-sprouted before planting. Show-

ing sprouts of 1-2 cm, whole seed tubers were cut into 2 -4

p ieces wi th s ter i l ized knives. After suber iza t ion for th ree

days or more indoors, 30 cut seed tubers of each 11 early-

maturing, 11 mid-maturing, and 28 late-maturing cul t ivars

were p lan ted in an a rea of 9 m s square (3x3 m) on 7 May,

1996. The experimental design was a randomized complete

b lock with three replicates. Just pr ior to planting, farmyard

manure mixed with horse feces and chemical fertilizers (N-P-

K) were applied 15 MT/ha and 150-180-120 Kg per ha, respec-

t ively. Other cu l tu ra l p r a c t i c e s were fo l l owed s t a n d a r d

cultivation, except no soil insecticides were applied.

Evaluation o f Resis tance and Stat is t ical Analys is

Potatoes were harvested by hand on 26 July, 18 August,

and 9 September, respectively. The number of tubers with

tunnel (s) by wireworms from each cultivar was counted for

evaluat ion, and one tunne l pe r t ube r was cons ide red the

same as two tunnels or more per tuber. Injury rate (IR) for

each cultivar to wi reworm was calculated by the equation,

IR (%) = (No. of damaged tubers/No, of total tubers) x 100.

The resistance responses were classified as follows: highly

resistant , IR <15%; resistant, IR 15-25%; susceptible, IR 26-

75%; and highly susceptible, IR >75%.

For all cultivars grouped by 3 maturing types, IRs were

analyzed with an analysis of variance (ANOVA), and signifi-

cant differences among cultivars means were separa ted by

using the Tukey 's Student ized Range Test at P=0.05 (SAS

Institute Inc., Cary, NC).

RESULTS AND DISCUSSION

In the wi reworm bait tests, we achieved relatively uni-

form infes ta t ions of 1.2 wi reworms p e r one po ta to piece.

Among four wireworm species attracted, about 95% (91/96)

of the total wireworms at tracted were S. puncticoUis larvae.

Park et al. (1988) repor ted that 14 spec ies of wireworm were

identified as pes ts of potato in Korea, and S. puncticottis was

the dominant species.

High levels of resistance to the infestation of wireworms

were observed for the cv. Anco (IR = 12.4%) and cv. Irish Cob-

bler (IR = 15.6%), whereas for the early-maturing cultivars

Korean cv. Namsuh and Canadian cv. Shepody were highly

suscep t ib le to wi reworms. The o the r cul t ivars exp res sed

moderate resistance to wireworms. Although significant dif-

ferences in injury levels mnong cultivars were detected, it was

difficult to est imate a true cultivar response to wireworms,

because the total number of tubers were quite variable.

A m e r i c a n cv. A lamo (IR = 1.1%) and J a p a n e s e cv.

Shinyuseo (IR = 14.7%) exhibited ext remely high resistance

to wi reworms for the mid-maturing cultivars. On the con-

trary, cvs AK-Red, Denali and Penobsco t were highly sus-

cept ible to infes ta t ion by wireworms. The o ther cul t ivars

were e i the r m o d e r a t e l y res i s tan t o r suscept ib le . Table 1

shows w i r e w o r m infes ta t ion levels for 28 la te -matur ing

cultivars. Of these, cvs Whitu, Sieglinde, Spunta, and Some

Miore were extremely resistant to wireworms. High levels of

resistance were observed on cvs Cardinal, Norin No. 2, Ojiro

and Rosa, whereas high susceptibil i ty was observed on cvs

Red Pontiac, Isola, Snowchip, Wheeler, and Allegany. The

other cultivars were moderately resis tant or susceptible.

Of course, the irregularity of emergence rates and in-

fection of viruses were also of concern with some cultivars

during growing season, especial ly wi th the early and mid-

maturing cultivars. The numbers of harvested tubers of cvs

Some Miore, Red Pont iac and I so la were fewer than ex-

pected, so that it is difficult to de termine whether they are

resistant or susceptible. But, according to the results of our

statistical analysis, those cultivars were grouped as resistant

cultivars. In this screening test, differences in tuber size were

not corre la ted posit ively or negatively with injury rates. This

is in cont ras t to results repor ted by Toba & Turner (1981)

suggest ing tha t pe rcen tage of in jured tubers damaged by

wireworms was higher in small tubers than in large ones.

There are seven reconunended pota to cultivars in Korea,

5 of which belong to the early-maturing type. All except cvs

Namsuh and Shepody showed medimn resis tance to wire-

worms in this screening test. For several decades, cvs Irish

1999 SHORT COMMUNICATION 319

TABLE 1.---Comparison of in jury rates for 50 cult±vats

grouped by maturing types in response to wire-

worms in the field.

