Rice growth and yield as affected by the whorl maggot Hydrellia philippina Ferino (Diptera: Ephydridae)

Grain yields of rice cultivars IR36 and IR40 artificially infested with Hydrellia philippina flies were compared with those of non-infested plants in two screenhouse and four field tests. Infestation rates as high as 800 flies per 49 plants resulted in 82% of the leaves damaged but did not reduce grain yields of either IR36 or IR40. Larval feeding decreased plant height and increased number of panicle-bearing tillers of IR36. Maturity of damaged plants was delayed 7–10 days.     

Management of nitrogen and phosphorus rates does not suppress verticillium wilt in yukon gold

Effect of nitrogen and phosphorus fertilization rates on the incidence of Verticillium wilt caused byVerticillium albo-atrum orV. dahliae and tuber yield in potato cv Yukon Gold was evaluated in field plots. In three years of study,V. albo-atrum caused a higher incidence of wilt symptoms (74%–100%) thanV. dahliae (5%–81%) resulting in lower marketable tuber yield. In plots infested withV. albo-atrum, tuber yield ranged from 12.3-22.8 T ha1 compared to 18.1– 31.5 T ha^-1 in plots infested withV. dahliae. Application of nitrogen above (280 kg ha^-1) or below (70 kg ha^-1) the recommended rate of 140 kg ha^-1 at planting did not suppress foliar symptoms or protect against yield loss caused by eitherV. albo-atrum orV. dahliae. Similarly, phosphorus rate adjustments did not consistently affect disease incidence regardless of the pathogen. Management of nitrogen or phosphorus fertility rates at planting does not appear to be a viable approach for suppressing Verticillium wilt in the determinant, wiltsusceptible cultivar Yukon Gold.     

Evaluation ofLaetisaria arvalis as a biological control agent ofRhizoctonia solani on white potato

Laetisaria arvalis, a soil-inhabiting basidiomycete, reducedRhizoctonia solani infection of white potato. A greenhouse study that monitored population levels of both fungi showed that soil infested withL. arvalis suppressed the growth ofR. solani after eight wks. Populations ofL. arvalis andR. solani increased after 11 wks. when both fungi were infested simultaneously and whenL. arvalis was introduced to soil previously infested withR. solani. Five years of field studies showed that variousL. arvalis seed treatments and soil amendments reducedR. solani infection of stems and stolons and sclerotial formation on tubers equal to the standard chemical treatment of pentachloronitrobenzene (PCNB) + thiabendazole. No relationship was shown between populations ofL. arvalis andR. solani in field plot soils, but native or wild strains ofL. arvalis were shown to be present at detectable levels in field soils.     

Movement and survival of corn rootworm in seed mixtures of SmartStax® insect-protected corn

SmartStax^® insect-protected corn (Zea mays L.) contains genes for six Bacillus thuringiensis (Bt) proteins controlling both lepidopteran pests and the corn rootworm complex (Diabrotica spp.). The properties of SmartStax, particularly the multiple effective modes of action (i.e., each Bt protein provides a high level of control of the target pests with a low probability of cross-resistance among the proteins), have provided the opportunity to add to previously approved structured refuge options by combining the non-Bt refuge seed with SmartStax seed in a seed mix. Seed mixes ensure that a refuge is present in every Bt field, remove concerns about grower compliance with refuge requirements, and provide grower convenience. However, seed mixes could increase the likelihood that larval insects move between Bt and non-Bt plants and vice versa. Assessing the insect resistance management (IRM) value of a seed mix refuge requires an assessment of the amount of larval movement, and the consequences of that movement, for the key target pests. The studies here present such data for control of corn rootworm by SmartStax corn, which contains the rootworm-active protein Cry3Bb1 and the binary protein Cry34Ab1/Cry35Ab1. In a growth chamber experiment, SmartStax was most effective against first instars and significantly effective against second instars, but did not control third instars. In a field study of movement from a heavily infested non-Bt plant onto surrounding plants, a larger percentage of insects successfully dispersed from the infested plant when the surrounding plants were non-Bt plants than when they were SmartStax plants. A paired-plant study showed that few larvae migrated from infested SmartStax plants and survived on nearby non-Bt plants; larvae that migrated from infested non-Bt plants had low survival if the adjacent plants were SmartStax. Replicated field studies of plant-to-plant movement indicated that the non-Bt plants in a 5% or 10% seed mix consistently supported large populations of susceptible insects and represented a productive refuge, whereas the SmartStax plants had few or no survivors. The timing of emergence from seed mix plots containing 5% or 10% non-Bt plants was more similar to that of the non-Bt plots than that of the SmartStax plots. Thus, the available growth chamber and field data indicate that a seed mix of 5% or more will provide an effective refuge for corn rootworm in SmartStax corn.     

