Amer J of Res (2006) 83:1-8 1

Development and Evaluation of Potato Breeding Lines with Introgressed Resistance to Columbia Root-Knot (Meloidogyne chitwoodi )

C. R. Brown 1., H. Mojtahedi 1, S. James 2, R. G. Novy 3, and S. Love 4

~USDA/ARS,Prosser, WA, USA 2Oregon State University, Central Oregon Experiment Station, Madras, OR, USA 3USDA/ARS,Aberdeen, ID, USA 4University of Idaho, Aberdeen Research and Extension Center, Aberdeen, ID, USA *Corresponding author: Tel: 509-786-9252; Fax: 509-786-9277; Email: [email protected]

ABSTRACT of the nematode to reproduce on the root systems, was sufficiently effective to prevent economic damage in a Columbia root-knot nematode (Meloidogyne chit- field exposure. All CRN-resistant clones are pollen ster- woodi) (CRN) is a serious pest of potato in the Pacific fie. Germplasm listed is available upon request. Northwest of the USA. Because this nematode can repro- duce rapidly within a single growing season, small initial RESUMEN populations are capable of causing crop loss in the Columbia Basin of Washington or Oregon. Presently, soil E1 nematodo del nudo de Columbia (Meloidogyne fumigation is the main treatment for controlling CRN on chitwoodi) (CRN), es un pardsito serio de la papa en la potato. Developing potato varieties with resistance to zona del Pacifico noroeste de los EUA. Poblaciones ini- CRN is highly desirable to reduce the cost of control and ciales pequefias son capaces de ocasionar la p6rdida del to alleviate concerns about the effects of fumigants on cultivo, debido a la h~bilidad de este nematodo a repro- the environment. Resistance to CRN race I was found in ducirse r~pidamente dentro de un mismo periodo de cul- two wild Solanum species. Resistance from S. bulbocas- tivo en los valles de Columbia de Washington u Oregon. tanum was introduced via protoplast fusion and from S. Actualmente, la fumigaci6n del suelo es el principal hougasii via sexual hybridization. Subsequent breeding m6todo de control del CRN de la papa. E1 desarrollo de consisted of repeated backcrossing and selection. The resistencia al CRN es muy deseable para reducir los cos- dominant monogenic inheritance was expressed in undi- tos de control y la preocupaci6n que se tiene de los fumi- minished fashion across several backcross generations. gantes sobre el medio ambiente. Se encontr6 resistencia When tested in replicated trials in three locations, a la traza 1 del CRN en dos especies sflvestres de selected resistant clones from the BC 4 and BC5 of the S. Solanum spp. La resistencia de S. bulbocastanum se bulbocastanum introgression populations had total introdujo por fusi6n de protoplastos y la de S. hougasii marketable yields and yields of >113-g (4 oz) tubers as por hibridaci6n sexual. Las siguientes pruebas de mejo- good or better than standard potato varieties tested in ramiento consistieron en retrocruzas repetidas y selec- replicated yield trials in three locations. Percenhage of ci6n. La herencia monog6nica dominante fue expresada tubers weighing more than 113 g in the highest yielding a lo largo de varias generaciones de retrocruza. Cuando clones was not significantly different from commercial se hicieron pruebas mdltiples en tres localidades, los standards. The resistance phenotype, typified by failure clones resistentes seleccionados de BC 4 y BC 5 de la poblaci6n de introgresi6n de S. bulbocastanum tuvo un Accepted for publication 3 June 2005. rendimiento total comerciable de tub6rculos por encima ADDITIONALIx~Y WORDS: breeding, germplasm, nematode resistance, , Solarium hougasii, Solanum tuberosum, de los 113g (4 onzas), tan bueno o mejor que las var- Meloidogyne chitwoodi iedades estdndar de papa evaluadas en pruebas de 2 AMERICAN JOURNAL OF POTATO RESEARCH Vol. 83

