فصلنامه تحقیقات غلات
سال نهم شماره 3 (پاییز 1398)

Blast disease caused by the Pyricularia oryzae is one of the major diseases of rice, which reduces the rice yield to 70-80% in some years. Appropriate methods of controlling this disease have always been of interest to the researchers, especially the introduction of tolerant cultivars has always been one of the most important breeding objectives of rice breeders. The objective of the present study was to screen rice genotypes for tolerance to leaf blast disease under field conditions. In this research, 121 rice genotypes from the germplasm collection of the Rice Research Institute of Iran (RRII) and International Rice Research Institute (IRRI) were selected and planted in a 11×11 lattice design with two replications under artificial inoculation with fungus causing the blast disease in research fields of RRII, Rasht, Iran, in 2015. The studied traits including the number of spots, number of sporulating spots, infected level, infected percentage, infected type and area under disease progressive curve (AUDPC) in inoculated plants with fungus in the blast nursery were measured. The results showed that there was a significant difference (P<0.01) among genotypes for all traits and most of the studied traits had high broad-sense heritability as well as phenotypic and genotypic coefficient of variation. Cluster analysis for classification of genotypes based on leaf blast related traits showed that the studied genotypes could be divided into three different groups based on leaf blast susceptibility and tolerance. In total, the results of the current study showed that among the studied genotypes, eight genotypes were tolerant to leaf blast disease and the most important and prominent genotypes of which were Neda and Khazar. The tolerant genotypes can be used to obtain leaf blast tolerant varieties in future breeding programs.

Under the iron toxicity conditions, one of the most important limiting factors of rice production in agricultural lands is the increase of active oxygen radicals and thus decrease of plant growth and development. In this study, the effect of iron induced toxicity at 0 (control), 100, 250, 400 and 500 mg/l (Fe-EDTA) levels were investigated on some morphological traits, relative expression of G6PDH photosynthetic gene and activity of peroxidase enzyme in two rice genotypes, Pokkali (tolerant) and IR64 (susceptible), at four-leaf growth stage under hydroponic conditions with Yoshida nutrient solution. The experiment was carried out as factorial with two factors, genotype and iron concentration (two and five levels, respectively), in a completely randomized deshgn with three replications. The results showed that the interaction of iron toxicity and genotype had significant effect on all studied traits except root dry weight. Cluster analysis using farthest neighbor divided the ten studied treatments into two separate groups. Principal component analysis showed also that 66% of the total variation was explained by two principal components. Applying iron toxicity stress reduced the relative expression of G6PDH gene in both genotypes, exept that the relative expression of this gene in the Pokkali genotype decreased with the application of low stress levels, but in the IR64 genotype, the decrease in expression of this gene observed only at high stress levels. The lowest activity of peroxidase enzyme was observed in both Pokkali and IR64 genotypes at 100 mg/l iron and the highest activity were observed at 400 and 250 mg/l, respectively. It seems that decreasing the expression of G6PDH gene at low stress levels and increasing the activity of peroxidase enzyme in the tolerant genotype can reduce the amount of hydrogen peroxide induced by iron toxicity.

Sheath blight disease of rice caused by Rhizoctonia solani AG-1 IA, has been recognized as one of the most economically important rice diseases in the worldwide. Predicting inoculum density and understanding their survival will lead to agronomic management and reducing the application of fungicides in controlling this disease. The objective of this study was to investigate the effect of overwintering sclerotial density on rate and density of sheat blight disease and rice yield loss in weather conditions of Guilan province, Iran. For this purpose, a field experiment was conducted in a randomized complete block design with three replications in research fields of Rice Research Institute of Iran (RRII), Rasht, Iran, during 2017-2019. Treatments were 0, 12, 24 and 36 sclerotia in a plot of 9 m2, respectively, and the studied variety was the Iranian improved variety, Shiroudi. The results showed that inoculum (sclerotial) density had a significant effect on the development of rice sheat blight and its high density in the field resulted to increased disease and yield loss in rice growth stages. Study on the overwintering sclerotial densities during two years of experiment also showed that the amount of post-harvest rainfall had a significant effect on the survival of sclerotia and reduced them. Therefore, elimination or reduction of primary inoculum and prediction of survival rate of the disease agent under field conditions can be one of the most effective strategies in controlling rice sheath blight disease.

