جستجوی مقالات مرتبط با کلیدواژه "rice cultivars" در نشریات گروه "گیاهپزشکی"

Rice (Oryza sativa L.) is one of the world’s most important staple food crops. In Asia, it is the main item of the diet of 3.5 billion people. Rice stem borers are common insect pests in many rice growing countries. Striped stem borer (Chilo suppressalis Walker), belonging to Lepidoptera and family of Pyralidae is the most important rice pest in the Northern Iran. Stem borer larva damages rice stem and disturbs nutrient translocation from root to leaf. As the result, tillers in vegetative stage died, which is called dead heart. When larva infests generative stage, it causes empty panicle, which is called white head. Integrated pest management (IPM) practices for controlling the stem borers in Iran have not been fully implemented because of limited control technologies which are available. Farmers often rely on heavily insecticide application, although many insecticide applications are not effective. Therefore, many physical and cultural practices have been suggested, including adjustment of planting time to escape the plant from heavy pest.
The study was conducted in deputy of rice research institute in Amol, Mazandaran, Iran, during 2011-2012. The experiment was arranged in split plot design with planting time as main plot and cultivar as subplot and was replicated three times. Three planting times tested were the first planting time i.e. 15 days before farmers’ planting time, the second planting time (simultaneously with farmers’ planting time), and the third planting time (15days after farmers’ planting time). Six rice cultivars tested, representing three types of rice cultivar, Tarom and Kohsar (early maturity cultivars), Shirodi and Fajr (medium maturity cultivars), Neda and Nemat (late maturity cultivar). Rice seedlings were transplanted at 25 cm planting distance in a 3 m x 9 m plot size. Weeding and fertilization were done as recommended. No insecticide was applied. Dead hearts and white heads were measured on 10 sample hills on each plot after the end of growth germination and before harvesting respectively. Rice yields were measured on 80 sample hills (5 m2) on each plot. Sample hills were chosen diagonally. Effect of planting times and rice cultivars on striped stem borer infestation were determined by analyzing of variance using by two-way Analysis Of Variance (ANOVA) and the mean difference were tested using Tukey test. Parameters were analyzed using the SAS software.
Analyses of variance showed that there was significant difference between stem borer infestation at three planting time, cultivars and their interaction. Stem borer infestation in the third planting time was significantly higher than the other two planting times. The most degree of dead hearts (11.9%) and white heads (31.23%) infestation were belonged to Tarom cultivar in the first planting time and Fajr cultivar in third planting time, respectively. The least degree of dead hearts (0.6%) and white heads (4.56%) infestation was observed on Neda in the first planting time. Also, grain yield of all rice cultivars grown at the first and second planting was higher than that of the third planting time. As earlier discussed, rice crop of the first planting time was heavily infested with stem borer during early vegetative stage. Although affected rice plants had been replaced and recovery of replanted tillers was good, they grew slower. Yield potential of all six cultivars was significantly different. Yield of a cultivar depends upon its yield potential. However, biotic and abiotic threats could reduce its yield potential. The present study showed that stem borers are potential threat when their population is higher as shown in the third planting time. The least mean rice yield (3.875 t/h) occurred in the third planting time compared to those found at the first and second planting time, i.e. 5.356t/h and 5.321 t/h respectively.
It is concluded that adjustment of planting time is feasible effort to reduce stem borer infestation because rice plant be able to escape damage under heavily population of striped stem borer but it depended cultivar and climate condition.