rendimiento con repeticiones en tres localidades. E1 (Brown et al. 1989, 1994, 1995, 2003). Janssen et al. (1996, porcentaje de tub~rculos con pesos mayores a los 113 1997) have also identified resistance to CRN and a newly gramos en el clon de mayor rendimiento, no mostr6 named root-knot nematode, M. fallax Karssen 1996 discovered diferencia significativa en comparaci6n con los estfin- in the Netherlands, in S. bulbocastanum, S. hougasii, and S. dares comerciales. La resistencia del fenotipo, tipificado fendleri Asa Gray. Not long after initiation of the screening por la falta de reproducci6n del nematodo en los sis- program, it was recognized that CRN consisted of two host temas de raices, rue suficientemente efectiva para pre- races (Santo and Pinkerton 1985) and a pathotype (Mojtahedi venir el dafio econ6mico en la exposici6n de campo. et al. 1994). Host race 1, which appears to be the most preva- Todos los clones resistentes CRN son de polen est~rfl. E1 lent race, falls to reproduce on alfalfa, whereas the race 2 col- germoplasma incluido en la lista est~ disponible para onizes it. A pathotype population that was isolated only once quien 1o solicite. from California was capable of overcoming the known resis- tant genes in S. bulbocastanum, S. hougasii, and S. fendleri INTRODUCTION (Mojtahedi et al. 1994). Successive passages of surviving M. chitwoodi (race 1) progeny reared on resistant S. fend/er/in Columbia root-knot nematode (Meloidogyne chitwoodi, the laboratory lead to an increased virulence ofM. chitwoodi Golden et al. 1980) (CRN) is a serious pest of potato, causing on resistant genotypes (Janssen et al. 1998). It is noteworthy galling of the tubers and blemishes in the tuber flesh. The that resistance to race 2 of CRN was not transmitted to and nenmtode penetrates the roots, establishes a feeding site, and thus far has not been introgressed into cultivated potato passes through several molts before producing an egg mass breeding lines (Brown et al. 1995). However, a successful that is extruded into the soil medium. Upon eclosion, J2 larvae introgression program was carried on for several backcross re-infest roots or enter tubers at 900-degree days accumulated cycles for resistance against CRN race 1. Pm assessment of post-planting (base temperature of 6 C) when lenticels are agronomic performance and resistance in germplasm derived developed on tubers (Pinkerton et al. 1991). The from S. bulbocastanum Dun. (P1275187) and S. hougasii Corr. mature, producing egg masses, which in turn cause visible (PI 161726) in several backcross generations is presented here. small brown dots in the tuber flesh. Accompanying this is the formation of galls on the tuber surface. Columbia root-knot MATERIALS AND METHODS nematode can reproduce up to five reproductive cycles on potato root system in the long, warm growing season of the Derivation of Genetic Materials Columbia Basin during which invasion of bullring tubers is The two sources of resistance were introgressed into the continuous. The most common rotation crops (e.g., wheat, cultivated gene pool through backcrossing. Solarium bulbo- corn, and ) are good hosts for CRN and ~ll not depress castanum accession 275187 (SB22) was hybridized with culti- the field population. Due to activity at lower temperatures, vated S. tuberosum by means of protoplast fusion (Austin et very small initial populations of CRN (one second-stage al. 1993). The somatic hybrid and selected BC1 were evaluated, juvenile/250 cm:~ soil at planting) are sufficient to damage a found to be resistant to CRN race 1, and constituted the source potato crop in the Pacific Northwest of the United States material to begin successive backcrosses (Brown et al. 1989, (PNW) (Santo et al. 1981). Thus the only defenses against CRN 1994, 1995, 2003). Resistance was attributed to a dominant are to use effective chemical fumigants, or to develop resistant monogene, RM¢l(blb), and mapped to the upper arm of chro- potato varieties through breeding. mosome 11 (Brown et al. 1996). Resistance to host races Currently no commercially available potato varieties derived from S. hougasii (PI 161726) was identified and the express economically viable resistance to CRN. In 1987, a inheritance was attributed to a single monogene mapped to a germplasm enhancement project was initiated by the USDA/ sinfilar location on chromosome 11 (Brown et al. 1991, 1999, ARS breeding program at Prosser, WA, with assistance from 2003). A summary of the pedigree developmen~t for materials USDA/ARS (Aberdeen, ID), University of Idaho, and Oregon tested is presented in Figure. 1. Two sources of resistance are State University scientists, to develop resistance to CRN. depicted. The initial hybrid with S. bulbocastanum was incor- Resistance genes were identified in wild Solanum species porated into the cultivated-type through subsequent back- 2006 BROWN et al.: M. CHITWOODI RESISTANT BREEDING LINES 3

