Manual Infestation Research Articles

Asian Corn Borer (Ostrinia furnacalis) Infestation Increases Fusarium verticillioides Infection and Fumonisin Contamination in Maize and Reduces the Yield.

Field trials based on manual infestation of the Asian corn borer (ACB) (Ostrinia furnacalis [Guenée]) and Fusarium verticillioides (Nirenberg) atomization were conducted on four maize hybrids to investigate the relationship between ACB infestation and F. verticillioides infection, yield loss, and fumonisin contamination in maize. Analysis of fumonisins B1 and B2 was carried out using an LC-MS/MS system. In this study, manual ACB infestation significantly promoted F. verticillioides infection (both symptomatic and symptomless) and grain fumonisin levels. Ear rot incidence and severity, symptomless kernel infection, and fumonisin contamination were significantly correlated to each other and to ACB damage severity. Manual ACB infestation increased fumonisin levels from 580 to 4,418 µg/kg in 2018; 6,059 to 10,681 µg/kg in 2019 spring-sown maize (2019A); and 2,042 to 5,060 µg/kg in 2019 summer-sown maize (2019B), with the threshold of the European Union (EU) being 4,000 µg/kg. The threshold was exceeded in spring of 2019 in untreated controls. Regarding yield, significant negative correlation between ACB damage and ear weight was observed in three seasons. These results indicated that ACB infestation can lead to severe quality degradation and yield loss of maize. Kernel fumonisin levels may exceed the concentration threshold of the EU in certain conditions, threatening the health of livestock and humans. Measures should be taken to reduce ACB infestation to ensure food and feed security.

Increase in foliar silicon content reduces defoliation by Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae) in maize

The effect of silicon (Si) on fitness and leaf consumption of the fall armyworm (FAW), Spodoptera frugiperda (Smith), has been observed in the laboratory, but the effects of Si on damage or defoliation reduction have not yet been determined under field conditions. Here, we evaluated the effects of amendment of soil with Si on defoliation by FAW and crop yield in maize. Two field experiments were carried out, with four doses of Si and a control (no Si amendment). Experiment #1 evaluated 150, 300, 450, and 600 kg of total Si·ha-1, with natural or manual infestation with FAW eggs, while Experiment #2 tested 600, 800, 1,000 and 1,200 kg of total Si·ha-1, with natural or manual infestation with FAW larvae. Defoliation reduction was observed with Si increasing in both Experiments #1 and #2. However, reduction was not observed in all evaluations, and it was dependent of infestation (natural and manual) and the time since manual infestation. Reduction in defoliation began at 600 kg Si·ha-1. In contrast, plant Si content increased linearly with increasing soil Si application. No effect of Si application was observed on maize kernel yield. The increase in leaf Si content reduced FAW defoliation, but it did not affect maize yield from 600 to 1,200 kg·ha-1 of Si. Amendment of soil with Si can be used as a strategy to optimize integrated pest management of FAW in maize.

Transgenic rice overexpressing insect endogenous microRNA csu-novel-260 is resistant to striped stem borer under field conditions.

RNA interference (RNAi) is a promising approach for developing insect-resistant crops. In the first two proof-of-concept studies, DNA fragments derived from essential insect genes were constructed into plant expression cassettes as inverted repeats, enabling long double-stranded RNAs (dsRNAs) to be transcribed in host plants (Baum et al., 2007; Mao et al., 2007). After ingestion, dsRNAs overexpressed in planta suppressed target gene expression via small interference RNA (siRNA)-mediated RNAi in western corn rootworm (Diabrotica virgifera virgifera) (Baum et al., 2007) and cotton bollworm (Helicoverpa armigera) (Mao et al., 2007), and thereby reduced their viability. Subsequent studies have mostly employed a similar approach and attempted to develop RNAi crops against various insect species (Liu et al., 2020). However, except for coleopterans that are generally susceptible to RNAi, most insects (e.g., lepidopterans, dipterans, hymenopterans, and hemipterans) exhibit unpredictable responses to dsRNA-induced RNAi, and this has become a hurdle for ubiquitous adaption of this strategy (Cooper et al., 2019). Potential factors influencing RNAi efficacy in insects involve dsRNA stability, cellular dsRNA absorption, core RNAi machinery integrity, systemic RNAi spread, and target gene amenability (Cooper et al., 2019).

