Variation in drought response of sal (Shorea robusta) seedlings

Plant development and distribution in areas with seasonal rainfall are often related to the ability of plants to postpone desiccation or tolerate low water potentials during drought. Regeneration of Shorea robusta Gaertn. (sal), a commercially valuable, widely distributed tree of the Indian tropical belt, is unsuccessful at the base of the Himalaya. Seedling shoots die back repeatedly during the long drought that follows the monsoon rain. During the course of one year, we monitored changes in plant and soil water potentials (Psi), leaf conductance (gw), osmotic and elastic adjustment, and xylem conductance of sal seedlings of different sizes from three landforms: an alluvial plain at 540 m elevation, a slope at 510 m, and a montane site at 1370 m. Predawn plant Psi and gw were lowest in the smallest seedlings (< 20 cm tall). Across sites and seasons, seedlings > 100 cm tall had higher morning gw than seedlings in the other size classes. In all size classes, plant Psi was lowest during early summer, when leafing begins. Among sites, Psi and gw were lowest in seedlings at the montane site. Osmotic potential was lowest during leaf development and highest during the rainy season, and tissue elasticity was highest during winter. As leaf area increased during leaf development, xylem conductance per unit of xylem cross-sectional area also increased. We conclude that low Psi is unlikely to be a major cause of seedling mortality. Small seedlings, with low Psi, had low leaf conductance. Adjustments of osmotic and elastic properties appear to aid responses of seedlings to drought.     

Leaf conductance of primary and mature leaves ofPinus roxburghii: A comparison

We used a null-balance porometer to measure leaf conductance of mature and primary leaves of natural seedlings, saplings, and trees ofPinus roxburghii (chir) during autumn at four sites at 1,320–1,930 m elevation in the central Himalaya of India. Our hypothesis that primary leaves had higher leaf conductance than mature leaves (needles in fascicles), based on measurements in other pines, was rejected. Comparisons on the same saplings and seedlings showed lower leaf conductance for primary leaves than for mature leaves. Primary leaves on seedlings and saplings also did not consistently have higher leaf conductance than mature leaves on near-by trees. Mature leaves on seedlings, however, did often have higher conductance than mature leaves on nearby trees. Mean values for leaf conductance (mmol m⁻² s⁻¹, based on total leaf surface area) ranged from 42–82 for mature leaves on trees, 60–121 for mature leaves on seedlings, and 28–67 for primary leaves on seedlings. Compared to published values for other pine species, conductance of mature leaves ofP. roxburghii is relatively low. Funding for this study was provided by grants from the United States National Science Foundation, INT-9312052 and INT-9404043. We appreciate the review of an early draft by Barbara Bond.     

Process Optimization for the Development of Nutritionally Enhanced Nuggets using Ficus geniculata: A Nutritional Approach

Plant Foods for Human Nutrition - Ficus geniculata (FG) is one of the underutilized fig species in India and throughout the world. However, the different parts of the plant have numerous...     

An evaluation of furrows for managing soil and water loss from a shallow Alfisol under simulated rainfall

Furrows are widely used in rainfed areas of semi-arid India for soil and water conservation. The orientation of furrows, either down or across slope, and their spacing influence the effectiveness of furrows as soil and water conservation measures. We evaluated treatments with furrows aligned down and across 3% sloping land at spacings of 90, 60 and 30 cm under simulated rainfall intensities of 80 and 100 mm/h on a shallow Alfisol. A bare plot without any furrows was considered as a control. A large (24 m × 3 m) rainfall simulator developed at the Central Research Institute for Dryland Agriculture (CRIDA), Hyderabad, was used for this controlled study. Run-off was measured by a calibrated tipping bucket run-off recorder. The effects of the treatments on peak flow rate (L/s), sediment loss with run-off water (kg/ha/mm), peak sediment concentration (g/L), run-off (per cent rainfall) and time to peak (min) were investigated. When compared with the control (no furrows), across slope furrowing with 60- and 30-cm spacing reduced sediment yields by 19.9 and 21.3 kg/ha/mm of run-off, respectively, under a rainfall intensity of 80 mm/h and 24 and 25.3 kg/ha/mm of run-off, respectively, under a rainfall intensity of 100 mm/h. For the control, sediment loss was 50.72 kg/ha/mm run-off and 56.68 kg/ha/mm run-off for rainfall intensities of 80 and 100 mm/h, respectively. Similar trends were recorded from observations of peak flow, time to peak and peak sediment concentration. Run-off hydrographs demonstrated the conservation value of across slope furrowing by delaying run-off initiation, reducing run-off and slowly releasing the run-off after the cessation of rainfall. The results show that furrow orientation has major effects on reducing run-off, whereas furrow spacing has insignificant effects.     

