Soil salinity: A serious environmental issue and plant growth promoting bacteria as one of the tools for its alleviation.

Stressful environments such as salinity, drought, and high temperature (heat) cause alterations in a wide range of physiological, biochemical, and molecular processes in plants. Photosynthesis, the most fundamental and intricate physiological process in all green plants, is also severely affected in all its phases by such stresses. Since the mechanism of photosynthesis involves various components, including photosynthetic pigments and photosystems, the electron transport system, and CO2 reduction pathways, any damage at any level caused by a stress may reduce the overall photosynthetic capacity of a green plant. Details of the stress-induced damage and adverse effects on different types of pigments, photosystems, components of electron transport system, alterations in the activities of enzymes involved in the mechanism of photosynthesis, and changes in various gas exchange characteristics, particularly of agricultural plants, are considered in this review. In addition, we discussed also progress made during the last two decades in producing transgenic lines of different C3 crops with enhanced photosynthetic performance, which was reached by either the overexpression of C3 enzymes or transcription factors or the incorporation of genes encoding C4 enzymes into C3 plants. We also discussed critically a current, worldwide effort to identify signaling components, such as transcription factors and protein kinases, particularly mitogen-activated protein kinases (MAPKs) involved in stress adaptation in agricultural plants.

Photosynthesis under stressful environments: An overview

Responses of photosynthesis, chlorophyll fluorescence and ROS-scavenging systems to salt stress during seedling and reproductive stages in rice.

Photosynthetic activity decreases when plants are grown under saline conditions leading to reduced growth and productivity. Leaf growth, gas exchange, and chlorophyll fluorescence of two sorghum [Sorghum bicolor (L.) Moench] varieties, Serena and Seredo, were measured in response to increasing NaCl concentration. Sorghum plants were grown in sand culture under controlled greenhouse conditions. The NaCl concentrations in complete nutrient solution were 0 (control), 50, 100, 150, 200, and 250 mM. Salinity significantly (P less than or equal to 0.01) reduced leaf area by about 86% for both varieties of sorghum. Chlorophyll a and b, met CO2 assimilation, stomatal conductance, and transpiration rate decreased significantly (P less than or equal to 0.01) with the increase in salinity, and these decreases were similar for the two sorghum varieties. Salt induced decreases for these physiological traits ranged from 75 to 94%. Photochemical efficiency of PSII (F(v)/F(m)) and photochemical quenching coefficient (qP) decreased by about 9 and 10%, respectively, for both varieties, and electron transport rate (ETR) decreased by 20 and 25% for Serena and Seredo. In contrast, non-photochemical quenching (NPQ) significantly (P less than or equal to 0.01) increased by 44 and 50% for Serena and Seredo. The results indicate that salinity affected photosynthesis per unit leaf area indirectly through stomatal closure, and to a smaller extent through direct interference with the photosynthetic apparatus. In addition, salinity decreases whole plant photosynthesis by restricting leaf area expansion. This effect starts from low levels of salinity, in contrast to that of net photosynthesis per unit leaf area, which occurs at higher levels of NaCl concentration.

Sorghum and salinity. II. Gas exchange and chlorophyll fluorescence of sorghum under salt stress

Agriculture and fishing are the primary source of almost all our food, as well as of many other products, so remain vital activities even though their share in the economy is small and in continuous decline. Partly for this reason public policy in these areas is almost entirely integrated at European level in the Common Agricultural Policy (CAP) and Common Fisheries Policy (CFP). Forestry policies are also heavily affected by EU-level decision-making. As agriculture dominates in terms of direct contribution to GDP and numbers of people engaged in it, as well as accounting for the largest amount of public support expenditure, it is agriculture that will receive the greatest attention here.

Agriculture, Forestry and Fisheries

Crops grown in salt affected soils may suffer from drought stress, ion toxicity, and mineral deficiency leading to reduced growth and productivity. The present study was conducted to determine how salinity affects growth, water relations, and accumulation of cations of nutritional importance in various organs of grain sorghum [Sorghum bicolor (L.) Moench]. Two Kenyan sorghum varieties, Serena and Seredo, were grown in a greenhouse in quartz sand supplied with a complete nutrient solution to which 0 (control), 50, 100, 150, 200, and 250 mM NaCl was added. The 250 mM NaCl treatment significantly reduced the relative shoot growth rates, measured 25 d after the start of salt application, by 75 and 73%, respectively, for Serena and Seredo, and stem dry weight by 75 and 53%. In a similar way, young leaves were affected, with leaf blades of both varieties being reduced by 67% while sheaths were reduced by 83 and 87% for Serena and Seredo, respectively. Leaf water potential, osmotic potential, leaf pressure potential, and relative water content significantly declined with increasing salt stress. Roots and stems accumulated substantial amounts of sodium, saturating at 150 mM external NaCl. Accumulation of K+ and Ca2+ in the roots, stems, and leaves was strongly inhibited by salinity. Magnesium concentration of the roots was minimally impaired but that of the stems and leaves was strongly affected. Leaves continuously accumulated sodium, which was preferentially deposited in the sheaths. Mature leaves contained more Ca2+ and Mg2+ than young ones. The two sorghum varieties appear to sequester Na+ predominantly in roots, stems, leaf sheaths, and older leaf blades sparing the growing tissues as a salt tolerance mechanism. Nevertheless, greatly reduced concentrations of Ca2+, K+, and Mg2+ in leaves under salinity could cause cation deficiency which reduces plant growth.

