Components of resistance to late leaf spot and rust among interspecific derivatives and their significance in a foliar disease resistance breeding in groundnut (Arachis hypogaea L.)

Late leaf spot (LLS) and rust cause substantial yield losses and reduce the fodder and seed quality in groundnut (Arachis hypogaea L.). Adoption of resistant cultivars by the semi-arid tropic farmers is the best option to overcome yield losses. Knowledge on components of resistance to these diseases should facilitate the development of groundnut cultivars with enhanced resistance to LLS and rust. The objectives of the experiments were to study the genetic variability and relationships among components of resistance to LLS and rust, and assess their significance in disease resistance breeding. Fifteen interspecific derivatives for LLS and 14 for rust and a susceptible control, TMV 2, were evaluated in a randomised complete block design with two or three replications under greenhouse conditions. The experiments were repeated twice. Genotypic differences were highly significant for all the traits studied. Resistance to LLS is due to longer incubation and latent periods, lesser lesions per leaf, smaller lesion diameter, lower sporulation index, and lesser leaf area damage and disease score. Selection based on components of resistance to LLS may not lead to plants with higher retained green leaf area. The remaining green leaf area on the plant should, therefore, be the major selection criteria for resistance to LLS in breeding programs. Resistance to rust is due to longer incubation and latent periods, fewer pustules per leaf, smaller pustule diameter, lower sporulation index, and lesser leaf area damage and disease score. Rust resistant components appear to work additively, therefore, selection based on resistance components together with green leaf area retained on the plant should be the basis of selecting for resistance to rust in breeding programs. ICGV 99005, 99003, 99012, and 99015 for rust and ICGV 99006, 99013, 99004, 99003, and 99001 for LLS are the better parents for use in resistance breeding programs. This revised version was published online in July 2006 with corrections to the Cover Date.     

Experimental evaluation of mass selection to improve red body colour in Fijian hybrid tilapia (Oreochromis niloticus × Oreochromis mossambicus)

Mass selection was trialed on Fijian hybrid tilapia (Oreochromis niloticus × Oreochromis mossambicus) to reduce the amount of black spots on otherwise red phenotypes. The responses of two selection intensities (low‐selection line, top 50% – L) and (high‐selection line, top 30% – H) were compared with that of a control line (no selection – C) across three generations. The relative growth performance of treatments (C, L and H) was examined in parallel in each generation to assess whether mass selection had a correlated negative effect on growth performance. The results show clearly that red phenotype can be improved significantly by applying mass selection, without affecting growth performance. We propose that black spots on an otherwise red phenotype could represent the allelic products of a second genetic locus influencing skin colour, which can be expressed in red individuals (genotype Rr) but which may be masked in black individuals (genotype rr).     

Two promoter rearrangements in a drug efflux transporter gene are responsible for the appearance and spread of multidrug resistance phenotype MDR2 in Botrytis cinerea isolates in French and German vineyards

In French and German vineyards, Botrytis cinerea isolates with multiple fungicide resistance phenotypes have been observed with increasing frequencies. Multidrug resistance (MDR) results from mutations that lead to constitutive overexpression of genes encoding drug efflux transporters. In MDR2 and MDR3 strains, overexpression of the major facilitator superfamily transporter gene mfsM2 has been found to result from a rearrangement in the mfsM2 promoter (type A), caused by insertion of a retroelement (RE)-derived sequence. Here, we report the discovery of another, similar RE-induced rearrangement of the mfsM2 promoter (type B) in a subpopulation of French MDR2 isolates. MDR2 isolates harboring either type A or type B mutations in mfsM2 show the same resistance phenotypes and similar levels of mfsM2 overexpression. RE sequences similar to those in mfsM2 were found in low copy numbers in other but not all B. cinerea strains analyzed, including non-MDR2 strains. Population genetic analyses support the hypothesis that the two rearrangement mutations have only occurred once, and are responsible for the appearance and subsequent spread of all known MDR2 and MDR3 strains in French and German wine-growing regions.     

Diurnal changes in moisture content and isothermal and thermally induced moisture fluxes under n-tillage and c-tillage in Nigeria

A study on the diurnal changes of soil moisture content and on the isothermal and thermally induced moisture fluxes was conducted on an Alfisol at the International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria, on no-tillage and conventional-tillage plots. These studies were conducted during the 1980 dry season, 9 years after initiating the tillage treatments in 1971. Three bare 5 × 5 m² plots per treatment were used to study diurnal changes in moisture content as soil dried from the initial moisture status of field capacity. The latter was attained by excessive and deep irrigation. Moisture content, moisture potential, and soil temperature were monitored three times a day (08:00, 14:00 and 18:00 h) at the depths of 0–7, 7–14 and 14–21 cm for four 7 day periods at weekly intervals. These results, along with physical characterization of the soil profile and changes in air temperature, were used to calculate isothermal, thermally induced liquid and vapor fluxes.

