HORTSCIENCE 31(7):1219–1222. 1996. agement in New York (Eckenrode and Nyrop, 1995; Eckenrode and Webb, 1994). There is an urgent need to expand the range Variation in Allium spp. Damage by of control options and to integrate them with still-effective chemicals. Rotation to Onion Maggot non-allium crops for 1 year reduces OM popu- lations temporarily, but because adult OM James R. McFerson flies can travel several kilometers (Martinson U.S. Department of Agriculture, Agricultural Research Station, Plant Genetic et al., 1989), relatively large areas must be rotated for maximum effectiveness. Removal Resources Unit, Cornell University, Geneva, NY 14456-0462 of all bulbs from the field at harvest will Thomas W. Walters minimize food for overwintering OM popula- tions but does not prevent adult immigration Department of Fruit and Vegetable Science, Cornell University, Ithaca, from nearby sites the following spring. Addi- NY 14853-5904 tional control options might also help to avoid or delay development of resistance to insecti- Charles J. Eckenrode cides in OM populations. Department of Entomology, Cornell University, Geneva, NY 14456-0462 Plant resistance is an attractive but unexploited OM control strategy. Evaluations Additional index words. Delia antiqua, leek, Allium ampeloprasum, plant resistance to of Allium germplasm for OM resistance have insects been reported from various regions (Ellis and Abstract. Nearly 350 germplasm accessions representing 25 Allium species were evaluated Eckenrode, 1979; Matthewman et al., 1953; for damage by onion maggot (OM) [Delia antiqua (Meigen)] in field experiments in 1989. McDonald et al., 1993a, 1993b; Perron et al., In 1990, 188 additional accessions and breeding lines were evaluated, and 36 entries from 1958; Scott and Franklin, 1972). Although the 1989 evaluation were re-evaluated. In both years, there were no significant differences some differences among A. cepa lines were in OM damage to seedlings among accessions within the species tested. However, differ- reported in these evaluations, A. cepa germ- ences among species were highly significant. Allium cepa L. (bulb onion) seedlings had plasm showed little evidence of variation for consistently high OM damage. Species with significantly less seedling damage than A. cepa resistance to OM in New York fields (Ellis et included: A. altaicum Pall., A. angulosum L., A. galanthum Kar. & Kir., A. pskemense B. al., 1979; Munger and Plage, 1974, 1975). Fedtsch., A. scorodoprasum L., A. ampeloprasum L. (leek), A. fistulosum L. (bunching However, bunching onion seedlings sustained onion), A. schoenoprasum L. (chive), and A. tuberosum Rottl. ex Spr. (garlic chive). Some low OM damage in New York (Ellis et al., species sustaining minimal damage as seedlings were nonetheless heavily damaged as 1979). mature plants by a later generation of OM. Allium cepa cultivars that were well-adapted The objectives of this research were to to local conditions were heavily damaged as seedlings, but their bulbs were less damaged evaluate Allium spp. injury levels from first- than those of poorly adapted A. cepa germplasm. Allium ampeloprasum seedlings and and third-generation (brood) OM in field plant- mature plants sustained low injury throughout both growing seasons. ings and to identify potential sources of resis- tance for onion breeding. We report here our survey of all Allium germplasm available in The onion maggot (OM) is a major pest of (A. fistulosum), garlic (A. sativum L.), leek (A. 1989–90 in the USDA–ARS collections, as onion and related crops in many temperate ampeloprasum), and chive (A. schoenoprasum) well as additional lines from the USDA–ARS regions of the world. Severe infestations can (Ellis and Eckenrode, 1979). and Univ. of Wisconsin onion breeding pro- destroy more than 50% of the seedlings in Each spring, gravid OM females lay eggs grams. Over 2 years, 535 Allium spp. acces- commercial fields when protection fails on or just under the soil surface near host sions and breeding lines were evaluated, in- (Eckenrode and Nyrop, 1995). In North seedlings. Larvae feed on the seedling bases cluding 380 A. cepa accessions and breeding America, the OM is particularly severe in New and roots, usually killing them. The first lines and 155 accessions of 24 other Allium York, Michigan, and Ontario, Canada, where above-ground symptom of OM injury on young species. conditions favor it and allium crops are grown plants is wilting. The whole plant subsequently in the same field or nearby fields year after collapses and dies. The most visible damage is Materials and Methods year. The host range of OM is limited to caused by first-generation larvae, which can alliums and it has been reported on various destroy many young seedlings. Injury due to 1989 evaluation. A total of 365 entries economically important crops, including bulb second- and third-generation larvae, although representing 25 Allium species were planted onion and shallot (A. cepa), bunching onion less visible