Arthropod pests and disease vectors are important limiting factors in the production of food crops and livestock, and thus hinder development in Africa and other tropical countries. The control of these arthropod pests and disease vectors has been relying on the use of synthetic chemical pesticides. This practice is not sustainable, and endangers biological diversity and environmental quality. Biological control using entomopathogens (bacteria, fungi, viruses, nematodes or protozoa) is one of the alternatives in reversing agriculture's hazardous dependence on synthetic pesticides and establishing a more environmentally friendly paradigm. The International Centre of Insect Physiology and Ecology (icipe) has been conducting research in development of entomopathogens against crop insect pests and disease vectors. The paper gives an account of some of the research activities undertaken at the centre.
A field experiment was conducted at the research farm of Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur, Bangladesh to study the effectiveness of Bradyrhizobium japonicum strains on two varieties of soybean viz. Sohag and Bangladesh Soybean-4. The treatments were non inoculated control, seed inoculation with either Bradyrhizobium japonucum strains TAL102, TAL1906 or the mixed culture of strains TAL102 and TAL1906, Nitrogen amount of 25 or 50 kg/ha. Bradyrhizobium inoculation had a significant positive effect on nodulation, nitrogenase activity, growth, dry matter production, N content in shoot, N uptake by shoot, yield attributes, protein content in seed and seed and stover yields of soybean. The highest seed yield of 2511 kg/ha was obtained in Bangladesh Soybean-4 inoculated with Bradyrhizobium japonicum strain TAL102. Treatments consisting of chemical nitrogen fertilizer did not perform well compared to those employing the Bradyrhizobium inoculant.
Phylogenic relationships of Rhizoctonia isolates of wormwood root between wormwood root endophytes and root soils fungi were investigated using fatty acid analysis and compared with their fatty acid methyl ester (FAME) profiles. The modified MIDI method was used and allowed a clear differentiation between the two Rhizoctonia and Rhizoctonia-like fungi, and fatty acid analysis was identified and classified these isolates as the Rhizoctonia serialis (AG-D). However, isolates of wormwood root endophyte was identified as AG-D (I), and isolates of Rhizoctonia-like fungi from wormwood root grown soils was identified as AG-D(II), respectively. In this experiment, we discovered the subgroup within same AG-D isolates and characterized the endophytic and endophytic related criteria within the same anastomosis groups and homologous to the subgroups levels.
A field experiment was carried out at the Bangabandhu Sheikh Mujibur Rahman Agricultural University farm to assess the effects of inorganic and organic fertilizers on vegetative, flowering and fruiting characteristics as well as yield attributes and yield of Ratan variety of tomato. The plots were treated with three levels each of N (62, 100 and 200 kg/ha), P (11.7, 17.5 and 35 kg/ha), K (26.7, 40 and 80 kg/ha), S (5, 7.5 and 15 kg/ha) and cowdung (5, 10 and 15 t/ha). There were three replications for each treatment. The highest plant height and dry weight of shoot, the maximum number of clusters of flowers and fruits/plant as well as the greatest fruit size and fruit yield/plant, fruit yield/ha were obtained from the application of the recommended dose of nutrients viz. 200 kg N + 35 kg P + 80 kg K + 15 kg S/ha, but similar results were obtained from the treatment receiving 5t cow dung/ha along with half of the recommended doses of nutrients (100 kg N+ 17.5 kg P + 40 kg K + 7.5 kg S/ha). The effect of 10t cow dung per ha, along with one third of the recommended dose of nutrients, was also comparable to the effect of employing the recommended dose of nutrients. It was further observed, from an economic standpoint, that the combination of 5t cow dung/ha along with half of the recommended doses of nutrients appeared to be a viable treatment which would offer the maximum benefit concerning cost ratio (4.38) for tomato production in the shallow red- brown terrace soil (AEZ-28) of Bangladesh.
We compared the photosynthetic carbon assimilation rate (A) and the simultaneously measured electron transport rate (ETR) through photosystem II in order to examine the reliability of the A estimation method based on the ETR values and A-ETR relationships under field conditions. We first compared the ETR with the A values, which were calculated using biochemical models, under different temperature conditions typical in August, November and February. We established the regression lines of A with ETR values at reference conditions (mean leaf temperature and leaf intercellular CO2 partial pressure, Ci in each season). When leaf temperatures and Ci changed from the reference conditions according to diurnal changes in the environment, the relationship between A and ETR changed from the regression lines, but the error of the estimated A values was modest in each season's biochemical calculations. The correlation of A with the ETR values derived from the data in the field measurements was, however, too weak to precisely regress the A values based on the ETR values. This weak correlation would be due to the low leaf internal conductance in the measured leaves and large differences in physiological traits, such as temperature dependence, among the leaves. Thus, we concluded that in a field with spatially and temporally heterogeneous environmental conditions, A estimation based on the ETR values would be difficult.