Quantitative Trait Loci Underlying Partial Resistance to Cercospora sojina Race 2 Detected in Soybean Seedlings in Greenhouse Assays

Cercospora sojina (Hara), an air-borne pathogen, infects soybean [Glycine max (L.) Merr.] leaves causing frog-eye leaf spot (FLS). Three major genes (Rcs1-3) underlie resistance to the major races of FLS but two were not yet mapped. In addition quantitative trait loci provide partial resistance to many strains. FLS race 2 was an isolate first collected in the 1950’s when damaging FLS first arose. ‘Essex’ was partially resistant while ‘Forrest’ was partially susceptible to mixed races of FLS. The objective here was to identify quantitative trait loci underlying resistance to FLS race 2 in the greenhouse using recombinant inbred lines (RILs) derived from the cross of Essex by Forrest. C. sojina race 2 (ATCC 44531) was used to induce leaf symptoms on one hundred F5:14 RILs derived from the cross of Essex by Forrest. The leaf symptoms were measured at 21 days after manual infestation by wounding (dai) and again at 42 dai to show resistance to reinfestation of new leaves from the primary lesions without wounding. Bags over leaves were not used to better simulate field conditions. However, there was no significant correlation between FLS severity at 21 and 42 dai (r =0.08 and P= 0.005). At 21 dai there was a strongly significant QTL near Satt319 on LG C2 (chromosome 7; LOD 3.8; R2 52%) where the Essex allele reduced leaf symptoms by 0.7 units. At 42 dai there was a strongly significant QTL near Satt632 on LG A2 (chromosome 8; R2 was 15%; LOD was 3.6) where the Essex allele reduced leaf symptoms by 0.4 units. Neither locus mapped to the location of Rcs3. By ANOVA thirteen additional minor loci were detected on LGs A1, B1, F, G, H, I, J, K, L, M and O. At two loci (LG B1 and O) the Forrest allele appeared to reduce FLS at both 21 and 42 dai. Eight loci may have reduced FLS at 21 dai (0.006 < P < 0.049; 4% < R2 > 9%) of which 5 had beneficial alleles from Forrest. Seven loci may have reduced FLS at 42 dai (0.001 < P < 0.04; 4% < R2 < 15%) of which 4 had beneficial alleles from Forrest. Therefore, quantitative resistance to race 2 of FLS was inferred to have major loci contributions from Essex and minor loci contributions from both Forrest and Essex. Resistance was dependent on plant age. Breeding and selection for FLS will be complex and may be more efficient with the markers, germplasm and models of inheritance reported here.

Quantitative Trait Loci Underlying Partial Resistance to Cercospora sojina Race 2 Detected in Soybean Seedlings in Greenhouse Assays

Cercospora sojina (Hara), an air-borne pathogen, infects soybean [Glycine max (L.) Merr.] leaves causing frog-eye leaf spot (FLS). Three major genes (Rcs1-3) underlie resistance to the major races of FLS but two were not yet mapped. In addition quantitative trait loci provide partial resistance to many strains. FLS race 2 was an isolate first collected in the 1950’s when damaging FLS first arose. ‘Essex’ was partially resistant while ‘Forrest’ was partially susceptible to mixed races of FLS. The objective here was to identify quantitative trait loci underlying resistance to FLS race 2 in the greenhouse using recombinant inbred lines (RILs) derived from the cross of Essex by Forrest. C. sojina race 2 (ATCC 44531) was used to induce leaf symptoms on one hundred F5:14 RILs derived from the cross of Essex by Forrest. The leaf symptoms were measured at 21 days after manual infestation by wounding (dai) and again at 42 dai to show resistance to reinfestation of new leaves from the primary lesions without wounding. Bags over leaves were not used to better simulate field conditions. However, there was no significant correlation between FLS severity at 21 and 42 dai (r =0.08 and P= 0.005). At 21 dai there was a strongly significant QTL near Satt319 on LG C2 (chromosome 7; LOD 3.8; R2 52%) where the Essex allele reduced leaf symptoms by 0.7 units. At 42 dai there was a strongly significant QTL near Satt632 on LG A2 (chromosome 8; R2 was 15%; LOD was 3.6) where the Essex allele reduced leaf symptoms by 0.4 units. Neither locus mapped to the location of Rcs3. By ANOVA thirteen additional minor loci were detected on LGs A1, B1, F, G, H, I, J, K, L, M and O. At two loci (LG B1 and O) the Forrest allele appeared to reduce FLS at both 21 and 42 dai. Eight loci may have reduced FLS at 21 dai (0.006 < P < 0.049; 4% < R2 > 9%) of which 5 had beneficial alleles from Forrest. Seven loci may have reduced FLS at 42 dai (0.001 < P < 0.04; 4% < R2 < 15%) of which 4 had beneficial alleles from Forrest. Therefore, quantitative resistance to race 2 of FLS was inferred to have major loci contributions from Essex and minor loci contributions from both Forrest and Essex. Resistance was dependent on plant age. Breeding and selection for FLS will be complex and may be more efficient with the markers, germplasm and models of inheritance reported here.