回交高代选择导入系的纹枯病抗性与抗旱性的遗传重叠研究

利用来自抗旱性较好的供体亲本（BG300和BG304）、具有两种遗传背景（IR64和特青）的水稻高代回交（BC2）抗旱选择导入系，通过人工接种的方法鉴定纹枯病抗性，考察纹枯病抗性与抗旱性之间可能存在的遗传重叠。通过与受体亲本的纹枯病抗性表现比较发现，具有特青背景的抗旱选择导入系倾向于纹枯病抗性的降低，而IR64背景的抗旱选择导入系则倾向于纹枯病抗性的增强。基于基因型与表型的方差分析共鉴定到6个与纹枯病抗性相关的位点，其中QSbr6在不同供体和背景的两个群体中分别检测到，而QSbr10则在同一供体的两个遗传背景下均检测到；有3个位点（QSbr6、QSbr8和QSbr10）与同一群体中检测到的抗旱性位点位置相近，很可能是两种抗性重叠的遗传基础。尽管方差分析的方法在选择导入系的非选择目标性状相关位点的鉴定中存在相当程度的偏低估计，本研究所检测到的纹枯病抗性位点，特别是那些与抗旱性重叠位点的分子标记以及相关的抗性株系仍将为进一步的水稻纹枯病抗性和抗旱性的多抗性育种和深入的遗传重叠研究提供有用的信息和材料。     

Genetic analysis and pyramiding of two gall midge resistance genes (Gm-2 and Gm-6t) in rice ( Oryza sativa L.)

Asian rice gall midge (Orseolia oryzae) is a major pest across much of south and southeast Asia. This pest is genetically diverse and many gall midge biotypes are known to exist in each country. During the last three decades, host plant resistance has proved to be the most effective mechanism of controlling the Asian rice gall midge. Seven genes conditioning resistance to gall midge larvae have been identified in rice (Oryza sativa) and are being used in cultivar improvement programs. However, some of these genes are rendered ineffective by new gall midge biotypes. Increased understanding of genetics, inheritance, allelic relationships and linkage is necessary to maximise the durability of major gene resistance by the pyramiding of these genes. The two genes, Gm-2 and Gm-6(t), are known to confer resistance against a number of biotypes in India and China, respectively. An F₃ population derived from a cross between Duokang #1 (donor of Gm-6(t)) and Phalguna (donor of Gm-2) was screened against Chinese gall midge biotype 4 at Guangdong, China, and Indian gall midge biotype 1 at Raipur, India. At each location, separately,a single gene governed resistance. The parallel segregation of 417 F₃progenies for both biotypes at two locations revealed that recombination had occurred between the two genes, establishing that the two genes are not allelic. However, the two genes Gm-2 and Gm-6(t), were found to be linked with a distance of ∼16.3 cM. A number of lines homozygous at one locus and segregating for the other locus were identified and selected. These lines were selfed to obtain lines homozygous for the favourable alleles at both loci (two locus pyramids). This is the first report on use of conventional host-pest interaction method for pyramiding two closely located Gm-resistance loci of dissimilar effects. The implications of deployment of these pyramids within and across country borders, with reference to the prevailing gall midge populations are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Organic aerosol growth mechanisms and their climate-forcing implications

Surface- and volume-limited chemical reactions on and in atmospheric aerosol particles cause growth while changing organic composition by 13 to 24% per day. Many of these particles contain carbonaceous components from mineral dust and combustion emissions in Africa, Asia, and North America and reveal reaction rates that are three times slower than those typically used in climate models. These slower rates for converting from volatile or hydrophobic to condensed and hygroscopic organic compounds increase carbonaceous particle burdens in climate models by 70%, producing organic aerosol climate forcings of as much as -0.8 watt per square meter cooling and +0.3 watt per square meter warming.     

