Resistance in sweetpotato to sweetpotato weevil

Abstract

Sweetpotato weevil, Cylas formicarius formicarius F is the most destructive pest of sweetpotato, Ipomoea batatas in tropical and subtropical regions. The larvae and adults feed on sweetpotato roots and crowns. For the past 12 years we have been screening sweetpotato germplasm for resistance to this pest in order to breed an agronomic cultivar with weevil resistance. Resistance screening is conducted at AVRDC and Penghu island in autumn and summer, respectively. Germplasm is planted between heavily infested source rows maintained in a weevil nursery. Roots are harvested, sliced into thin pieces, and the number of insects (larvae + pupae + adults) per unit weight, as well as the weight of damaged and healthy root slices, are recorded. The resistance rating is based mainly on the number of insects found in the root. Considerable differences in resistance rating are observed from location to location and season to season. Even at one location, tremendous differences are observed in weevil infestation of a particular entry among the replicates. Although over 1000 sweetpotato accessions have been screened, we have not found any that is consistently less damaged over several seasons at either location. Our recent screening of a population of/, trifida x /. batatas crosses show certain hybrids with high yield and low weevil infestation. These hybrids need to be evaluated further to confirm their resistance.Resume-Le charancon Cylas formicarius formicarius F. est le ravageur le plus destructif de la patate douce dans les regions tropicales et subtropicales. Les larves et les adultes attaquent les racines et les couronnes. Nous nous sommes atteles, durant les 12 demieres annees, a trier le germplasme de patate douce pour la resistance au ravageur dans le but de developper des varietes resistantes et interessantes agronomiquement. Le triage pour la resistance etait conduit a PAVRDC en automne et dans Tile de Penghu en ete. Le germplasme est plante entre des rangees de patate douce tres infestees maintenues dans une pepiniers a charancon. Les racines sont deterrees, decoupees en tranches fines, et le nombre d'insectes (larves + pupes + adultes) par unite de poids est determine, ainsi que le poids des tranches attaquees et saines. La reaction de resistance est determinee principalement en fonction du nombre d'insectes trouves a l'interieur des racines. Des differences considerables de resistance sont observees d'un endroit a l'autre et d'une saison a l'autre. Meme dans un meme endroit, il existe souvent d-enormes differences dans le niveau d'infestation entre differentes repetitions de la meme entree. Quoique nous ayons jusqu'a present teste plus de 1000 entrees de patate douce, nous n'en avons trouve aucune qui soit systematiquement moins attaquee dans l'un ou l'autre des deux sites experimentaux. Notre travail recent devaluation d'une population issue de croisements /. trifida x I. batatas revele certains hybrides a haut rendement et a bas niveau d'infestation par le charancon. Ces hybrides meritent d'etre evalues plus en p...

A NewPest of Cotton: Cylds puncticollis BOH. (Coleoptera: Brenthidae) in Adamawa State, Nigeria

“…It is worth noting that possible source of hibernation, dissemination (movement and dispersal) of C. puncticollis from along distance could be through the Ipomoea weed from farm to farm, dispersal by wind or flooded water from potato farms, or through debris, from animals such as cattle, sheep and goat by the nomadic Fulani group especially in the northern parts of the country. This further corroborates the findings of Sutherland (1986), Talekar(1982) and(1987), Chalfantet al (1990) and Smit, (1997) adults per 5 plants were found on cotton during the rainy season and 5 adults/5 plants on ratoon cotton plants during the off-season. The weevils have been on cotton for over 9 years, and the increase in their number poses a threat to the cotton industry.…”

Crops that feed the world 5. Sweetpotato. Sweetpotatoes for income and food security

“…Efforts to develop integrated weevil management was successful in the Caribbean (Maza et al 2000), but is more challenging in Africa (Smit and Odongo 1997). Studies on sweetpotato weevil resistance indicated variable resistance in the field (Mullen et al 1985;Talekar 1987b) and laboratory (Story et al 1999a, b, c). However, little success has attended efforts to obtain elite breeding lines owing to inconsistency of performance (Talekar 1987a, b) and a lack of understanding of the resistance mechanisms (Mao et al 2001).…”

Pre-and Postharvest Changes in Sweetpotato Root Surface Chemicals Modulating Insect Resistance

“…Based on variation in the level of resistance within a cultivar relative to growing season and location, and the absence of a reliable allelochemical source of resistance, Talekar (1987aTalekar ( , 1987b suggested an allomone (deterrant) is absent because the insect seldom endangers the growth, reproduction, or survival of sweetpotatoes in the field. However, he postulated the possible existence of kairomones (stimulants) evolving through the convolution of the sweetpotato and the weevil because of the weevil's monophagous habit.…”