Antibiosis resistance to cereal leaf beetle,Oulema melanopus (L.) (Coleoptera: Chrysomelidae), in Central Asian wheat germplasm

The cereal leaf beetle, Oulema melanopus (Coleoptera: Chrysomelidae), is a new invasive pest of cereals in western Canada. Host plant resistance is a potential option in the integrated management of this insect. Wheat (Triticum aestivum L.) genotypes are known to possess antixenosis against O. melanopus; however, mechanisms involving antibiosis are relatively less explored. We present results of an investigation exploring antibiotic resistance in wheat germplasm of Central Asian origin with putative resistance to O. melanopus. Our laboratory assessment of development and survivorship of O. melanopus on test genotypes indicated antibiotic properties in four of the six genotypes evaluated. Antibiosis effects were reflected through lower survivorship, extended developmental periods and low adult fitness. However, two genotypes were excellent hosts, and beetles had higher survivorship and fitness on them. The performance of O. melanopus on these two genotypes was comparable to that on the susceptible genotype CDC GO included as a check. The genotypes with antibiotic resistance identified by this research can now serve as sources of genetic resistance for breeding cultivars adapted to western Canadian conditions.     

Anther culture of kale (Brassica oleracea L. convar.acephala (DC.) Alef.)

The pollen development and androgenic ability of 18 kale (Brassica oleracea convar.acephala) genotypes was observed during an anther culture study. Anther culture was successful in 6 of the genotypes and the highest yield obtained was 17 embryos per 100 anthers plated. Two stages of anther development were identified as being responsive to anther culture. The first and most responsive was that corresponding to the late uninucleated stage and the second to the late binucleated stage. These stages correspond with the onset of mitotic events in the microspores. Pollen viability was studied and low viability was noted which declined to zero after 9 days of anther culture. The initial viability level however was not clearly related to androgenic ability. The significance of the production of haploid and dihaploid kale genotypes in the study and breeding of resistance to clubroot is discussed.     

Resistance Against Drechslera teres (Sacc.) Shoem. in Progenies of in vitro Selected Callus Derived Plants of Barley (Hordeum vulgare L.)

Immature embryo derived callus cultures of barley were selected in vitro against a toxin (culture filtrate-methanol supernatant) produced by Drechslera teres. Both S₁ and S₂ progenies of regenerated plants (selected by toxin application and non-selected ones) were tested for their toxin tolerance and disease resistance. For this purpose, it was possible to use different culture filtrates and pathogen isolates, produced and maintained at two phytopathological institutes. Twelve out of 26 S₂ progenies examined had a significantly reduced toxin sensitivity in comparison to the donor. Nine of these genotypes also expressed an isolate-dependent improvement of their disease resistance. At the level of individual plants, 9 progenies showed a correlation between toxm tolerance and resistance against the pathogen. Somaclonal variation in reactions of non-selected regenerated plants occurred. A mutagen treatment increased the number of toxin tolerant plants within s, progenies, and segregation took place for this trait.     

Development of a bioassay to assess resistance to Fusarium oxysporum (Schlecht.) in asparagus (Asparagus officinalis L.)

Fusarium oxysporum is one of the major pathogens causing root and crown rot in asparagus. Breeding of cultivars resistant to F. oxysporum would be the most efficient strategy for pathogen control. In this study, a bioassay was developed for screening seedling resistance. The non‐destructive bioassay comprises inoculation with a highly aggressive F. oxysporum isolate, incubation in a climate chamber and quantification of disease symptoms by a digital image analysing system and a PTA‐ELISA. This bioassay is simple to implement and demonstrated high reproducibility. Subsequently, it was used to determine the resistance behaviour of 16 asparagus genotypes to F. oxysporum. The asparagus cultivars revealed different levels of susceptibility, whereas the wild relative A. densiflorus was confirmed to be resistant.     

Genetic mapping of a fusarium wilt resistance gene (Fom-2) in melon (Cucumis melo L.)