above ground, is significant be- with a hand seeder in randomized complete cause damaged bulbs must be sorted out and blocks 20 to 21 Apr. in a commercial field near discarded after harvest (Ellis and Eckenrode, Potter, N.Y. (lat. 42°40’N, long. 77°0’W). Received for publication 29 Nov. 1995. Accepted 1979). Plots were 4.6 m long with two replications. for publication 9 July 1996. Mention of a vendor or Where onions are grown year after year in Seeding rates were adjusted to ≈30 viable proprietary product does not constitute a guarantee cool-season climates favoring OM develop- seeds/m. The center 1.5 m of each single-row or warranty of the product by the U.S. Dept. of Agriculture and does not imply its approval to the ment, an in-furrow insecticide application is plot containing the most even stand was marked exclusion of other products that also may be suit- essential. However, the insect has developed for subsequent stand and OM damage counts. able. This research was supported in part by funding resistance to insecticides, due in part to its Eighteen commercial cultivars of A. cepa were from the USDA–ARS, contract 58-43YK-9-0013, narrow host range, which maximizes selection used as treated controls and received an and by the New York State Onion Research and pressure for resistance to the few chemicals in-furrow insecticide application of Development Program. Onion breeding lines were used for OM management (Ellis and chlorpyrifos (Lorsban 15G; Dow Elanco, In- generously supplied by W.H. Gabelman, Univ. of Eckenrode, 1979). Thus, many compounds dianapolis, Ind.) at 1.4 g/4.6 m row. To mini- Wisconsin–Madison and M.J. Havey, USDA–ARS. recommended in the past have become inef- mize onion smut (Urocystis cepulae Frost), all Technical support was provided by the USDA–ARS fective (Harris and Svec, 1976; Harris et al., plots were treated with zinc ion and manga- Plant Genetic Resources Unit staff and by P.S. Robbins. The cost of publishing this paper was 1982). There is increasing evidence that the nese ethylene bisdithiocarbamate (mancozeb) defrayed in part by the payment of page charges. OM has developed low but significant levels (Dithane DF; Rohm and Haas, Philadelphia) Under postal regulations, this paper therefore must of resistance to O,O-diethyl-O-(3,5,6-trichloro- at the recommended rate of 0.6 g/4.6 m row. be hereby marked advertisement solely to indicate 2-pyridinyl) phosphorothioate (chloropyrifos), Cultural and other pest management practices this fact. the current insecticide of choice for OM man- followed commercial recommendations. HORTSCIENCE, VOL. 31(7), DECEMBER 1996 1219 BREEDING, CULTIVARS, ROOTSTOCKS, & GERMPLASM RESOURCES To determine initial plant populations be- had species and blocks as main effects and true extent and utility of their response to OM. fore serious OM injury occurred in the plots, transformed seedling loss and mature plant Significantly lower first-brood injury was mea- emerged seedlings were counted 2 to 5 June. damage as dependent variables. Species means sured in A. altaicum, A. angulosum, A. Plots infested with first-brood OM were as- were compared to the mean of the untreated A. galanthum, A. pskemense, A. scorodoprasum, sessed twice weekly, 2 June to 10 July. Plants cepa accessions using Dunnett’s comparison and in the cultivated species A. ampeloprasum, were considered damaged if they showed ob- with a control. Transformations and analyses A. fistulosum, A. schoenoprasum, and A. vious wilting. Damaged plants were removed were performed with JMP Version 3 Statisti- tuberosum. Other species (A. cernuum Roth, and examined for larvae to confirm OM at- cal Software for the Macintosh (SAS Institute, A. fuscoviolaceum Fomin, A. glaciale Vved., tack. In both years, infestations by first-brood Cary, N.C.). A. prostratum Trevir, and A. OM were uniformly heavy, allowing clear pseudoampeloprasum Miscz. ex Grossh.) sus- distinction between damaged and undamaged Results and Discussion tained even less first-brood injury, but the few plants during the ≈20,000 individual observa- entries within these species precluded statisti- tions throughout the season. Second-brood 1989 evaluations. Differences among spe- cal significance. Numerous accessions of A. OM injury was not evaluated. However, third- cies for both first-brood OM seedling loss and ampeloprasum (52), A. cepa (192), A. brood assessments were made 4 Oct. by re- third-brood OM mature plant damage (Table fistulosum (35), and A. schoenoprasum (17) moving up to 10 remaining plants per plot and 1) were highly significant (ANOVA, P ≤ were evaluated, but there was no significant examining their bases for naturally occurring 0.001). Block effects were also highly signifi- effect of accession within any of these species, larvae and feeding damage. Percent plants cant and the coefficient of variation was 37%. except for seedling loss within A. damaged was calculated from these assess- The physical extent of the experiment and an ampeloprasum (ANOVA, P ≤ 0.05).