Characterization of Callosobruchus chinensis (L.) resistance in Vigna umbellata (Thunb.) Ohwi & Ohashi

Abstract

Resistance to azuki bean weevil, Callosobruchus chinensis, was studied in a series of field and laboratory experiments in two accessions of rice bean (Vigna umbellata (Thunb.) Ohwi & Ohashi), one accession of black gram (V. mungo (L.) Hepper), and one accession of mungbean, (V. radiata (L.) Wilczek). Weevil damage to immature pods of the rice bean accessions, ‘Menaga’ and ‘Miyazaki’, was significantly less than to the susceptible mungbean, VC1973A. In mature pods, the pest damage to the pod wall of Menaga was significantly higher than to VC1973A, whereas the damage to Miyazaki was similar to VC1973A. Seeds within the pods of both rice bean accessions were resistant no matter when the pods were harvested. When the insects were exposed directly on dry seeds, both rice bean accessions and a black gram accession VM2164 were resistant to them. In artificial seeds made by mixing flour of the individual resistant Vigna accessions with VC1973A and subsequently exposed to bruchid oviposition, the higher the quantity of resistant Vigna flour the lower the number of bruchids that emerged from such seeds. No bruchids emerged from artificial seeds containing crude starch fraction from the three resistant Vigna accessions when such seeds were exposed to bruchid infestation, whereas many insects emerged from the seeds containing starch of VC1973A or flour of VC1973A alone. In artificial seeds made by mixing crude protein fractions of the three resistant Vigna accessions with flour of VC1973A, as the concentration of protein increased the number of C. chinensis adults that emerged decreased. Fractionation of crude proteins into acetone-precipitable proteins and peptide and amino acid portions resulted in the loss of antibiosis effect. Artificial seeds made from purified starch-polysaccharides fraction, however, exhibited antibiosis effects if prepared from the rice bean seed of Menaga and Miyazaki but not if made from the black gram seed, VM2164.

Introduction

Mungbean, Vigna radiata (L.) Wilczek, is an important legume produced mainly in South and Southeast Asia. This crop is a major source of dietary protein for poor people in the region and an important nitrogen-fixing legume in tropical cropping systems. Poor genetic background and damage by insect pests and diseases limit the seed yield of this crop. Among several insect pests that attack this crop, two beetle species, azuki bean weevil, Callosobruchus chinensis (L.), and cowpea weevil, C. maculatus (F.), are the most destructive. The initial infestation takes place in the field, where the adult bruchid lays eggs on green pods and the larvae bore through the pod cover and feed concealed within developing seeds (Southgate, 1979). When such seeds are harvested and stored, the insect continues feeding, eventually emerges as an adult, and causes secondary infestation which, at times, results in total destruction within 3–4 months (Banto and Sanchez, 1972). Since mungbean is generally grown by small land-holders, poor storage facilities are prevalent in such households, and the seeds are frequently used for family consumption, the application of fumigants or insecticides is not suitable (Talekar and Lin, 1981). Efforts have been made to identify sources of resistance and breed a bruchid-resistant mungbean. Among 525 accessions screened for C. chinensis resistance at the Asian Vegetable Research and Development Center (AVRDC), two black gram, V. mungo (L.) Hepper, accessions, VM2011 and VM2164 were resistant to C. chinensis (Talekar and Lin, 1981). The VM2011 exhibited less damage to pods when the insect infestation occurred in the field, while the VM2164 had highly resistant seeds in laboratory tests. Transfer of insect resistance genes, however, from VM2164 into mungbean cultivars was not successful (Fernandez and Talekar, 1990). Two mungbean accessions, V2709 and V2802, were moderately resistant to the bruchid in seeds (Talekar and Lin, 1992). One accession of mungbean, TC1966, V. radiata var. sublobata, was resistant to C. chinensis (Fujii and Miyazaki, 1987). Crosses between TC1966 and other mungbeans were made successfully (Tomooka et al., 1992), but since TC1966 is a wild legume and not consumed by humans anywhere the possibility of some undesirable traits present in the seeds of the progeny of some of the crosses could not be ruled out (Watanasit and Pichitporn, 1996). A feeding test was conducted by Miura et al. (1996) using BC₁₄F₄ seed of the cultivar ‘Osaka Ryokutou’ with TC1966 as the donor of the gene conferring the resistance. They found that the glutamic-oxalacetic transaminase activity was higher and the total cholesterol concentration was lower in female mice fed with the resistant line compared with the control mice. Sugawara et al. (1996) isolated the chemicals responsible for azuki bean weevil resistance in TC1996 and named the mixture vignatic acid. Its major component is cyclopeptide alkaloids. This makes the use of TC1966 questionable for breeding mungbean, which is widely consumed as fresh sprout, resistant to seed-feeding pests such as C. chinensis.

Recently, Tomooka et al. (2000) found two cultivated varieties of rice bean, V. umbellata (Thunb.) Ohwi & Ohashi, a food legume, to be completely resistant to C. chinensis and C. maculatus. Both accessions, ‘Menaga’ and ‘Miyazaki’, are land races of cultivated rice bean from Japan. Kashiwaba et al. (2003) prepared artificial seeds from various proportions of rice bean (resistant) and azuki bean (susceptible) flour and fed these to C. chinensis, C. maculatus and Graham bean weevil (C. analis (F.)). They reported that the number of bruchid adults emerging decreased, and the larval development period (days) was extended, when artificial seed with an increasing proportion of rice bean flour were used. They concluded that a chemical component(s) contained in the cotyledon of rice bean has an inhibitory effect on growth of these bruchid species. They did not attempt to fractionate and characterize the compounds responsible for the resistance. In this study, we partially characterize the mechanism of resistance of these varieties as well as that of VM2164 to C. chinensis.