Microbial and Enzyme Activities of Saline and Sodic Soils

Salinization and sodication are abiotic soil factors, important hazards to soil fertility and consequently affect the crop production. Soil salinization is of great concern for irrigated agriculture in arid and semi‐arid regions of the world; sodicity is characterized by an excessively high concentration of sodium (Na) in their cation exchange system. In recent times, attention has been turned to study the impacts of these factors (salinity and sodicity) on soil microbial activities. Microbial activities play central role in degradation and decomposition of soil organic matter, mineralization of nutrients and stabilization of soil aggregates. To understand the ecology of soil system, therefore, it is important to be conversant with the soil microbial activities, which show quick response to little change in the soil environment. Microbial activities (generally measured as C–N dynamics, soil respiration–basal respiration, or CO₂ emission), microbial abundance, microbial biomass, quotients (microbial and metabolic) and microbial community structure, and soil enzymes have been considered as potential indicators to assess the severity of the land degradation and the effectiveness of land use management. Therefore, it is important to synthesize the available information regarding microbial activities in use and management of salt‐affected soils. The reclamation and management of such soils and their physico‐chemical properties have been reviewed well in the literature. In this review, an attempt has been made to compile the current knowledge about the effects of soil salinization and sodication on microbial and enzyme activities and identify research gaps for future research. Copyright © 2015 John Wiley & Sons, Ltd.     

Tillage Effects on Crop Yield and Physicochemical Properties of Sodic Soils

Tillage modifies soil structure and has been suggested as a practice to improve physical, hydrological and chemical properties of compacted soils. But little is known about effect of long‐term tillage on physicochemical soil properties and crop yield on sodic soils in India. Our objective was to investigate the effect of different tillage regimes on crop yield (wheat and paddy rice) and physicochemical properties of sodic soils. Two sodic sites under conventional tillage for 5 (5‐YT; 5‐year tillage) and 9 (9‐YT; 9‐year tillage) years were selected for this study. Changes in crop yield and physicochemical soil properties were compared with a control, sodic land without any till history, that is, 0‐year tillage/untilled (0‐YT). Five replicated samples at 0‐ to 10‐cm and 10‐ to 20‐cm soils depths were analysed from each site. In the top, 0‐ to 10‐cm soil depth 5‐YT and 9‐YT sites had higher particle density (Pd), porosity, water holding capacity, hydraulic conductivity, organic carbon, total nitrogen (N_t), available nitrogen (N_avail), phosphorus (P_avail) and exchangeable calcium (Exch. Ca⁺⁺) than 0‐YT, whereas bulk density (Bd), C : N ratio and CaCO₃ were significantly lower. Bd, pH, EC and CaCO₃ increased significantly with depth in all the lands, whereas Pd, porosity, water holding capacity, hydraulic conductivity, organic carbon, N_t, N_avail, P_avail and Exch. Ca⁺⁺ decreased. We conclude that continuous tillage and cropping can be useful for physical and chemical restoration of sodic soils. Copyright © 2014 John Wiley & Sons, Ltd.     

Breeding crops for reduced-tillage management in the intensive, rice–wheat systems of South Asia

The importance of reduced tillage in sustainable agriculture is well recognized. Reduced-tillage practices (which may or may not involve retention of crop residues) and their effects differ from those of conventional tillage in several ways: soil physical properties; shifts in host–weed competition; soil moisture availability (especially when sowing deeply or under stubble); and the emergence of pathogen populations that survive on crop residues. There may be a need for genotypes suited to special forms of mechanization (e.g. direct seeding into residues) and to agronomic conditions such as allelopathy, as well as specific issues relating to problem soils. This article examines issues and breeding targets for researchers who seek to improve crops for reduced-tillage systems. Most of the examples used pertain to wheat, but we also refer to other crops. Our primary claim is that new breeding initiatives are needed to introgress favourable traits into wheat and other crops in areas where reduced or zero-tillage is being adopted. Key traits include faster emergence, faster decomposition, and the ability to germinate when deep seeded (so that crops compete with weeds and use available moisture more efficiently). Enhancement of resistance to new pathogens and insect pests surviving on crop residues must also be given attention. In addition to focusing on new traits, breeders need to assess germplasm and breeding populations under reduced tillage. Farmer participatory approaches can also enhance the effectiveness of cultivar development and selection in environments where farmers’ links with technology providers are weak. Finally, modern breeding tools may also play a substantial role in future efforts to develop adapted crop genotypes for reduced tillage.     

Geographical distribution of the DL1 and DL2 genes causing hybrid dwarfism in Phaseolus vulgaris L., their association with seed size,and their significance to breeding

Summary Dwarlism in F₁ hybrids has been observed in over 100 crosses of dry beans (Phaseolus vulgaris L.) at the Centro Internacional de Agricultura Tropical (CIAT), Cali, Colombia. In each cross, one parent always had small seeds and the other parent either medium or la ge ones. This apparent incompatibility between the two groups of germplasm was controlled by two complementary, dominant genes: DL₁ and DL₂. Smallseeded bean lines carried gene DL₁ and originated in Brazil, Colombia, Guatemala, and Mexico; medium for large-seeded bean lines carried gene DL₂ and were from Bolivia, Brazil, Chile, Colombia, Turkey, The United States, and West Germany. Thes two genes have probably played an important role in the evolution of dry bean forms of different seed sizes by serving as a genetic barrier or isolating mechanism, thus limiting free genetic recombination between the two germplasm groups.Apparent differences in the adaptiveness and yielding ability of the two groups of bean germplasm, smallys, medium- and large-seeded, and some breeding implications for manipulation of the genes causing F₁ hybrid dwarfism were also discovered.     