crosses that were always performed with the resistant parent materials were challenged with race 1 in pot tests, and natural as the female parent owing to complete pollen sterility. race 1 infestation in field screening at IAREC. Seed tubers for Selected materials from the third, fourth, and fifth backcross the yield trials were produced from virus-indexed seed tubers generations were yield tested. The S. hougasii source of resis- grown at the Oregon State University, Central Oregon Experi- tance (PI 162726-5 = 95A2.5 in Figure 1) was initially intro- ment Station facility in Powell Butte, OR. duced via sexual hybridization. Only one BC.~ selection from the S. hougasii source was included in the yield trial, RF value, Yield Trials and field damage studies. Crosses were made at the Yield trials were conducted at three locations in 2003: the USDA/ARS Prosser facility; tuber families were grown in the USDA/ARS-Paterson Systems Research site at Paterson, Wash- greenhouse at the USDA/ARS, University of Idaho, Aberdeen ington, and Pear Acres and the Roza Unit of the WSU-IAREC. facility. Single hills and 12-hill plots were grown and used as a Details of trials and conditions are shown in Table 1. Entries basis for selection of horticultural traits. Selection in the sin- were prepared as cut seedpieces 43 to 85 g (1.5 to 3.0 oz) in gle-hill and 12-hill stages was based primarily on tuber shape size, planted in 10-seedpiece plots in a randomized complete (oblong), tuber skin (russeting preferred), and tuber size and block design with four replications. Plants were 23 cm (9 in.) total yield similar to standard checks in the field. Selection of apart in rows with spacing between rows of 86 cm (34 in.). The the nematode-resistance phenotype was performed initially in harvested tubers were graded first to remove cull tubers. The a field infested with CRN race 1 on the Washington State Uni- remainder, denoted "total marketable yield," was separated versity Irrigated Agriculture Research and Extension Center into <113 g and >113 gm (4 oz) in weight. Those in the >113 (WSU-IAREC) Roza Unit, Prosser, WA, on the basis of nema- grams portion were denoted "No. ls." Yield was expressed in tode damage scores in five-hill plots replicated six times. The metric tons per hectare (tons/h). Several nematode-suscepti- ble introgressants were included Solanum bulbocastanum Solanum hougasii in the trials (Table 2).

Screening for Host SB22~,,~+ R4 (4x-tbr) 95A2.5 (hz~_~x A77715-6 (4x-tbr) Suitability in Pot Tests Resistance to the nematode F 1 CBP233 x Summit Russet 96A2.1 x A89875-5 (4x-tbr) was determined by inoculation of J 5000 eggs of CRN race 1 (denoted 7 as WAMcl, which is maintained BC1 DG17 x Summit Russet 53.56 x A9289-2 at the WSU-IAREC, Prosser, WA). J 7 The potato plants were grown in BC2 398 x various 4xtbr POROOHG5-1 20-cm-diameter clay pots with a J soil composition of 84% sand: 10% BC3 PO94A x various4xtbr silt:6% clay previously fumigated with methyl bromide. Four repli- J cations of each genotype were BC 4 PA95B, PA98NM, PA98N x various 4x-tbr inoculated when the plants were J 15 cm tall, and maintained for 55 BC 5 PA99N days at 20 C in a greenhouse. Eggs were extracted from the FIGURE 1. root system using the method of Derivation of M. chitwoodi-resistant genetic materials. Solanum bulbocastanum clone SB22 was hybridized through protoplast fusion with a tetraploid cultivated parent. Subsequent back- Hussey and Barker (1973). The crosses were performed with the M. chitwoodi-resistant selections as pistillate parents in freedom of the inoculum from crosses due to pollen sterility in all progeny. Resistant Solanum hougasii clone 95A2.5 was hybridized sexually with tetraploid cultivated potato and subsequent backcrosses were per- CRN (M. chitwoodi) race 2 formed with selected resistant progeny as pistillate parents again due to pollen sterility. (CRN-2) and M. hapla, another 4 AMERICAN JOURNAL OF POTATO RESEARCH Vol. 83

TABLE 1--Locations conditions and management of yield trials of breeding materials resistant to M. chitwoodi.

Planting/Harvest Fertilizer Regime Herbicide Post Location dates kg/ha N/P/K Soil Type Irrigation Type Planting Fungicide Insecticide

Pear Acres April 14/ 112/224/336 Sand solid set Rimsulfuron chlorothalonil imidicloprid September 17 carbamate Roza April 20/ 112/224/336 Silt solid set Rimsulfuron chlorothalonil imidicloprid September 20 carbamate Paterson April 23/ 345/135/0 Quincy overhead Prowl dithane asaana October 5 sand center Rimsulfuron chlorothalonil pivot acrobat

TABLE 2--Total marketable yield (Total) and yield >113-g tuber size (4 oz--No, ls) in metric tons/ha ofM. chitwoodi- resistant and susceptible breeding lines and snsceptible standard commercial varieties at three locations in 2003.