Root deterioration in the potato early dying syndrome: Causes and effects of root biomass reductions associated with colonization byVerticillium dahliae

Russet Burbank potatoes were grown in the greenhouse in a split-root culture system to assess the impact of pathogens associated with the Potato Early Dying Syndrome (PED) on root deterioration. Plants were grown with all, half, or none of the root system in steamed soil infested withVerticillium dahliae, or in field soil infested withV. dahliae and other PED pathogens. The direct impact of pathogens on root deterioration versus indirect effects resulting from premature senescence of the whole plant was evaluated. Root biomass did not differ significantly between root halves from the same plant in infested and uninfested soil. Root biomass from plants with both halves of the root system in uninfested soil was usually greater than from plants with one or both halves growing in infested soil. Root biomass decreased rapidly after plant stems were inoculated with conidial suspensions ofV. dahliae. Root deterioration in PED was associated with premature senescence of foliar tissue and occurred independently of root colonization by root-colonizing pathogens.     

Effects of infestation with Globodera rostochiensis (Wollenweber) Behrens Rol on the growth of four potato cultivars

Four potato cultivars were grown in plots which, following previous treatments, contained few or many Globodera rostochiensis (Wollenweber) Behrens Rol. Soil moisture content, leaf water potential and percentage ground cover were measured each week, and whole-plant samples (including roots) were taken $\text{6}\text{1}\text{2}$ and 9 weeks for planting. Leaf areas, fresh and dry weights and inorganic nutrient contents were measured on these samples. Stomatal resistance was measured on one occasion, 13 weeks after planting, and soil samples were taken midway between plants on the same date and roots extracted from them. Yields were measured 30 weeks after planting. In terms of yield Cara, which contains the resistance gene H₁, tolerated nematode attack better than the other cultivars. Of the non-resistant cultivars, Pentland Crown was the most tolerant and Pentland Dell the least; the fact that Maris Peer yielded less than Pentland Dell in heavily infested plots is probably attributable to its early maturity date and lower yield potential. The shoot:root ratio measured 9 weeks after planting was similar for all cultivars following the same previous treatment, but was decreased from 11·9 when the previous crop was Maris Piper to 5·6 when the previous crop was Pentland Crown. Good yields in the presence of nematodes were produced by Cara (and to a lesser extent Pentland Crown) because it produced extra roots in the heavily infested plots; Pentland Dell and Maris Peer produced fewer roots in heavily infested plots. Measuring leaf water potentials and soil water contents was of little value for estimating tolerance but the least tolerant cultivar, Pentland Dell, showed the largest increase in stomatal resistance in heavily infested plots, with Cara showing the smallest. Percentage ground-cover measurements through the growing season gave the best overall picture of the reactions of the four cultivars to nematode infestation, but were time-consuming. Concentrations of potassium in haulm dry matter were decreased and those of calcium increased by nematodes, with the magnitudes of the effects least in Cara and greatest in Pentland Dell. The prospect of developing an assay for tolerance sufficiently convenient for use by plant breeders must depend upon adapting a simple test of this type to a pot scale.     