Screening and selecting novel AM fungi and Azotobacter strain for inoculating apple under soil solarization and chemical disinfestation with mulch practices for sustainable nursery management

The objective of this study is to investigate the response of screening, and selection of novel indigenous AM fungal species and Azotobacter chroococcum strains for inoculating apple under different soil disinfestations and moisture conservation mulch practices for sustainable nursery management. Two local AM fungal species namely, Glomus fasciculatum (Thaxter sensu Gerdemann) and Glomus mosseae (Nicol. & Gerd.), and two strains of A. chroococcum viz., A. chroococcum strain-I (AZ₁) and A. chroococcum strain-II (AZ₂) were inoculated at nursery stage under soil solarization, chemical disinfestation and natural soil conditions at four different mulch materials namely, black plastic mulch (BPM), and organic mulches, i.e. grass mulch (GM); cover crops (CC); green manuring + clean cultivation (Gm + Cc). The comparative performance of the seedlings on the impact of local AM species and A. chroococcum strains on growth characteristics, microbial population, root colonization and leaf nutrient status was evaluated. The inoculation of seedlings to G. fasciculatum and AZ₁ increased all growth characteristics (plant height, stem diameter, leaf area and total root length), microbial consortium of the rhizosphere soil and leaf N, P, K and Zn content in all those plots where soil solarization and black plastic mulching was used followed by chemical disinfestations and natural soil conditions at all other mulch types used. These findings suggested that the soil inoculation of G. fasciculatum and AZ₁ strain to seeds and/or the saplings under soil solarization with black plastic mulch attained a desirable plant height and become ready for grafting which however saved a period of 1 year for nursery management compared to traditional nursery raising practice, and thus, it may be a viable and feasible approach to maintain soil productivity under nutrient limited soils for sustainable apple nursery production under temperate rain-fed conditions.     

Combining sub-lethal heating and on-farm wastes: effects on <Emphasis Type="BoldItalic">Fusarium oxysporum</Emphasis> f.sp. <Emphasis Type="BoldItalic">cumini</Emphasis> causing wilt of cumin

In a 2-year field study, the effects of four heating regimes established by varying temperature or duration of heating on efficiency of on-farm wastes as soil amendments in controlling Fusarium oxysporum f.sp. cumini (Foc) causing wilt on cumin (Cuminum cyminum L.), were ascertained. Significant improvement in reduction of Foc propagules was achieved with the increase in duration and amount of heat. In 2000, mild heating under shade (heat level 4), 31.8–65.9% reduction in Foc propagules was estimated in all the amendments at 0–30 cm soil depth, which improved by 75.7–86.5% in the treatment where Foc-infested soil brought from the laboratory was exposed to direct heat (heat level 3) and amendments and irrigation were applied. Foc propagules were reduced by 76.6–88.3% when infested soil was exposed continuously to dry heat for 56 days (heat level 2), improving efficiency of amendments by 0.9–13.5% compared with heat level 3. After 56 days of exposure to dry heat, elevating the temperature by mulching amended soil with a transparent polyethylene film (50 μm thick) for 20 days (heat level 1) augmented reduction by 80.2–95.5%. In the second season, combining 0.04% of onion, Verbisina encelioides or mustard oil-cake with mustard residues (0.18%) improved the reduction in Foc propagules at all heat levels even at the lower soil depth. Maximum reduction (94.9–100%) in Foc propagules at heat levels 1 to 3 was achieved when residues of Verbisina were supplemented with those of mustard. These results suggest a new approach to improve the control of Foc by combining prolonged heating with on-farm wastes such as Verbisina residues and one summer irrigation.     

Effect of sewage sludge–coir pith pellets on dry matter yield and trace metal concentration in various plant parts of forage maize

Sewage sludge (SS), a highly heterogeneous semisolid fraction of sewage water (about 1% of the sewage water), contains various amounts of nitrogen (N) and phosphorus (P) as well as trace elements such as cadmium (Cd), lead (Pb), copper (Cu), nickel (Ni) and zinc (Zn) with extremely variable physical and chemical compositions. Application of SS improves soil properties, increases yield and simultaneously increases trace metal content in soil and plants. The difficulty in handling, transporting and applying SS and its adverse effect, especially trace metal content in soil and plant, can be overcome by SS–coir pith pelletization (SSCP) or mixing with sewage sledge–coir pith mixture (SSCM). A study was undertaken to evaluate the prepared SSCM and SSCP (1:1 ratio of SS and coir pith) along with SS on dry matter yield, trace metal content in soil and plant parts. The results showed that increased rates of application of SS or SSCM or SSCP increased the green and dry fodder yield of forage maize. Application of SS as either SSCM or SSCP at 1.2 and 2.4 g pot^?1 significantly reduced the trace metal content diethylene triamine pentaacetic acid (DTPA extractable) in soil and plant parts (leaves steam and root) compared to SS application. Therefore, in order to reduce the bioavailability of trace metal in soil and its uptake by plant, application of SSCM or SSCP at 1.2 or 2.4 g pot^?1 proved to be a better option than SS application.