Changes of Weed Flora and Species Diversity in Wheat (Triticum aestivum) Field of Gloestan Province after One Decade

Wheat, as a strategic crop, has a special place in agricultural production of Iran and it has the highest cultivation area in the country. One of the most important limiting factors of wheat production in the world and in the country is weeds. Having comprehensive knowledge of the flora and species diversity of weeds is one of great importance for wheat management and it perceived as a primary need for production management and effective method of weed control in wheat farming program. In order to study of weed flora and evaluation of species, functional and structural diversity of weeds in wheat field of Golestan province, weeds population were surveyed at different cities during 2015 and the results were compared with the findings of last decade surveys. Randomized sampling method as W shape was conducted systematically using 0.5×0.5 m quadrate. All weeds in each quadrate were identified, counted and recorded for subsequent data entry and analysis. Mean density, frequency and uniformity percentage and relative abundance were calculated based on Thomas, 1985. Species Similarity index between different cities and Shannon and Simpson species diversity indices in each city were calculated based on available formula. Then cluster analysis based on average linkage method is carried out by SAS 9.2 for clustering different cities on basis of calculated traits that mentioned above. In this study, 51 plant species from 20 families were recorded. The most number of weeds were recorded in Poaceae, Fabaceae and Asteraceae families with 14, 7 and 6 weed species, respectively, but Poaceae, Polygonaceae and Brassicaceae were the most important weed families in wheat fields of Golestan provice, based on their relative abundance, respectively. The results showed that 78.43 % of recorded weeds were annual and the rest were perennial, 29.41 % of weeds were monocotyledons and 70.48% were dicotyledones. Avena ludoviciana and Phlaris minor with 40.21 and 37.11% relative abundance were the most important weed from narrow-leaved weeds and Sinapis arvensis with 32.42% relative abundance was the most important weed from broad-leaved weeds. P. minor, A. ludoviciana ،Veronica persica poir. and Stellaria media (L.) Vill. had the highest mean density in wheat fields of provice, respectively. The result of this study showed that the density of Avena ludoviciana, Sinapis arvensis, Phalaris minor, Lolium rigidum, Polygonum aviculare, Fumaria officinalis and Veronica persica has increased while the density of Polygonum convolvulus and Melilotus officinalis decreased over time gradually. Increase of narrow-leaved weeds than last decade may be related to continuous application of aryloxy phenoxy propionate herbicides for the years and resistance of weeds to this group of herbicides. Decrease of P. convolvulus density than last decade can be contributed to successful control of this weed by available herbicides such as tribenuron methyl, bromicid M.A. (bromoxinil+MCPA) and 2, 4, D. The most uniformity index was observed in A. ludoviciana (29.15), S. arvensis (26.57), P. minor (21.90) and V. persica (18.03), respectively. S. arvensis, A. ludoviciana, P. minor and V. persica with 42.55, 41.49, 41.49 and 30.85 % had the most frequency, respectively. The highest richness (the number of species) was observed in Khan Bebin (26 species) and the lowest (8 species) was in Kord Koy. Low richness in Kord Koy may be contributed to poor drainage of soil in this city that many of weed species cannnot adapt with this condition. The highest and Shannon diversity index was observed in Gonbad (2.48) and Khan Bebin (2.44) and the lowest value was observed in Kord Koy (1.18). The highest Simpson diversity index was observed in Kalaleh (0.43) and Minoo Dasht (0.4) and the lowest value was observed in Gonbad (0.11) and Khan Bebin (0.11). Different cities of Golestan Provience were grouped in 7 clusters for weed uniformity and weed abundance but for weed density they were grouped in 8 clusters. The most important weed in Aq qala, Bandargaz, Khan Bebin, Kord Koy, Kalaleh and Gorgan cities were Melilotus officinalis, P. minor, S. arvensis, Phalaris paradoxa, P.convolvulus, V. persica. A. ludoviciana was the most important weed in Ali Abad, Gonbad and Minoo Dasht cities. In general A. ludoviciana (40.21), P. minor (37.11), S. arvensis (32.42), and V. persica (27.96) had the most relative abundance in wheat fields and study of their control methods must be considered as research priorities in Golestan provice.