Amendment of soil with African marigold and sunn hemp for management of Meloidogyne incognita in selected legumes

Field experiments were conducted in 2008 and 2009 in the tropical rainforest zone of Nigeria to investigate the effects of amendment of soil with seedlings of African marigold (Tagetes erecta) and sunn hemp (Crotalaria juncea) incorporated singly in plots on Meloidogyne incognita and yield of cowpea and soybean. The experimental field, which was naturally free of plant-parasitic nematodes, was inoculated with chopped roots of M. incognita race 2-infected Celosia argentea roots and planted to tomato to increase M. incognita population at the site.Eight week-old marigold seedlings were incorporated in cowpea or soybean field and eight week-old sunn hemp seedlings were also incorporated in cowpea or soybean field. At the ends of the experiments, M. incognita population densities were significantly higher in control plots than those of the plots amended with marigold or sunn hemp with correspondingly higher grain yield in the amended plots in both cowpea and soybean fields in both years. A significantly higher population of the nematode and consequently, lower yield was associated with cultivar Ife Brown than cultivar Ife Bimpe of cowpea for each treatment whereas in soybean cultivars, the pattern was not definite. Also twelve seedlings of marigold or sunn hemp per plot incorporated into the soil produced significantly higher grain yield in cultivar Ife Brown of cowpea and cultivar TGX 1440 of soybean compared to six seedlings per plot. The results of this study suggest that incorporating marigold or sunn hemp in M. incognita-infected cowpea or soybean field has potentials to suppress M. incognita population and reduce nematode damage on yield of the associated leguminous crops.     

Potato production and incidence ofVerticillium dahliae following rotation to nonhost crops and soil fumigation in the state of Washington

For three years, potato yields, tuber quality, and incidence ofVerticillium dahliae were measured in field plots previously cropped for one year to the following nonhosts: sudan grass, green peas followed by sudan grass (same year), spring wheat, spring wheat followed by sudan grass (same year), sweet corn and field corn. One year rotation to nonhosts did not reduce the population ofV. dahliae propagules in the soil and in only one of the three years wereV. dahliae propagule numbers in potato stems significantly reduced in plots following nonhost crops, compared with plots following potatoes. Verticillium wilt symptoms in potatoes were not reduced by one year rotation to any of these crops and only in one year in three was yield significantly increased. In two of three years, percent U.S. No. 1 tubers was increased following one-year rotation with green peas plus sudan grass, and in one of the two years, specific gravity was increased by rotation. Rotational cropping to nonhosts for two years between potatoes significantly reduced preplant soil populations ofV. dahliae propagules in the soil and in potato stems the following fall. However, soil populations in these two year rotational plots the spring following potato were not reduced compared to plots previously cropped to potatoes two consecutive years. Cropping to nonhosts for two years had no consistent effect on incidence of Verticillium wilt in subsequent potato crops. Two years’ rotation to nonhosts increased plant height and yield compared to continuous cropping to potato but not percent U.S. No. 1 tubers. The various nonhost crops all had about the same non-significant effect on yield. In two out of three years’ trials, fumigation significantly reduced both the incidence of Verticillium wilt and number ofV. dahliae propagules in stems in plots compared to plots non-fumigated. In only one trial, fumigation significantly increased tuber yields and percent U.S. No. 1 tubers.     

Effects of Soil Water Level,Black Dot (Colletotrichum coccodes) Infested Soil and Nutrient Depletion on Potato in a Controlled Environment