A laboratory experiment using Calcareous, Non - Calcareous and acid Piedmont soils was conducted to estimate the phosphorus (P) sorption characteristics. Evaluation of the fitness of Langmuir, Freundlich and Tempkin equations was performed to elucidate the relationships of P sorption parameters with soil acidity, organic carbon and iron content. Fifteen different soil samples (0 - 15 cm) were shaken with 20 ml 0.01 M CaCl2 solution containing 0- 1000 mg kg-1 P separately for 16 hours. P subject to sorption was inferred from the difference between concentration of soluble P added to the initial solution and the concentration of P in the solution at equilibrium. The tested soils varied in P sorption, energy of adsorption, adsorption maxima and buffering capacity. Application of P increased the adsorbed P linearly and the coefficient of determination (R2) varied from 0.9988 to 0.9997. Adsorption of P by the soils showed a good relationship with pH, free Fe and amorphous Fe but not with crystalline Fe and organic carbon. The slope of P adsorption decreased significantly (P< 0.001) with an increase in pH. The P adsorption isotherm for all three studied soils fit well into Langmuir, Freundlich and Tempkin models (R2 = 0.8139 to 0.9709). The Tempkin adsorption equation fit better than the Langmuir and Freundlich equations. The maximum P adsorption capacity varied based on background P concentration of soils and varied from 617 to 1481 mg g-1 where the highest value was observed in Calcareous Soil (S1) and the lowest in extremely acidic Piedmont soil (S15). The energy of adsorption was highest (1.80 μg ml) in Piedmont Soil (S15) and lowest (0.75 μg ml-1) in Calcareous Soil (S1). The buffering capacity was varied from 144 to 183 where the highest value was found in Piedmont Soil (S13) and the lowest in Calcareous Soil (S1). Soil pH was positively correlated with maximum adsorption capacity (b), negatively correlated with energy of adsorption (k), buffering capacity (BP) and intercept of the Freundlich adsorption isotherm (a). The adsorption parameters of the soils showed good relationship with each other. The maximum adsorption capacity showed a significant negative correlation with buffering capacity (r = -0.62) and with intercept of Freundlich equation (r = -0.81). Energy of adsorption showed a significant positive liner relationship with buffering capacity (r = 0.79). The relationship between buffering and intercept of Freundlich equation was also positive (r = 0.87).
A field and laboratory experiment was conducted during 2000-2001 and 2001-2002 to estimate the tillage and mulch effects on physical properties of soil. The experiment was laid out in split-plot design with three replications. Four different tillage methods were used in the main plots: minimum tillage (MT), conventional tillage (CT), disc ploughing (DP) and chisel ploughing (Chp), and four different mulch treatments were used in the sub-plots including rice straw mulch (RSM), water hyacinth mulch (WHM), white polyethylene mulch (WPM) and no mulch (NM). The physical properties of the soil were markedly influenced by tillage and mulch. The bulk density was significantly altered by different tillage practices. The lowest bulk density was observed in disc ploughing at the 0-10 cm-soil depth. The lowest value of soil strength was recorded in the ploughed zone, which used disc and chisel ploughing, and the highest values came from area of minimum tillage. Mulch had less effect on bulk density and soil strength. Marked differences in weekly mean and diurnal soil temperature under different mulch practices were observed. Polyethylene mulch showed the highest temperature and the lowest was observed under straw mulch. It was observed that minimally tilled plots showed the maximum level of soil temperature at the 10 cm depth throughout the day. Similar trends in the results were also observed for weekly mean soil temperature. The cumulative infiltration and infiltration rates increased with pulverization of soil and increasing depth of ploughing. Cumulative infiltration and infiltration rates were higher in disc and chisel ploughing and lower in minimum and conventional tillage methods.
