فصلنامه علوم زراعی ایران
سال هفدهم شماره 1 (پیاپی 65، بهار 1394)

To investigate the effect of heat stress during grain filling period on photosynthesis, gas exchanges and chlorophyll fluorescence parameters of bread wheat genotypes, two different experiments in the field and phytotron of Chamran University in Ahwaz, Iran, was implemented during 2010-2011 growing season. In the first experiment, 10 medium maturity spring bread wheat genotypes in two; optimum (1 Nov.) and late (21 Dec.) sowing dates as a factorial arrangements in randomized complete block design with three replications were planted. In the second experiment the same genotypes were planted in the pots in randomized complete block design with three replications. Ten days after anthesis, all pots of each genotype were divided in two groups randomly, and then were moved to two separate phytotrons with different temperature treatments i.e.; normal (25/16 °C (max/min)) and heat stress (37/25 °C (max/min)). Pots remained in this condition until maturity. Results showed that under heat stress condition, due to late sowing, flag leaf net photosynthetic rate decreased by at least 11% and at the most 29.5% depending on wheat genotypes. Mesophyll conductance reduction and increasing stomatal conductance were associated with photosynthetic rate reduction. But in cv. Falat and line S- 78-11, stomatal conductance was reduced under heat stress conditions due to late sowing, and stomatal closure was a determining factor in photosynthetic loss. Non-stomatal factors contributed to photosynthetic loss in other genotypes. In late sowing date (mild heat stress conditions in the field) the quantum yield of PSII (ΦPSII) and maximum quantum efficiency of PSII under given light conditions (F′v/F′m) decreased, however, nonphotochemical quenching (NPQ) increased and despite a significant decrease in maximum quanthum yield of PSII under given dark conditions (Fv/Fm), it remained in normal range, due to increase in photoprotective. In severe heat stress conditions (in phytoteron) ΦPSII, F′v/F′m and Fv/Fm parameters significantly reduced, and NPQ values decreased. In fact, under severe heat stress conditions, sensitivity electron transport chain and Fv/Fm parameter increased in sensitive genotypes. Considering the lack of correlation between grain yield and chlorophyll fluorescence parameters in both experiments and also the different rankings of genotypes in different environments, chlorophyll fluorescence parameters solely can not be used as a criterion for the selection of heat tolerant wheat cultivars.

To study the possibility of integrated chemical and non-chemical methods for weeds management in sugar beet, field experiments were conducted in research station of Iranian Research Institute of Plant Protection, Meshkindasht, Karaj, Iran, in 2009 and 2010. Split-split plot arrangement in randomized complete block design with four replications was used. Experimental treatments consisted of three sugar beet planting patterns (including: single rows evenly spaced 50 and 60 cm apart and twin rows spaced 60 cm apart) in main plots, mechanical weed removal stages (in 4-6, 10-12 and 14-16 sugar beet leaf stages) as sub plots and herbicides (including: application of Metamitron and Triflusulfuron-methyl) in sub-sub plots. Only experimental error of total weed biomass and sugar beet root yield were homegeniuos, therefore combined analysis of variance was performed for these two traits. Results showed that single rows spaced 50 cm apart and twin rows had similar weed biomass. The best time for mechanical weed control was 4-6 sugar beet leaf stages, and was more effective when Metamitron was applied in twin rows. Weed removal time had significant effect on sugar beet root yield and higher root yield (37.5 ton.ha-1) was obtained when weeds removed in 2-4 sugar beet leaf stages.

To study the effect of plant density and nitrogen rate on forage quantity and quality of cultivated amaranth (Amaranthus cruentus L.), a field experiment was conducted at Tarbiat Modares University, Iran, on 2012 growing season. Three nitrogen rate (60, 120 and 180 kg N. ha-1) and three plant density (70000, 105000 and 140000 plant. ha-1) were studied as factorial arrangement in randomized complete block design with three replications of. Sampling was performed for morphological characters in early flowering stage. Forage quality (crude protein, soluble carbohydrates, cell wall, acid detergent fiber (ADF) and digestible dry matter) were studied in flowering stage. Results showed that the effect of nitrogen fertilizer rate was significant on morphological traits, forage quantity and some quality traits, however, had no significant effect on some forage quality traits (NDF and ADF). The effect of plant density was not significant on forage quality traits but significantly influenced the morphological traits. The highest forage yield (8776 kg. ha-1) was obtained in plant density of 140000 plant.ha-1 with 180 kg N.ha-1. Also the highest crude protein 21.8%), digestible dry matter (54.4%) and total ash (13.4%) were obtained from 180 kg N.ha-1 treatment. Generally, response of forage quality and quantity of cultivated amaranth to nitrogen fertilizer was positive and linear.