The discoloration of rice grains is a complex disease due to infection by certain microorganisms on the glumes, kernels, or both, and its extension is different according to cultivar, season and locality. To access resistance source to rice grain discoloration disease, 66 Iranian local and improved, and foreign cultivars of rice were grown at the Rice Research Institute of Iran in Rasht county. After panicle exertion, plants were kept wet to develop grain discoloration until the evaluation time by a water sprayer system, above the tested plants in the field. Assessment of cultivars was done by sampling of 15 main panicles in each cultivar, seven to 10 days before harvest. The recorded data analysis revealed a wide variability among cultivars in terms of disease index, percentage of unfilled seeds and 100 seed weight. On the bases of disease index results, the local cultivars Hassansaraei Attashgah, Ali Kazemi, Hashemi, Sadrei and Binam showed significant resistance reaction to grain discoloration disease in the field conditions. From the fungi that were isolated from discolored grain, virulence of Bipolaris oryzae, Fusarium fujikuroi, Fusarium graminearum, Curvularia sp. and Alternaria sp. were confirmed on two local and improved cultivars namely Binam and Khazar respectively, whereas no disease symptom was appeared due to Nigrospora sp. and Ulocladium sp.

The present investigation was carried out to examine virulence diversity among the 291isolates (seven populations) of Rhizoctonia solani AG-1 IA causing sheath blight of rice by sclerotia production and pathogencity studies on four rice cultivars representing different observed disease reactions, using detached leaf inoculation method in conjunction with mycelia growth measuring. Based on pathogencity test four tested cultivars were significantly differed from each other in response to each population of pathogen. In each population, all the test isolates exhibited varying degree of virulence on each four cultivars and were variable both in mycelial and sclerotial (number and weight) parameters. There was found one group in each population having more stable performance in virulence in a range of genetically different rice cultivars based on their virulence on each four cultivars and along with their coefficient of variation by cluster analysis method. According to these finding, six, two, five and one high-virulence isolates respectively from populations of Rasht, Tonekaboon, Amol and Golestan can be used to future greenhouse or field tests, selecting most suitable isolates for identification of accurate reaction of rice cultivars / lines for rice breeding programs in north of Iran.

Rice sheath blight disease caused by Rhizoctonia solani AG1- IA is the second economically important disease of the crop in most rice- growing regions of the world، including Northern of Iran. The disease is mainly controlled through application of fungicides. The present study was performed to identify the candidate cultivar (cultivars) as source of resistance to the pathogen in rice field conditions in Northern Iran. Thirty seven vs twenty three rice cultivars respectively from Iranian Local (IL) and Iranian Improved (II) cultivars along with ten Foreign Resistant (FR) cultivars were field grown at the Rice Research Institute of Iran. They were inoculated with the mycelial mass of a virulent isolate (G309) of pathogen، 45 days after being transplanted. To supply favorable humidity for disease development، the plants were kept wet until the evaluation time through 2-5 times of daily water spraying، while applying a overhead water sprayer system available on the field. Assessment of cultivars، reaction was done by recording the Sheath Blight Severity as appeared on the sheath (SSS)، number of Lesions on the Sheath (LS)، Relative Lesion Height (RLH)، percentage of Infected Tiller (IT)، number of Dead and Green Leaves (DL and GL)، Number of tillers (Nt)، Tiller Angle (TA)، Stem Width (SW)، and Plant Height (PH). Results indicated that، the group of FR cultivars significantly differed from groups (IL) and (II) cultivars by exhibiting less SSS، LS، DL vs more GL. Cluster analysis of the cultivars as based on RLH، SSS and DL، using UPGMA method revealed 4 groups. One of the grpups comprised of: Jasmine 85، Teqing، Pecos and Tetep was observed as resistant، whereas، another one containing Swarna (Foreign susceptible)، Moosatarom، Hassansaraei، Jamshidjo، Khazar، Shiroodi، D4 (IL and II)، and Fujiminori was recorded as susceptible. Analysis of the relationship between plant traits and disease response indicated that RLH and SSS were not significantly correlated with the assessed morphological characteristics as regarded FR cultivars، whereas a positive significant correlation was observed between SSS and TA (r = 0. 20، P. value= 0. 033)، and a negative one between RLH and PH (r = -0. 29، P. value= 0. 002) as detected on local cultivars.