Techniques for evaluating biological control of cassava mealybug (Phenacoccusmanihoti Matile-Ferrero), mango mealybug (Rastrococcus invadens Williams), and spiralling whitefly (Aleurodicus dispersus Russell) are described. In each case, two exotic hymenopterous parasitoids were introduced. Alone or together, they brought the pests under control, while indigenous and exotic coccinelIids played a minor role. Control was achieved in large areas where the exotic parasitoid(s) had been present for more ...

Flavonoid chemical markers together with other biochemical markers and/or morphological data can provide useful characters for defining species in Vigna genus. In this paper flavonoid HPLC fingerprints have been utilized to assess taxonomic relationships amongst species and accessions of Vigna.Within the taxa analysed there is evidence of both infra- and interspecific chemical variations. In some species chromatographic data support evidence for the existence of different flavonoid chemotypes, ...

The effects of moisture content and temperature on the medium-term (3-4 months) storage of conidia of Metarhizium flavoviride were investigated. Conidia harvested after 24 days of culturing on rice showed greater tolerance to long storage than conidia from 12-day cultures. The moistut-e content of the conidia was of greatest importance; at harvest from the culture. conidial moisture contents could be > 40%, while the optimal moisture content for storage was found to be 4-5%. Dried conidia stored ...

(ACMV) were assessed in shoots regenerated from single-node cuttings of three cassava genotypes differing in resistance to ACMV. Plants of the moderately resistant TMS 4(2)1425 and susceptible TMS 60506 did not recover from the disease as rapidly as those of the resistant TMS 30001, Recovery was manifested earlier on leaves of shoots from nodes collected from the shoot tip area than on those from below in all genotypes. Generally, a greater percentage of symptomless plants developed from single-node ...

Appropriate 15N-labeling methods are crucial for estimating N2-fixation in trees used in agroforestry systems. A 4-year field experiment was conducted on an Alfisol in Southwestern Nigeria to compare the estimates of Na fixed in Leucaena leucocephala, using two non-N2-fixing leguminous trees, Senna siamea and S. spectabiIis, as reference plants and three different methods of introducing 15N into soil. The atom % 15N uptake pattern (as reflected in the leaves) was identical in both N2- and non-N2-fixing ...

Twelve herbaceous and shrub legume species were grown in pot and field experiments in five sites representing three agroecological zones in moist savanna in Nigeria. The objectives were to: (1) assess natural nodulation of the legumes and characterize their indigenous rhizobia, (2) determine their need for rhizobia inoculation and (3) estimate the amount of N2 fixed by each of these legumes. At 4 weeks after planting (WAP), Crotolaria verrucosa was not nodulated at any of the sites while Centrosema ...

A laboratory incubation experiment with 15N labeled root and leaf residues of 3 agroforestry species (Leucaena leucocephala, Dactyladenia harto'i and Flemingia macrophylla) was conducted under controlled conditions (25 °C) for 56 days to quantify residue C and N mineralization and its relationship with residue quality. No uniform relation was found between the chemical composition of the above and below residues. The leucaena and dactyladenia roots contained more lignin (8 and 26% respectively) ...

A study is presented showing that the entomopathogenic fungus , Metarhizium avoviride, can persist in fragments of infected grasshopper cadaver and survive the Sahelian dry season. A significant positive relationship was identified between the probability of mortality at the beginning of one season and the density of infected cadaver s present in the habitat at the end of the previous season. Furthermore, survival analysis revealed a steady decline in the mean survival time of grasshoppers exposed ...

Fifty-five samples of diseased cassava (Manihot esculenta) crowns and shoots and discoloured chips were collected from Benin and Cameroon, Africa. Pieces of infected tissue were cultured on agar and incubated for a week. Over 36% of fungal isolates were Fusarium spp. Of the Fusarium isolates, 55% were from rotted roots and crowns of young and old plants and 45% were from chips. Over 44% of Fusarium isolates from the chips were F. moniliforme [Gibberella fujikuroi]. G. fujikuroi was reisolated from ...