Variation among Accessions of Pisum fulvum for Resistance to Pea Weevil

tents reduces yield, while feeding scars and holes on testa reduce the quality and marketability of pea seed. The pea weevil, Bruchus pisorum (L.) (Coleoptera: Bruchidae), is In addition, weevil-damaged seed has lower germination one of the most intractable pest problems of cultivated pea, Pisum sativum L. The availability of resistant cultivars would give growers rates and is prone to structural weakening during harmore pest management options. Searches for plant resistance to pea vest (Brindley and Hinman, 1937; Baker, 1990). High weevil were expanded to the Pisum secondary gene pool (P. fulvum levels of weevil-infested seed have been reported in Sm.) because seed resistance had not been located in P. sativum and Australia (10.6 to 71.5%; Horne and Bailey, 1991), subspecies. The objectives of this study were to determine the extent Spain (12.2 to 25.7%; Marzo et al., 1997), and the USA of pod and seed resistance to pea weevil in P. fulvum, and to use the (up to 64%; Pesho et al., 1977; Bragg and Burns, 2000). life table format to characterize weevil stage-specific mortality and Worldwide, pea producers rely mainly on contact insurvivorship on different P. fulvum accessions. Mortality of first instar secticides to control adults in pea fields before females larvae on pods, mortality of all weevil stages within seed, adult emerlay eggs on pods (Horne and Bailey, 1991; O’Keeffe et gence from seed, and seed damage levels were quantified. In two al., 1992; Clement et al., 2000). However, timing chemigreenhouse trials, more larvae died (14 to 50% averages) on pods of P. fulvum accessions than on pods of ‘Alaska 81’ (6% average), and cal applications to coincide with female egg laying is mortality of first instar larvae entering seed of P. fulvum accessions difficult. More than one application may be required if averaged 83.7%. Seed damage ratings (1 feeding scar on seed testa, weevil invasions continue for 2 to 4 wk in a pea field 0-1% cotyledon tissue eaten, dead first instar larva; 5 extensive (Michael et al., 1990). The development and use of cultidamage, live adult) averaged 3.0 for 26 P. fulvum accessions, comvars with pod and seed resistance to B. pisorum would pared with mean ratings of 4.9 for Alaska 81. Using weevil mortality reduce control costs and provide an environmentally and survivorship values in life tables and adult emergence rates, entries safer option than contact insecticides for adult weevil were classified as susceptible (two controls and five accessions), modcontrol. erately resistant (14 accessions), and resistant (12 accessions). AntibioSome P. sativum lines with the Np gene respond to sis resistance was based on the death of weevil larvae on pods and the presence of pea weevil eggs on pods by forming seed testa and cotyledon tissues. The results identify sources of natural weevil resistance in the Pisum genome (26 moderately resistant and callus (neoplastic pod trait) that reduces larval entry resistant accessions of P. fulvum ) to endow pea cultivars with pod into the pod (Hardie, 1990; Berdnikov et al., 1992; Doss and/or seed resistance to B. pisorum. et al., 2000). In a field trial, this pod-based resistance was responsible for a lower rate of weevil infested seed (62.2%) in Np plants compared with that in a susceptible I pests are a major problem in the worldwide line (85.4%) (Doss et al., 2000). In addition, plant bioproduction of field pea, with the pea weevil being technology has the potential to protect peas from B. one of the most destructive pests of this grain legume pisorum damage, as evidenced by the development of (Clement et al., 2000). Adult weevils leave winter hibertransgenic P. sativum for resistance to Callosobruchus nation sites and invade pea fields in the spring to feed weevils (Shade et al., 1994) and B. pisorum (Schroeder on pea pollen and other parts of the pea flower (Brinet al., 1995; Morton et al., 2000). This resistance is based dley, 1933; Clement, 1992). Females must feed on pollen on the insecticidal activity of the -amylase inhibitor in before they can lay eggs and pea pollen is most effective seeds of bean, Phaseolus vulgaris L., which blocks the in promoting oogenesis (Pesho and Van Houten, 1982). action of the starch-digesting enzyme -amylase and Eggs are laid on the surface of immature pea pods and thus prevents weevil larvae from digesting starches in hatch to produce first instar (neonate) larvae that chew seed. More research is required before weevil-resistant through the pod wall from the underside of eggs. Once transgenic peas can be released to growers (Morton et a neonate larva bores through a pod wall and reaches al., 2000). Moreover, any concerns about the biosafety the inside of a pod, it soon locates and starts to feed on of genetically engineered peas, as voiced by consumer a developing seed (Brindley, 1934). There are four larval and environmental groups for transgenic crops (Stewart instars, with second, third, and fourth instars consuming et al., 2000), must be addressed by researchers and proa large part of the cotyledon contents of seed (Brindley, ducer groups before transgenic peas are commercially 1933; Smith, 1990). Before pupating, a larva chews a deployed for weevil protection. circular window in the seed testa that is pushed open An alternative to genetically engineered crops is the by the emerging adult. Larval consumption of seed condevelopment and deployment of crop cultivars with natural insect resistance from primary and secondary gene S.L. Clement and L.R. Elberson, USDA–ARS Plant Germplasm pools. In the absence of seed resistance to pea weevil Introduction and Testing Research Unit, Washington State Univ., in the Pisum primary gene pool (P. sativum and all subPullman, WA 99164-6402; D.C. Hardie, Entomology Section, Dep. species) (Hardie, 1990; Clement et al., 1994), searches of Agriculture Western Australia, 3 Baron-Hay Court, South Perth, for resistance were expanded to the secondary gene WA, 6151 Australia. Received 3 Aug. 2001. *Corresponding author ([email protected]). Abbreviations: GRIN, Genetic Resources Information Network. Published in Crop Sci. 42:2167–2173 (2002).