A. Mirzai- Asl, B. Yazdi- Samadi Et.al.,
Volume 6, Issue 1 (4-2002)
Abstract
To evaluate cold resistance in wheat in laboratory and to find fast and effective methods of evaluation, nine wheat genotypes were studied in three experiments at the College of Agriculture, University of Tehran, Karaj, Iran. Genotypes consisted of four Iranian cultivars, Sabalan, Boulani, Khalij and Naz one Russian cultivar, Bezostaya and four Iranian accessions, 518, 583, 592 and 1255. In experiment 1, genotypes were grown in 10-cm diameter pots and after hardening in the open, their LT50s were determined in cold chamber. Their cytoplasmic membrane stability were also measured at -12°C through electrolyte leakage measurements. In experiment 2, the genotypes were grown in the field to practice hardening in winter then plant crowns were transferred to the lab and their LT50s were determined. Water content of crowns and leaves, sugar content of crowns, and plant erectness were also measured. In experiment 3, water content of crowns and leaves of the genotypes were measured in non-hardened plants.
Cytoplasmic membrane stability, crown water content and crown sugar content of plants showed significant correlations with LT50. Membrance stability had the highest correlation with LT50 (r=0.88). A high correlation was found between crown LT50 of plants taken from field and LT50 from the plants in the lab (r=0.98). It was found that plant water content reduces with cold hardening. Water content reduction was higher in resistant genotypes compared to susceptible ones. There was no significant correlation between crown and leaf water contents with LT50 in non-hardened plants. Bezostaya with LT50=-16.7°C was the most cold resistant genotype and accession 518 with LT50=-8.2°C was the most susceptible genotype, in this study.
S.a. Safavi, Gh.r Rassulian Etal,
Volume 6, Issue 1 (4-2002)
Abstract
Pathogenicity and virulence of entomogenous fungus, Verticillium lecanii, was studied on the pea aphid, Acyrthosiphon pisum. Vertalec, a commercial product of V. lecanii, was evaluated under controlled conditions. Second instar nymphs were inoculated with conidial suspensions at concentrations ranging from 104 to 108 conidia/ml, and sterile distilled water (containing wetting agent) as control, then caged on cutted alfalfa stems. Each concentration was replicated three times with 30 aphids treated per replicate. Temperature, relative humidity and photoperiod were maintained at 23±1 °C, %97±3, and 16:8 (L:D), respectively. Aphids were monitored daily over 12 days for mortality and nymph production. All newborn nymphs and dead aphids were removed daily.
Vertalec significantly increased aphid mortality (mean mortality because of mycosis increased form %45.55±6.93 at 104 conidia/ml to %95.55±4.45 at 108 conidia/ml). The LC50 value for pathogen was 5.l4×l04 conidia/ml. LT50 values for 105, 106, 107 and 108 conidia/ml were 10, 8, 6.5 and 5 days, respectively. At 104 conidia/ml LT50 value was not determined at experimental period. Ro values significantly decreased with increasing conidial concentration (mean R0 altered from 28.l5±5.38 in control to 5.15±1.81 at 108 conidia/ml). Results indicated that vertalec can be an effective agent against pea aphids. Further studies are recommended for its evaluation under natural conditions.
A. Nezami, A. Bagheri, H. Rahimian, M. Kafi, M. Nasiri Mahalati,
Volume 10, Issue 4 (1-2007)
Abstract
The present experiment was aimed to evaluate the freezing tolerance of two cold tolerant (MCC426 and MCC252) and a cold susceptible (MCC505) chickpea genotypes. The study was carried out in a split-plot factorial design with three replications. Factorial arrangement of genotype and acclimation (acclimation and non acclimation) were imposed as main plot and temperatures (0, -4, -8, -12, 16, -20ºC) as subplot. The effect of freezing temperature (FT) on plant survival was significantly different among genotypes (p<0.05). According to the average effects of acclimation and FT, the plant survival in MCC426 and MCC252 was 40% and 31% respectively more than in MCC505. Lethal temperature for 50% response (LT50) and temperature resulting in 50% lower dry matter (DMT50) in MCC426 were –10.8ºC and
–8.4ºC, respectively and were lower than the other genotypes. Acclimation increased the freezing tolerance such that MCC426 tolerated up to –12ºC without any mortality, however, at this temperature, plant mortality rates in MCC252 and MCC505 were 25.7% and 67.7%, respectively. Plant regrowth was affected by the intensity of FT, such that plant dry weight (PDW) and stem height (SH) in –12ºC decreased about 63% and 50%, respectively, compared with non - frozen control plants. The most freezing damage was observed in MCC505, -12ºC treatment caused 90% decreases in PDW and SH, but at this temperature, PDW and SH in MCC425 decreased 55% and 49% and in MCC252, the reduction was about 60%and 54%, respectively. It seems that the use of controlled experiments would contribute to the evaluation of freezing tolerance and screening programs in chickpea germplasm for the estimation of LT50 and DMT50 .