BC generation -Roza- ---Paterson--- Pear Acres. Identity (source ~) Phenotypes2 Total signs No. ls sign Total sign No. ls sign Total sign No. ls sign

-Yield (tons/ha). POR00HG5-1 2 (hou) res 29.2 fgh 8.5 i 18.6 g 18.6 fgh 13..4 de 5.7 bc PO94A9-2 3 (blb) res 36.0 defg 20.2 fghi 66.9 ab 34.2 defg 34.4 ab 20.8 a PO94A9-7 3 (blb) susc 32.1 efgh 28.0 cdefgh 44.8 cdef 38.3 efgh 25.8 abcde 17.5 abc PO94A9-10 3 (blb) susc 38.3 cdefg 23.4 efghi 58.7 abcde 33.0 cdefg 27.5 abcde 11.7 abc PO94A10-3 3 (bib) res 44.8 bcde 38.9 bcde 43.7 cdef 34.6 bcde 15.5 cde 8.0 abc PO94A12-2 3 (blb) susc 55.6 b 43.6 bcd 42.2 def 16.4 h 24.4 abcde 13.4 abc PA95B1-53 4 (blb) res 52.0 bc 39.1 bcdef 38.7 ef 23.0 bc 32.9 ab 15.8 abc PA95B24 4 (blb) res 35.5 defg 25.9 defghi 50.4 bcde 36.1 defg 24.4 abcde 14.5 abc PA95B4-67 4 (blb) res 45.1 bcde 37.0 bcdef 55.6 bcde 40.5 bcde 32.5 ab 21.2 a PA98N4-2 4 (blb) res 20.1 h 13.8 hi 27.1 fg 15.9 h 12.3 e 4.6 c PA98N5-2 4 (blb) res 54.2 b 48.0 b 64.5 ab 54.5 b 28.0 abcde 16.7 abc PA98N13-3 4 (blb) res 42.8 bcdef 32.4 bcdefg 74.7 a 52.4 bcdef 23.4 acde 9.8 abc PA98NM38-1 4 (blb) res 47.4 bcd 38.5 ghi 52.6 bcde 35.3 bcd 26.2 abcde 16.7 abc PA98NM38-8 4 (blb) susc 29.6 fgh 18.8 ghi 48.1 bcde 28.9 fgh 25.5 abcde 17.5 abc PA98NM39-1 4 (blb) res 72.9 a 66.0 a 75.1 a 57.6 a 28.7 abc 13.3 abc PA99N82-4 5 (blb) res 54.2 b 46.3 bc 56.7 abcde 42.8 b 38.3 a 21.4 a PA99N88-2 5 (blb) res 36.2 defg 30.3 bcdefgh 51.5 bcde 19.5 defg 21.6 bcde 13.9 abc Russet Burbank - susc 26.0 gh 19.3 fghi 62.8 abc 44.1 gh 34.6 ab 20.3 a Norkotah Russet - susc 49.6 bcd 44.1 bcd 46.7 abcde 46.7 bcd 20.5 bcde 10.0 abc Dark Red Norland - susc 51.1 bc 41.1 bcde 61.9 abc 47.3 bc 29.9 abc 19.1 ab ~Source: bib = S. bulbocastanum; hou = S. hougasii SPhenotype resistance: res = resistant, susc = susceptible sYields not sharing the same letter are significantly different at the P < 0.05 level using the Duncan's Multiple Range Test.

root-knot nematode species common in the PNW, was verified 5000 eggs). The non-host, poor host, and good host status was by differential host tests: i.e., non-host responses on alfalfa and indicated by RF _< 0.1, 0.1 < RF < 1.0, and RF _> 1.0, respectively pepper indicate absence of both nematodes (Sasser et al. 1984; (Oostenbrink 1966). Mojtahedi et al. 1988). Hence, the inocuium was introduced to 'Rutger' tomato, a suitable host, 'California Wonder' pepper (a Field Screening for Tuber Damage non-host for CRN-1, but a suitable host for M. hapla) and Field tests were conducted at the Roza Unit of the WSU- 'Thor' alfaffa (a non-host for CRN-1, but a host for CRN-2). IAREC in a field where CRN has been maintained for 10 years Resistance was expressed as the reproductive factor (RF = by alternate potato and field corn rotations without any con- final egg count/initial inoculum, where the initial inoculum is trol measures. Before planting, nematode populations ranged 2006 BROWN et al.: M. CHITWOODI RESISTANT BREEDING LINES 5