The effects of soil water level and soil infested or not infested with Colletotrichum coccodes were quantified and compared on Umatilla Russet potato in repeated greenhouse trials. Nitrogen levels in leaflets and tuber yield differed significantly for effect of water level but there was no effect for soil infestation in both trials. More leaflet N as measured by chlorophyll and less tuber yield occurred in the low than the medium and high soil water treatments. Number of progeny tubers was not affected by C. coccodes but numbers were significantly less for the low water level than the high water level in one trial. Root weight was significantly reduced by C. coccodes in both trials and was significantly less in the high than the low and medium soil water levels in one trial. Incidence of infected progeny tubers was significantly reduced in infested soils for the low soil water compared to the medium or high soil water levels in one trial. The effect of increasing levels of water in infested soils had large and significant increases for percentage of stem area with sclerotia in both trials. Managing soil water by not overwatering in irrigated potato fields in the presence of C. coccodes may reduce black dot severity and quantity of sclerotia that potentially can overwinter and serve as sources of infection for subsequent crops. Analyses demonstrated a potential for significant associations between plant and disease variables not evidence for cause and effect.     

Comparison of stem borer damage and resistance in semidwarf Indica rice varieties and prototype lines of a new plant type

The rice (Oryza sativa L.) “new plant type” (NPT), currently under development at the International Rice Research Institute, Philippines, differs in genetic background and plant architecture from the semidwarf Indica varieties that now predominate in tropical lowland areas. The NPT is derived from tropical Japonica germplasm and has fewer and larger stems and panicles than do semidwarf Indica varieties. We compared stem borer damage and resistance in NPT lines and semidwarf Indica varieties under field and greenhouse conditions. Stem borer damage in field plots of the NPT lines IR65564 and IR68011 was higher than in plots of the Indica varieties IR64 and IR72 during the 1999 dry season but not the wet season. In both seasons, IR68011 had higher densities of egg masses of the striped stem borer (SSB, Chilo suppressalis) than did the other three entries. There were no consistent differences among entries in density of egg masses of the yellow stem borer (YSB, Scirpophaga incertulas). In the 2000 wet season, stem borer populations were low, but SSB egg masses were found only on IR68552-100, the only NPT line in the experiment. In all three seasons, NPT lines had higher proportions of SSB larvae and pupae in stems after harvest, and lower proportions of YSB, than did Indica varieties. In artificially infested field cages, SSB larval survival was highest on reproductive stage plants of IR68011 in the 1999 dry season and there was a trend of higher YSB adult weight on IR68011 in the 1999 dry and wet seasons. Three NPT lines and three Indica varieties evaluated under greenhouse conditions showed no consistent differences in resistance to either stem borer species, as measured by percent survival from egg to adult and female development time and weight. The lack of consistent differences in stem borer survival and development between the NPT lines and Indica varieties was contrary to the expectation that the morphology of the NPT would render it more susceptible to stem borers. Our results indicate that NPT lines are not consistently or strongly more susceptible to stem borers than are improved Indica varieties and suggest that ovipositional attractiveness to SSB is a factor contributing to higher stem borer damage to some NPT lines.     

Mechanisms of resistance to potato leafhopper,Empoasca fabae (Harris), in potato

Potato genotypes were evaluated for resistance to natural infestations of the potato leafhopper,Empoasca fabae (Harris), in the field. Characterization of Type A and B glandular trichomes, phenolic properties of Type A trichomes, glycoalkaloid content and composition,E. fabae adult and nymph infestation, leaf damage (hopperburn), yield, and yield reduction were determined on genotypes PI 473331 and PI 473334 (accessions ofSolatium berthaultii (Hawkes)), NY123 and Q174-2 (advanced hybrids), and Elba and Allegany (commercial cultivars). Regarding the Type A trichome, PI 473334 was most pubescent, followed by PI 473331, both had high levels of enzymatic browning; on PI 473334 no glycoalkaloids were detected, while on PI 473331 solamargine and solasonine were present. Those genotypes were the least infested by adults; moreover, nymphs were never found on their leaves. PI 473331 and Q174-2 possess Type B trichomes, the latter had levels of Type A trichome comparable to the first and to NY123, while displaying high levels of phenolic oxidation of Type A and very low levels of glycoalkaloids. Although Q174-2 had intermediate infestation ofE. fabae, it suffered a yield reduction comparable to the control cultivar Allegany. The density of Type A trichomes of NY123 was relatively low, even though the browning assay results were significantly elevated. Foliage of this genotype was found to contain the four types of glycoalkaloids studied at high levels.Empoasca fabae infestation on NY123 was intermediate, and it yielded well on infested plots, but suffered an intermediate yield reduction. Elba presented densities of Type A similar to NY123. It suffered the lowest yield reduction despite its high levels of leafhopper infestation and hopperburn. Its tolerance might be associated with its phenology, since it is a late-maturing cultivar. High scores of the modified enzymatic browning assay were correlated with high infestation and high leaf damage. Results indicated a significant correlation between leafhopper infestation and hopperburn.     