Wild relatives of sorghum as sources of resistance to sorghum shoot fly, Atherigona soccata

AbstractThe levels of resistance to shoot fly, Atherigona soccata in sorghum germplasm are low to moderate and therefore, we evaluated 17 wild relatives of sorghum under field and greenhouse conditions as an alternate source of genes for resistance to this pest. Thirty‐two accessions belonging to Parasorghum, Stiposorghum and Heterosorghum did not suffer any shoot fly damage under multi‐choice conditions in the field, while one accession each of Heterosorghum (Sorghum laxiflorum) and Chaetosorghum (S. macrospermum) suffered very low shoot fly damage. Accessions belonging to S. exstans (TRC 243601), S. stipoideum (TRC 243399) and S. matarankense (TRC 243576) showed absolute non‐preference for oviposition under no‐choice conditions. Accessions belonging to Heterosorghum, Parasorghum and Stiposorghum were preferred for oviposition, but suffered low deadheart formation. Manual infestation of seedlings with shoot fly eggs did not result in deadheart formation in some of the accessions belonging to S. exstans (TRC 243601), S. stipoideum (TRC 243399), S. matarankense (TRC 243576) and S. purpureosericeum (IS 18944). Larval mortality was recorded in main stems of the Parasorghums. Within section Sorghum, accessions belonging to S. bicolor ssp. verticilliflorum were highly susceptible to shoot fly, as were those of S. halepense. However, a few accessions such as IS 18226 (race arundinaceum) and IS 14212 (S. halepense) resulted in reduced survival and fecundity. Wild relatives of sorghum exhibited very high levels of antibiosis to A. soccata, while only low levels of antibiosis have been observed in the cultivated germplasm. Therefore, wild relatives with different mechanisms of resistance can be used as a source of alternate genes to increase the levels and diversify the basis of resistance to shoot fly, A. soccata.

Effect of Transgenic <I>Bacillus thuringiensis</I> Rice Lines on Mortality and Feeding Behavior of Rice Stem Borers (Lepidoptera: Crambidae)

Ten transgenic Bacillus thuringiensis Bt rice, Oryza sativa L., lines with different Bt genes (two Cry1Ac lines, three Cry2A lines, and five Cry9C lines) derived from the same variety Minghui 63 were evaluated in both the laboratory and the field. Bioassays were conducted by using the first instars of two main rice lepidopteran insect species: yellow stem borer, Scirpophaga incertulas (Walker) and Asiatic rice borer, Chilo suppressalis (Walker). All transgenic lines exhibited high toxicity to these two rice borers. Field evaluation results also showed that all transgenic lines were highly insect resistant with both natural infestation and manual infestation of the neonate larvae of S. incertulas compared with the nontransformed Minghui63. Bt protein concentrations in leaves of 10 transgenic rice lines were estimated by the sandwich enzyme-linked immunosorbent assay. The cry9C gene had the highest expression level, next was cry2A gene, and the cry1Ac gene expressed at the lowest level. The feeding behavior of 7-d-old Asiatic rice borer to three classes of Bt transgenic rice lines also was detected by using rice culm cuttings. The results showed that 7-d-old larvae of Asiatic rice borer have the capacity to distinguish Bt and non-Bt culm cuttings and preferentially fed on non-Bt cuttings. When only Bt culm cuttings with three classes of different Bt proteins (CrylAc, Cry2A, and Cry9C) were fed, significant distribution difference of 7-d-old Asiatic rice borer in culm cuttings of different Bt proteins also was found. In the current study, we evaluate different Bt genes in the same rice variety in both the laboratory and the field, and also tested feeding behavior of rice insect to these Bt rice. These data are valuable for the further development of two-toxin Bt rice and establishment of appropriate insect resistance management in the future.