Results showed that there was a general increase in soil moisture content with sampling depth during the night (18:00 to 08:00 h), and a general decrease with depth during the day (08:00 to 18:00 h). The amplitude of the diurnal cycle of water content changes decreased with depth, and was superimposed on a progressive depletion in water content in the layers studied. The first layer of the conventional-tillage treatment dried to a lower water content than that of the no-tillage treatment. Partition of moisture fluxes, induced by isothermal and thermal conditions, showed that isothermal liquid flux was dominant in no-tillage, and that thermal vapor flux was very important as soil dried in conventional-tillage.

The direction of the fluxes observed (i.e. isothermal liquid flux always being positive upwards and thermal vapor flux positive during the night and negative downwards during the day) was of critical importance as the soil dried. The liquid fluxes became less important and thermal vapor and probably isothermal vapor fluxes became more important with soil moisture depletion. Vapor movement under these circumstances may have played an important role in supplying water to roots both during the day (deep roots) and night (shallow roots) depending on the magnitude of the fluxes. Vapor fluxes were higher and started earlier in conventional-tillage than in no-tillage.     

Development of non-narcotic (opiumless and alkaloid-free) opium poppy, Papaver somniferum

A mutation breeding programme using gamma rays and ethyl methane sulphonate (EMS) was carried out for genetic conversion of narcotic ‘opium poppy’ into non-narcotic ‘seed poppy’. Two families contained 31 latexless (opiumless) and 23 partial latex-bearing plants which were identified in the M² and confirmed in the M³ generations by the ‘ray-pluck’ method. Thin-layer chromatography (TLC)-densitometry of powdered capsule hulls (straw) from 22 representative plants also revealed that none of the five opium alkaloids (morphine, codeine, thebaine, papaverine and narcotine) was present in the straw. Six plants also possessed high seed yield (4.0–5.66 g/capsule vs. 3.39 g for control) and seven had a high seed oil content (50.7-53.5%). The best mutant genotype, LL-34 of the family C¹-Comb-113-2, with 5.66 g/capsule seeds containing 52.6% oil was designated as cv. ‘Sujata’. This, perhaps the world's first opiumless and alkaloid-free seed poppy cultivar, offers a cheap and permanent (fundamental) solution to the global problem of opium-linked social abuse. Simultaneously, it serves as a safe and potential food crop with protein-rich seeds and healthy unsaturated seed oil.     

Mechanized tillage systems effects on soil erosion from an alfisol in watersheds cropped to maize

The degradative effects of mechanized farming operations on soils in the tropics are not widely documented. This study was conducted to quantify the effects of mechanized no-till and conventional tillage systems on runoff, erosion and changes in soil properties. Experiments were conducted on twin watersheds of about 5 ha each. Only the conventionally plowed watershed was terraced to control erosion. Measurements made with a rate-measuring H-Flume indicated that runoff and erosion from the terraced and conventionally tilled watershed were several times greater, compared with the unter-raced no-till watershed. Cumulative runoff in 1979 was 10 times and erosion 42.2 times higher from the plowed watershed than from the no-till watershed. The infiltration capacity 5 years after land development was 3.8 cm h^?1 for the plowed and 10.4 for the no-till watershed. Surface soil from the no-till watershed retained more water at all soil water potentials than that from the plowed treatment. The gravel content in the surface layer of the plowed watershed was 25.1%, compared with 15.8% in the no-till watershed. The maize grain yield from the twelfth consecutive crop was 3 Mg ha^?1 for the no-till and 1 Mg ha^?1 for the plowed watershed.     

Micronutrients (Fe,Mn, Zn and Cu) balance under long-term application of fertilizer and manure in a tropical rice-rice system

Purpose

The balance of micronutrients in soils is important in nutrient use efficiency, environmental protection and the sustainability of agro-ecological systems. The deficiency or excess of micronutrients in the plough layer may decrease crop yield and/or quality. Therefore, it is essential to maintain appropriate levels of micronutrients in soil, not only for satisfying plant needs in order to sustain agricultural production but also for preventing any potential build-up of certain nutrients.

Materials and methods

A long-term fertilizer experiment started in 1969 at Central Rice Research Institute, Cuttack, Odisha, India. Using this experiment, a study was conducted to analyze the balance of micronutrients and their interrelationship. The experiment was composed of ten nutrient management treatments viz. control; nitrogen (N); N + phosphorus (NP); N + potassium (NK); nitrogen, phosphorus and potassium (NPK); farmyard manure (FYM); N + FYM; NP + FYM; NK + FYM; and NPK + FYM with three replications. Micronutrients in soil (total and available), added fertilizers and organic manures and in rice plant were analyzed. Besides, atmospheric deposition of the micronutrients to the experimental site was also calculated. A micronutrient balance sheet was prepared by the difference between output and input of total micronutrients.