Inoculum potential of Verticillium species in crop and weed residues overwintering in infested soil

Viable propagules ofVerticillium albo-atrum were recovered from roots and stems of naturally infected weeds and sunflower cultivars before or after burial in the field and from stems and roots of certain non-infested crops after burial in the field for seven months.Verticillium dahliae was recovered less frequently, then only from the roots ofSolanum nigrum (black nightshade). Survival of these pathogens after burial for 7 months varied considerably, ranging from 38 to 58% in sunflower stems and from 19 to 235% in roots of weeds. In stems of weeds and crops which did not contain propagules ofV. albo-atrum before burial, the fungus was recovered consistently after burial, indicating that saphophytic colonization probably occurred during interment.     

Weed competitiveness of the lowland rice varieties of NERICA in the southern Guinea Savanna

Weed competition is a major constraint to lowland rice production in West Africa. Interspecific rice varieties named New Rice for Africa (NERICA) may have superior weed competitiveness and could as such play an important role in integrated weed management. The NERICA varieties were developed from the wide cross between high-yielding Oryza sativa (L.) and weed competitive and disease resilient Oryza glaberrima (Steud.). In this study weed competitiveness of all 60 lowland varieties of NERICA (NERICA-L) was compared with their most frequently used parents [IR64 (O. sativa) and TOG5681 (O. glaberrima)], the weed competitive variety Jaya (O. sativa) and the O. glaberrima upland NERICA parent CG14. During the 2006 and 2007 rainy seasons these varieties were grown under weed-free and weedy conditions in a lowland farmers’ field with partially controlled irrigation in south-east Benin. Weedy plots included single hand weeding at 28 days after sowing, whereas weed-free plots were weekly weeded.     

Yield stability of faba bean lines under diverse broomrape prone production environments

Faba bean (Vicia faba L.) is one of the important pulse crops grown in many parts of the world. Its production and productivity are affected by different biotic and abiotic stresses. Broomrape (Orobanche and Phelipanche spp.) causes yield losses of 7- 80% in major faba bean growing countries mainly in the Mediterranean Basin and Nile Valley countries. Host plant resistance is found to be the most effective and economic method of broomrape control. Efforts made at the International Center for Agriculture Research in the Dry Areas over many years to develop advanced breeding lines with acceptable resistance and tolerance levels to broomrape have resulted in the identification of several useful breeding lines. These lines were shared with National Agricultural Research Systems (Egypt, Sudan, Tunisia and Portugal) as part of the Faba Bean Orobanche International Nursery, in order to test their stability across three seasons (2005, 2006 and 2007). The results showed that Orobanche plant number, dry weight, Orobanche index, flowering date, maturing date and grain yield were significantly different among lines and locations. AMMI analysis showed that some lines derived from hybrid bulk populations “HBP/DS0/2000” and “HBP/ES0/2000” showed acceptable levels of yield stability in the presence of Orobanche infections across all environments compared with susceptible check. In highly infested soils, the tolerant and resistant lines gave acceptable levels of yield compared with the susceptible check. However, the yield potential of resistant and tolerant lines in non-infested soils was lower than the highly susceptible check.     