Effect of Transgenic Bacillus thuringiensis Rice Lines on Mortality and Feeding Behavior of Rice Stem Borers (Lepidoptera: Crambidae)

Ten transgenic Bacillus thuringiensis Bt rice, Oryza sativa L., lines with different Bt genes (two Cry1Ac lines, three Cry2A lines, and five Cry9C lines) derived from the same variety Minghui 63 were evaluated in both the laboratory and the field. Bioassays were conducted by using the first instars of two main rice lepidopteran insect species: yellow stem borer, Scirpophaga incertulas (Walker) and Asiatic rice borer, Chilo suppressalis (Walker). All transgenic lines exhibited high toxicity to these two rice borers. Field evaluation results also showed that all transgenic lines were highly insect resistant with both natural infestation and manual infestation of the neonate larvae of S. incertulas compared with the nontransformed Minghui63. Bt protein concentrations in leaves of 10 transgenic rice lines were estimated by the sandwich enzyme-linked immunosorbent assay. The cry9C gene had the highest expression level, next was cry2A gene, and the cry1Ac gene expressed at the lowest level. The feeding behavior of 7-d-old Asiatic rice borer to three classes of Bt transgenic rice lines also was detected by using rice culm cuttings. The results showed that 7-d-old larvae of Asiatic rice borer have the capacity to distinguish Bt and non-Bt culm cuttings and preferentially fed on non-Bt cuttings. When only Bt culm cuttings with three classes of different Bt proteins (Cry1Ac, Cry2A, and Cry9C) were fed, significant distribution difference of 7-d-old Asiatic rice borer in culm cuttings of different Bt proteins also was found. In the current study, we evaluate different Bt genes in the same rice variety in both the laboratory and the field, and also tested feeding behavior of rice insect to these Bt rice. These data are valuable for the further development of two-toxin Bt rice and establishment of appropriate insect resistance management in the future.

Bt rice harbouring cry genes controlled by a constitutive or wound‐inducible promoter: protection and transgene expression under Mediterranean field conditions

Seven homozygous transgenic lines of two European commercial cultivars of rice (Ariete (A) and Senia (S)), harbouring the cry1B or cry1Aa Bacillus thuringiensis (Bt) delta-endotoxin genes, were field evaluated for protection from striped stem borer (SSB) (Chilo suppressalis) damage during the 2001 and 2002 summer crop seasons in the Delta de l'Ebre region, Spain. The plant codon-optimized toxin gene was placed under the control of the promoter of either the constitutive ubi1 gene or the wound-inducible mpi gene from maize. Stable, high-level, insecticidal protein accumulation was observed throughout root, leaf and seed tissues of field-grown plants harbouring the cry1B (lines A64.1, A33.1, A3.4 and S98.9) or cry1Aa (lines S05.1 and A19.14) genes under the control of the ubi1 promoter. Conversely, no toxin was detected in unwounded vegetative tissues of the A9.1 line harbouring the cry1B gene controlled by the mpi promoter, indicating that natural environmental stresses did not trigger the activity of the wound-inducible promoter. However, the toxin accumulated at 0.2% total soluble proteins in A9.1 sheath tissue exhibiting brown lesions resulting from SSB damage. The agronomical traits and performance of the transgenic lines were generally comparable with parental controls, except in the two lines accumulating Cry1Aa, which exhibited a high frequency of plants non-true to type. Natural infestation was assisted with manual infestations of L2/L3 SSB larvae in border control plants surrounding the experimental plots, which served as a reservoir for the second-cycle SSB population. The observation of damage (brown lesions and dead hearts) during the crop season and dissection of plants at harvest stage revealed a range of protection amongst the transgenic lines, which was highly consistent with the level of toxin accumulation and with previous experience in greenhouse assays. Lines A3.4 and S05.1 were found to exhibit stable and full protection against SSB attacks, mediated by the accumulation of Cry1B and Cry1Aa toxin, respectively, which was comparable with that afforded by the spraying of chemical insecticides on control plants. The wound-induced A9.1 line exhibited a satisfactory level of protection, with a notably low level of penetration of SSB larvae in the stems, but higher external symptoms than constitutive lines, probably due to the time lag to benefit from the protective effect of Cry1B.

