سال:1391 | دوره: | شماره: |تعداد مقالات:7

Traits related to nitrogen fixation may be used as indirect selection criteria for aflatoxin resistance in peanut. The aim of this study was to investigate the relationship between N2 fixation traits and aflatoxin contamination in peanut under different drought conditions. Eleven peanut genotypes were evaluated under three water regimes for two seasons in the field. Data were observed on kernel infection byAspergillus flavus, aflatoxin contamination, total nitrogen content, N2 fixation and its related traits viz. nodule number, nodule dry weight and nitrogenese activity. Drought stress reduced total nitrogen content and N2 fixation, but it increased kernel infection and aflatoxin contamination. Total nitrogen content, N2 fixation and its related traits had negative and significant effects on kernel infection and aflatoxin contamination especially under drought conditions. In addition, negative correlations between kernel infection and aflatoxin contamination with drought tolerance index (DTI) of N2 fixation traits were also found. The results indicated that the ability to maintain high N2 fixation under drought conditions of peanut genotypes can result in better resistance to aflatoxin contamination.

Straw nursery pots (SNPs), which utilize agricultural residues such as wheat straw and corn stalks as raw materials, can be widely used in the transplanting of seedlings of crops, vegetables, flowers and trees. Plastic nursery pots (PNPs) and direct sowing (DS) were used as controls in evaluating the effects of SNPs on plant growth, dry matter partitioning, yields and economic benefits of transplanted cotton. SNPs significantly increased the rate of emergence, shortened the convalescent period by about 7 d and increased the transplant survival rate by 8.8% compared to PNPs. This led to significantly increased dry matter accumulation: that of reproductive parts for SNP seedlings were 1.5- and 1.8-fold of that for PNPs and DS, respectively. The lint yield using SNPs was 11.5 and 17.5% greater than for PNPs and DS, respectively. Boll number per plant with SNPs was 7.5 and 23.3% greater than for PNPs and DS, respectively; lint weight was not significantly different than with PNPs and was 5.8% greater than for DS. There were no significant differences in lint percentage among the three systems. Further benefit analysis showed that net revenue per hectare from using SNPs in cotton production was US$108 and US$279 greater than for PNP and DS, respectively. This was mainly due to significantly increased output, a reduced number of seedlings needed, nursery pot costs accounting for a relatively small proportion of total investment, and the relatively low labor costs in China.

Isabgol (Plantago ovata Forsk) seed germination and emergence in response to drought (Polyethylene glycol 8000) and salinity stress (NaCl), temperature, pH and planting depth were studied in laboratory and greenhouse experiments. Base, optimum and ceiling germination temperature were estimated as 3.35, 21.24 and 35.04oC, respectively. Isabgol seed is rather tolerant to low water potential and high salt stress. Salinity stress up to 200 mM had no effect on Isabgol seed germination, but the germination decreased by increasing the salt concentration. The drought and salinity required for 50% inhibition of maximum germination were 328 mM and -1.24 MPa, respectively. High percentage of seed germination (>93%) was observed at pH=4-6 and declined to 52-58% at alkaline (pH 7-9) pH. Maximum seedling emergence occurred when the seeds were planted on the soil surface and decreased with increasing the depth of planting; no seed emerged from depth of 3 cm.

Crops growing in salt-affected soils may suffer from physiological drought stress, ion toxicity, and mineral deficiency which then lead to reduced growth and productivity. A pot experiment was conducted to study the effect of different salinity levels, i.e. ECe=3 dS m-1 (control), 8, 12 and 16 dS m-1 on wheat grain yield, yield components and leaf ion uptake. Desired salinity levels were obtained by mixing adequate NaCl before filling the pots. Soil water was maintained at 70% of available water holding capacity. Results revealed that Kouhdasht and Tajan showed highest and lowest grain yield and yield compomnents as compared to others. Leaf Na+ and Cl- concentrations of all genotypes increased significantly with increasing soil salinity, with the highest concentrations in Tajan, followed by Rasoul, Atrak and Kouhdasht. Highest leaf K+ concentration and K+: Na+ ratio were observed in Kouhdasht, followed by Atrak, Rasoul and Tajan, respectively.Based on higher grain yield production, higher leaf K+ concentration, K+: Na+ ratio and lower leaf Na+ and Cl- concentrations, Kouhdasht and Atrak were identified as the most salt-tolerant genotypes.