Fusarium wilt caused by Fusarium oxysporum f.sp. melonis is one of the most devastating diseases in melon production worldwide. The most effective control measure available is the use of resistant varieties. Identifying molecular markers linked to resistance genes can serve as a valuable tool for the selection of resistant genotypes. Bulked segregant analysis was used to identify markers linked to the Fom-2 genes, which confers resistance to races 0 and 1 of the fungal pathogen. Pooled DNA from homozygous resistant or homozygous susceptible progeny of F₂ cross between MR-1 and AY was screened using 240 PstI/MseI and 200 EcoRI/MseI primer combinations to identify AFLP markers linked to Fom-2. Fifteen markers potentially linked to Fom-2 were identified, all with EcoRI/MseI primer pairs. These were mapped relative to Fom-2 in a backcross (BC) population of 60 progeny derived from MR-1 × AY with AY as recurrent parent. Two AFLP markers (ACT/CAT1 and AAC/CAT1) flanked the gene at 1.7 and 3.3 cM, respectively. Moreover, AFLP marker AGG/CCC and the previously identified RAPD marker 596-1 cosegregated with Fom-2. These two dominant markers were converted to co-dominant markers by designing specific PCR primers that produced product length polymorphisms between the parents. A survey of 45 melon genotypes from diverse geographic origins with the co-dominant markers demonstrated a high correlation between fragment size and the resistance phenotype. These markers may therefore be useful in marker-assisted breeding programs.     

Physiological Basis for Differences in Resistance to Microdochium nivale (Fr.) Samuels and Hallett in Two Androgenic Genotypes of Festulolium Derived from Tetraploid F1 Hybrids of Festuca pratensis × Lolium multiflorum (Festulolium)

The aim of this study was to investigate the physiological basis for differences in resistance to pink snow mould (Microdochium nivale) in two androgenic genotypes of Festulolium (Festuca pratensis × Lolium multiflorum) which differed in terms of their resistance to M. nivale. Genotype 716 was more resistant than genotype 729. The study consisted of two experiments. The aim of the first experiment was to estimate the ability of the plants to survive winter conditions. The aim of the second experiment was to find physiological markers of resistance to snow mould. Festulolium plants were infected with M. nivale mycelium after pre‐hardening and hardening. After 2 weeks in the dark at 2°C, there was a sharp increase in the phenolic content in both genotypes. The increase was greater in the more resistant genotype 716 than in genotype 729. Phenolics therefore may play a very important role in overwintering in grasses, similar to carbohydrates. Based on the differences between the two genotypes, potential indicators of resistance to M. nivale in Festulolium include increased soluble carbohydrate content, increased phenolic content, increased hydrogen peroxide accumulation, decreased catalase activity, increased abscisic acid content and reduced heat emission.     

Defense response of resistant and susceptible genotypes of castor (Ricinus communis L.) to wilt disease

The biochemical basis of resistance in castor (Ricinus communis L.) to Fusarium wilt, caused by the pathogen Fusarium oxysporum f. sp. ricini, was investigated. Induction of plant defence against pathogen attack is regulated by a complex network of different signals. Thus changes in various biochemical defenses including antioxidant enzymes, phenolic compounds and pathogenesis related (PR) proteins were investigated in the roots of resistant and susceptible genotypes of castor at 0, 24, 48 and 72 h.a.i. Infection by F. oxysporum significantly increased the superoxide dismutase (SOD) and peroxidase (POX) activities in the roots of susceptible genotypes, while the catalase (CAT) activities were appreciably higher in the roots of resistant genotypes at different stages. Constitutive levels of ascorbate peroxidase (APX) and polyphenol oxidase (PPO) were higher in the resistant genotypes. Also, the activities of phenylalanine ammonia lyase (PAL) and β 1, 3 glucanase significantly increased in the roots of the resistant genotypes after infections. The rate of increment of thiobarbituric acid reactive substances (TBARS) was higher in resistant genotypes after infection. Analysis of isozyme banding pattern of SOD, POX, PPO and esterase on native PAGE electrophoresis revealed that interaction between plant and fungi invoked various isozymes at 48 h of infection. SOD 3 was observed only in resistant genotypes at 24 h.a.i. except Geeta. Similarly induction of POX 5 was observed only in resistant genotypes at 48 h of infection, though the intensity of POX 5 was very less.     

Identification and evaluation of two diagnostic markers linked to Fusarium wilt resistance (race 4) in banana (Musa spp.)