from 50 to 200 CRN J2 per 250 cm 3 of soil in different samples. icant Difference at P < 0.05 probability level. Correlation coef- Clones were planted in a randomized complete block design ficients were calculated and the significance determined at with four blocks. Each plot consisted of 10 seedpieces planted P < 0.05 (Steel and Torrie 1980). on 15 May and harvested four months later on 15 September 2003. Ten tubers from each replicate were selected at random RESULTS AND DISCUSSION from the plots, peeled, and scored according to a tuber dam- age index varying between 0 and 6, where 0 = 0, 1= 1-3, 2 -- 4- Yield Trials 5, 3 = 6-9, 4 = 10-49, 5 = 50-99, and 6 = 100+ nematode infection Breeding lines performed over a broad range, including sites visible on a peeled tuber, respectively (Mojtahedi et al. very low yields and yields that were not significantly different 1993). from standard cultivars in some environments (Table 2). Breeding line POR00HG5-1 consistently presented the lowest Statistical Analysis yield of all the resistant clones at all locations. This was The yield and grade data were subjected to a one-way expected, as it is relatively less advanced introgressant at the analysis of variance, and means were separated using the Dun- BC~ generation from the S. hougasii resistance source. Two can's Multiple Range Test. Mean separation and orthogonal breeding lines derived from S. bulbocastanum were consis- comparisons between different backcross progenies of the tently among the top performers, PA98NM39-1 and PA99N82-4, mean total yields and percentage No. 1 tubers was performed from BC4 and BCs generations, respectively. Breeding line using the genotype × trial interaction term as the error mean PA98N13-3 outperformed all other materials at Paterson, but square from a two-way ANOVA. RF values and root mass from was not a top performer at the other two locations. The total the host suitability pot test were subjected to a one-way anal- yield and yield of No. 1 tubers for PA99N82-4, PA98N5-2, and ysis of variance, and means were separated using Least Signif- PA98NM39-1 was higher than one or more of the three stan- dard varieties at one or more locations. These results suggest that it is possible to select lines that are agronomically competi- BC3 BC4 BCs tive with standard commercial 70 i a - 90 varieties from as early as the BC4 : b ab- 70 generation. Solanum bulbocas- 50 ; b b -- 60 tanum is a tuber-bearing wild species that is genetically quite ] distinct from cultivated potato, 20 30 20 which is reflected in the difficulty 10 10 of hybridization with cultivated 0 ~ - " + - 0 ";,,IJill IIIiIII$ ° potato through sexual means (Debener et al. 1990). The emer- gence of introgressants with yield

Clones and Varieties performance equivalent to stan- dard commercial potatoes in the i I Total Yield • Percent No. 1"s BC4 is noteworthy. The average yield (over three trial sites) and FIGURE 2. percentage of No. 1 tubers is Total marketable yield (tons/ha) and percentage >113 g (No. 1) tubers for resistant and sus- ceptible breeding lines and standard commercial varieties. Mean marketable yields not sharing depicted in Figure 2. The 2-way the same letter are significantly different at the P < 0.05 level using Duncan's Multiple Range ANOVA performed on percentage Test. Genotype × environment mean square was used as the error mean square in mean separa- of No. 1 tubers failed to find sig- tion tests and orthogonal comparisons. Percentage of No. 1 tubers was not significant source of variation in ANOVA. nificance differences between 6 AMERICAN JOURNAL OF POTATO RESEARCH Vol. 83

genotypes. The highest performers, PA98N5-2, 80- T6 PA98N13-3, PA98NM39-1, and PA99N82-4 also 70 ~- had, therefore, percentages of No. 1 tubers (g 60 r = 0.61. P < 0.05 4 -- U. 50 that were not significantly different from Q 40 3 standard commercial varieties. 3 "O 30 2 Orthogonal contrasts (using the geno- Q. type x environment interaction source as the 0 10 1 O~ error term) failed to fred significant differ- 0 i n : o ences between the backcross generations or with the standard varieties in any pair-wise comparison. The data reported in this study represent clonal selections out of popula- tions, and do not represent the mean popula- Clones and VarieiUes tion performance. le-'.-= Reproductive Factor ~Tuber damage i