Maturing Resistance Cultivar %, Injury Rate type category (Mean+SD)

Early Highly resistant Anco 12.37± 1.5Od ~ Resistant Irish Cobbler 15.57+3.00d

Maritta 21.59+2.28cd Superior 21.91_+2.34cd Jopung 24.30+3.01bcd

Susceptible Warba 34.22+2.44bc Desiree 35.44~:0.97bc Carlton 36.57+4.30bc Sandra 38.94+3.95b

Highly susceptible Shepody 80.90+11.13a Namsuh 93.66~=11.03a

Mid Highly resistant Alamo 1.14+ 1.00e Shinyuseo 14.74+1.01de

Susceptible Russet Norkotah 30.23±5.04cd Nicola 30.43+2.26cd Toyoshiro 32.21+6.22cd Norgold Russet 35.62±0.69c Norland 35.97+4.71c Epicure 47.34±5.33bc Denali 63.02~4.40b

Highly susceptible Penobscot 82.62±1319a A K - R e d 84.15~13.39a I

Late Highly resistant Whitu 3.48+0.301 Sieglinde 3.68±2.031 Spunta 5.90±0.15gl Some Miore 6.13± 1.08gl Ojiro 10.40-~2.42kl Conne 10.95+3.80jkl Rosa 11.47±2.13jkl Nor±n#2 14.95~:1.32ijkl

Resistant Renemahue 15.81 + 1.72hijkl M a r i j k e 21.55±3.69ghijl Jidose 23.56±l.33ghijk

Susceptible Bintje 25.51:~l.76fghij Cardinal 26.22+4.1 lfghi Dejima 27.44±0.84fghi Recent 30.13+3.68efgh Hatsuhubuki 32.69+4.50efg Atlantic 34.15±4.13efg Shimabara 38.38+8.85def Pentland Envoy 39.18±5.20def Sebago 42.10+8.00cde Kumsisuh 49.16+ 12.15cd Eigenheiner 55.24±4.36bc Red Lasoda 66.40+4.57b

Highly susceptible A l l e g a n y 87.92=~1.61a Wheeler 89.06±4.42a Snowchip 90.48+6.22a Isola 93.74~2.11a Red Pontiac 96.58±6.42a

~Means with the same letter are not significantly different by Tukey's Studentized Range Test, P=0.05.

Cobbler and Superior have been preferred cult±vats for many

growers in Korea, because of high-yield and taste. The cv

Jopung was bred at NAAES in Korea by using the Dutch cv

Resy as a seed pa ren t and the Amer ican cv Superior as a

pol len p a r e n t (Kim et al. 1990). This cul t ivar has been

dis t r ibuted na t ionwide since 1988, because of its s trong

res is tance to potato leafroll virus and pota to late blight,

Phytophthora infestans (Mont.) de Bary.

The results of this screening test suggest that 2 early-

maturing cultivars (cvs Anco, Irish Cobbler), 2 mid-maturing

cultivars (cvs Alamo, Shinyuseo), and 4 late-maturing culti-

vars (cvs Sieglinde, Some Miore, Spunta , Whitu) have

promise as wireworm resistant potatoes. The reason why

these cult±vats show resistance to wireworms was not exam-

ined. In general, mechan i sms of p lan t res is tance to pest

insects can be classified as either a physical or a chemical

defense mechanism. Physical mechan i sms include plant

color, sldn hardness and leaf trichomes. Chemical defense

mechanisms are based upon secondary plant compounds

such as insecticidal or repellent substances.

GlycoaIkaloids (a-solanine and a-chaconine) are known

to possess insecticidal properties against certain insects feed-

ing on potato leaves. Little information is available regarding

the effect of glycoalkaloids found in tubers on soil-dwelling

insects. Jonasson & Olsson (1994) reported that two resis-

tant cultivars (cvs SiUa and Ulster Chieftain) to wireworms

had a lower sugar and a higher glycoalkaloid concentration

than susceptible cultivars.

Based on our results, we plan to select and breed new

cultivars with wireworm-resistance. Furthermore, investiga-

tion on the resistance mechanism of screened cultivars is in

progress.

LITERATURE CITED Jonasson, T. and K. Olsson. 1994. The influence of glycoalkaloids, chloro-

genic acid and sugars on the susceptibility of potato tubers to wireworm. Potato Research 37:205-216.

Kim, KS., H.J. Kim, H.Y. Kim, J.K. Kim, Y.I. Hahm, and B.H. Hahn. 1990. Jopung: A new early maturing, disease-resistant and high-yielding potato variety. Rural Development Admims' tration J A4~. Sci (Hor- ticulture) 32 (2):50-54.

Kwon, M., C.S. Park, and Y.I. Hahm. 1996. Modified sampling method of potato wireworm, Sdatosomus puncticoUis (Mot.). Abstracts of the annual meeting of the Korean Society of Applied Entomol- ogy (Korean). p. 68.

Park, C.S., Y.I. Hahm, S.R. Cheoug, and S.H. Lee. 1989. On the kinds, occurrence and chemical control of wireworms collected in Daekwallyong, Korea (Korean). RDA J Agr Sci (Crop Protection) 31 (3):34-37.

Toba, H.H. and J.E. Turner. 1981. Wireworm injury to potatoes in rela- tion to tuber weight. J Econ Entomo174:514-516.