Fusarium wilt caused by the fungus Fusarium oxysporum f. sp. cubense race 4 (FOC4) results in vascular tissue damage and ultimately death of banana (Musa spp.) plants. Somaclonal variants of in vitro micropropagated banana can hamper success in propagation of genotypes resistant to FOC4. Early identification of FOC4 resistance in micropropagated banana plantlets is difficult, however. In this study, we identified sequence-characterized amplified region (SCAR) markers of banana associated with resistance to FOC4. Using pooled DNA from resistant or susceptible genotypes and 500 arbitrary 10-mer oligonucleotide primers, 24 random amplified polymorphic DNA (RAPD) products were identified. Two of these RAPD markers were successfully converted to SCAR markers, called ScaU1001 (GenBank accession number HQ613949) and ScaS0901 (GenBank accession number HQ613950). ScaS0901 and ScaU1001 could be amplified in FOC4-resistant banana genotypes (“Williams 8818-1” and Goldfinger), but not in five tested banana cultivars susceptible to FOC4. The two SCAR markers were then used to identify a somaclonal variant of the genotype “Williams 8818-1”, which lost resistance to FOC4. Hence, the identified SCAR markers can be applied for a rapid quality control of FOC4-resistant banana plantlets immediately after the in vitro micropropagation stage. Furthermore, ScaU1001 and ScaS0901 will facilitate marker-assisted selection of new banana cultivars resistant to FOC4.     

Conventional Breeding and Molecular Markers for Blast Disease Resistance in Rice (<i>Oryza sativa</i> L.)

Monogenic lines, which carried 23 genes for blast resistance were tested and used donors to transfer resistance genes by crossing method. The results under blast nursery revealed that 9 genes from 23 genes were susceptible to highly susceptible under the three locations (Sakha, Gemmeza, and Zarzoura in Egypt); Pia, Pik, Pik-p, Piz-t, Pita, Pi b, Pi, Pi 19 and Pi 20. While, the genes Pii, Pik-s, Pik-h, Pi z, Piz-5, Pi sh, Pi 3, Pi 1, Pi 5, Pi 7, Pi 9, Pi 12, Pikm and Pita-2 were highly resistant at the same locations. Clustering analysis confirmed the results, which divided into two groups; the first one included all the susceptible genes, while the second one included the resistance genes. In the greenhouse test, the reaction pattern of five races produced 100% resistance under artificial inoculation with eight genes showing complete resistance to all isolates. The completely resistant genes: Pii, Pik-s, Piz, Piz-5 (=bi2) (t), Pita (=Pi4) (t), Pita, Pi b and Pi1 as well as clustering analysis confirmed the results. In the F₁ crosses, the results showed all the 25 crosses were resistant for leaf blast disease under field conditions. While, the results in F₂ population showed seven crosses with segregation ratio of 15 (R):1 (S), two cross gave segregated ratio of 3 R:1 S and one gave 13:3. For the identi- fication of blast resistance genes in the parental lines, the marker K3959, linked to Pik-s gene and the variety IRBLKS-F5 carry this gene, which was from the monogenic line. The results showed that four genotypes; Sakha 105, Sakha 103, Sakha 106 and IRBLKS-F5 were carrying Pik-s gene, while was absent in the Sakha 101, Sakha 104, IRBL5-M, IRBL9-W, IRBLTACP1 and IRBL9-W(R) genotypes. As for Pi 5 gene, the results showed that it was present in Sakha 103 and Sakha 104 varieties and absent in the rest of the genotypes. In addition, Pita-Pita- 2 gene was found in the three Egyptian genotypes (Sakha 105, Sakha 101 and Sakha 104) plus IRBLTACP1 monogenetic. In F2 generation, six populations were used to study the inheritance of blast resistance and specific primers to confirm the ratio and identify the resistance genes. However, the ratios in molecular markers were the same of the ratio under field evaluation in the most population studies. These findings would facilitate in breeding programs for gene pyramiding and gene accumulation to produce durable resistance for blast using those genotypes.     

Assembling complex genotypes to resist Fusarium in wheat (Triticum aestivum L.)

Fusarium head blight of wheat is a major deterrent to wheat production world-wide. The genetics of FHB resistance in wheat are becoming clear and there is a good understanding of the genome location of FHB resistance QTL from different sources such as Sumai3, Wuhan, Nyubai and Frontana. All the components needed for assembling complex genotypes through large-scale molecular breeding experiments are now available. This experiment used high throughput microsatellite genotyping and half-seed analysis to process four independent crosses through a molecular breeding strategy to introduce multiple pest resistance genes into Canadian wheat. This included two backcrosses and selection for a total of six FHB resistance QTL, orange blossom wheat midge resistance (Sm1) and leaf rust resistance (Lr21). In addition, the fixation of the elite genetic background was monitored with 45–76 markers to accelerate restoration of the genetic background at each backcross. The strategy resulted in 87% fixation of the elite genetic background on average at the BC₂F₁ generation and successfully introduced all of the chromosome segments containing FHB, Sm1 and Lr21 resistance genes. The molecular breeding strategy was completed in 25 months, at an equal pace to conventional crossing and selection of spring wheat.     