FIGURE 3. Screening for Host Suitability Reproductive Factor (RF = final egg count/initial inoculum, 5000) and tuber dam- in Pot Tests age index (0-6, where 0 = 0, 1 = 1-3, 2 = 4-5, 3 = 6-9, 4 = 10-49, 5 = 50-99, and 6 = 100+ nematode infection sites on a peeled tuber). RF values behaved as a discrete The RF values of resistant and suscepti- character, either near zero for resistant clones or well over 1 for susceptible clones. ble breeding lines and standard varieties are Tuber damage was at the maximum when RF > 1.0, while it was below the commer- shown in Table 3. In this test, the RF values cially acceptable threshold (tuber damage < 2) when RF < 0.1. for pepper, alfalfa, and tomato were 0, 0.12, and 22.9, respectively. The resistance pheno- of Meloidogyne chitwoodi type introgressed from S. hougasii and S. TABLE 3---Reproductive factor (RF = Pf/Pi) z on selected potato cultivars and breeding lines, 55 days after bulbocastanum is expressed as a failure of inoculating with 5,000 eggs. the J2 to establish a feeding site in the root (Mojtahedi et al. 1995). Generally, an RF > 1 is Potato cultivars and breeding lines Root weight (g)2 Reproductive factor (RF) 2 a high enough rate of reproduction to cause PO94A12-2 9.3 bcde 68.7 a unacceptable damage to tubers in a field set- PO94A9-7 12.8 ab 46.1 b Russet Burbank 12.1 abc 17.3 c ting. Rarely, however, is an'RF value interme- PA98NM38-8 13.8 a 15.4 c diate, i.e., it is either close to zero or well over Russet Norkotah 3.5 g 13.7 c PO94A9-10 9.2 bcde 11.2 c 1, in resistant and susceptible genotypes, Dark Red Norland 2.8 g 3.7 c respectively. PA95B2-4 8.6 cdef 0.07 d Weight of roots is shown to demonstrate PA98N13-3 11.0 abc 0.06 d PA98NM39-1 14.1 a 0.05 d that near-zero RF values (i.e., resistant host PO94A9-2 5.8 efg 0.02 d reaction) are not due to insufficient root PA98NM38-1 8.6 cdef < 0.01 d PA99N82-4 4.7 g < 0.01 d mass in the study. There is a trend that root PA95B4-67 4.8 gf 0.0 d mass is often higher when RF is elevated; PO94A10-3 4.0 g 0.0 d however, the correlation, r = 0.35, between PA98N5-2 6.5 defg 0.0 d POROOHG5-1 10.3 abcd 0.0 d root mass and RF is not significant in this PA95B1-53 5.3 fg 0.0 d test. The RF values are dichotomous in that ~Pf = final egg count; Pi = initial egg count = 5,000. they are clearly RF < 0.1 or RF > 1.0. The dis- ~Fhe mean for root weight and RF values based on six observations and those not sharing tribution of resistance is discretely bimodal the same letter differ significantly at P > 0.05 according to LSD test. The LSD values for root = 3.86, and for RF = 15.84. as would be expected from the original description of expression and inheritance (Brown et al. 1996). It is important to note 2006 BROWN et al.: M. CHITWOODI RESISTANT BREEDING LINES 7

TABLE 4--Ancestry of breeding lines emerging from introgression of resistance to Columbia root-knot nematode (M. chitwoodi) derived from S. hougasii (S. hou) and S. bulbocastanum. (S. blb).

- H Identity Pedigree POR00HG5-1 ((S. hou x A77715-6) x A89875-5) x A9289-2 PO94A9-2 (((S. blb + R4) 1 x Summit Russet)) x Summit Russet).51 x Ranger Russet PO94A9-7 (((S. blb + R4) x Summit Russet)) x Summit Russet).51 x Ranger Russet PO94A9-10 (((S. blb + R4) x Summit Russet)) x Summit Russet).51x Ranger Russet PO94A10-3 (((S. blb + R4) x Summit Russet)) x Summit Russet).51 x Lemhi Russet PO94A12-2 (((S. blb + R4) x Summit Russet)) x Summit Russet).75 x Lemhi Russet PA95B1-53 (((S. blb + R4) x Summit Russet)) x Summit Russet).8 x Lemhi Russet PA95B2-4 ((((S. blb + R4) x Summit Russet)) x Summit Russet).86 x Lemhi Russet)\ x A8259-5 PA95B4-67 ((((S. blb + R4) x Summit Russet)] x Summit Russet).86 x Lemhi Russet) x A86102-6 PA98N4-2 ((((S. blb + R4) x Summit Russet)) x Summit Russet).51 x Lemhi Russet) x A89875-5 PA98N5-2 ((((S. blb + R4) x Suramit Russet)) x Summit Russet).51 x Ranger Russet) x A89875-5 PA98N13-3 ((((S. blb + R4) x Summit Russet)) x Summit Russet).51 x Lemhi Russet) x A89875-5 PA98NM38-1 ((((S. blb + R4) x Summit Russet)) x Summit Russet)89 x Lemhi Russet) x Summit Russet. PA98NM38-8 ((((S. blb + R4) x Summit Russet)) x Summit Russet).89 x Lemhi Russet) x Summit Russet PA98NM39-1 ((((S. blb + R4) x Summit Russet)) x Stmu~it Russet).89 x Lemhi Russet) x A9289-2 PA99N82-4 (((((S. blb + R4) x Summit Russet)) x Summit Russet).58 x Ranger Russet) x A86102-6) x Oblong Russet pollen bulk PA99N88-2 (((([(S. blb + R4) x Summit Russet)) x Summit Russet).58 x Ranger Russet) x A86102-6) x Oblong Russet pollen bulk 1S. bib + R4 = Initial F1 was a somatic hybrid between SB22 and R4, a tetraploid S. tuberosum breeding line. S. hou =Solanum hougasii, S. btb = Solanum bulbocastanum. Ranger Russet, Lemhi Russet, and Summit Russet are oblong russet-skinned varieties named in Northwest Tri-State Variety Development Program. A77715-6, A8259-5, A86102-6, A89875-5, and A9289-2 are oblong shaped, russet-skinned breeding lines from the USDA/ARS, Aberdeen, ID, Potato Breeding project.