Assessment of Experimental Bt Events Against Fall Armyworm and Corn Earworm in Field Corn

Performance of experimental Bacillus thuringiensis (Bt) MON events alone and pyramided with MON810 were evaluated over 3 yr in Georgia and Alabama. Ability of events to prevent whorl defoliation by the fall armyworm, Spodoptera frugiperda (J. E. Smith), and natural ear feeding damage by the corn earworm, Helicoverpa zea (Boddie) was assessed. In each year, near-isogenic hybrids with novel single transformation events and crosses pyramided with the MON810 event were compared with the standard single MON810 event and nontransformed susceptible control. Events were tested for resistance to whorl damage by manual infestations of fall armyworm and ear damage by natural infestations of corn earworm. All Bt events tested reduced fall armyworm whorl damage ratings per plant compared with the susceptible hybrid. All Bt treatments also had considerably less ear infestation and damage by corn earworm compared with the nontransgenic isoline. The MON841, MON849, and MON851 events reduced ear damage by H. zea but were not as effective as other novel events and were not advanced for further testing after the 1999 season. Pyramiding events compared with single events did not improve control of fall armyworm whorl damage, but they generally did prevent more ear damage by corn earworm. The MON84006 event singly and pyramided with MON810 had superior control of whorl-stage damage by S. frugiperda and ear damage by H. zea compared with MON810. Deployment of new events and genes could provide additional tools for managing the potential for insect resistance to Bt toxins. Furthermore, improved control of whorl and ear infestations by H. zea and S. frugiperda would increase the flexibility of planting corn, Zea mays L., and permit double cropping of corn in areas where these pests perennially reach damaging levels.

Assessment of experimental Bt events against fall armyworm and corn earworm in field corn.

Performance of experimental Bacillus thuringiensis (Bt) MON events alone and pyramided with MON810 were evaluated over 3 yr in Georgia and Alabama. Ability of events to prevent whorl defoliation by the fall armyworm, Spodoptera frugiperda (J. E. Smith), and natural ear feeding damage by the corn earworm, Helicoverpa zea (Boddie) was assessed. In each year, near-isogenic hybrids with novel single transformation events and crosses pyramided with the MON810 event were compared with the standard single MON810 event and nontransformed susceptible control. Events were tested for resistance to whorl damage by manual infestations of fall armyworm and ear damage by natural infestations of corn earworm. All Bt events tested reduced fall armyworm whorl damage ratings per plant compared with the susceptible hybrid. All Bt treatments also had considerably less ear infestation and damage by corn earworm compared with the nontransgenic isoline. The MON841, MION849, and MON851 events reduced ear damage by H. zea but were not as effective as other novel events and were not advanced for further testing after the 1999 season. Pyramiding events compared with single events did not improve control of fall armyworm whorl damage, but they generally did prevent more ear damage by corn earworm. The MON84006 event singly and pyramided with MON810 had superior control of whorl-stage damage by S. frugiperda and ear damage by H. zea compared with MON810. Deployment of new events and genes could provide additional tools for managing the potential for insect resistance to Bt toxins. Furthermore, improved control of whorl and ear infestations by H. zea and S. frugiperda would increase the flexibility of planting corn, Zea mays L., and permit double cropping of corn in areas where these pests perennially reach damaging levels.