Soil suppressiveness to Meloidogyne javanica as induced by organic amendments and solarization in greenhouse crops

We assessed soil suppressiveness against root-knot caused by Meloidogyne javanica, following the incorporation of crop residues (organic amendments [OA]) and soil solarization, under agricultural conditions. Two field experiments were established in tomato greenhouses and a third in a nethouse for growing Antirrhinums, all infested with M. javanica. Dried residues of wild rocket (WR) were incorporated into the soil and then it was solarized to moderate temperatures to partially effect the pathogen population. Root galling on the roots of the successive tomato crop was significantly reduced to different levels by WR, solarization or their combination, in two experiments. Solarization, alone or combined with WR amendment, significantly reduced root knot incidence in the roots of snapdragon, but suppression of root galling in the roots of snapdragon in the following crop was not evident. We further assessed the potential of various herb residues, incorporated in small plots, and solarization to induce soil suppressiveness against root-knot caused by M. javanica. Amending soil with residues of WR, tarragon, peppermint or sage induced soil suppressiveness to root knot even when M. javanica was introduced into the soil after the termination of the treatment, and reduced the galling index in subsequently grown tomato plants, compared with non-amended soil. Our findings further validate the potential role of OA and solarization in inducing soil suppressiveness, which contributes to sustainable management of soilborne pathogens.     

Variation in the responses of melon and watermelon to Macrophomina phaseolina

Macrophomina phaseolina is the causal agent of charcoal rot disease, which attacks many plant species, including those in the Cucurbitaceae. The fungus is frequently isolated from wilted melon and watermelon plants in Israel. Nevertheless, the role of M. phaseolina in disease progress and induction of wilting or yield reduction in watermelons and melons is not clear and not similar. Precise disease identification is important in order to suggest effective control measures. The objective of the current study was therefore to investigate disease progress and document its damage in watermelon and melon. Watermelons and melons were seeded in a field naturally infested with M. phaseolina and in the greenhouse in 10-L pots containing dune sand. Plants were inoculated at 35 days of age using two methods: drenching with macerated fungus around the crown area or stabbing the lower stem with an M. phaseolina-infested toothpick. Disease progress was documented in the field and in the greenhouse. Plant colonization and symptom development were more pronounced in melon than in watermelon. Large lesions and significant internal rotting developed in melon plants inoculated by the two methods in both field and greenhouse. In watermelon, however, no lesions or internal rotting were observed. Disease effect on melons and watermelons was observed only in the field, a short time before harvest, and was expressed as partial wilting and significant loss of shoot and fruit fresh weight similarly to disease appearance under natural infection. No wilting of melons or watermelons was observed in the greenhouse experiment.     

Control of stem nematode,Ditylenchus dipsaci,in narcissus with aldicarb

The efficacy of aldicarb in controlling stem nematode, Ditylenchus dipsaci (Kühn, Filipjev) in narcissus in the field was investigated. Although the proportion of infested narcissus bulbs was reduced when aldicarb (Temik 10G) granules were applied at 6kg a.i./ha in the autumn and spring, some infested bulbs remained and it is concluded that complete eradication of D. dipsaci is not possible.     

Herbicide savings and economic benefits of several strategies to control Sorghum halepense in maize crops

This study was conducted to assess the herbicide savings and the cost efficiency of site-specific herbicide application strategies in comparison with other strategies based on uniform application of herbicides throughout the whole field. The specific situation considered was Sorghum halepense infested maize fields in Spain. The results from a theoretical economic model were contrasted with the information derived from a S. halepense survey conducted in 37 commercial maize fields distributed over three Spanish maize production areas. Seven application strategies were simulated: 1) no herbicide; 2) overall full-rate; 3) overall half-rate; 4) and 5) site-specific spraying infested cells with full- and half-rate, respectively; 6) and 7) site-specific spraying infested cells plus adjacent buffer areas with full- and half-rate, respectively. The simulation results showed that site-specific weed management was the most profitable strategy when S. halepense infested area ranged between 6.5 and 18.7%. This scenario was present in 22% of the surveyed fields. In fields with less than 6.5% infestation (a situation present in 51% of the surveyed fields), yield losses were slight and the most profitable strategy was using no herbicide. When the infested area ranged between 18.7 and 40.8% (19% of the surveyed fields), no significant differences were observed between the net benefits of the various strategies. Full rate herbicide applications throughout the entire field resulted in the highest net returns in fields with more than 40.8% weed infestation (8% of the surveyed fields). In these cases, the added costs of weed detection, mapping and site-specific herbicide application were not justified by the herbicide savings obtained. Likewise, herbicide savings obtained with the various strategies depended on the proportion of the field infested. Considering the high difference between site-specific treatments and uniform application of herbicides when the infested area ranged between 18.7 and 40.8%, and that no significant differences in net returns were observed in this range, site-specific treatments should be preferred. Adding a buffer area to the site-specific treatments does not seem a suitable strategy due to the considerable increases in costs and reductions in herbicide savings.     