that the monogenic dominant nature of resistance is expressed and yield of No. 1 tubers at one or more locations. It seems undiminished into the BC 5 generation. that introgressants that perform as well as commercial stan- dards appear in the BC4. Some caution with this conclusion Field Screening for Tuber Damage must be exercised. O:¢er~ performance may not be compara- The relationship of RF value as evaluated in greenhouse ble especially when processing quality, attractiveness of rus- pot tests and tuber damage from field exposure to M. chit- seting, and other traits are considered. It is more reasonable to woodi is shown in Figure 3. All the clones with low RF values assume that introgression through backcrossing beyond the showed levels of tuber damage that would be commercially BC~ will be desirable and eventually lead to introgressants that acceptable. Breeding lines and standard varieties that were will be acceptable as new varieties. suitable hosts in the pot tests showed maximum levels of tuber The detailed pedigrees of the materials examined in this damage. The high level of tuber damage expressed by the study are shown in Table 4. In the case of both sources of resis- standards would translate In an industry venue into total crop tance, a single resistant wild species selection was used as the loss. initial parent. The ensuing introgression consisted of use of single initial hybrids and BC1 parents (Figure 1). Six BC2 resis- CONCLUSIONS tant selections, derived from the S. bulboeastanum source, formed the population that gave rise to ft~her backcross gen- Resistance to M. chitwoodi race 1 (CRN-1), derived from erations. The pool of recurrent cultivated tetraploid parents S. bulbocastanum and S. hougasii has been successfully consisted of a total of eight oblong-shaped, russet-skinned incorporated into the cultivated potato gene pool. The S. bul- varieties and selections, and in the case of the BC5 population, bocastanum source of resistance has been introgressed using a composite pollen bulk consisting of a collection of such a backcrossing technique and has produced clones that are breeding lines and varieties. equal in yield performance to standard commercial varieties in The resistance phenotype, expressed as failure of repro- BC4 and BCs. Selected clones PA98NM39-1 and PA99N82-4, for duction of the nematode on the root system, originally instance exceed one or more standard varieties in total yield described as monogenic dominant, appears to be fully 8 AMERICAN JOURNAL OF POTATO RESEARCH Vol. 83