Sources and inheritance of earliness in tropically adapted indeterminate common bean

Summary Nineteen early maturing, indeterminate common bean parents were crossed with a tester line of normal maturity. All parents, F₁ hybrids, F₂'s, and backcross generations were evaluated at CIAT-Palmira, Colombia. All 19F₁ populations flowered and matured almost as early as the respective early parent (mean of 61 vs 59 days). The F₂ populations were slightly less early (63 days), but were still earlier than the mean of the two parents (65 days). Additive effects for days to maturity were usually larger than dominance or interaction effects. Narrow sense heritability for days to flower and maturity were high (greater than 0.67), while heritabilities of absolute and relative duration of pod filling were low (0.17 to 0.50). Also, our data indicated that for each day of increase in earliness, yield potential will decrease 74 kg/ha.     

Protein electrophoresis as an aid to oat variety identification

Summary Ten cultivars of oats (Avena sativa L.) were investigated for their isozymes of esterase (E), leucine aminopeptidase (LAP), and anodal and cathodal peroxidase (APX and CPX).From repeated observations, a typical zymogram was prepared for each enzyme system, and the frequencies of the isozyme bands were scored for each variety separately. The results showed that: (1) most of the isozyme bands are very stable in their appearance on the gel: (2) each variety has a characteristic isozyme pattern; (3) 7 out of 10 oat cultivars showed no intravarietal isozyme variation. Some variation was found for the varieties Mesa, Rapida and Curt. This overall high level of homozygosity and homogeneity of these varieties for the isozyme bands makes this technique useful for varietal identification.     

Introgression of low temperature tolerance and red rot resistance from Erianthus in sugarcane

Eighteen clones involving Erianthus, as one of the parents, were evaluated in a randomised block design under sub-tropical conditions of Karnal (Haryana, India). Fifteen characters, which contribute towards stalk yield and juice-quality, were studied. The growth of these clones was monitored during peak winter months of December and January. Significant variability existed among the clones for all the traits studied, except for pol % in juice at 10-month crop age, indicating potentiality of the clones to select desirable types. Nine clones showed significant increase in stalk length during winter months over the better standard Co 1148. Whereas 6 clones developed more number of leaves than Co 1148. Both these characters showed high genetic variability, high heritability and hence, high expected genetic gain. Path analysis revealed that these traits contributed about 16%, 5% and 4% to the total genetic variability in juice quality traits (pol % and CCS %), stalk yield and CCS yield, respectively. Growth in winter months has resulted in an increase in stalk yield and CCS yield. This may help in reducing the yield gap between tropical and sub-tropical regions. Majority of clones showed resistance to red rot disease (major disease of sugarcane in sub-tropical region). Hence, hybridization of Erianthus with sugarcane has resulted in introgression of genes for cold tolerance and red rot resistance. As Erianthus is known for its hardiness, resistance, of these clones, to other abiotic and biotic stresses is to be ascertained. This revised version was published online in August 2006 with corrections to the Cover Date.     

Virulence characteristics of a new race of the parasitic angiosperm,Striga gesnerioides,from southern Benin on cowpea (Vigna unguiculata)

An in vitro growth system was used to determine the virulence of two samples of Striga gesnerioides from Zakpota in southern Benin. Cowpea variety B301, previously considered resistant to all races of S. gesnerioides, was susceptible to both samples of the parasite. Two other cowpea varieties, 58–57 and IT81D-994, were totally resistant. Resistance in 58–57 was associated with a hypersensitive necrosis of infected roots, whilst IT81D-994 supported production of small S. gesnerioides tubercles with stems which failed to develop. Striga gesnerioides from southern Benin is the fourth race of the parasite to be identified, and the first with virulence on variety B301. The implications for breeding cowpeas with resistance to S. gesnerioides are discussed.Abbreviations IITA International Institute of Tropical Agriculture - LARS Long Ashton Research Station - SAFGRAD Semi-Arid Food Grain Research and Development     

Male Sterility in Barley

The anther form and development of eight two-rowed genie male sterile barley mutants are abnormal. The male sterility in each mutant is conditioned by single non-allelic recessive genes. These mutant genes cause reductions in anther size and lumen diameter. Though in seven mutants, the male meiosis is normal until microspore liberation, the micro-spores abort in all cases after release from the PMCs. In one mutant, the microspores degenerate at the tetrad stage before release from the PMCs. In four mutants, the tapetal development and disintegration are normal, in four others they are abnormal. Despite these variations, the male sterility in all the eight mutants is complete.     

Possibility of genetic improvement of pigeonpea (Cajanus cajan (L.)Millsp.) utilizing wild gene sources

Summary Various wild relatives of pigeonpea,Cajanus cajan, namely some species ofAtylosia andRhynchosia, possess desirable characteristics that could be utilized for effecting genetic improvement of this crop. In total 73 cross combinations among two cultivars ofC. cajan and one accession each of eightAtylosia species and one ofRhynchosia were attempted. Twelve hybrids were obtained. Seven of these were analysed for F₁ fertility and their utility for agronomic improvement of theC. cajan. Fertility behaviour of the different F₁ hybrids varied and indicated that potential of gene transfer between the two genera,Atylosia andCajanus, was as good as within the genusAtylosia. From F₂ and F₃ families ofC. cajan × A. scarabaeoides andC. cajan × A. albicans, plants were selected with greater physiological efficiency and agronomic superiority. The prospects of transferring pod borer resistance and higher seed protein content from someAtylosia species to pigeonpea are discussed.