Electrical resistance changes during exposure to low temperature measure chilling and freezing tolerance in olive tree (Olea europaea L.) plants

Electrical resistance changes in different organs of four olive tree (Olea europaea L.) varieties, characterized by different tolerance to chilling and freezing, were examined, during exposure to low temperature. Apparent critical temperatures (CT) and freezing temperatures (T_fr) were identified on the basis of the electrical resistance changes. Both temperatures were lower for the more chilling‐tolerant genotypes. From the apparent critical temperatures, the absolute critical temperature (CT_abs) and the time delay of the chilling signal transduction process were calculated. In shoots, CT_abs varied from 8·8 °C for Ascolana (chilling‐tolerant variety) to 13·6 °C for Coratina (chilling‐sensitive variety). The magnitude of the transduction time was very similar (about 2 min) for the three genotypes that are more sensitive to chilling, whereas it was significantly higher (about 3 min) for the most tolerant genotype. Different freezing temperatures were observed for different organs. It would appear from this experiment that the order of sensitivity is roots > leaves > shoots > vegetative buds. Accord was found between the absolute critical temperature of electrical resistance and the critical temperature of membrane potential. The occurrence of electrical resistance changes in the tissues of the olive trees exposed to low temperature suggests the use of this experimental procedure as a quick, easy and non‐destructive tool to screen plant tissues for chilling tolerance. The strong dependence of the electrical resistance on low temperature, and the critical temperature of around 10 °C, can yield interesting information about the lowest thermal limits for the continuation of normal physiological processes and therefore about the adaptability of plants to particular environments.     

Differential Interaction Between PAV-like Isolates of Barley Yellow Dwarf Virus and Barley (Hordeum vulgare L.) genotypes

Four PAV-like isolates of barley yellow dwarf virus (BYDV) were identified as causing very severe (RG), severe (2t), moderately severe (3b) and mild symptoms (13t) in barley (Hordeum vulgare) cultivar Plaisant in a growth chamber at 25 days after inoculation. These isolates had different effects on a range of barley genotypes. Cultivar Vixen, which contains the Yd2 resistance gene, and 80-81 BQCB10 were not affected by any isolate. Five other genotypes were significantly affected by at, least one of the isolates. Line Ea52 (which is a mutant of the Japanese cultivar Chikurine Ibaraki) was more susceptible to BYDV-PAV than Chikurin Ibaraki 1. No serological differences were detected between the four isolates using monoclonal or polyclonal antibodies. Virus antigen concentration, estimated by enzyme-linked immunosorbent assay (ELISA), was correlated with the decrease in the shoot fresh weight for all isolates and all genotypes except for Vixen and 80-81BQCB10. In field tests, the severity of symptoms induced by the BYDV-PAV isolates was in accordance with that estimated in the growth chamber. However isolate 2t was more severe on cultivar Vixen and overcame the partial resistance of Chikurin Ibaraki 1 to the three other isolates. The results show that virus antigen concentration not only contributes to characterizing the resistance levels of barley genotypes but also the severity of BYDV-PAV isolates.     

Differential Interaction Between PAV-like Isolates of Barley Yellow Dwarf Virus and Barley (Hordeum vulgare L.) genotypes

Four PAV-like isolates of barley yellow dwarf virus (BYDV) were identified as causing very severe (RG), severe (2t), moderately severe (3b) and mild symptoms (13t) in barley (Hordeum vulgare) cultivar Plaisant in a growth chamber at 25 days after inoculation. These isolates had different effects on a range of barley genotypes. Cultivar Vixen, which contains the Yd2 resistance gene, and 80–81BQCB10 were not affected by any isolate. Five other genotypes were significantly affected by at least one of the isolates. Line Ea52 (which is a mutant of the Japanese cultivar Chikurine Ibaraki) was more susceptible to BYDV-PAV than Chikurin Ibaraki 1. No serological differences were detected between the four isolates using monoclonal or polyclonal antibodies. Virus antigen concentration, estimated by enzyme-linked immunosorbent assay (ELISA), was correlated with the decrease in the shoot fresh weight for all isolates and all genotypes except for Vixen and 80–81BQCB10. In field tests, the severity of symptoms induced by the BYDV-PAV isolates was in accordance with that estimated in the growth chamber. However isolate 2t was more severe on cultivar Vixen and overcame the partial resistance of Chikurin Ibaraki 1 to the three other isolates. The results show that virus antigen concentration not only contributes to characterizing the resistance levels of barley genotypes but also the severity of BYDV-PAV isolates.     