Sorghum and salinity: I. Response of growth, water relations, and ion accumulation to NaCl salinity

Though the majority of people in Kenya and at Kopsiro Division in particular, rely on ethnomedicinal plant species to manage human ailments, the indigenous knowledge largely remains undocumented. Therefore, an ethnobotanical study was conducted on medicinal plant species used to manage human ailments at Kopsiro Division Mt. Elgon District Kenya. The objectives were to identify and document plants traditionally used for medicinal therapy by the Sabaots, to find out the method used for preparing and administering the drugs and to find out the conservation practices for the medicinal plants. Observations and semi-structured interviews were used to gather ethnobotanical data. 107 plants belonging to 56 families were identified and reported to be of medicinal value to the locals. Roots (47.3%) were the most frequently used parts of the plant followed by the bark (23.35%) then leaves (22.75%). The whole plant (1.8%), seed (1.2%), fruit (1.2%), sap (1.2%), flower (0.6%) and wood (0.6%) are least used in that order. The study revealed other hitherto undocumented medicinal plant species that may be new records for treating various ailments. Traditional medicine in Kopsiro division offers cheap, accessible and convenient remedy that suits the traditional lifestyle of the local community in comparison to the conventional medicine. Most medicinal plant species reported in this study were found to be under threat and this calls for urgent conservation measures so as to maximize the sustainable use of these vital resources in the study area.

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Ethnobotanical study of medicinal plants used by Sabaots of Mt. Elgon Kenya.

Striga spp. is renowned for causing great losses in cereal production in sub-Saharan Africa. Crop competitiveness with parasitic weeds such as Striga is an important criterion for selection in an initiative to produce and release rice cultivars to farmers that are able to give high and stable yields under low-input conditions. The symptoms of Striga infected rice plants are chlorosis, wilting and stunted growth. Rice yield is reported to be reduced by more than 50% in areas that are infested by the weed. In addition, areas that are heavily infested have been abandoned and rendered unfit for crop production. Notable advances in Striga weed control technology have been made, yet the weed continues to be a major cause of low agricultural production. This is an indication of poor linkage between research institutions and agricultural extension which is a bottleneck to research findings to benefit farmers.

/pdf/evaluation-of-ecologies-and-severity-of-striga-weed-on-rice-3t48ah8p78.pdf

Evaluation of ecologies and severity of Striga weed on rice in sub-Saharan Africa

Water deficit affects growth and development of rainfed rice leading to a considerable yield reduction or crop failure. Although the rice crop is susceptible to water deficit, there is a marked genotypic variation in protein and chlorophyll content in response to water deficit. The objective of this research was to investigate the effects of water deficit on chlorophyll fluorescence, protein and chlorophyll content of three recently developed rainfed rice varieties that is, New Rice for Africa (NERICA coded as N2, N4 and N11) with a view of determining their tolerance levels to water d deficit. This study was carried out in the University Botanic Garden, Maseno during 2005- 2006. Plants were subjected to water deficit treatments in the green house and in the field in a factorial set up. The seeds of the three NERICA cultivars of rice were planted in 20 Litre PVC pots in the greenhouse and in the experimental plots in the field, arranged in a completely randomized block design (CRBD) with four treatments and four replications. The treatments included watering a litre of water once a day (control), Watering every 2, 4 and 6 days. The parameters measured included chlorophyll fluorescence, protein and chlorophyll content. The Water deficit had no significant effect on chlorophyll fluorescence parameters. The total chlorophyll and protein content declined with increasing water deficit. Results indicate that under moisture deficit conditions, there is no significant damage to the photosynthetic apparatus of the three rice varieties. NERICA 2 exhibited superior qualities indicating that it may perform well under water deficit conditions.

J. C. Onyango

Papers

Sorghum and salinity. II. Gas exchange and chlorophyll fluorescence of sorghum under salt stress

Sorghum and salinity: I. Response of growth, water relations, and ion accumulation to NaCl salinity

Ethnobotanical study of medicinal plants used by Sabaots of Mt. Elgon Kenya.

Evaluation of ecologies and severity of Striga weed on rice in sub-Saharan Africa

Chlorophyll fluorescence, protein and chlorophyll content of three nerica rainfed rice varieties under varying irrigation regimes