فصلنامه تحقیقات غلات
سال دهم شماره 1 (بهار 1399)

To study the genetic diversity and grouping of rice recombinant inbred lines (RILs), 144 RILs derived from a cross between two Iranian rice varieties, Nemat and Hashemi, were evaluated in Rice Research Institute of Iran, Rasht, Iran, in two crop seasons, 2018 and 2019. The experiment was carried out based on augmented design with four varieties (two parents, Hashemi and Nemat, and two other varieties, Ali Kazemi and Khazar) as control treatments in randomize complete block design with three replications. The results of data analysis of variance showed that there was a significant difference among rice genotypes for all studied traits. The highest coefficient of variation in both years was observed for panicle exertion and grain yield, respectively, and the lowest for milling ratio. Comparison of means showed that some lines were superior to others in terms of yield and other important agronomic traits. Cluster analysis based on the average of two years data grouped the studied genotypes into four clusters. The results of principal component analysis showed that five independent principal components explained about 82% of the total variation and the related two dimensional plot also classified the studied genotypes into three groupes. According to the results of comparison of means, cluster analysis and principal component analysis, the RILs 157, 113, 114, 142 and 130 with the highest grain yield and the lowest early maturity were selected as the superior lines in this study and can be used to introduce cultivar and/or hybrid production in future breeding programs.

The most important breeding objective in most crop plants is to increase grain yield, however, the complex genetic nature of grain yield and the influence of other traits make direct selection based on grain yield less successful. Therefor, it is necessary to introduce the other traits with simpler inheritance and higher heritability than grain yield as selection criteria, so that indirect selection based on them can lead to improve grain yield in the studied population. The objective of this study was to identify and introduce appropriate selection criteria to improve grain yield in an F11 rice population using base selection index. The plant materials of this study were 141 recombinant inbred lines of F11 generation derived from a cross between two Iranian rice cultivars, Gharib and Sepidrood, which were planted in a randomized complete block design with three replications at research field of Faculty of Agricultural Sciences, University of Guilan, Rasht, Iran, in 2018. The studied traits were included days to 50% flowering, days to maturity, plant height, number of total tiller and panicle per plant, panicle length, number of filled and unfilled grain per panicle, number of spikelet per panicle, panicle fertility percentage, 1000 grain weight, grain length, width and shape and grain yield. The results of phenotypic and genotypic path analysis showed that number of panicle per plant, number of grain per panicle and 1000-grain weight had the most positive and significant direct effects on grain yield. Assessing the base selection indices and comparing them based on different evaluated criteria, specially genetic advance of each trait and relative efficiency of index- based selection than direct selection of grain yield also showed that the use of base selection indices based on phenotypic and genotypic correlation cefficients as well as path coefficients of number of panicle per plant, number of filled grain per panicle and 1000-grain weight were the most appropriate indices for selecting high yielding lines in the studied F11 population.

Due to the importance of canola cultivation as a second crop, the present study was aimed to appraisal of financial indices and affecting variables on acceptance of canola cultivation as second crop in paddy fields of Guilan province, Iran, in 2018-2019 crop year. This study was a causal-descriptive study and a researcher-made questionnaire was used to collect data. A total of 150 farmers from the states level were studied as sample. Validity of the questionnaire was obtained from a panel of experts and its reliability was assessed by Cronbach's alpha and its value was calculated 0.87. The results of appraisal of financial indices showed that canola cultivation for Guilan rice farmers in the present conditions is less financially justified. The results of regression analysis to investigate the factors affecting the acceptance of rice farmers for canola cultivation showed that participation in extension training classes, average canola income, age of farmer and history of canola cultivation in total explain 84% of the changes in the dependent variable. Based on the results of exploratory factor analysis, barriers and limitations of canola cultivation were categorized into three factors from the perspective of rice farmers in province, problems with planting and maintenance of canola, post-harvest problems of canola and problems regarding economic conditions, climatic conditions, land conditions and insurance of canola cultivation conditions. In general, the results of this study showed that by stablishing higher quality extensional-educational classes according to the needs of farmers, effective communication between actors and the establishing canola processing factories, it is possible to eliminate barriers to canola cultivation as a second crop in paddy fields of Guilan province.

Maize in response to salinity stress exhibits different responses during different growth stages and reproductive growth stage is the most sensitive stage of plant growth. The objective of the present study was to evaluate the ability of salinity simulator models to estimate maize (SC704) yield, during reproductive growth stage. Process-physical models including Maas and Hoffman, van Genuchten and Hoffman, Dirksen et al. and Homaee et al. models were used to access this objective. In order to create real growth conditions in saline soils, natural saline water of Nough lake in Rafsanjan, Kerman province, Iran, with electrical conductivity of 42.6 dS.m-1, was used and diluted with normal fresh water for preparation of salinity treatments studied in this experiment. Treatments used in this study were five salinity levels of 1, 2, 4, 6 and 8 dS/m with a non-saline water (as check treatment) that were studied in three replications. The results of modified efficiency coefficient (E'), modified agreement index (d') and coefficient of residual mass (CRM) statistics showed that the van Genuchten and Hoffman model with the highest accuracy (E'=0.87, d'=0.91) was the most accurate model for shoot height, while for shoot dry weight, the Nonlinear model of Homaee et al. (with the accuracy of E'=0.86 and d'=0.90) and for final grain yield, the Maas and Hoffman model (with the accuracy of E'=0.94 and d'=0.96), had the most accuracy and the best estimate. In total, the results of this study showed that salinity simulation models had good ability to estimate maize yield under salinity stress and better management of allocation of low quality water resources in different stages of plant growth. In other words, the four models of Maas and Hoffman, van Genuchten and Hoffman, Dirksen et al. and Homaee et al. can be effective tools in using saline water sources with varying degrees of salinity to achieve optimal maize production. Therefore, by precisely determining the optimal model for each growth stage and accepting the risk of yield loss due to salinity of irrigation water, low-quality water resources can also be considerably utilized in maize yield production.