Results and discussion

Application of FYM alone or in combination with chemical fertilizer increased the diethylenetriamine pentaacetate (DTPA)-extractable Fe, Mn and Zn over the control treatment. The treatment with NPK + FYM had the highest soil DTPA-extractable Fe, Mn, Zn and Cu after 41 years of cropping and fertilization. Application of chemical fertilizers without P decreased the DTPA-extractable Zn over the control while the inclusion of P in the fertilizer treatments maintained it on a par with the control. The application of P fertilizer and FYM either alone or in combination significantly increased the contents of total Fe, Mn, Zn and Cu in soil mainly due to their micronutrient content and atmospheric depositions. A negative balance of Zn was observed in the N, NP, NK and NPK treatments, while a positive balance observed in the remaining treatments. The balance of Mn was negative in all the treatments, due to higher uptake by the rice crop than its addition.

Conclusions

Long-term application of chemical fertilizers together with FYM maintained the availability of micronutrients in soil and, thus, their uptake by rice crop.

     

Changes in CO<Subscript>2</Subscript>, <Superscript>13</Superscript>C abundance,inorganic nitrogen, β-glucosidase,and oxidative enzyme activities of soil during the decomposition of switchgrass root carbon as affected by inorganic nitrogen additions

This study was conducted to investigate the effect of inorganic nitrogen (N) and root carbon (C) addition on decomposition of organic matter (OM). Soil was incubated for 200 days with nine treatments (three levels of N (no addition (N0) = 0, low N (NL) = 0.021, high N (NH) = 0.083 mg N g⁻¹ soil) × three levels of C (no addition (C0) = 0, low C (CL) = 5, high C (CH) = 10 mg root g⁻¹ soil)). The carbon dioxide (CO₂) efflux rates, inorganic N concentration, pH, and potential activities of β-glucosidase and oxidative enzyme were measured during incubation. At the beginning and the end of incubation, the native soil organic carbon (SOC) and root-derived SOC were quantified by using a natural labeling technique based on the differences in δ ¹³C between C3 and C4 plants. Overall, the interaction between C and N was not significant. The decomposition of OM in the NH treatment decreased. This could be attributed to the formation of recalcitrant OM by N because the potentially mineralizable C pool was significantly lower in the NH treatment (3.1 mg C g⁻¹) than in the N0 treatment (3.6 mg C  g⁻¹). In root C addition treatments, the CO₂ efflux rate was generally in order of CH > CL > C0 over the incubation period. Despite no differences in the total SOC concentration among C treatments, the native SOC in the CH treatment (18.29 mg C g⁻¹) was significantly lower than that in the C0 treatment (19.16 mg C g⁻¹).     

Variability of soil physical quality and erodibility in a water-eroded cropland

Physical degradation of the soil increases its susceptibility to erosion by water action. However, relatively few studies have evaluated the opposite, i.e., the impact of water erosion on soil erodibility. This study was conducted in a corn field in Ohio. Some sites within the field have experienced water-induced soil erosion following heavy rainstorms. Physical characteristics of the soil were compared between eroded (ER) and un-eroded sites (UN). Compared with ER, the soil in UN had lower penetration resistance (4.87 vs. 4.53 MPa), bulk density (1.45 vs. 1.33 Mg m^?3), and sand content (17.4 vs. 14.2%), and higher shear strength (80.1 vs. 125.3 KPa), hydraulic conductivity (3.0 vs. 3.4 cm h^?1), intrinsic permeability (31.9 vs. 36.4 × 10^?10 cm²), and contents of soil organic carbon (36.1 vs. 32.1 g kg^?1), total nitrogen (3.3 vs. 3.1 g kg^?1), clay (25.2 vs. 24.2%), silt (60.5 vs. 58.4%), and very fine sand (3.4 vs. 1.1%). Also Munsell's variables differed between ER and UN (1.24 vs. 0.54 for hue, 4.59 vs. 4.35 for value, and 1.99 vs. 1.79 for chroma, respectively). The erodibility factor (K) was lower in UN than in ER (0.00327 vs. 0.00354 Mg ha h ha^?1 MJ^?1 mm^?1, respectively). Hence, it is suggested the ER sites within the corn field agroecosystem are more susceptible to accelerated erosion as compared with UN sites.     

Effects of slope length on runoff from alfisols in Western Nigeria

The effects of 5, 10, 15 and 20 m slope lengths were investigated on runoff for natural slope gradients of about 1, 5, 10 and 15%. These studies were conducted on field runoff plots on natural slopes and under natural rainfall conditions at Ibadan in western Nigeria. The runoff, based on individual rainfall events, was not significantly correlated with either of three erosivity indices (EI₃₀, KE > 1, AI_m) and only a maximum of 36% of variability in runoff could be attributed to rainfall erosivity. Runoff per unit area decreased with increase in slope length. The mean annual runoff was of the order of 100, 87, 80 and 69 for 1977 and 100, 66, 49 and 35 for 1978 for 5, 10, 15 and 20 m slope lengths, respectively. Regression analyses indicated that the annual runoff was related to slope length according to the regression equation W = 773 L^?0?53, where W is annual runoff in mm and L is slope length in meters. When fitted to data from all plots on a given slope steepness, for individual years the numerical value of length exponent b ranged from 0.153 to ?0.865.