The feeding behaviour of Nilaparvata lugens (Stal.) was electronically monitored on three rice varieties showing different levels of resistance in the Philippines, over an 8 h period, using a DC amplifier and a video-assisted observation method to simultaneously record honeydew production.Six electrical penetration graph (EPG) patterns are described by their frequency and amplitude characteristics. Patterns 4 and 5 were associated with the production of two different types of honeydew; basic honeydew containing amino acids was produced during Pattern 4 and acidic honeydew with no amino acids was produced during Pattern 5. These patterns are thought to indicate phloem and xylem ingestion by N. lugens respectively.Insects produced shorter periods of Pattern 4 on moderately resistant IR46 and resistant IR62 rice varieties than on susceptible IR22, although the time taken to produce the first period of Pattern 4 from the start of EPG recording did not differ between varieties. This suggests that N. lugens has the ability to initiate phloem ingestion on all three varieties, but that resistance mechanisms in IR46 and IR62 prevent sustained phloem ingestion, at least within the first 8 h of contact.

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The probing activities of Brevicoryne brassicae (L.) on a host plant Brassica oleracea (L.) were electronically monitored using a direct current (DC) device. Two electrical penetration graphs are described, including a pattern, D + E, at two different potential levels; the normal level of pattern C, D + E(c), and the potential drop level, D+E(pd). Stylets were amputated during these patterns, sap exudation from the stumps was scored, and the penetrated leaf area with the remnants of the stylets were processed for EM. Sap was not produced from stylets cut during D + E(c). About 70% of stylets cut during the D+E(pd) pattern produced sap and in micrographs, stylet tips had pierced the sieve element plasmalemma and were found inside the cell lumen. This supports the earlier hypothesis that the D+E(pd) pattern is related to intracellular sieve element penetration. The relation of D + E(c) and D+E(pd) with ingestion is discussed. RÉSUMÉ Infrastructure de la pénétration des vaisseaux conducteurs par les stylets des aphides pendant l'enregistrement électrique Les pénétrations par Brevicoryne brassicae de la plante‐hôte Brassica oleracea étaient enregistrées électriquement au moyen d'un montage au courant continu. Deux signeaux sont décrits avec l'onde D+E à deux niveaux de potentiel électrique: le niveau normal de l'onde C, D+E(c), et un niveau bas après une chute de potentiel, D+E(pd). Au cours de ces deux ondes les stylets étaient amputés, on a pu observer le jaillisement de sève hors du moignon; on a ensuite préparé une partie de la feuille avec les restes des stylets pour le microscope électronique. Au cours de l'onde D+E(c) on observait aucune production de sève. Environ 70% des stylets amputés pendant l'onde D+E(pd) produisaient de la sève et dans deux de ces cas, dont les signeaux sont décrits, les pointes des stylets se trouvaient dans une cellule des vaisseaux conducteurs en ayant pénétrés le plasmalemme. Ces résultats confirment l'hypothèse antérieure, selon laquelle l'onde D+E(pd) est liée à une pénétration intracellulaire d'un vaisseau conducteur. La relation de l'onde D+E(c) et D+E(pd) avec l'ingestion par l'aphide est discutée.

The sequences of the coat protein gene of a representative sample of 40 isolates of Rice yellow mottle virus (RYMV) from 11 African countries were analysed. The overall level of nucleotide diversity was high ( ,14 %). Great geographical distances between the sites where isolates were collected were consistently associated with high genetic distances. In contrast, a wide range of genetic distances occurred among isolates spread over short geographical distances. There was no evidence of long-range dispersal. RYMV diversity in relation to land area was eight times greater in East Africa than in West/Central Africa. West/Central African isolates with up to 9 % divergence belonged to a monophyletic group, whereas the East African isolates with up to 13 % divergence fell into distantly related groups. In East Africa, each Tanzanian strain had a specific and restricted geographical range, whereas West/Central African strains had large and partially overlapping geographical distributions. Overall, our results suggest an earlier RYMV diversification in East Africa and a later radiation in West/Central Africa. The West African situation was consistent with virus adaptation to savanna, forest and other ecological conditions. In contrast East Africa, as exemplified by the Tanzanian situation, with numerous physical barriers (mountain chains, sea channel, lakes), suggested that RYMV strains resulted from divergence under isolated conditions. For RYMV and for two other viruses, phylogenetic relationships were established between isolates from Madagascar and isolates from the Lake Victoria region.

Groundnut rosette disease is the most destructive viral disease of peanut in Africa and can cause serious yield losses under favourable conditions. The development of disease-resistant cultivars is the most effective control strategy. Resistance to the aphid vector, Aphis craccivora, was identified in the breeding line ICG 12991 and is controlled by a single recessive gene. Bulked segregant analysis (BSA) and amplified fragment length polymorphism (AFLP) analysis were employed to identify DNA markers linked to aphid resistance and for the development of a partial genetic linkage map. A F(2:3) population was developed from a cross using the aphid-resistant parent ICG 12991. Genotyping was carried out in the F2 generation and phenotyping in the F3 generation. Results were used to assign individual F2 lines as homozygous-resistant, homozygous-susceptible or segregating. A total of 308 AFLP (20 EcoRI+3/MseI+3, 144 MluI+3/MseI+3 and 144 PstI+3/MseI+3) primer combinations were used to identify markers associated with aphid resistance in the F(2:3) population. Twenty putative markers were identified, of which 12 mapped to five linkage groups covering a map distance of 139.4 cM. A single recessive gene was mapped on linkage group 1, 3.9 cM from a marker originating from the susceptible parent, that explained 76.1% of the phenotypic variation for aphid resistance. This study represents the first report on the identification of molecular markers closely linked to aphid resistance to groundnut rosette disease and the construction of the first partial genetic linkage map for cultivated peanut.