عنوان مقاله [English]
Introduction: Distribution characteristics of weed species are key variables for weed management. Abundance and frequency show the number of individuals of a population in a given area. Distribution is a measure of the geographical domain of weeds. Identification of environmentally suitable areas for invasive of weed species is a great opportunity for management of weed invasion.
Materials and Methods: In order to specify the infection hotspots of wild wheat (Triticum boeoticum Boiss) and wild barley (Hordeum spontaneum K.Koch) weeds in rainfed wheat fields of Lorestan province, Iran, an indicator of the presence severity was defined. Presence Severity Index (PSI) indicates the portion of each field of the total contamination for a weed species in a given area. Data on grass weed species occurrence in rainfed wheat were collected in spring 2014 and 2015 from the 397 rainfed wheat fields throughout Lorestan province. Equations were fitted by Sigmaplot 12.3 and the ArcMap 10.1 software was used to drawing geographic weed maps. In drawing geographic weed maps, data grouped according to Jencks natural classification algorithm with minimal variance within groups and maximize variance between classes.
Results and Discussion: The optimum altitude for the presence of wild wheat and wild barley were estimated 1856 and 1703 m above sea level, respectively. The average altitude of wild wheat-infested wheat fields was significantly higher than the average altitude of wheat fields contaminated with wild barley. The range of altitude for the wild wheat presence in the wheat fields was form 1564 to 2169 m with an average of 1839 m above sea level. The range fo the wild barley presence in the wheat fields was from 885 to1982 m with an average of 1587 m above sea level. However, the range of altitude of all sampled wheat fields was form 697 to 2239 m above sea level. Generally wild wheat was not observed in all wheat fields of Poldokhtar, Kuhdasht and Doreh Chegeni. Among the 397 studied rainfed wheat fields in Lorestan, the highest level of presence severity index of wild wheat belonged to a wheat field in Vazlh village in the east of Khorramabad. The average wild wheat spike density of infected wheat fields was 42.1 spikes per square meter. Among the wild wheat-infected wheat fields, the highest spike density were belonged to the wheat fields in Khorramabad, Aligoudarz and Delfan, with a density of 54.7, 51.4 and 45.1 spikes per square meter, respectively. The north-east areas of Khorramabad and the east of Aligudarz and Delfan, with infested fields by presence severity index of more than 3%, were identified as the most important spots of this grass weed infestation in Lorestan province. Among the wild wheat-contaminated areas, the highest relative importance mean (44%) belonged to the Delfan, which showed the higher importance of wild wheat infestation compared to the other grass weeds in this area. The relative importance mean for wild wheat in Aligudarz, Selseleh, and Khorramabad were 34.6%, 34.2% and 20.6%, respectively. Wild barley was not found at all visited wheat fields in Azna and Aligoudarz. Based on the presence severity index, the contamination of wild barley in the wheat fields of Poldokhtar, Borujerd, Delfan and Doreh Chegeni also was not significant (the average of presence severity index of less than 1.0%). The highest level of presence severity index for wild barley (6.1) was observed for a wheat field in the Chaghalvandy area of Khorramabad. The average spike density of wild barley in wheat fields of Lorestan was 42 spikes per square meter. If we consider the average of 11 seeds per spike for wild barley, weed seed rain on the infected wheat fields of this province was estimated to 404 seeds per square meter. The presence severity index of wild barley for Khorramabad, Dorood, Kuhdasht, and Selseleh were 0.45%, 0.44%, 0.34%, and 0.28%, respectively. The highest level of wild barley relative importance index (50.7%) was belonged to Kuhdasht, which show the higher importance of wild barley compared to other grass weeds in this area. Wheat fields located in the northern of Khorramabad, the eastern areas of Kuhdasht, the central area of the Selseleh and Chegeni and the northeast areas of Delfan were identified as the main spots of wild barley infestation in the Lorestan province.
Conclusions: The Presence altitude domain for wild barley in rainfed wheat fields of Lorestan was 81.3% more than wild wheat that demonstrate the more possibility of wild barley invasion in a broader altitude scope.