Aphid–plant interactions depend on genotypes of both organisms, which determine the two-way molecular exchange that leads to compatible or incompatible outcomes. The underlying genes are mostly unknown, making it difficult to predict likelihood of aphid success or host resistance, and hampering crop genetic improvement. Here we screened eight pea aphid clonal genotypes collected from diverse legume hosts, on a species-wide panel of Medicago truncatula (Mt) genotypes. Aphid virulence was measured by survival, fecundity and growth rate, together with scores for chlorosis and necrosis as host response indicators. Outcomes were highly dependent on the specific aphid–host genotype combinations. Only one Mt line was fully resistant against all clones. Aphid-induced host chlorosis and necrosis varied greatly, but correlated with resistance only in a few combinations. Bi-clustering analysis indicated that all aphid clones could be distinguished by their performance profiles across the host genotypes tested, with each clone being genetically differentiated and potentially representing a distinct biotype. Clones originating from Medicago sativa ranged from highly virulent to almost completely avirulent on both Medicago species, indicating that some were well adapted, whereas others were most likely migrants. Comparisons of closely related pairs of Australian Mt genotypes differing in aphid resistance revealed no enhanced resistance to European pea aphid clones. Based on the extensive variation in pea aphid adaptation even on unfamiliar hosts, most likely reflecting multiple biotype-specific gene-for-gene interactions, we conclude that robust defences require an arsenal of appropriate resistance genes.

Root lesion nematodes of the genus Pratylenchus are important pests in crop cultivation that cause severe damage to crops throughout the world. P. neglectus is one of the most important members of this genus. The present study aimed to select barley accessions with resistance to P. neglectus in a greenhouse resistance test and to detect resistance quantitative trait loci (QTLs). Infection rates have been found to vary greatly among different barley accessions; however, immunity could not be found. An existing Igri × Franka doubled-haploid mapping population was used to map resistance genes after artificial inoculation with P. neglectus under controlled environment. QTLs were found with a likelihood of odds score between 2.71 and 6.35 and explaining phenotypic variation of 8 to 16%.

Introduction. Root-knot nematodes (Meloidogyne sp.) cause significant economic damage to Prunus species in China. One of the most economical and environmentally sustainable methods to reduce the impact of root-knot nematodes is the use of resistant rootstock cultivars. Our aim was to examine resistance to M. incognita and its mechanisms. Materials and methods. Four rootstocks were assessed: Tsukuba-4 (P. persica), Tsukuba-5 (P. persica), Nanking cherry (P. tomentosa) and wild peach (P. persica). The susceptible tomato (Lycopersicon esculentum Mill.) cultivar ‘Baiguoqiangfeng’ was used as a positive control. Results. Nematodes did not penetrate roots of Tsukuba-4 and Tsukuba-5, which were considered to be immune varieties. Nanking cherry was highly resistant to M. incognita, whereas wild peach was susceptible. Conclusion. The differences in resistance among the rootstocks were not attributed to differences in effects of root diffusates, but were related to the different structural organizations of the root tips. The epidermal structure of Tsukuba-4 and Tsukuba-5 completely prevented the penetration of second-stage juveniles of M. incognita (J2). In Nanking cherry, penetration of J2 juveniles was reduced, and the development of nematodes from the J2 to female stage was delayed.

The highly efficient plant binary expression vector pGBIF4ABCVHB was constructed using the artificially modified, synthesized VHb gene and fused insectidal gene (GFMcryIA and CPTI). Transgenic tobacco plants were obtained by Agrobacterium-mediated transformation. For 32 plants, the bivalent genes were inserted successfully into the tobacco genome and detected by polymerase chain reaction (PCR) amplification. Southern blot and Western blot analyses showed that VHb gene was expressed in the transgenic plants. Toxicity assay indicated that the fused insectidal gene expressed pesticidal toxin protein. The net weight of transgenic tobacco plants exceeded that of non-transgenic ones by 8%. Compared to non-transgenic tobacco plants, transgenic plants appeared to be high-yielding, insect-resistant varieties.

Introduction. Diverses espèces de pyrales peuvent s'attaquer aux dattes. Ce ravageur cause jusqu'à 30 % de pertes parmi les récoltes de dattes au Maroc. L'étude présentée a cherché à identifier les espèces de pyrales des dattes et leurs parasitoïdes, en précisant leurs importances relatives, et à dégager les facteurs influençant l'infestation des dattes. Matériel et méthodes. Des prospections ont été menées durant les années 1997 et 1998 dans 16 sites répartis dans les principales palmeraies de la région de Tafilalet. Des échantillonnages ont été effectués sur régimes et sur dattes tombées au sol. Les fruits infestés ont été dénombrés puis placés dans des éclosoirs jusqu'à la sortie des adultes des pyrales et de leurs parasitoïdes. Résultats et discussion. Trois espèces de pyrales peuvent se développer sur les dattes au champ avec des incidences différentes. Le principal ravageur est Ectomyelois ceratoniae. En revanche, Plodia interpunctella et Ephestia figulilella sont des déprédateurs secondaires. L'infestation des dattes varie d'une année à l'autre, les années humides favorisant la pullulation de la pyrale. Les dégâts dus à la pyrale ont varié selon la variété de palmier dattier : la variété Bou feggous à dattes de maturité précoce et à épiderme fin a été la plus vulnérable à l'attaque de la pyrale. L'ensachage des régimes permet de réduire notablement l'infestation des dattes. Les populations d'E. ceratoniae peuvent être également limitées par deux parasitoïdes : Phanerotoma ocuralis sur dattes en régime et Bracon hebetor dans les dattes tombées au sol. Conclusion. L'application de certaines pratiques culturales pourraient aider les agriculteurs à réduire significativement l'infestation des dattes au champ.