Concentration of moniliformin produced by Fusarium species in grains of transgenic Bt maize hybrids compared to their isogenic counterparts and commercial varieties under European corn borer pressure

AbstractThe European corn borer (ECB), Ostrinia nubilalis Hb., is a major pest of maize in Central Europe and is suspected to promote infection of maize with Fusarium species. The objectives of this study were to (1) determine moniliformin (MON) concentration in early maturing European Bt maize hybrids, their isogenic counterparts, commercial cultivars and experimental hybrids, (2) evaluate the association between MON concentration and ECB resistance and (3) correlate MON concentration with concentrations of other mycotoxins determined from the same plant materials. The field experiments were performed at five locations in Germany. MON concentration was significantly higher with manual infestation of ECB larvae (296 μg/kg) than under insecticide protection (66 μg/kg). Bt hybrids showed significantly lower MON concentrations and higher grain yields under manual ECB infestation than their corresponding isogenic counterparts, as well as commercial and experimental hybrids. All ECB resistance traits and grain yield under ECB infestation were significantly correlated with MON concentration. Correlations between concentrations of MON and other Fusarium mycotoxins were not significant. The use of Bt maize hybrids or insecticides to control ECB reduces the contamination of maize grains with MON in Central Europe. The presence of resistance genes against Fusarium species in the current elite maize germplasm was indicated by ECB susceptible non‐Bt hybrids with low‐MON concentrations.

A Comparison of Maize Stalk Rot Occurrence in Bt and Non-Bt Hybrids.

Stalk rots, caused by a complex of fungal species, are among the most widespread and destructive diseases of maize. Larvae of the European corn borer (ECB) (Ostrinia nubilalis) promote stalk rot development by creating entry points for fungi, serving as vectors of pathogens, and causing physiological stress that may predispose plants to stalk decay. Field experiments were conducted in 1998, 1999, and 2000 to determine whether the use of transgenic Bt hybrids expressing insecticidal proteins would influence stalk rot symptoms (pith disintegration, pith discoloration, and lodging). Five hybrids representing different Bt types (or "Bt events") (176, BT11, MON810, DBT418, and CBH351) were paired with their near-isogenic, non-Bt counterparts and subjected to treatments of manual and natural infestation with ECB larvae. Manual infestation resulted in significantly more ECB tunneling than natural infestation in 1998 and 1999 and significantly more lodging in 1998. There were significant linear correlations between ECB injury and stalk rot symptoms in non-Bt hybrids in 1998 and 1999, but not in 2000. A standard foliar insecticide treatment for ECB did not significantly affect stalk rot symptoms. In 1998, Bt hybrids had significantly less ECB tunneling, stalk discoloration, pith disintegration, and lodging compared with non-Bt hybrids, but these effects depended upon the Bt event and the infestation treatment. Similar but less pronounced effects of Bt events were observed in 1999. The 2000 results were more variable; the amount of pith disintegration was significantly lower but discoloration was significantly higher in the BT11 hybrid compared with its non-Bt counterpart, and the amount of lodging was significantly higher in the event 176 hybrid compared with its non-Bt counterpart. The ratio of stalk strength to grain weight did not consistently differ between Bt and non-Bt hybrids. These results indicate that, although specific Bt events in some years may cause reductions in stalk rot, the overall effect of Bt transformation on stalk rot occurrence is highly variable.

Ear Damage of Sweet Corn Inbreds and Their Hybrids under Multiple Corn Borer Infestation

In Mediterranean countries, the principal corn (Zea mays L.) pest is the pink stem borer (PSB) (Sesamia nonagrioides Lef.), followed in importance by the European corn borer (ECB) [Ostrinia nubilalis (Hübner)]. Our objective was to quantify injury by these pests in a set of inbreds that showed different levels of ear damage by the PSB in a previous study and in their hybrids. A diallel among seven sweet corn inbreds that varied for ear damage by PSB was evaluated in three environments under PSB and ECB infestations. The importance of general combining ability (GCA) and specific combining ability (SCA) for ear damage by corn borer was determined. Inbred parents were also tested under manual infestation conditions with both borers. There was variability for ear damage traits among sweet corn inbred lines, but none of them were completely resistant. General combining ability effects were significant for the general appearance of the ear, ears with damaged grain, and ears with damaged shanks under PSB infestation. Under PSB infestation, SCA was not significant for any trait. Most traits showed significant GCA effects under ECB infestation, although SCA effects were also important for some damage traits. The inbred EP61 could supply some favorable alleles because it showed negative and significant GCA effects for ear damage under infestation by both species. Inbreds EP59 and V7726 showed negative and significant GCA effects for ear damage by ECB. These inbreds could be included in a sweet corn synthetic population that would be improved to decrease ear damage by corn borers.