Parasitism by Striga hermonthica (Del) Benth is a severe constraint in maize production in sub-Saharan Africa. Varying levels of tolerance to Striga attack have been identified and exploited in breeding programs of several crops. However, the level and stability of the tolerance is generally unacceptable in field-practice. Only limited exploration has been undertaken among the farmers’ landraces to find the presence of viable sources of resistance to Striga. The objective of this study was to examine and document the presence of the Striga germination stimulants from a collection of some 420 maize landraces, populations and elite inbred lines. The genotypes were variously sourced from International Maize and Wheat Improvement Center (CIMMYT), International Institute for Tropical Agriculture (IITA) and Kenya Agricultural Research Institute (KARI). The ability to effect germination as a measure of the amount of germination stimulant produced was used to assess the materials, using the standard procedures. Data were recorded on Striga germination by counting Striga seeds with protruding radicle. Highly significant (P=0.001) differences were observed among the germplasm screened. Several landraces were found to stimulate low levels of Striga germination compared to the commercial checks. Landraces CRIC 51, CUBA T-31, BRAZ 1758, BRAZ 1279 and VERA 217 exhibited the lowest Striga germination, an indication of high level of resistance to Striga. The inbred lines were found to have a higher Striga germination percent compared to the landraces, a likelihood of a higher concentration of strigol, the stimulant causing chemical. CIMMYT lines CML 202 IR, CML 445 IR and CML 204 IR induced the least amount of Striga seeds to germinate. Higher levels of germination of Striga seeds were found in the IITA lines which are known to beresistant, depicting a probable avoidance root architecture mode of resistance as opposed to low production of strigol. It was concluded that the landraces with low Striga germination percent can be used by breeders in the extraction of new Striga resistant inbred lines. The resistant inbred lines can be recommended for direct use in the formation of maize synthetics and hybrids resistant to S. hermonthica.

The present study was a part of a long time screening experiment that included a high number of wheat landraces (Triticum aestivum L.) cultivated in Greece, and focused on the agronomic point of view and the drought adaptation for some of these landraces. One of the most acceptable ways for the assessment of drought resistance is the examination of yield and yield components in different water regimes. Therefore, in our two-years experiments parameters of plants water relations and yield components such as grain yield, total biomass, number of kernels per spike and mean grain weight were recorded for the several cultivars.The data obtained during the two experimental seasons clearly pointed out the differential behavior of wheat landraces under water stress conditions. The populations that exhibited the greater adaptability (low bN) were Grinias Zakinthou (biomass, grain yield) and Skilopetra Ptolemaidas (harvest index, kernels per spike) and they could be used in breeding programs in Greece and other arid regions.

We simulate the effect of climate change on water requirements of cold season wheat in various climatic zones of Iran. The research considers both observed climate (temperature and precipitation) changes during recent decades (1960-2009) based on instrumental records and projected future changes to 2100 based on the MAGICC/SCENGEN 5.3 compound model.20 General Circulation models are used based on a single scenario known as P50, which is the average of SRES or emission scenarios. Results indicate that whilst winter precipitation has marginally increased across the country as a whole, a significant decline in mean spring precipitation is recorded between 1960 and 2009. However, considerable variability in trends is measured across various climatic regions of Iran. Mean annual temperature / rainfall changes in the various climate zones of Iran for the period 1960-2009 follow: +0.1°C / decade /+0.43 mm / decade in arid regions, -0.1°C / decade / -1.7 mm / decade in semi-arid regions, +0.1°C / decade / -1.33 mm / decade in Mediterranean / semihumid regions and -0.01°C / decade / -0.04 mm / decade in humid / hyper humid regions. Temperature projections to 2100 indicate an overall temperature rise of ca.4.25°C relative to that for 1961-1990, with increases projected for all climatic regions of Iran. Despite an overall projected mean precipitation increase of 36% for the year 2100, relative to that for 1961-1990, these are insufficient to compensate for temperature increases. Consequently, calculated water deficits during the growing season (autumn to spring) in Iran’s wheat producing areas are expected to increase from 5.2% in 1980 to over 23% by 2050 and 38% by 2100.