نشریه به زراعی نهال و بذر
سال بیست و پنجم شماره 2 (1388)

Increased grain yield in modern wheat cultivars has been achieved by increasing grain numbers in spike, which has been associated with a greater contribution of the more distal grains (C, D& E) in the wheat spikelet. However, because distal grains are smaller and lighter than basal grains (A and B) they reduce the average grain weight of modern wheat cultivars. The objectives of this study was to determine the contribution of basal (A& B) and distal (C& D) grains formed in various positions on of spikelet on winter and facultative wheat grain yield in terminal drought stress and normal irrigation conditions. The experimental design for both trials was a randomized complete block with three replications. Five winter and facultative wheat genotypes were studied in normal irrigation and terminal drought stress conditions at two locations (Karaj and Ardabil) in 2003-04 and 2004-05 growing seasons. Cv. Gaspard winter wheat had the highest grain yield (7288 kg/ha) under normal irrigation, while the genotypes grown under terminal drought stress conditions had no significant differences in grain yield. Combined analysis of variance showed that the effect of the position of grains was highly significant (P<0.01) under normal irrigation conditions. Under drought stress conditions, differences due to position of grains was significantly different (P<0.01), the position of grain × location interaction was also highly significant (P<0.01), indicating a considerable variation for this character in different environments. All genotypes had significant differences in the weight of grains in the basal (A& B =38 mg), and distal (C & D = 27-32 mg) grains in the spikelets with lighter grains in the C (32 mg) and D (27 mg) grains in spikelets. However, the weight of grains in the A and B position in the spikelets were heavier. The contribution of the basal grains to grain yield was about 28%, while the contribution of C and D grains were about 22.6% and 19.6% respectively, under terminal drought stress conditions. Breading line as C-80-10, which produced heavier basal (40 mg under stress and 48 mg under normal irrigation) and distal grains (33 and 39 mg under stress and irrigation conditions, respectively) are suitable for both emvironments. More physiology- breeding researches are needed for selection of genotypes with larger and uniform grain size for regions prone to terminal drought stress conditions in winter wheat areas of Iran.

Fire blight causal agent (Erwinia amylovora) naturally induces systemic acquired resistance (SAR) in host plants. This study was carried out to evaluate the induction of SAR by salicylic acid (SA) on fire blight infections in two host plant species, apple (Malus domestica Borkh.) and pear (Pyrus communis L.). Apple rootstocks, MM-111 (tolerant) and MM-106 (moderately-susceptible) and pear cultivars, Harrow Sweet (tolerant) and Spadona (moderately-susceptible) were micropropagated and inoculated from basal parts with strain Ea273 of E. amylovora. The pathogen activity was traced by adding Green Bromo Cresol, and evaluating the pH variation in media. SA treatments were applied by concentration (0.05, 0.1, 0.5, 1, 2, 5, 10 and 0 mgl-1 as control) and days before co-culture (1, 3, 5, 7 days and 0 as control). Effects of SA on the disease development were evaluated by necrosis progress rate, as well as number of necrosed internodes in a 240 h period from inoculation. Results showed that SA did not cause similar effects on disease development in two tested host plant species, apple and pear. SAR induction by salicylic acid application, could not reduce the disease progress in tested apple rootstocks, but also increased development of bacteria on this host plant. In pear, presence of SA successfully decreased disease development rate in shoots. Results confirm that E. amylovora uses induced SAR to become more virulent in interaction with host apple tissues. It is conduded that, the interaction mechanisms of pathogen with SAR in pear and apple are different, and only in pear the SAR induction could be an efficient strategy for management and control of the disease development.

Application of plant growth promoting rhizobacteria (PGPR) as biofertilizers have important role in crops productivity and yield. Bacterial biofertilizers application through seed inoculation is the most important method of application. In order to study the effect of Azotobacter chroococcum, Azospirillum lipoferum and Pseudomonas fluorescens application on late maturity maize (Zea mays L.) hybrids (SC700, SC 704 and a promising single cross; B73×K18) seedling emergence and establishment and grain yield a field experiment was conducted in two cropping seasons. Expriment treatments including hybrids seeds were inoculated with one by one bacteria and co-inoculated by two, and three bacterial combined inoculants and no inoculation as control. Characteristics measured included 50% of primary and final seedling emergence, mean and final emergence time, rate of field emergence and commulative emergence rate, field emergence index, plant height and leaf area, plant dry matter, seedling vigour index (30 days after planting) and grain yield. Results revealed that interaction of hybrids×PGPR was significant on all measured traits. Likewise, the application of inoculant of three bacteria combination had the highest promoting effect on seedling emergence rate and related traites in hybrids. Azotobacter chroococcum and Pseudomonas fluorescens and seed inoculation by single bacterium had the most growth promoting effect, respectively. Seedling emergence and other characteristics were more effected by growth promoting rhizobactoria. B73×K18 and SC700 were also affected by PGPR. There were significant relationship between different characteristics. Therefore, application of studied PGPR has considerable effect on enhancement of seedling emergence and establishment as well as grain yield in studied maize hybrids.

To study the effect of deficit irrigation during different phenological stages of fruit growth and development of almond (cv Mamaei) four experiments were separately carried out using radamized complete block design with three replications. In each experiment, levels of deficit irrigation were T1 (100% ETc, full irrigation), T2 (80% ETC, deficit irrigation), T3 (40% ETC, deficit irrigation) and T4 (0 % ETc, drought). In the first experiment levels of deficit irrigation were applied in fruit growth stage, in the second experiment, irrigation levels were applied in kernel growth stage, in the third experiment irrigation levels were applied in harvest stage. Each experiment were separately conducted in 2002 and 2003 growing seasons. The fourth experiment was carried out as split plot arrangement in randomized complete block design with three replications. In this experiment, the main plots were four different stages of growth including: fruit growth, kernel growth, pre-harvest period and post-harvest period. The sub-plots were different irrigation levels. Results showed that deficit irrigation significantly decreased fruit size and increased fruit drop in first experiment (fruit growth stage). Deficit irrigation decreased fruit fresh weight and kernel fresh and dry weight in kernel growth stage, but in pre-harvest period there was not significant effect on fruit and kernel characteristics. Flower bud density and proportion of initial and final fruit set decreased with deficit irrigation in fourth experiment, hence, yield decreased in following year. Results also showed that the effect of deficit irrigation during pre- and post-harvest was more pronounced on decreasing flower bud density in following growing season.

Two Experiments were conducted to study the effect of benzyladenin and gibberellin on runner production and comparing some vegetative traits of three strawberry cultivars in greenhouse and laboratories of Deparrtment of Horticultural Science, University of Tehran in 2006 and 2007. In the first year (2006), the experiment was carried out as factorial in a completely randomized design (CRD), with two factors; hormonal treatments and strawberry cultivars and in three replications. Hormonel treatments had two levels: the mixture of BA (Benzyladenin) 1200 ppm and GA (Gibberellin) 300 ppm, and control (0ppm). Three strawberry cultivars (Pajaro, Queen Eliza and Paros) were sprayed in April and June. The second experiment (2007) was conducted as factorial in a completely randomized design (CRD), with five replications with two factors; hormonal treatments and strawberry cultivars. Hormonal treatments had five levels. In the first year, results showed that the effect of hormonel treatments was not significant on any trait. In the second year, results showed that the effect of hormonel treatment were significant on all traits. Highest number of plantlets were observed in the second treatment (mixture of BA 1200 ppm and GA 300 ppm sprayed in April) with a standard crown diameter of 6.15 mm. However, highest number of runners in each mother plants and highest crown diameter of plantlets were observed in control (0 ppm).