Drought stress is one of the most important environmental factors limiting sugar beet production in arid and semi-arid regions of the world including Iran. Development of drought tolerant varieties is a sustainable approach to mitigate the effect of this limitation. To develop drought tolerant varieties, it is necessary to understand the genetic basis and to map the genomic positions (QTLs) of the traits associated with drought tolerance. To identify the genomic regions of root yield and some leaf traits such as leaf number, leaf chlorophyll content, specific leaf weight, percent green crop cover, carbon isotope discrimination (Δ), leaf succulence index, leaf wilt score and leaf scenecense score, 142 F2:3 families derived from crosses between two parental lines (R49 as tolerant and S501 as sensitive) were studied using simple lattice design under non-stress and water-deficit stress conditions at Kamalabad Research Station, Karaj, Iran, in 2010. Linkage analysis was carried out using 759 simple sequence repeat (SSR) and single nucleotide polymorphism (SNP) markers with a minimum LOD value of 2.5. Eighteen QTLs were identified in the two moisture regime environments. The highest number of QTLs was found on chromosomes 4 and 6 indicating that these chromosomes play an important role in genetic control of the traits studied. In non-stress condition, one QTL was found for specific leaf weight and leaf succulence index, two QTLs for root yield and five QTLs for Δ. In stress condition, one QTL was identified for root yield, leaf number, leaf chlorophyll content, leaf succulence index and leaf scenecense score, and two QTLs for Δ and leaf wilt score. The proportion of variance explained by each QTL ranged from 10.63 to 25.70% in non-stress and from 9.12 to 21.78% in stress conditions, respectively. In stress condition, the QTL of root yield was co-located with that of leaf scenecense score. Makers tightly linked with the major QTLs, especially the QTLs of root yield (qRY4s), leaf scenecense (qSen4s) and leaf wilt (qWilt4s), which could be exploited in marker-assisted selection programs for selection of superior drought tolerant lines and transfer of desirable alleles into improved varieties.

This study was performed at Khuzestan Sugarcane Development Company during 2013- 2014 on CP54-614 variety to evaluate the effect of chemical ripeners on yield and technological ripening at harvest time of sugarcane. A randomized complete block design with four replications was used where three chemical ripeners and untreated control were randomly distributed in plots. The chemical ripeners were Ethrel hormone, Glyphosate herbicide and Fitomas M growth regulator that four doses (0.5, 1, 1.5 and 2 l.ha-1) for each. Results showed that different doses of glyphosate caused reduction of stalk height, invert sugar %) and cane yield and increased brix, pol, recoverable sugar and fiber as compared to control. However, increase (%) in quality yield was more than decrease (%) in cane yield. Therefore, ethrel without decreasing cane yield led to increasing in pol and recoverable sugar in higher doses. On the other hand, Fitomas without increasing cane yield when compared to control led to decrease in pol (%). In conclusion, one liter of glyphosate, decreased cane yield (8%) and increased recoverable sugar (10.6%) and harvest index, and 1.5 liter of ethrel that increased pol (5.6%) were identified as suitable treatments.

Baking quality is one of the most important priorities in bread wheat breeding programs. Therefore, breeding of high yielding cultivars with high baking quality is very important. In the present study, allelic diversity of low-molecular-weight glutenin genes was analyzed in 154 Iranian spring bread wheat landraces and Chines Spring variety using group-specific primers. In Glu-A3, Glu-B3 and Glu-D3 loci, in total 12, and 9 alleles, were amplified, respectively. In Glu-A3 locus, using two primer pairs Glu3A.2 and Glu3A.3 gene sub-groups coding proteins with the N-terminal sequences of MDTSCIP- and METSCIP- was amplified. The fragment of 700-bp length with 45.3% and fragment with size of 742-bp with 0.2% showed maximum and minimum frequency in this locus. In Glu-B3 locus, using Glu3B.2 primer pair designed based gene on sub-groups coding proteins with the N-terminal sequence of METSHIPG-, two fragments of 440 and 421-bp with frequency of 73.2 and 26.8%, were amplified, respectively. The Glu3D.2, Glu3D.3 and Glu3D.4 primer pairs designed, based on gene sub-groups coding proteins with the N-terminal sequences of METSRV-, METCIP and METSCIP-, were used to amplify Glu-D3 locus. The 700-bp allele with 34% and 589-bp allele with 0.7% showed maximum and minimum allele frequency in this locus. The PIC value ranged from 0.09 to 0.72 with an average of 0.22 and gene diversity or expected heterozygosity was in the range of 0.1 to 0.76 and mean value of 0.24. Molecular analysis of variance for allele diversity of LMW-GS genes showed that the variances within groups and between groups were 87 and 13%, respectively.