This research was conducted to compare the salinity tolerance of wheat promising lines during 2015-2017. The greenhouse experiment was carried out at Seed and Plant Improvement Institute, Karaj, Iran, and the field experiment was conducted at National Salinity Research Center, Yazd, Iran. The treatments in greenhouse experiment were irrigation water salinity at two levels (2 and 14 dS.m-1) and five wheat genotypes (MS-89-13, MS-89-12, MS-90-13, MS-90-15 and Narin as check, and in the field experiment including salinity of irrigation water at five levels (2, 5, 8, 11 and 14 dS.m-1) and the same five wheat genotypes mentioned above. The results of greenhouse experiment showed that salinity stress of 14 dS.m-1 significantly decreased plant height, leaf area, shoot fresh and dry weight and root length and dry weight in all genotypes and increased chlorophyll index only in MS-89-12 genotype. Narin as well as MS-90-15 and MS-90-13 genotypes with the lowest reduction percentage due to salinity stress were determined as the most tolerant genotypes. The results of field experiment also indicated that salinity stress, depending on its severity, significantly reduced plant height, ear length, fertile spikelet number in ear, grain number per spike and thousand grain weight, which led to considerable decrease in grain and biological yield. Under control conditions (2 dS.m-1), the highest and lowest grain yield were obtained from MS-90-13 and Narin (6.91 and 5.81 t.ha-1, respectively), and under 14 dS.m-1 salinity conditions, Narin and MS-90-15 genotypes had the highest and lowest grain yield (3.23 and 1.51 t.ha-1, respectively). The threshold levels of salinity tolerance for MS-89-13, MS-90-13, MS-90-15, Narin and Ms-89-12 were evaluated to be7.41, 6.30, 4.92, 4.84 and 4.20 dS.m-1, respectively. The results showed that MS-89-13 had the higher salinity tolerance at salinity of less than 8 dS.m-1, but at higher salinity levels, Narin and MS-90-13 genotypes similar to greenhouse experiment were more tolerant than the other genotypes. According to the relatively similar results of greenhouse and field experiments, MS-90-13 line for lower salinity levels and Narin variety and MS-90-15 line for higher salinity levels were the more suitable genotypes, which could be recommended with due to considerations.

To investigate the response of new maize hybrids to different environmental conditions and determine their grain yield stability, an experiment was conducted using eight maize hybrids in a randomized complete block design with three replications in six locations in 2016. Due to the significant hybrid × environment (G × E) interaction, stability analysis was performed using two multivariate methods, AMMI and GGE-biplot. The results of the AMMI model showed that only the first principal component (AMMI1) was significant and accounted for 72.52% of the G×E variation. Based on AMMI model statistics (SPCA1 and ASV), the hybrids No. 1 ( KSC715B) and 5 (KSC706) were selected as the highest stable hybrids. The results of stability anlaysis by GGE-biplot procedure showed that 83.32% of the total grain yield variation was explained by the first and second component of GGE-biplot and the hybrids No. 1 (SC715B) and 7 (SC703) were identified as the hybrids with higher stability. In total, based on grain yield and the results of stability analysis using these two methods, the hybrids No. 7 (SC703) and 1 (SC715B) with grain yield of 13.16 and 12.82 t/ha, respectively, were identified as the most stable hybrids with most high yielding and due to high general adaptability, cab be cultivated in different regions of Iran. Also, biplot of correlation among environments revealed that Moghan, Shiraz and Kerman as well as Ghaemshahr, Kermanshah and Karaj, were very close to each other and were similar in ranking the studied hybrids. Considering high dicreament power of hybrids in Shiraz, Kerman, Karaj and Ghaemshahr regions and in order to save the costs of future experiments, it is recomanded that the experiments be carried out in these four regions instead of six.

In field studies of weeds in the wheat fields of Kurdistan province, Iran, an alien plant from Brassicaceae species were observed for the flora of the province. This plant has been a weed in the wheat fields of Dehgolan, Ghorveh, Bijar and Divandareh (all of Kurdistan, Iran) for less than a past decade and its population has increased extremely in the last three to four years. According to the Turkish flora, this plant is nominated waxy leaved mustard and its scientific name is Boreava orientalis Jaub & Spach. The flora of Iran introduced this species as the synonym of Isatis quadrualata. In this study, weed density and distribution of B. orientalis was investigated in three regions, Dehgolan, Ghorveh and Bijar, and 15 fields from each region and compared with common weeds of the region. Data were collected by observational method and scoring was performed on a scale of 0 to 100. GIS software (ver. 10) was used to construct the distribution map of this weed and sampling data were interpolated using the inverse distance weighting (IDW) method. The results of this study showed that the regions infected to waxy leaved mustard were more in Sanandaj to Dehgolan, Sanandaj to Bijar and Dehgolan to Bijar path and weed density in these areas was about 40 plants/m2. The seeds of this weed will fall after maturity and before harvesting wheat and germinate under favorable environmental conditions from late November to late December. The distribution of waxy leaved mustard is clumpy and in some fields covers about 35% of the field surface and wheat yield loss at this high densities was estimated to be 70%. The density of this weed in the irrigated fiels is higher than in the dry fields and causes more damage. Although this weed has been present in the region for about six years, but its spread is intense and worrying. It is recommended that more comprehensive studies be carried out on the different characteristics and appropriate methods of controlling this weed.

The field of association mapping studies has recently received major attention for genetic studies of quantitative traits in many important plants. Access to next generation sequencing technologies, high phenotypic data and a variety of sophisticated statistical tools have enabled association mapping studies in plants to be successful in identifying gene loci controlling quantitative traits. Due to the importance of association mapping method in mapping studies of the quantitative traits, the present paper was prepared to explain the association mapping method and its use in plant breeding especially cereals. This paper, also provides some information about statistical softaware packages used in association mapping and then the opportunities and challenges of association mapping and post-genome wide association studies at the whole genome level will be discussed. Finally, linkage disequilibrium value and association mapping analysis will be evaluated based on general linear model (GLM) and mixed linear method (MLM) using a simple example.