Heterogeneous genetic invasions of three insecticide resistance mutations in Indo‐Pacific populations of Aedes aegypti (L.)

Nations throughout the Indo‐Pacific region use pyrethroid insecticides to control Aedes aegypti, the mosquito vector of dengue, often without knowledge of pyrethroid resistance status of the pest or origin of resistance. Two mutations (V1016G + F1534C) in the sodium channel gene (Vssc) of Ae. aegypti modify ion channel function and cause target‐site resistance to pyrethroid insecticides, with a third mutation (S989P) having a potential additive effect. Of 27 possible genotypes involving these mutations, some allelic combinations are never seen whereas others predominate. Here, five allelic combinations common in Ae. aegypti from the Indo‐Pacific region are described and their geographical distributions investigated using genome‐wide SNP markers. We tested the hypothesis that resistance allele combinations evolved de novo in populations versus the alternative that dispersal of Ae. aegypti between populations facilitated genetic invasions of allele combinations. We used latent factor mixed‐models to detect SNPs throughout the genome that showed structuring in line with resistance allele combinations and compared variation at SNPs within the Vssc gene with genome‐wide variation. Mixed‐models detected an array of SNPs linked to resistance allele combinations, all located within or in close proximity to the Vssc gene. Variation at SNPs within the Vssc gene was structured by resistance profile, whereas genome‐wide SNPs were structured by population. These results demonstrate that alleles near to resistance mutations have been transferred between populations via linked selection. This indicates that genetic invasions have contributed to the widespread occurrence of Vssc allele combinations in Ae. aegypti in the Indo‐Pacific region, pointing to undocumented mosquito invasions between countries.     

Jasmonic Acid-Mediated-Induced Resistance in Groundnut (Arachis hypogaea L.) Against Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae)

Jasmonic acid (JA) acts as a signal molecule to induce resistance in plants against herbivores and its levels are elevated in plants after wounding or insect damage. Groundnut is an important crop in many tropical and subtropical regions worldwide, but there is surprisingly little knowledge on its induced defenses against herbivores. The effect of JA as a spray on induced resistance in three groundnut genotypes, namely, ICGV 86699 (resistant), NCAc 343 (resistant), and TMV 2 (susceptible), against Helicoverpa armigera was studied. The activity of oxidative enzymes [peroxidase (POD) and polyphenol oxidase (PPO)] and the amounts of other host plant defense components [total phenols, hydrogen peroxide (H₂O₂), malondialdehyde (MDA), and protein content] were recorded at 24, 48, 72, and 96 h after pretreatment (1 day) with JA followed by infestation with H. armigera (PJA + HIN) and H. armigera infestation with simultaneous JA application (HIN + JA) to understand the consequences of induced resistance in groundnut. The plant damage, larval survival, and larval weights were also recorded. There was a significant increase in POD and PPO activities and in the amounts of total phenols, H₂O₂, MDA, and proteins in PJA + HIN- and JA + HIN-treated plants as compared to the plants treated with JA and infested with H. armigera individually and to untreated control plants. Among all the genotypes, the strongest induction of defense was observed in the ICGV 86699 genotype. It is concluded that pretreatment with JA and its application during low levels of insect infestation can increase the levels of host plant resistance against herbivorous insects and reduce the pest-associated losses in groundnut.     

Increased accumulation of phenolic metabolites in groundnut (Arachis hypogaea L.) genotypes contribute to defense against Sclerotium rolfsii infection

Abstract

Fungal infections cause several metabolic changes to the plants, which can affect its physiology and survival in various ways. In the present study, we have analysed various phenolic compounds and activity of oxidative enzymes in healthy and Sclerotium rolfsii-infected groundnut genotypes. Increased phenolics content and higher activity of oxidative enzymes was observed in the tolerant genotype (CS 19, GG 16) followed by susceptible genotype (GG 20, TG 37A). Among the phenolic compounds tested, chlorogenic acid content has increased greatly in leaf, stem and root of infected tolerant genotypes compared to the respective controls. In vitro growth of S. rolfsii showed significant inhibition at concentrations 500 and 1000 µg/mL of phenolic compounds in the radial growth inhibition assay. These results have strongly suggested that, higher accumulation of chlorogenic acid could be an important factor in imparting resistance and protecting groundnut against S. rolfsii infection in tolerant genotypes.     