expressed in the all backcross generations. This undiminished Brown CR, H Mojtahedi, and GS Santo. 2003. Characteristics of resis- tance to Columbia root-knot nematode resistance introgressed expression augurs well for continued use of this genetic from several Mexican and American wild potato species. Acta source for the goal of mitigating M. chitwoodi where it occurs. Hort 619:117-125. At a cost of $700 per ha for fumigation (187 L Telone II per ha Brown CR, C-P Yang, H Mojtahedi GS Santo, and R Masuelli. 1996. RFLP analysis of resistance to Columbia root-knot nematode alone, or 140 L per ha of metham sodium and 132 L per ha of derived from Solanum bulbocastanum in a BC2 population. Telone II) the economic burden of root-knot control exceeds Theor Appl Gen 92:572-576. 15% of the cost of production in the PNW in 2004. A reduction Debener T, F Salamini, and C Gebhardt. 1990. Phylogeny of wild and in, or omission of, fumigation under some circumstances cultivated Solanum species based on nuclear restriction frag- ment length polymorphisms (RFLPs). Theor Appl Genet 79:360- would improve the cost profile of potato production and 368. enhance profitability. In addition, presence of M. chitwoodi is Hussey RS, and KR Barker. 1973. A comparison of methods of collect- a substantial production risk under any circumstances due to ing inocula of Mdoidogyne spp. including a new technique. Plant Dis Rep 57:1025-1028. its high reproductive rate at relatively low soil temperatures. Janssen GJW, OE Scholten, A van Norel, and CJ Hoogendoorn. 1998. Host resistance combined with green manure control of the Selection of x4rulence in Meloidogyne chitwoodi to resistance in nematode or use of less costly palliative nematicidal treat- the wild potato Solanumfendleri. Eur J of Plant Pathol 104:645- 651. ments (e.g., oxamyl) may be an attractive alternative to full- Janssen GJW, A van Norel, R Janssen, and J Hoogendoorn. 1997. Dom- scale soil fumigation. This type of host resistance offers the inant and additive resistance to the root-knot nematodes grower latitude for different means of control and production Meloidogyne chitwoodi and M. fallax in Central American Solanum species. Theor Appl Genet 94:692-700 cost containment. Janssen GJW, A van Norel, B Verkerk-Bakker, and R Janssen. 1996. This source of M. chitwoodi resistance is available as Resistance to Meloidogyne chitwoodi, M. faUax, and M. hapla field-grown tubers for use as parents in breeding programs. All in wild tuber-bearing Solanum spp. Euphytica 92:287-294. Mojtahedi H, CR Brown, and GS Santo. 1995. Characterization of resis- clones are male-sterile and are relatively difficult to induce to tance in a somatic hybrid of Solanum bulbocastanum and S. flower for unknown reasons. Clones will be sent upon request tuberosum to Meloidogyne chitwoodi. J Nematology 27:86-93. to cooperators. Mojtahedi H., GS Santo, CR Brown, H. Ferris, and V. Williamson. 1994. A new host race of Meloidogyne chitwoodi from California. Plant Dis 78:1010. LITERATURE CITED Mojtahedi H, GS Santo, and JH Wilson. 1988. Host tests to differentiate Meloidogyne chitwoodi races 1 and 2 and M. hap/a. J Nematol- Austin S, JD Pohlman, CR Brown, H Mojtahedi, GS Santo, D Douches, ogy 20:468-473. and JP Helgeson. 1993. Interspecific somatic hybridization Mojtahedi H, GS Santo, JH V~rLlson,andAN Hang. 1993. Managing M. between Solanum tuberosum L. and S. bulbocastanum DUN. as chitwoodi on potato with rapeseed as green manure. Plant Dis a means of transferring nematode resistance. Am Potato J 77:42-46. 70:485-495. Oostenbrink M. 1966. Major characteristics of the relation between Brown CR, H Mojtahedi, and GS Santo. 1989. Comparison of reproduc- nematodes and plants. Mded Lanbouwhogeschool, Wageningen tive efficiency of Meloidogyne chitwoodi on Solanum bulbocas- 66:3-46. tanum in soil and in vitro tests. Plant Dis 73:957-959. Pinkerton JN, GS Santo, and H Mojtahedi. 1991. Population dynamics Brown CR, H Mojtahedi, and GS Santo. 1991. Resistance to Columbia of ofMeloidogyne chitwoodi on Russet Burbank potato in rela- mot-knot nematode in Solanum ssp. and in hybrids of S. tion to degree day accumulation. J Nematology 23:283-290. hougasii with tetraploid cultivated potato. Am Potato J 68:445- Santo G S, JH O'Bannon, AP Nycezpir, and RP Ponti. 1981. Ecology and 452. control of root-knot nematodes on potato. Proceedings of the Brown CR, H Mojtahedi, GS Santo, and S Austin-Phillips. 1994. Enhanc- 20th Annual Washington State Potato Commission, Moses Lake, ing resistance to root-knot nematodes derived from wild WA. pp 135-139. Solanum species in potato germplasm. In: GW Zehnder, ML Santo GS, and JN Pinkerton. 1985. A second race of Meloidogyne chit- Powelson, RK Jansson, and KV Raman (eds), Advances in woodi discovered in Washington State. Plant Dis 69:361. Potato Pest Biology and Management. Am. Phytopathology Sasser JN, CC Carter, and KM Hartman. 1984. Standardization of host Society, Minneapolis, MN. pp 426438. suitability studies and reporting of resistance to root-knot nema- Brown CR, H Mojtahedi, and GS Santo. 1995. Introgression of resis- todes. North Carolina State University Graphics, Raleigh, NC. tance to Columbia and Northern root-knot nematodes from Steel RGD, and JH Torrie. 1980. Principles and procedures of statistics: Solanum bulbocastanum into cultivated potato. Euphytica A biometrical approach. McGraw-Hill, New York. 83:71-78. Brown CR, H Mojtahedi, and GS Santo. 1999. Genetic analysis of resis- tance to Meloidogyne chitwoodi introgressed from Solanum hougasii in cultivated potato. J Nematology 31:264-271.