Elite Indica transgenic rice plants expressing modified Cry1Ac endotoxin of Bacillus thuringiensis show enhanced resistance to yellow stem borer (Scirpophaga incertulas).

Bt-transgenics of elite indica rice breeding lines (IR-64, Pusa Basmati-1 and Karnal Local) were generated through biolistic or Agrobacterium-mediated approaches. A synthetic cry1Ac gene, codon optimised for rice and driven by the maize ubiquitin-1 promoter, was used. Over 200 putative transformants of IR-64 and Pusa Basmati-1 and 26 of the Karnal Local were regenerated following use of the hpt (hygromycin phosphotransferase) selection system. Initial transformation frequency was in the range of 1 to 2% for particle bombardment while it was comparatively higher (approximately 9%) for Agrobacterium. An improved selection procedure, involving longer selection on the antibiotic-supplemented medium, enhanced the frequency of Bt-transformants and reduced the number of escapes. Molecular evaluation revealed multiple transgene insertions in transformants, whether generated through biolistic or Agrobacterium. In the latter case, it was also observed that all genes on the T-DNA do not necessarily get transferred as an intact insert. Selected Bt-lines of IR-64 and Pusa Basmati-1, having Bt-titers of 0.1% (of total soluble protein) and above were evaluated for resistance against manual infestation of freshly hatched neonate larvae of yellow stem borers collected from a hot spot stem borer infested area in northern India. Several Bt-lines were identified showing 100% mortality of larvae, within 4-days of infestation, in cut-stem as well as vegetative stage whole plant assays. However, there was an occasional white head even among such plants when assayed at the reproductive stage. Results are discussed in the light of resistance management strategies for deployment of Bt-rice.

Comparison of Bt maize hybrids with their non‐transgenic counterparts and commercial varieties for resistance to European corn borer and for agronomic traits

AbstractThe European corn borer (ECB), Ostrinia nubilalis (Hübner), is a major pest of maize (Zea mays L.) in Central Europe. In order to compare transgenic Bt maize hybrids with their non‐transgenic counterparts and commercial hybrids, field trials and a laboratory bioassay were conducted. The field experiments were performed at four locations with natural and manual infestation of ECB larvae in 1998 and 1999. Transgenic Bt hybrids showed significantly lower means than their corresponding non‐transgenic counterparts and commercial hybrids for all resistance traits (damage rating of stalks, number of larvae per plant, and percentage of damaged plants or ears under infestation). Bt hybrids containing the CryIA(b) gene under the control of green tissue and pollen‐specific promoters (event 176) showed a significantly higher percentage of damaged ears than Bt hybrids carrying the CryIA(b) gene under the control of a constitutive promoter (Mon810). Bt and non‐Bt hybrids showed no significant differences for all agronomic traits, except for plant height under insecticide protection and grain yield reduction under infestation, whereas Bt hybrids had significantly lower means than their non‐transgenic counterparts and other commercial hybrids. All resistance traits were significantly correlated with grain yield reduction. The laboratory bioassay confirmed the level of antibiosis of Bt hybrids against neonate ECB larvae. Bt hybrids showed the highest level of ECB resistance and therefore are an attractive method of preventing ECB damage within an integrated pest‐management system.

Field performance of transgenic elite commercial hybrid rice expressing Bacillus thuringiensis δ-endotoxin

Here we describe development of transgenic elite rice lines expressing a Bt fusion gene derived from cryIA(b) and cryIA(c) under the control of rice actinI promoter. The lines used in the study were indica CMS restorer line of Minghui 63 and its derived hybrid rice Shanyou 63. The level of Bt fusion protein CryIA(b)/CryIA(c) detected in Minghui 63 (T51-1) plants was 20 ng/mg soluble protein. The Bt Shanyou 63 was field-tested in natural and repeated heavy manual infestation of two lepidopteran insects, leaffolder and yellow stem borer. The transgenic hybrid plants showed high protection against both insect pests without reduced yield.