Drought resistance of bermudagrass (Cynodon spp.) ecotypes collected from different climatic zones

The objectives of this paper were to (1) evaluate drought resistance of a large number of bermudagrass ecotypes collected from different climatic zones of regional Australia and compare their performance to commercial cultivars, (2) describe the mechanisms of drought resistance observed, and (3) investigate the relationship between geographic origins of the ecotypes and their drought resistance. Fifty-two genotypes of bermudagrass were evaluated in two field experiments using lysimeters 40 cm deep. The grasses were grown in well-watered conditions and then a drought treatment was imposed by withholding water and excluding rainfall using a portable rain-out shelter. Two criteria were used to select for drought resistance, i.e. survival period (SP), defined as the number of days after water was withheld to the stage when 100% leaf firing had occurred and Days₅₀ defined as the days required to reach 50% green cover. These experiments suggested that genotypes with superior drought resistance had lower stomatal conductance in the earlier phases of the dry-down period as suggested by less water use and higher canopy temperature depression. Lower water use during the early stage of dry-down resulted in more soil available water at the end of the drought period to extend green-leaf cover. There was no correlation between root dry matter and survival period/Days₅₀. We also found some ecotypes performed better in drought conditions than popular commercial cultivars. There was no relationship between drought resistance and geographic origins, suggesting that drought resistant ecotypes could be obtained from any climatic zone sampled in this study.     

Pollen effects on fruit and seed characteristics in pistachio (Pistacia vera L.)

The agronomic profitability of nut production in pistachio (Pistacia vera L.) is hampered by several factors such as the production of empty nuts, the small size and dry weight of the edible kernel and the low percentage of endocarp dehiscence. The causes underlining these problems are still unknown. The effect of pollinations with pollen from P. atlantica and six different P. vera genotypes on several fruit, nut and embryo characters was compared to study possible xenic and/or metaxenic effects. The use of P. atlantica pollen affected some traits, but there were no clear differences when the pollen of the different P. vera genotypes was used suggesting that, at the intraspecific level, the main limitation to pistachio fruit production problems might not be due to pollen factors.     

Molecular progress on the mapping and cloning of functional genes for blast disease in rice (Oryza sativa L.): current status and future considerations

Rice blast disease, which is caused by the fungal pathogen Magnaporthe oryzae, is a recurring problem in all rice-growing regions of the world. The use of resistance (R) genes in rice improvement breeding programmes has been considered to be one of the best options for crop protection and blast management. Alternatively, quantitative resistance conferred by quantitative trait loci (QTLs) is also a valuable resource for the improvement of rice disease resistance. In the past, intensive efforts have been made to identify major R-genes as well as QTLs for blast disease using molecular techniques. A review of bibliographic references shows over 100 blast resistance genes and a larger number of QTLs (～500) that were mapped to the rice genome. Of the blast resistance genes, identified in different genotypes of rice, ～22 have been cloned and characterized at the molecular level. In this review, we have summarized the reported rice blast resistance genes and QTLs for utilization in future molecular breeding programmes to introgress high-degree resistance or to pyramid R-genes in commercial cultivars that are susceptible to M. oryzae. The goal of this review is to provide an overview of the significant studies in order to update our understanding of the molecular progress on rice and M. oryzae. This information will assist rice breeders to improve the resistance to rice blast using marker-assisted selection which continues to be a priority for rice-breeding programmes.     

Temperature influences the expression of resistance of soybean (Glycine max) to the soybean aphid (Aphis glycines)

Resistance of plants to arthropods may be lost at low or high temperatures. I tested whether the relative resistance of five genotypes of soybean, Glycine max (L.) Merr., to three isolates of the soybean aphid, Aphis glycines Matsumura, was influenced by three temperatures, 14, 21 and 28°C, in no‐choice tests in the laboratory. The interaction between temperature and the genotype of soybean influenced the population sizes of two isolates of A. glycines. Two genotypes of soybean, LD05‐16611 and PI 567597C, which usually are resistant to isolate 1 and 3, became susceptible: LD05‐16611 at the low temperature and PI 567597C at the high temperature. The genotypes PI 200538 and PI 567541B usually are susceptible to isolate 3 but were resistant at 21 and 28°C. I can only speculate as to the reason why temperature influences resistance of some genotypes of soybean to A. glycines: A. glycines may be directly influenced by temperature or indirectly influenced by changes in the host plant. Nevertheless, my results suggest that temperature may be one factor that influences the expression of resistance of soybean to A. glycines, so genotypes of soybean should be screened for resistance to the aphid at multiple temperatures.