Detection of head blight (Fusarium ssp.) in winter wheat by color and multispectral image analyses

The use of camera vision to automatically detect head blight (scab) on wheat ears could provide information about the severity of this dangerous disease and help meet future food traceability requirements. Fusarium spp. is dangerous for both human and animal consumption and the ability to monitor symptom location and severity before the harvested product is further processed or stored could help determine whether the grain is fit for human/animal consumption, for bio-conservation, or is completely unusable.To generate various infection levels, field trials were conducted in 2008 and 2009 using wheat varieties with differing levels of susceptibility to the disease; plots were artificially infected with a spore suspension. A color (red, green, and blue) and a multispectral (red, infrared) camera system with real-time image analysis software were developed and compared to detect disease symptoms in the plots.The chlorophyll defect of the infected wheat ears was classified against the image background by setting binarization thresholds. The result was a black and white image. Single pixels or tiny clusters of pixels not belonging to the symptoms were eliminated by setting an area threshold. For both systems, a linear correlation was found between the camera and the visually detected disease levels of the wheat ears in the plots.In the non-infected control plots without disease symptoms, the multispectral system accurately measured “no disease” even though the digital color system detected too much infection (i.e., a false positive). The multispectral system showed a superior calibration capacity. While the color system had to calibrate for each variety, the multispectral system used only one calibration step before starting the measurements.     

Influence of transgenic hybrid rice expressing a fused gene derived from cry1Ab and cry1Ac on primary insect pests and rice yield

Although dozens of transgenic Bacillus thuringiensis (Bt) rice lines have been developed, none of them has been released to farmers. Under field conditions, we evaluated the influence of a hybrid Bt rice on the primary rice insect pests and rice yield in 2005 and 2006. Four treatments were evaluated, including Bt and non-Bt rice treated with insecticides when necessary, and unprotected Bt and non-Bt rice. Unprotected Bt rice exhibited stable and high control of the three primary lepidopteran pests, Chilo suppressalis Walker, Tryporyza incertulas Walker and Cnaphalocrocis edinalis Güenée. Under unprotected conditions, larval densities of these three pests in Bt plots decreased by 87.5–100% compared to those in non-Bt plots, and percentages of damaged stems and leaves remained less than 0.6% during the entire rice growing season. In early rice growth stages, populations of two important planthoppers, Nilaparvata lugens Stål and Sogatella furcifera Hovarth, were significantly affected only by protection level (protected vs unprotected). However, in late rice growth stages (filling and maturing), densities of planthoppers were significantly affected both by protection level and by rice type (Bt vs non-Bt), and densities of N. lugens were significantly higher in Bt plots than in non-Bt plots under unprotected conditions. Pesticide sprays were reduced by 60 and 50% in protected Bt vs protected non-Bt plots in 2005 and 2006, respectively. Yield of unprotected Bt rice increased by 60–65% compared to unprotected non-Bt rice, but decreased by 28–36% compared to protected Bt rice. These results show that Bt rice increased yield greatly, but still required pesticide sprays to avoid losses caused by non-target insect pests.