Evaluation of Transgenic, Bt -Containing Corn Hybrids

European corn borer [ECB; Ostrinia nubilalis (Hubner]) is a major economic pest of corn (Zea mays L.) throughout the Corn Belt. Transgenic corn hybrids containing a modified Bacillus thuringiensis (Bt) gene were evaluated at four Corn Belt environments as a novel method of managing ECB. Manual infestation was done to insure the presence of ECB, and Bt-based insecticides were used to control natural infestations. First generation ECB damage, estimated by leaf damage ratings, and second generation ECB damage, estimated by amount of stalk tunneling, were reduced or eliminated with the use of the Bt hybrids. Grain yield, stalk lodging, and test weight of the transgenic hybrids were not affected by first or second generation ECB infestation. Grain yields of six nontransgenic hybrids were not affected by first generation ECB infestation, but second generation ECB infestation damage, even though relatively low in the environments tested, reduced grain yield in these hybrids by 4.0 to 6.6%, slightly increased stalk lodging, and slightly decreased test weight. In the absence of ECB pressure, the transgenic hybrids performed the same as their non-transgenic counterparts. It is clear that the incorporation of the Bt gene into corn hybrids provides a high level of protection against ECB, with little if any effect on agronomic performance.

European Corn Borer (Lepidoptera: Pyralidae) Larvae as Vectors of Fusarium moniliforme, Causing Kernel Rot and Symptomless Infection of Maize Kernels

Field and greenhouse experiments were conducted to assess the ability of Ostrinia nubilalis (Hubner) larvae to act as vectors of Fusarium moniliforme J. Sheld. from maize leaf surfaces to kernels. Leaf surfaces of plants in the dough stage were sprayed with a spore suspension of F. moniliforme strain EA-2, after which plants were manually infested with O. nubilalis larvae or kernels were mechanically wounded. In 2 greenhouse experiments, O. nubilalis larvae significantly increased incidence of kernel rot symptoms and symptomless infection. Strain EA-2 was detected on O. nubilalis larvae, in plant debris in the leaf axils, and in 28–39% of F. moniliforme -infected kernels from plants manually infested with O. nubilalis. In the field, O. nubilalis infestation significantly increased incidence of kernel rot symptoms (1995) and symptomless infection (1994 and 1995). Symptomless infection was highest for treatments in which larvae were artificially contaminated with F. moniliforme strain EA-4 prior to manual infestation of plants. F. moniliforme strain EA-2 (from leaf surfaces) and strain EA-4 (from larvae) were recovered from kernels in the O. nubilalis -infested treatments in 1995. Results indicated that O. nubilalis larvae can act as vectors of F. moniliforme, increasing symptoms of Fusarium kernel rot and symptomless infection of kernels by F. moniliforme. Kernel wounding also is an important factor contributing to this disease.

Damage and Grain Yield Losses Caused by European Corn Borer (Lepidoptera: Pyralidae) in Early Maturing European Maize Hybrids

The European corn borer, Ostrinia nubilalis (Hubner), is a major pest of maize, Zea mays L., in Central Europe. The resistance of 8 early maturing commercial maize hybrids and 6 experimental hybrids against European corn borer was assessed during 1996 and 1997 in Germany. Resistance was evaluated by yield reduction and damage ratings under natural and manual infestation in 11 or 6 environments, respectively. The infestation level of European corn borer was assessed by the percentage of damaged plants and number of larvae per plant in each environment. Average grain yield of the commercial hybrids was reduced by 0.28% for each 1% of damaged plants and by 6.05% for each European corn borer larvae per plant. All commercial and experimental hybrids were susceptible to European corn borer attack. The commercial hybrids showed little variation in their resistance to European corn borer. The experimental hybrids derived from crosses between resistant inbreds were more resistant than crosses between intermediate and susceptible inbreds. The evaluation of yield reduction required manual infestation because of the low natural infestation level in most environments. However, a comparison of error variances and repeatabilities revealed that they were of similar magnitude for environments with a high level of natural and manual infestation. Yield reduction and damage ratings were highly correlated ( r p ≤ 0.85) under both infestation regimes. Consequently, the latter trait should be useful for indirect selection to improve European corn borer resistance in maize.