Some chemical and physical properties of four ant mounds were measured to determine the bioturbation effect of ant mounds on surrounding environment, compared ant mounds and their surrounding surface soils. Values of pH in H2O of drier ant mounds were almost same as those of the surrounding soils. Mounds were richer in finer particles of silt and clay fractions. Nitrogen and phosphorus fertility are lower in ant mounds, therefore, ant mounds of Messor aciculatus and Cataglyphys aenescens formed in desert zone in Mongolia were found not to be hot spot of the ecosystems, contrary to our expectations.
A study was conducted on chickpeas at AEZ-28 (CARS, Joydebpur) and AEZ-11 (RARS, Ishurdi) during the rabi season of 1999-2000 to assess the effect of organic, inorganic and bio-fertilizers on the natural occurrence of arbuscular mycorrhizal (AM) fungi in chickpeas. The variety BARI Chhola-5 and the peat based rhizobial inoculum (Rhizobium strain RCa-220) were used in this experiment. The experiment was composed of six fertilizer treatments arranged in RCBD having four replications. At AEZ-28 (Joydebpur), the highest root colonization in chickpea (65.0%) was recorded with treatment T4 (Cowdung + Inoculum). But the highest spore number (132.0 per 100 g soil) was recorded with T2 (P50 K50 S20 Zn5 + Inoculum). At AEZ-11 (Ishurdi), maximum root colonization (82.5%) was recorded with T3 (CD + P25 K25 S10 Zn2.5 + Inoculum). However, the highest spore number (246.3 per 100 g soil) was recorded with T4. The lowest colonization and spore number was recorded with T1 (full dose of fertilizers). Root colonization and spore population were also found to have varied greatly from location to location. The highest root colonization was recorded at AEZ-11 (Ishurdi) for each treatment except T5 (Inoculum) compared to AEZ-28 (Joydebpur). The highest spore population was also recorded at AEZ-11 (Ishurdi) for all the treatments. Only small quantities of Glomus and Acaulospora were observed in the treatments of T1 and T2, but in treatments of T3, T4 and T5, Glomus, Gigaspora, Acaulospora and Scutellospora were found in abundance. Variation in occurrence of different genera between two locations was not prominent.
Arbuscular mycorrhizal (AM) fungi in agricultural crops grown under AEZ-28 (CARS, Joydebpur), AEZ-9 (RARS, Jamalpur), AEZ-11 (RARS, Ishurdi) and AEZ-23 (RARS, Hathazari) in Bangladesh were assessed during 1999 and 2000 to study the effect of edaphic factors on AM colonization and spore population. Mainly cereals, pulses, oilseeds, vegetables and spices were selected for the assessment. The average root colonization of mycorrhizal fungi in all the selected crops during two years differed with the location. Average colonization in 1999 was the highest (43.0%) at AEZ-9 (Jamalpur) and the lowest (37.0%) at AEZ-23 (Hathzari) but in 2000, the highest colonization (45.0) was found at AEZ-11 (Ishurdi) and the lowest (39.0%) at AEZ-28 (Joydebpur). Considerable variation was also observed in average spore number recorded in the 4 AEZs. Maximum average spore numbers (148.0 and 167.0 per 100g soil) were recorded at AEZ-23 (Hathazari) and the minimum (92.0 and 106.0 per 100g soil) at AEZ-28 (Joydebpur) during 1999 and 2000. The spore number varied within and between sites. Edapho-climatic factors played an important role causing variation in AM colonization and spore population. Soil moisture, pH and nutrient levels influenced colonization and spore number. Soil moisture, OM, total N and soil potassium were insignificantly and positively correlated to root colonization. A negative and insignificant correlation of root colonization was observed only with soil phosphorus. A positive but insignificant correlation existed between spore number and edaphic factors.
In keeping with the growing concern over sustainable development, there is an increasing need for clearer goals and applicable techniques to achieve ecological conservation and restoration. To accomplish nature-oriented planning and management, it is essential to understand the ecology and habitat requirements of target species. In this study, we applied the information-theoretic approaches of the Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC) to identify the best model and most significant factor which can explain the habitat selection of Japanese medaka (Oryzias latipes). A fuzzy preference intensity model (FPIM), i.e. a hybrid model of simplified fuzzy reasoning and a genetic algorithm, was introduced to evaluate the habitat preference of the fish. The present result suggests that the lateral cover ratio is the most significant factor governing the habitat preference of the fish, and the FPIM that considers the four factors of water depth, current velocity, lateral cover ratio, and percent vegetation coverage has the best prediction ability among the candidates.