Selection of high yielding and stable genotypes is especially important for rainfed conditions. The objective of this study was to use the genotype by yield × trait (GYT) biplot method to select superior bread wheat genotypes based on yield-trait combinations under rain-fed conditions. To this end, 16 bread wheat genotypes were assessed in a randomized complete block design with four replications in two cropping seasons, 2017-2019. Comparison of average grain yield of genotypes in the experimental years showed that genotypes G1 (Aftab), G15 and G8 had the highest grain yield with an average yield 3433, 3269 and 3233 kg/ha, respectively. The result of polygon view of GYT biplot showed that G8 was the best genotype in combining grain yield with 1000-kernel weight, number of grain per spike and spike length. Similarity, G1 also had a relative superiority in combining grain yield with number of spikelet per spike, awn length and early maturity. Average tester coordinate (ATC) view of GYT biplot indentified genotypes G8, G1 and G15 with all positive yield-trait combinations as the best genotypes and genotypes G14, G4, G13 and G7 as the weakest genotypes. Genotypes G15 and G16 were also balanced for yield- trait combinations. Ranking of the genotypes based on GYT index showed that genotypes G8, G1 and G15 had the best genotypes in combining grain yield with the evaluated traits in the experimental years. Based on the results of this study, high correlations were observed between 1000-kernel weight, number of grain per spike and grain weight per spike in combination with grain yield, indicating high efficiency of combining these traits with grain yield to improve productivity of bread wheat genotypes under rainfed conditions.

Knowledge of freezing stress tolerance in wild barley and feral rye as the most important weeds in wheat fields can be used to predict their geographical distribution and management plannings. To this end, an experiment was conducted in Faculty of Agriculture, Ferdowsi University of Mashhad, Mashhad, Iran, in autumn 2017. Two wheat genotypes (cultivar Pishgam and Iranian landrace Ghezel Khoushe) and two weeds (wild barley and feral rye) were grown up to two to four true leaves stage under natural conditions and then exposed to a temperature range of +4 to -20 °C (+4 oC as control and 0, -4, -8, -12, -16 and -20 oC as freezing temperatures). The results showed that reducing temperature from -8 to -12 °C led to a 36% decrease in survival of wild barley, while the survival of wheat (Pishgam and Ghezel Khoushe) and feral rye was 100%. Wild barley had the highest lethal temperature reducing 50% of survival (LT50su = -12.8 °C) and temperature rducing 50% of leaf area (RLAT50 = -11.2 °C). Among the studied plant species, wheat (landrace Ghezel Khoushe) and feral rye with -11.8 °C and -11.6 °C, respectively, had the lowest temperature rducing 50% of shoot dry weight (RSDWT50), while the wild barley with -8.1 °C had the highest RSDWT50. The highest and lowest chlorophyll content (SPAD) among the living plants were observed at +4 and -12 °C, respectively, and  feral rye with 19.5 and wild barley with 10.3 SPAD unit showed the highest and lowest chlorophyll content, respectively. The results of this study showed that high tolerance of feral rye to freezing stress is probably one of the main reasons for its widespread distribution in winter wheat fields. Therefore, it is necessary to predict dispersion and possible invasion and consequently appropriate strategies to manage this weed in areas with cold climates.

By understanding the diversity and dominance of weed species, which is affected by changes crop management systems and weed control practices, these plants can be managed more efficiently. In this study, the diversity of weed species of irrigated wheat fields was studied in an area of ​​less than one, one to two, two to four, four to eight and more than eight hectare in the central region of Arak, Iran, in 1919. A total of 74 weed species were identified from 25 plant families, of which 61 species were dicotyledons and 13 species monocotyledons, 78.38% annual and 21.62% perennial as well as 95.95% C3 and 4.05% C4. Also, Asteraceae and Brassicaceae families among dicotyledons and Poaceae family among monocotyledons had the highest species diversity. According to the dominance index, ten dominant weed species were flixweed (Descurainia Sophia), binweed (Convolvulus arvensis), foxtail grass (Alopecurus myosuroides), common thistle (Cirsium arvense), Iranian knapweed (Centaurea depressa), lowgrass (Polygonum aviculare), corn cleavers(Galium tricornutum), Syrian mustard (Eeuclidium syriacum), goldbachi (Goldbachia laevigata) and nodding hypecoum(Hypecoum pendulum). There was a significant inverse relationship between field size with Shannon-Wiener and Pielou's uniformity indices and their highest values (2.58 and 0.84, respectively), was obtained in the fields less than 1 ha and the lowest values (1.48 and 0.61, respectively), in the fields more than 8 ha. In contrast, the relationship between field size and Simpson's dominance Index was positive and significant and its value was calculated 0.1 and 0.33 for fields less than 1 ha and more than 8 ha, respectively. In total, the results of this study showed that a few weed species in most wheat fields in this region were well distributed and had high density, abundance, uniformity and dominance index and if the usual farm management methods continue, there is a possibility that species diversity will decrease and the problematic weeds will dominate.